MSc Project

Teesside University School of Science and Engineering BEng (hons) Mechanical Engineering

Aerodynamics Investigation of Rear Vehicle (Backlight angle) By: SAUD HASSAN Supervisor: SAJID ABDULLAH

A thesis submitted in partial fulfilment of the requirements for the award of Bachelor with honours Degree in Mechanical Engineering April 2014

-0-

Abstract Road vehicle aerodynamics has been treated by Barnard (1996), who gives a very readable account, and also by Hucho (1998a), who gives a particularly comprehensive treatment. The main developments with vehicle aerodynamics probably occurred during the early 198Os, and the use of low-drag vehicles has now become common. The development of low-drag vehicle shapes is now more rapid because of greater past experience and better computational techniques.” (R Stone 2004).

The primary aim is to research and investigate an aerodynamic study of a vehicle body design focusing rear back light angle. Computational Fluid Dynamic simulation studies investigated the effect of geometric form design, with a focus on rear vehicle backlight angle, to determine upon drag and lift values. A real-life automobile is very complex shape to model or to study experimentally. However, the simplified vehicle shape employed by Ahmed et al. (1984). “The Ahmed body is a “bluff body” simplified car used in automotive industry to investigate the influence of the flow structure on the drag.” (Emmanuel Guilmineau, 2007).

In this project flow around the Ahmed body is investigated. For this flow over the bluff body were considered which with different slant angles. A case study is presented in this report to determine optimum design of the back light angle of a vehicle body (rear), which the author concludes around 30 degrees. Observation findings on air flow around the body are highlighted here with particular emphasis on the results from CFD simulation. This was determined utilising the Ahmed model with different backlight angles such as 0o, 5o, 12.5o, 20o, 30o, and 40o were utilsed in the case study presented. The behavior of these backlight angles was studied, and compared to the results with the different literature research papers.Finally the modification and the future advancement have been proposed on the basis of the outcome results.

-i-

Acknowledgements I would like to thank my supervisor Sajid Abdullah who helped me with all my concerns regarding my project, and also allowed me to attend the MEng degree lectures relating to car aerodynamics and vehicle design.

I also would like to thank all of my friends who supported me in meeting deadline and proofing the final report. I would like to thank the technician staff in particular Guy Morgan who provided all the technical support during all the project even though I couldn’t able to conduct the wind tunnel testing but still thank for his all the support. Finally I would like to thank to my family and everyone who supported me during my BEng degree.

- ii -

Table of Contents ABSTRACT................................................................................................................................................. I ACKNOWLEDGEMENTS ..................................................................................................................... II LIST OF FIGURES: ..................................................................................................................................V ACRONYMS TERMS ........................................................................................................................... VII CHAPTER 1: INTRODUCTION ............................................................................................................. 8 1. INTRODUCTION ................................................................................................................................. 9 1.1 BACKGROUND................................................................................................................................... 10 1.2 AERODYNAMICS DESIGN .................................................................................................................. 12 1.2.1 Explaining the equations ........................................................................................................... 12 1.3 DISSERTATION STRUCTURE .............................................................................................................. 12 1.4 OBJECTIVES OF THE PROJECT ............................................................................................................ 13 1.5 LIMITATIONS AND DEPENDENCIES: ................................................................................................... 13 CHAPTER 2: LITERATURE REVIEW ............................................................................................... 14 2. LITERATURE REVIEW ................................................................................................................... 15 2.1 INTRODUCTION ................................................................................................................................. 15 2.2 AERODYNAMICS FORCES .................................................................................................................. 16 2.2.1 Drag Force ................................................................................................................................ 16 2.2.2 Pressure drag ............................................................................................................................. 16 2.2.3 Surface Drag ............................................................................................................................. 17 2.2.4 LIFT ............................................................................................................................................... 17 2.2.5 Turbulent and the laminar boundary layers .............................................................................. 18 2.2.6 Difference between the turbulent body flow and the separated flow ........................................ 18 2.3.1 Streamline flows ....................................................................................................................... 19 2.3.2 Stagnation regions ..................................................................................................................... 19 2.3.3 Separation bubbles .................................................................................................................... 19 2.3.4 Reynolds Number ..................................................................................................................... 19 2.3.5 Turbulence ................................................................................................................................ 20 2.3.6 Three dimensional flow ............................................................................................................ 20 2.3.7 Vortices ..................................................................................................................................... 20 2.3.8 Karman Vortices ....................................................................................................................... 21 2.4 AHMED MODEL ................................................................................................................................ 21 2.5 BODY OF VEHICLE AND ITS CONCEPTS .............................................................................................. 22 2.5.1 Height from the ground level .................................................................................................... 22 2.6 FLUID (AIR) FLOW STRUCTURE AROUND THE VEHICLE WITH DIFFERENT BACKLIGHT ANGLE: .......... 23 2.7 AERODYNAMICS PRINCIPLES ............................................................................................................ 26 2.7.1 Navier-stroke equations ............................................................................................................ 26 2.7.2 Bernoulli equation:.................................................................................................................... 27 2.8 CFD SIMULATION ............................................................................................................................. 28 2.8.1 Working of CFD ....................................................................................................................... 29 ............................................................................................................................................................... 30 CHAPTER 3: RESEARCH .................................................................................................................... 32 3 RESEARCH DATA AND METHODS ............................................................................................... 33 3.1 INTRODUCTION ................................................................................................................................. 33 3.2 DATA USED ...................................................................................................................................... 33 3.3 INITIAL METHOD .............................................................................................................................. 34 3.4 CFD (COMPUTATIONAL FLUID DYNAMICS) SIMULATION SETUP ........................................................ 35 3.3.1: A SPECIFIC METHOD ...................................................................................................................... 37

- iii -

CHAPTER 4: RESULTS ........................................................................................................................ 38 4. RESULTS .......................................................................................................................................... 39 4.1 INTRODUCTION ................................................................................................................................. 39 4.2 AHMED MODEL TESTING ................................................................................................................... 39 4.2.1 Introduction ............................................................................................................................... 39 4.2.2 Flow simulation on the Square back or 0 degrees back light angle .......................................... 40 4.2.3 Flow simulation on the on 5 degrees back light angle: ............................................................. 41 4.2.4 Flow simulation on the on 12.5 degrees back light angle: ........................................................ 42 4.2.5 Flow simulation on the on 20 degrees back light angle: ........................................................... 42 4.2.6 Flow simulation on the on 30 degrees back light angle: ........................................................... 43 4.2.7 Flow simulation on the on 40 degrees back light angle: ........................................................... 44 4.3 DISCUSSION OF RESULTS ................................................................................................................... 44 CHAPTER 5: DISCUSSION .................................................................................................................. 45 5. DISCUSSION ....................................................................................................................................... 46 5.1 INTRODUCTION ................................................................................................................................. 46 5.2 DISCUSSION ON THE DRAG COEFFICIENT CD FOR DIFFERENT AHEAD MODEL..................................... 46 ........................................................................................................................................................... 47 5.3 DISCUSSION ON THE LIFT COEFFICIENT CL FOR DIFFERENT AHEAD MODEL: ..................................... 58 5.4 DISCUSSION ON PRESSURE AREAS ON DIFFERENT BACKLIGHT ANGLE:.............................................. 60 CHAPTER 6: CONCLUSIONS ............................................................................................................. 61 6.1 CONCLUSIONS ................................................................................................................................... 62 6.2 RECOMMENDATIONS / FUTURE WORK............................................................................................... 63 BIBLIOGRAPHY/REFERENCE .......................................................................................................... 64 APPENDICES .......................................................................................................................................... 66 APPENDIX A ........................................................................................................................................... 67 0 DEGREE ................................................................................................................................................ 68 5 DEGREES .............................................................................................................................................. 72 12.5 DEGREES ......................................................................................................................................... 76 20 DEGREES ............................................................................................................................................ 80 30 DEGREES ............................................................................................................................................ 84 40 DEGREES ............................................................................................................................................ 88

- iv -

List of Figures: FIGURE 1: AHMED MODEL (BLUFF BODY) ..................................................................................................... 9 FIGURE 2: JELLY MOULD SHAPE (CENTURION MAGAZINE ONLINE, 2011) .................................................. 10 FIGURE 3: WIND TUNNEL ........................................................................................................................... 11 FIGURE 4: CFD SIMULATION (RINGIS, 2013).............................................................................................. 11 FIGURE 5: WIND TUNNEL TESTING (AUDIAG, 1999) .................................................................................. 11 FIGURE 6: FORCES AND MOMENTS ACTING ON THE VEHICLE. (GENTA, 2008) ............................................. 15 FIGURE 7: PRESSURE DISTRIBUTION OVER A CAR BODY. ............................................................................. 17 FIGURE 8: FORCE ACTING ON ONE SURFACE ELEMENT. ............................................................................... 17 FIGURE 9: FLOW LAYERS ON THE TOP OF THE BUS. ..................................................................................... 18 FIGURE 11: SEPARATED FLOW BODY VS STREAMLINE BODY ..................................................................... 18 FIGURE 10: SMALL ZONE OF TURBULENCE ................................................................................................. 18 FIGURE 12: SEPARATION AND REATTACHMENT OF THE FLOW. ................................................................... 19 FIGURE 13: KARMAN VORTICES ................................................................................................................. 21 FIGURE 14: AHMED MODEL DIMENSIONS IN MM ......................................................................................... 21 FIGURE 15: VELOCITY AGAINST THE RATIO HEIGHT OVER LENGTH ............................................................ 22 FIGURE 16: FASTBACK WITH THE FLOW PATTERNS (BARNARD, 1996) ........................................................ 23 FIGURE 17: RESULTS FROM W.E LAY’S STUDY WITH DIFFERENT TAIL LENGTHS. (BARNARD, 1996) .......... 24 FIGURE 18: MERCEDES-BENZES CLS-CLASS (FASTBACK) .......................................................................... 24 FIGURE 19: SQUARE BACK WITH RE-CIRCULATORY VORTICES (HAPPIAN-SMITH, 2004) ........................ 25 FIGURE 20: BACKLIGHT ANGLE AGAINST DRAG COEFFICIENT (HAPPIAN-SMITH, 2004)......................... 25 FIGURE 21: EQUATIONS AGAINST THE COMPLEX GEOMETRY (JOSEPH, 1995, P. 94) .................................... 28 FIGURE 22: FLOW OVER THE TWO DIMENSIONAL MODEL OF MAZDA RX-7 CAR. (JOSEPH, 1995, P. 95) ...... 29 FIGURE 23: COMPUTATIONAL DOMAIN ....................................................................................................... 30 FIGURE 24: HIGHLIGHTED IS A MID-SURFACE SHEET METAL (LEFT), NODES SHOWN AND THE SHELL ELEMENT CREATED AT MID SURFACE (RIGHT) .............................................................................................

30

FIGURE 25: AHMED MODEL MADE IN SOLIDWORKS ................................................................................... 33 FIGURE 26: SIDE DIMENSIONS IN (MM) ....................................................................................................... 34 FIGURE 27: FRONT DIMENSION IN (MM) ...................................................................................................... 34 FIGURE 28: COMPUTATIONAL DOMAIN IN SOLIDWORKS ............................................................................ 36 FIGURE 29: AHMED MODEL WITH 12.5O ...................................................................................................... 39 FIGURE 30: AHMED MODEL WITH 5O ........................................................................................................... 39 FIGURE 31: AHMED MODEL WITH 0O ........................................................................................................... 39 FIGURE 32: AHMED MODEL WITH 40O ......................................................................................................... 40 FIGURE 33: AHMED MODEL WITH 30O ......................................................................................................... 40 FIGURE 34: AHMED MODEL WITH 20O ......................................................................................................... 40 FIGURE 35: PRESSURE TRAJECTORIES (SIDE BACK VIEW) SQUARE BACK..................................................... 41 FIGURE 36 : PRESSURE TRAJECTORIES (SIDE BACK VIEW) 5 DEGREES ......................................................... 41 -v-

FIGURE 37: PRESSURE TRAJECTORIES (SIDE BACK VIEW) 12.5 DEGREES ..................................................... 42 FIGURE 38 : PRESSURE TRAJECTORIES (SIDE BACK VIEW) 20 DEGREES ....................................................... 43 FIGURE 39: PRESSURE TRAJECTORIES (SIDE BACK VIEW) 30 DEGREES ........................................................ 43 FIGURE 40: PRESSURE TRAJECTORIES (SIDE BACK VIEW) 40 DEGREES ........................................................ 44 FIGURE 41: MAX AND MIN DRAG AREAS .................................................................................................... 48 FIGURE 42: PRESSURE TRAJECTORIES (SIDE VIEW) ..................................................................................... 48 FIGURE 43: PRESSURE TRAJECTORIES (BACK VIEW).................................................................................... 49 FIGURE 44: PRESSURE TRAJECTORIES (LEFT BACK SIDE VIEW) ................................................................... 49 FIGURE 45: PRESSURE TRAJECTORIES (SIDE BACK VIEW) ........................................................................... 49 FIGURE 46 : PRESSURE TRAJECTORIES (BACK VIEW) ................................................................................... 50 FIGURE 47: PRESSURE TRAJECTORIES (BACK SIDE VIEW) ............................................................................ 50 FIGURE 48: PRESSURE TRAJECTORIES (SIDE BACK VIEW) ............................................................................ 50 FIGURE 49: MAX AND MIN DRAG AREAS .................................................................................................... 51 FIGURE 50: PRESSURE TRAJECTORIES (SIDE BACK VIEW) ............................................................................ 51 FIGURE 51: PRESSURE TRAJECTORIES (BACK VIEW).................................................................................... 51 FIGURE 52: PRESSURE TRAJECTORIES (SIDE BACK VIEW) ............................................................................ 52 FIGURE 53: MAX AND MIN DRAG AREAS .................................................................................................... 52 FIGURE 55: PRESSURE TRAJECTORIES

(BACK SIDE VIEW)..................................................................... 53

FIGURE 54: PRESSURE TRAJECTORIES (BACK VIEW).................................................................................... 53 FIGURE 56: PRESSURE TRAJECTORIES (COMPLETE VIEW FROM LEFT BACK) ................................................ 53 FIGURE 57: MAX AND MIN DRAG AREAS .................................................................................................... 54 FIGURE 59: PRESSURE TRAJECTORIES (BACK VIEW).................................................................................... 54 FIGURE 58: PRESSURE TRAJECTORIES (BACK SIDE VIEW) ......................................................................... 54 FIGURE 60: MAX AND MIN DRAG AREAS .................................................................................................... 55 FIGURE 61: PRESSURE TRAJECTORIES (SIDE BACK VIEW) ............................................................................ 55 FIGURE 62 : PRESSURE TRAJECTORIES (BACK VIEW) ................................................................................... 55 FIGURE 63: PRESSURE TRAJECTORIES (COMPLETE VIEW FROM LEFT BACK) ................................................ 56 FIGURE 64: MAX AND MIN DRAG AREAS .................................................................................................... 56 FIGURE 65: MAXIMUM DRAG AREAS ON DIFFERENT BACKLIGHT ANGLES ................................................... 57 FIGURE 66: LIFT PRODUCING AREAS ........................................................................................................... 59 FIGURE 67: PRESSURE DISTRIBUTION OVER DIFFERENT BACKLIGHT ANGLES OF THE AHMAD MODEL ........ 60

- vi -

Acronyms Terms ASM

=

CAD Assembly file

=

Viscosity

=

Velocity

=

Body force (Mostly gravity)

P

=

Pressure (Pa)

V

=

Velocity of the fluid

h

=

Height (m)

g

=

Gravitational acceleration

=

Fluid density

CFD

=

Computational fluid dynamics

CL

=

Coefficient of Lift

CD

=

Coefficient of Drag

- vii -

CHAPTER 1: Introduction

-8-

1. INTRODUCTION Motor vehicle aerodynamics is a complex subject because of the interaction between the air flow and the ground, and the complicated geometrical shapes that are involved. (R Stone 2004). Dr Dominey of Durham University points out that the stability of regulations has led to a convergence of design which means that competitive circuit performance now depends on fine tuning of aerodynamic design (Fenton J 1999). This project investigates the basic knowledge about the aerodynamics of the of the rear backlight angle of the car. To study the behaviour of the aerodynamics the Solid work flow simulation were chosen and design of the bluff body (Ahmed model) (G.Franck, N.Nigro, & D'elia, 2009) were considered. This is investigated using the CFD simulation. The chosen model for this investigation looks at the bluff body (Ahmed model) which is shown in the figure below. The Ahmed’s model is a popular bluff body with different backlight angle used by the different researchers and in different literature to explain the theory of coefficient of drag and the coefficient of lift.

For example Simon and

Gioacchion explained that vehicle aerodynamics researches most commonly use the reference models to do the better understanding of the flow structures that may that might one vehicle can exhibit when it on the road. So on the basis of this they used Ahmad model for this study. (Watkins & Vino, 2008). Emmanuel investigated the flow over the simplified car body by using the Ahmed model with other several turbulence bodies. (Guilmineau, 2008). R H Barnard

describe in (Barnard, 1996). The Ahmed

model has the quite sensitive flow turbulence, road simulation and floor Clarence, method of mounting.

Figure 1: Ahmed model (Bluff body) -9-

Fundamental aerodynamics over the bluff body (Ahmed Model) has been done with the computational fluid dynamics (CFD) technology by using the Solid works 2013 flow simulation. It was focused on the backlight angle. To achieve this Ahmed model with the different angles were employed. So on the basis of results obtained the future advancement on the research and the modifications. 1.1 Background The vehicle shape and design until the recent years were just only the symbol of fashion which normally doesn’t have any concern with the aerodynamics of the car. In early 70’s the 1st step was taken for the aerodynamics in the production for the cars because of the price increase in the fuel prices. Since then the only factors which used to consider were the vehicle mass and the engine efficiency apart from the road vehicle aerodynamics properties. In the starting the research on aerodynamics mostly focussed on the drag reduction while on the other hand the lift coefficients were only practiced for the race cars. So with the advancement of engines in the automotive industry the speed of the car goes on increasing. The researchers also staring to analysing the drag and the lift reduction, and how they can minimise these forces which effect the efficiency and the stability of the on the road while it’s running with the speed. Low drag model was built in early 1980’s which is also known as the ‘jelly-mould’ shape. These type model cars usually have the less drag acting on the car. However, it has the low stability in the crosswinds conditions. The following figure shows the shape of the car. Those cars have the slop base so in these kinds of slopes the flow doesn’t have the large-separations.

Figure 2: Jelly Mould shape (Centurion Magazine online, 2011) - 10 -

So as the time passing the speed of the car goes on increasing so the driver safety and the car performance, it is now very important to that all the aerodynamics and the moments acting on the surfaces of the car are considered. The wind tunnel testing and the CDF flow simulation were carried out to study the aerodynamics of the car all the other moment forces. Wind tunnel is actually the large tunnel like apparatus which is able to produce the airstream with the known velocity of running car, airplanes etc. This is normally used to investigate the air flow over the cars, airplane etc. the following figure shows the structure of the wind tunnel.

Figure 3: Wind Tunnel (Allpar, 2014)

The standard way to study the flow over the car and the airplane surfaces are the CFD flow simulation over the car 3d models. This way is way cheaper than the wind tunnel because this involves the designing part and then CFD flow simulation which saves lots of times and the effort. (cfdanalysisservices, 2014) The two figures are describing the wind tunnel and the figure 4 describes the CFD flow simulation over the cars.

Figure 5: Wind tunnel testing

Figure 4: CFD Simulation (Ringis, 2013)

(AudiAG, 1999) - 11 -

There are lots of research were taken on the aerodynamics of the vehicle body, to analysis the drag and the lift coefficient acting on the car body. 1.2 Aerodynamics Design It is the design of the car which has the low drag and the low coefficient of lift. Cars are like the bluff bodies which has the drag coefficient of raging from 0.3-0.4. (Watkins & Vino, 2008). The researches have trying to design which has the low number of drag coefficient and the coefficient of lift and other side moments of the cars. This increases the stability of the car while it’s moving and also gives the driver the confidence in handling properly. The back shape has more effect on reducing the drag and the lift. 1.2.1 Explaining the equations To find the coefficient of lift and the coefficient of drag there are mainly two equation used even when to find it numerically or by using the CFD flow simulation. These equations are Navier-stroke equations Bernoulli’s equation. With this equation the coefficient of lift and the drag and pressure coefficient can be explained more. The CFD flow simulation software mostly uses the same equation to calculate the coefficient of drag and the lift to calculation these two coefficients over the cars, airplanes and the air foils surfaces. Studies and research has been done on this CFD technology and its importance in the design of the car body especially at the rear end (back light angle). Following are the two equations used. The more details of these equations can be found in the chapter 2 literature reviews. Equation 1

Equation 2) 1.3 Dissertation Structure The dissertation includes the introduction and the background of the aerodynamics of the cars. Then in the second chapter which is literature review which better explains all the theories and the equation on which all the dissertation is based. This also gives the inside of the aerodynamics forces and the different back types of the car such as the notchback, hatchback and the square back. It also explains the flow separation on the entire different back angle of the car. Then after this there is the section of research which includes the data used for the experiments and all the methods and techniques.

- 12 -

The section of research comes after that which includes all the CFD simulation results described. In this section the Ahmed model were tested on different backlight angles and then the results were obtained. Discussion of the results comes after that. Then at the end the Conclusion comes into place. 1.4 Objectives of the Project The main object of the project is to study the aerodynamics simulation by using CFD technology. The primary aim is to research and conduct an aerodynamics study of the vehicle back light angle. To achieve this aim, there are following objectives were considered during the project: 

Formation of the Ahmed model (bluff body) in the SolidWorks 2013. Computational Fluid Dynamics (CFD) technology (SolidWorks 2013 simulation) is used to study the effect on the rear vehicle body back light angle.



Flow over the bluff bodies were considered which with different slant angles the area of the concentration was the back light angle which has different angles and all the bodies with different angles were tested one by one.



Analysis of the effect which causes on all the different backlight angle angles. That where is the air flow showing the large separation and where it showing the vertices and low separation areas.



Based on the results then the design with the low drag and the low lifts is proposed and also the future advancement is proposed.

1.5 Limitations and dependencies: The main limitation of the project was that there was no access to the big wind tunnels so that the actually test were done on the different cars with different car angles and then the results were compared with the CFD flow simulation results.

- 13 -

CHAPTER 2: Literature Review

- 14 -

2. LITERATURE REVIEW 2.1 Introduction In early years there were no such considerations when drawing designs of the car. It was in 1970s the increase in fuel consumption and the fuel prices put stress on the engineering to actually think about the body design. The aerodynamics researchers initially focused on the reduction of the drag force; on the other hand there was the lift problem which causes the low vehicle stability. So there was great need of considering all the forces while designing the vehicle body. In the regards Computational Fluid Dynamics (CFD) played its vital role in determining the vehicle body shaping. To understand and for the clear explanation of the theory and the subject area of the topic the literature review has been split into different sections. The topics these sections cover include the basis aerodynamics of the car body, drag, lift and other different parameters for example height and the pitch which causes on the moving vehicle body. Then, the main area will be covered which is CFD simulation. The main model for the research is the Ahmed model to have the better understanding of the aerodynamics forces at the back light angle of the car. A moving object which is exposed to air always experience three main forces and movements respectively as shown in the figure. (Genta, 2008)

Figure 6: Forces and moments acting on the vehicle. (Genta, 2008) These moments and forces which are acting on a car in the above figure are as follows: 

Earth fixed axis system XYZ: It can be described as the right angled frame fixed on the road. In which X and Y coordinates are in the horizontal plane however the Z is in the vertical direction pointing upwards. All these coordinates can be divided as there is 90 degrees angle between them.

- 15 -



Vehicle axis frame xyz. Again this is the right angled frame but this time it is assumed to be fixed with the vehicle and also it moves along with it. The z force called the lift force which is acting on upwards and x is the horizontal force which is moving opposite to the vehicle body called drag. At the last force on the side horizontally called the side force which causes the momentum force.

2.2 Aerodynamics Forces 2.2.1 Drag Force As discussed earlier, the body shape when it exposed to air experience the different pressure on the surface. By breaking this into five constituent elements will gives a better understanding of drag force acting on the vehicle body. As it says in (Happian Smith, 2004:p112-113).

2.2.2 Pressure drag This is the component which is identified on the external surface of the car. As when the vehicle moves with the forward direction of the air then the surface of the car experience the pressure which is vary over the different points of the car as shown in the following figure. To have a look it very closely the small area of the flat surface is considered then the force which is acting on the axis of the car the drag force depends on the magnitude of the pressure. (Happian Smith, 2004:p112-113).

Drag Force is calculated as: …………… (Equation 3)

Where; FD = Aerodynamic Drag Force, N ρ = air density, Kg/m3 V = velocity, m/sec A = Frontal Area, m2 Cd = Drag Coefficient

- 16 -

Figure 7: Pressure distribution over a

Figure 8: Force acting on one surface

car body.

element.

2.2.3 Surface Drag This type of drag is due to the stress and drag values which is from the friction between air and the body surface for a small element. This type of drag only happens due to the effect of viscosity at the surface of the car. 2.2.4 Lift In the simple words lift in the vehicle is the pressure difference between the upper and the down side of the car. Nowadays higher top speed modern cars are manufactured which high stability need while on the road. Upper surface area near the hood, wind shield and underbody such as suspension, exhaust system are the main dependents of lift force. Studies shows that it is not the common problem at the low speed but when the vehicle goes to the high speed and then the pressure difference is a lot then lift force is the problem.

Lift Force is calculated as: (Equation 4) Where; FL = Aerodynamic Lift Force, N ρ = air density, Kg/m3 V = velocity, m/sec A = Frontal Area, m2 CL = Lift Coefficient

- 17 -

2.2.5 Turbulent and the laminar boundary layers Boundary layer flow has two distinctive types when the flow layer passes over the surface of the vehicle. The following figure 9 shows the flow layers on the top of the bus. Smooth air flow can be seen in the front edge. In this as it is clear that the moment of the outer layer is faster than the inner layers because the friction is effecting on the inside layer which has the direct contact to the surface. This type of flow is known as the Laminar flow. Mostly the turbulent body flow is streamlined.

Figure 9: Flow layers on the top of the bus. (Barnard, 1996)

2.2.6 Difference between the turbulent body flow and the separated flow The stream line flow is mostly knows as the turbulent body flow. Which always follows with the outlines of the body on the other hand the separated flow doesn’t follow the outline of the body. (Scott, 2005)

Figure 10: Separated flow body VS Streamline body

Figure 11: Small zone of turbulence

(Scott, 2005)

(Scott, 2005) - 18 -

2.3 Different types of fluid over the vehicle body 2.3.1 Streamline flows Streamline flow is a kind of flow which at any point over the car surface remains constant with the same pattern. On the other hand if the flow follows the outline of the vehicle body which is streamlined. In this case the flow can be say that it is attached. It is shown in the figure 8. (Barnard, 1996, pp. 6-7) 2.3.2 Stagnation regions This is the nature of the air which is strikes a vehicle body it divides into the different flow lines over the body. The divided flow goes over and under the body. The point where the air strikes and then stays stationary the position or the part where this occurs is known as the stagnation region. (Barnard, 1996, p. 8).

2.3.3 Separation bubbles When the air touches the surface of the car at some points the air doesn’t perform the streamline flows it detaches. So the separation bubbles are formed in the area between the air flows separates and then reattaches. (Barnard, 1996, pp. 12-13) The figure 12 shows the separation and the reattachment of the flow.

Figure 12: Separation and reattachment of the flow. (Barnard, 1996)

2.3.4 Reynolds Number Boundary layer and the thickness of the layer affect the friction on the surface, flow separations etc. The flow patterns depends on the length of the body, viscosity, speed and the density which can also be name as the one quantity as knows as the Reynolds Number. It can be expressed as follows: (Barnard, 1996, pp. 13-14) - 19 -

This is has the same value in any system of units. If the value of density and the viscosity is constant this number is totally depends on the speed and the size of the vehicle body. So as it is studied that if the speed of the car increase the Reynolds number goes on increasing which gives the thinner boundary layers. So it is clear that this number is very important in determining the type of flow over the surface of the car. 2.3.5 Turbulence It can be defined as the unsteady or the unusual manner of the flow over the car body is known as the turbulence flow. This can be termed as the swirling or the eddies turbulent motions which varies of sizes. (Barnard, 1996, p. 14) 2.3.6 Three dimensional flow The road vehicle mostly has the three dimensional flow patterns over them. Which mostly includes the circular patches, eddies and the swirling which form the three dimensional flow patterns. 2.3.7 Vortices In the flow regions there are some parts which often knows as the vortices which is mostly formed by the swirling flow structures, which mostly occurs with the whirlwinds. This project is given based on the backlight angle of the car so the vortices which formed at the back of the car are knows as the trailing vortices. These vortices also decide the lift situation of the car which either is positive or the negative. These vortices do not exist on the very long length in space. It merges in the surface or formed the closed loop shape for example like a smoking ring. (Barnard, 1996, pp. 1516)

- 20 -

2.3.8 Karman Vortices These types of vortices are formed mostly in the flow over the bluff bodies like buses, trucks or the simple car body shapes like Ahmed model to study the basic aerodynamics

Figure 13: Karman Vortices of the vehicle body. These types of vortices have the alternative patterns at a regular frequency.

The frequency of these vortices is known as the Strouhal frequency.

(Barnard, 1996, pp. 16-17) 2.4 Ahmed Model To study the aerodynamics over the car body at the back angle by using the CFD technology for this report it is proposed to study the air flow by using the Ahmed model. For the designing of this model solid works was used. The dimensions of the Ahmed model are as follows. (G.Franck, N.Nigro, & D'elia, 2009)

Figure 14: Ahmed model dimensions in mm

- 21 -

2.5 Body of Vehicle and its concepts The saloon cars are described in different books in different theory books. Cars are the bluff bodies with the drag coefficient of 0.3-0.4. (Watkins & Vino, 2008) There are multiple theories behind the vehicle body and its concepts. When the solid body start to experience any fluid either it is gas or the liquid, the fluid resists the motion of the object in the opposite direction. The large effect on the aerodynamics of the body is dependent on the geometry of the object. Drag and lift depends mainly on the size of the object which experience under the fluid. Form drag is determined by the cross-sectional shape of the object. (National Aeronautics and Space Administration, 2012) 2.5.1 Height from the ground level This include in the increase of down force acting on the car which helps it to stick it to the ground. If the space between the cross-sectional area of the vehicle body and the ground is reduced then the flow of the air under the body of the vehicle will increase which result in lower the pressure underneath the car and it means it will give the more down force which help to main the stability while the vehicle body is in motion under the fluid. This down force is also known as ground effect. Jim Hall in 1961 builds the Chaparral to study the aerodynamics problem within the car. Joseph Katz in race car aerodynamics explains the down force. That it can be increased with the smaller ground clearance. In addition the down force values can be increased by adding the skirts alongside of the vehicle body. (Hall, 2013) Following graph shows that lift and the drag verses ground clearance for a model with the generic underbody tunnel.

Figure 15: Velocity against the ratio height over length - 22 -

2.6 Fluid (Air) Flow structure around the vehicle with different backlight angle: This project basically focused on the rear backlight angle of a car. The area of this research will be based on the three common backlight angles which can be classified as follows: 

Fast back



Square back



Backlight angle

Fast back A vehicle with the fast back is with the roof which has steady slant from the front of the vehicle body to the back. On the other hand it is the roof which proceeds to the rear and near the base of the car it gets closer. These fast back mostly have the curved shapes vehicles from the back. The fast back is rarely found in the today’s vehicle design. (Brennan, 2011)

Figure 16: Fastback with the flow patterns (Barnard, 1996)

It is clearly seen in the above figure. In these types of cars the upper surface has relatively pressure which draws the air along sides of the car upwards and it will leads to the creation of intense, conical vortices. (HAPPIAN-SMITH, 2004, pp. 114-115) On the other hand in olden days teardrop-based cars with the extend tail these kind of cars were the old shape of fast back cars. It was considered as the very useful shape because the size of this shape was huge and it produces the long vehicles. This type of vehicle has increase in the chamber which used to increase the lift. In the figure.17 Lay from the university of Michigan in 1930s explain the results of the rear-end - 23 -

. (Barnard, 1996, p. 75)

Figure 17: Results from W.E Lay’s study with different tail lengths. (Barnard, 1996)

Configuration Number 1

Value of Drag coefficient (Cd ) 0.30

2

0.23

3

0.21

4

0.12

Table 1: different values of drag with different tail lengths (Barnard, 1996)

As it is clearly seen from the above figure and the values of the drag as tail length is increase the drag coefficient goes in increasing.

Figure 18: Mercedes-Benzes CLS-class (fastback) - 24 -

Square back These types of vehicle bodies mostly have the square back. Happian explains the flow structure of this vehicle as it is characterized by large, low pressure wake. In this case the airflow unable to follow the body surface around the sharp edges, it is clearly shown in the figure.19. (HAPPIAN-SMITH, 2004) The square back air flow shows the large turbulent wake. This will lead to the large number of drag because the air flow is unable to attach the surface of the vehicle body.

Figure 19: square back with re-circulatory vortices (HAPPIAN-SMITH, 2004) Relationship between the fastback and the square back:

Figure 20: Backlight angle against drag coefficient (HAPPIAN-SMITH, 2004)

It is clearly seen from the above graph that the fastback cars mostly fall in the category of cars with the backlight angle ranging from 0 to 30. The graph shows that the in fast

- 25 -

back vehicles at around 15o the minimum drag can be achieved. On the other hand as the angle goes on increasing it will give the high number of drag, this is in the case of square back vehicles. (HAPPIAN-SMITH, 2004, p. 116) 2.7 Aerodynamics Principles 2.7.1 Navier-stroke equations The relationship between the pressure, viscous and momentum forces in a fluid flow can be explained by the Navier-stroke equations. Air is known as a Newtnian fluid and its motion is directed by the Navier-Strokes equations are as follows: (E.L, A.P, H, & T, 2013, pp. 113-115) Equation 5 ) From the above equation number (5) = density = viscosity = Velocity P = Pressure = Body force (Mostly gravity) In the low speed aerodynamics applications (less than 300 mph – 133m/s) the density is effectively constant, to which will give rise to the incompressibility conditions. This can be expressed by the following equation: (Equation 6) So on the basis of that the equation number (1) can be written as: Equation 7)

- 26 -

2.7.2 Bernoulli equation: The most important equation in the aerodynamics analysis is the Bernoulli equation. This equation is used to compare the values of velocities and the pressure difference between the two points in the flow.

Figure 22a: The venture meter

Equation 8) So P = pressure (Pa) V = velocity of the fluid h = height (m) g = gravitational acceleration = fluid density

So on the usual car speed the air density is constant which is at the usual car speed for example below than (300mph- 133

). The equation number (8) can be written as

follows: (Equation 9)

So as a result (Equation 10) The equation number (10) explains the pressure difference on the two points of the fluid.

- 27 -

2.8 CFD Simulation The term CFD stands for computational fluid dynamics. The equation of continuity and the momentum can be solved with the help of computational fluid dynamics (CFD) technology. In 70’s there was 1st time that the 2D simulation were used to solve the basic equations which is only apply to airplanes. (Nasira, et al., 2012) The aerodynamics force which is acting on the vehicle is determined by calculating the pressure and flow velocities around the surface of the body, which can only be done by solving the equation of, motion of fluids for example the Navier-stroke equations and the Bernoulli equation. Fluids like (Gas and liquid) their flows are calculated by partial differential equations, represents the law of conservation for the mass, momentum and the energy. ‘(CFD) computational fluid dynamics is the art of replacing such PDE system by the set of algebraic equations which can be solved using digital computers.’ (Huerta, 2003) 

Qualitative and quantities fluid flow provided by the (CFD) computational fluid dynamics can predict from the flowing means:



CFD software’s like Solid works, NX idea, solver, post processing utilities.



Numerical methods



Mathematical modelling

The following figure shows the variation of (CFD) computational fluid dynamics over the years and complexity of the geometry of the model.

Figure 21: Equations against the complex geometry (Joseph, 1995, p. 94) - 28 -

One of the main advantages of using the CFD technology is that the architects get a chance to design structures in the safe environment. After designing they can analyse the stress, pressure on the particular part which can save lots of their time and efforts. This even saves lots of money, otherwise in olden days which were not possible. Automotive engineers can improve the vehicle aerodynamics which can solve lots of complex equations like Navier-stroke equations and the Bernoulli equation. CFD technology is very economically effect it saves the lot of effort to perform the actual wind tunnel testing which is very time consuming and costly. For example the flow of the air fluid over the Mazda Rx-7 which is the very complex 3d simulation. Following is the figure of air flow (Navier-Strokes) simulation of the 2 dimensional model of Mazda RX-7 car. (Joseph, 1995)

Figure 22: Flow over the two dimensional model of Mazda Rx-7 car. (Joseph, 1995, p. 95)

On the other hand many designs of the different models of the car can be analysed. This can be done to come up with the final model so which will be ready for the wind tunnel testing. This is cheaper way to finalising the design and do some post analysis.

2.8.1 Working of CFD CFD simulations create cells which is the division of fluid volume in a finite number of blocks. To divide the fluid into number of blocks or to create the finite number of cells a finite volume around the selected model is created which is known as the Computational domain. For the accuracy it all depends on the structure and the size of the cells. Following is the figure showing the computational domain.

- 29 -

Figure 23: Computational domain (SolidWorks, 2014) For this project the Solid works has been chosen to study the aerodynamics acting on the different car models. SolidWorks element techniques were considered. After the solid model is formed then meshing is applied then the software automatically generates the mixture of contact, shells, solid and spring elements which are totally based on the geometry of the model. The following meshes will be automatically be created by the SolidWorks CFD software. (SolidWorks, 2014) Shell mesh These types of meshes are for the sheet metals. The program automatically creates these types of meshes for the sheet metals which has the uniform thickness. For these kind of models the mesh is generated from the mid-surface. Following are the two examples of the Shell mesh.

Figure 24: Highlighted is a mid-surface sheet metal (left), nodes shown and the shell element created at mid surface (right) (SolidWorks, 2014)

- 30 -

Mixed mesh: This type of mesh is for the complex geometries model. Solid mesh: This type of mesh is created for the tetrahedral 3d mesh solid elements for all solid components for all the solid components in the parts. For the bulky objects tetrahedral elements are suitable. So the process includes the formation of the model with all the parameters and geometry configuration. Then the next step will be making the Conceptual domain around the model. This will define the area where the tests have to perform. The end step is to perform the flow simulation. This will give the aerodynamics flow over the desire body or shape of the model.

- 31 -

CHAPTER 3: Research

- 32 -

3 RESEARCH DATA AND METHODS 3.1 Introduction This project consists of the CFD simulation of Ahmed model in solid works 2013 and also consists of some tests on the wind tunnel. So 1st of all Ahmed model was designed with the original dimensions and with different slant backlight angels.

And also

performed tests and results are gathered from different car models. 3.2 Data Used The road vehicles are mostly defined as the bluff-bodies. The aerodynamics researches mostly use the reference models to study the basis of aerodynamics acting on the road vehicle. It also let the researchers to understand the flow structures which are unveiled in the road vehicle wakes. Car shapes can be represents by these bluff-bodies models as they are capable of generating the same flow features with keeping the same geometry with very less shape changes. In 2004 Le Good and Garry observed that Ahmed model is the most common which is very good to study the air flow over the vehicle body. (Watkins & Vino, 2008) The Ahmed model was made in 1984. This model is using with the different slant angles are used to studying the flow of air over the different backlight angles there are 0 , 5, 12.5 ,20 , 30, 40.

Figure 25: Ahmed model made in SolidWorks

- 33 -

The following figure shows the dimension for the Ahmed model.

Figure 26: Side dimensions in (mm)

Figure 27: Front dimension in (mm)

3.3 Initial Method In the initial stage the Ahmed model was completed in the CAD software Solid works 2013 as the body and the dimensions were discussed earlier. The second and the most important step is to start the solid works flow simulation 2013. It can be done by going to add in and by marking the solid works flow simulation 2013. The test simulation results for each test can be seen in the appendix A. The chosen CAD program to complete the model and the CFD flow simulation is was the Solid works 2013. The main purpose for choosing this program was it has the inside flow simulation to perform the CFD technique and find the fundamentals of the basic flow other the Ahmed model. On the other hand this software was faster to perform the - 34 -

CFD flow simulation tests on the Ahmed model and even better for the designing. This software is very user friendly and gives lots options like flow trajectories and the pressure surfaces and the play the flow animation which was done.

3.4 CFD (computational fluid dynamics) simulation setup There are some process which involved in the CFD (computational fluid dynamics). The CFD (computational fluid dynamics) simulation analysis is explained below. (W.Slater, 2008) a) Define the Problems : The 1st and the most starting of the step is to define the problem and then start to analysis that how this can be solved by using the CDF flow simulation software. The objective of the analysis is defined. So for this project the objective is to study the flow of the air fluid over the different vehicle with the different back light angle. To analyse this bluff-body is designed called the Ahmed model to analysis the flow over the different angles of this bluff-model. For this project the model to analyse is 3d Ahmed model so because of this the dimensions will be 3d. The next step is to create the flow domain or the computational domain. This defines the flow around the 3d model and which area the flow is restricted to. The nature of the viscous flow is determined. Inlet air flow is determined and the outlet. b) 3d modelling. For this project the Ahmed model is designed with the same parameters as used in the conducting in the actually tests. Figure 25 showing the Ahmed model. c) Flow domain or the computational domain: The area around the 3d model, which defines the flow simulation the restricted area, is known as the computational domain. This defines the boundary under which the flow simulation will take place. The general figure 23 shows the basis of the computational domain. The following figure 28 shows that actual computational domain for the experiment.

- 35 -

Figure 28: Computational domain in SolidWorks

Computational Domain Size used in the project X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Table 2: Computational domain size used in the project d) Creating mesh The basic mesh is used in this project. It can be say that the system auto generated meshing were used. Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Table 3: Basic mesh dimensions

Total cells Fluid cells Solid cells Partial cells Irregular cells Trimmed cells

101520 98392 1912 1216 0 0

Table 4 : Number of cells

- 36 -

e) Initial and the boundary conditions As the Flow domain or the computational domain was established then physical conditions are needed for the boundary of the computational domain. The software package needs to start solution and use series of methods to reach the final point. f) Establishing the Goals: After completing all the steps the goals like lift and drag are introduced which will defined the nature of the flow simulation over the body. All the results will be based on the goals provided. By solving the goals then the parameters like cut plot, surface plot and the flow trajectories can be examined for any pressure plot or the velocity. For this project the velocities like lift and drag are considered.

g) Performing the Simulation After completing the entire step then the software is ready to perform the tests. It is to make sure that the hard disk must have the enough places to store the results. Sometimes the software gives some error which ones need to check for the error and resolve the issue to perform the simulation again. h) Results of the simulation After completing the simulation the results are ready to view. There lots of ways to check and note down the results. The results can be obtained in the form of the word documents and the plots graph between the coefficient of lifts and the coefficient of drag of each sample. 3.3.1: A specific method So as descried earlier that the CDF flow simulation method are used to perform the flow simulation tests on the designed Ahmed model with the different backlight angle. This can be down by following all the steps and procedures explained earlier under the CFD (computational fluid dynamics) simulation setup. To perform this Simulation the CAD software Solid Works 2013 was used. The main advantage of this software is that it is the user friendly and give the details of all the analysis which is carried about to analyse the aerodynamics of the car.

- 37 -

CHAPTER 4: Results

- 38 -

4. RESULTS 4.1 Introduction This section covers all the results from the simulations undertaken with the CAD software solid works 2013. And then the results will be presents in the form of tables and charts, pictures taken directly from the solid works while analysing the results. This result section contained Ahmed model (bluff body) with the different back light angle. The different backlight angles there are 0o, 5o, 12.5o, 20o, 30o, and 40o. Then the results of coefficient of lift and the coefficient of drag are compared with the different backlight angle. This is shown in the graph and with the combination of the pictures. 4.2 Ahmed model testing 4.2.1 Introduction To analyses the flow over the vehicle back light angle. It was important to analyse any 3d bluff body model. As it is known as the car are like the bluff bodies which runs over the road. As it is can be seen from the literature review that as many researchers conducted in the as on the aerodynamics over the car body. Every time the researcher used the simplified bluff-body to perform the tests on and then compared the results with the original shape of the car. There are different parameters which are compared between different backlight angles of the Ahmed model. Following are the figure of Ahmed model with different backlight angles.

Figure 31: Ahmed model

Figure 30: Ahmed model

Figure 29: Ahmed model

with 0o

with 5o

with 12.5o

- 39 -

Figure 34: Ahmed model with

Figure 33: Ahmed model

20o

with 30o

Figure 32: Ahmed model with 40o

There are 5 Ahmed model back light angle’s variations are investigated by using the Solid Works flow simulation. These different angles are as following: 

0 degree



5 degrees



12.5 degrees



20 degrees



30 degrees



40 degrees

According to the (G.Franck, N.Nigro, & D'elia, 2009) the slant angle is equal to the , where

and the

Slant angle

Nature of Flow Nearly 2D attached Hugely separated 3d Nearly 2d attached

Table 5: Slant angle and the nature of flow

4.2.2 Flow simulation on the Square back or 0 degrees back light angle First of all the 0 degree or the square back was analysed under the flow simulation software. Which is

. It can be clearly from the diagram that the two

wakes appearing is almost the 2 dimensional. These are attached with the top and the near bottom of the back of the model. The wake which is near has the two circulatory flows pattern are created. - 40 -

Figure 35: Pressure trajectories (side back view) square back 4.2.3 Flow simulation on the on 5 degrees back light angle: On the other hand the slant angle when it is 5 degrees which is nearly equal to the 0 degree or the square back of the Ahmed model. It is

. The

flow near the wake according to the table.5 is 2 dimensional which is attached on the top and the bottom back surfaces as it is cleared from the figures. There are two wakes

Figure 36 : Pressure trajectories (side back view) 5 degrees which is near to the surfaces which are one above the other. This can be clearly seen in the figure.36.

- 41 -

4.2.4 Flow simulation on the on 12.5 degrees back light angle: This test was performed on the Ahmed model which the 12.5 degrees back light angle. As the angle is

. According to the table.5 the results are almost 2d attached.

Again in this case it can be clearly observe that there are two wakes appearing at almost in the same position like in the last case. These were above one above another. This can be clearly seen in the figure.37. Similarly on the other side if the streamline over these two wakes is seen it has slightly aligned unlike in the last case.

Figure 37: Pressure trajectories (side back view) 12.5 degrees

4.2.5 Flow simulation on the on 20 degrees back light angle: When the slant angle

is between the both

slant angle is greater then

and

. It mean the angle when the

and less than the

.

So in this case three dimensional behaviour can be seen. Due to this the flow of the fluid in the near-wake is quick. Helical motion is produced because of streamline are fed by a centred rotation motion. (G.Franck, N.Nigro, & D'elia, 2009)

- 42 -

Figure 38 : Pressure trajectories (side back view) 20 degrees

4.2.6 Flow simulation on the on 30 degrees back light angle: When the slant angle is 30 degrees which is

. It almost gives the same wakes

and the structures just like in the last case. But if the wakes positions are observed that it was 2 wakes structure very near to the back surface and near to the bottom, one above the other.

Figure 39: Pressure trajectories (side back view) 30 degrees

- 43 -

4.2.7 Flow simulation on the on 40 degrees back light angle: And at the last when the slant angle is

. The flow in this case is again the

two-dimensional. Again the two wakes are formed but this time as compared to other last two cases the wakes are bigger the upper wake are more on the slope. It was the more pressure area of drag on the slope.

Figure 40: Pressure trajectories (side back view) 40 degrees 4.3 Discussion of results All the results of the different slant angle of the Ahmed model are described earlier in the results section. The main part of the discussion is how the different slant angle of the Ahmed model shows which effects they put on the coefficient of drag and the coefficient of lift. The comparison of the coefficient of lift and the coefficient of drag with the different slant angles are also included in the discussion.

- 44 -

CHAPTER 5: Discussion

- 45 -

5. DISCUSSION 5.1 Introduction This section consists of the all discussion on the aerodynamics of the Ahmed model with different slant angles. The main discussion is circulating around the Lift and the drag coefficient of the Ahmed model with different slant angles. Then on the basis of the results found the Ahmed model of minimum Coefficient of drag and the lift is proposed. On the other hand the explanation is provided as well to support the fact. “Drag reduction is not the only aerodynamic consideration. The air flow also will affect the aerodynamic lift forces and the position of the center of pressure, both of which can have a profound effect on vehicle handling and stability”. (R.Stone 2004).

5.2 Discussion on the drag coefficient Cd for different Ahmed model It is discussed earlier in the literature review that when the car is moving forward in the direction the air. Then air exerts pressure on the surface of the car. This is different for different points on the surface. In order to study the behaviour of this Drag force acting on the surface on the backlight angle the bluff body (Ahmed model) with different back angles were tested with the help of Solid works simulation. The arrangement of these tests and all the parameters were discussed before in the previous chapter. The air speed was 55 (mile/h). It can be seen in the table and the graph that the maximum drag was at the 0 degrees angle and the minimum drag can get on 30 degrees angle. After the 40 degrees the drag and the drag coefficient start to gain the high value. Drag force and the drag coefficients after performing the simulation tests are as follows: Backlight angle (degrees) Drag (mile/h) Coefficient of Drag (no units)

0

5

12.5

20

30

40

20.323

16.454

13.844

0.093

0.063

0.075

14.519

8.263

9.776

0.066

0.0377

0.044

Table 6: Drag values and Coefficient of Drag

- 46 -

Backlight angle Vs Drag Drag(mile/h)

25 20 15 10 5 0 0

10

20

30

40

50

Backlight angle(degrees)

Graph 1: Drag against the backlight angle

Backlight angle Vs Coefficient of drag (Cd)

Coefficient of drag

0.1 0.08 0.06 0.04 0.02 0 0

10

20

30

40

50

Backlight angle (degrees)

Graph 2: Backlight angle against Coefficient of drag Cd It can be clearly seen that the drag at the 1st point with the back light angle of 0o the drag force and the Coefficient of drag Cd has the values of 20.323 mile/h and 0.093 respectively. It has the highest number of drag among all the other models. The high value is because the body is not completely streamlined. Mostly the stream line bodies have the less drag due to the formation of the streamline flow. This high number of drag is due to the plane complete square back which is responsible of creating the two circulatory streamlines at the near wake. The air from the top surfaces has to cover the long way till the back of the model which makes the air flow. - 47 -

Figure 41: Max and Min drag areas

From the above picture as it is clear that the maximum drag is exerting at the end of the pic. The air flow took the same time to reach the end of the model so it makes the same wake structures from the top and the bottom.

Figure 42: Pressure trajectories (side view)

From the above figure it can be seen that the flow over the body is the stream line flow as it described earlier that and as soon as the air flow reached at the end point where the sharp edge is then the flow suddenly separates and forms the large numbers of circulatory sub-flows.

- 48 -

Figure 44: Pressure trajectories (left back

Figure 43: Pressure trajectories (back

side view)

view)

As it is clearly seen from the above figures that the complete square back have the large number of re-circulatory time-averaged flow which is forming like a set of circles moving in a arc in between the up and down of the flow lines and it also as the small number of re-circulatory flow new the bottom wake. It makes the formation of coil elastic ring which is all over the top wake of this square model.

Figure 45: Pressure trajectories (side back view) The side view is showing that the coil elastic rings are creating in between the two up and the down streamline flows. The flow was attached on the top and the bottom surfaces of the bluff body.

- 49 -

Secondly, the Ahmed model with the slant angle 50 were tested with the SolidWorks simulation all the conditions were same. The air flow speed was 55 miles/h with the same domain size and the parameters. The values of drag and the coefficient of drag are 16.454 (miles/h) and 0.063 respectively. This value of drag has a sudden decrease of

Figure 47: Pressure trajectories (back side

Figure 46 : Pressure trajectories (back

view)

view)

Figure 48: Pressure trajectories (side back view)

- 50 -

Around 4 points as the angle is create at the back The flow is almost 2-d attached. The flow nature is changed. As there are still some recirculatory times averaged sub flows near the wake. The two set of trailing vortices are formed in this case as it is shown in the figure.49. Although it is not very obvious in 5o angle case.

Figure 49: Max and Min drag areas

From the above diagram it is showing that in the where the two re-circulatory flow regions are it has the maximum value of drag on the other hand the green region above and below the re-circulatory flows showing the less drag. Onwards the value of drag and the drag coefficients are decreasing in the case of 12.5o the values of drag and the drag coefficients are 13.844 miles/h and 0.075 respectively.

Figure 51: Pressure trajectories (back

Figure 50: Pressure trajectories (side back

view)

view) - 51 -

Figure 52: Pressure trajectories (side back view) The physical feature of this angle was discussed in the article (G.Franck, N.Nigro, & D'elia, 2009). The vortices are organized in such a manner which leads the flow to become the two dimensional. The some of the vertical base and the

Figure 53: Max and Min drag areas

Slant angle have the edges which is responsible for the formation of vortices. On the side the longitudinal vortices are formed. On the bottom and the top of the longitudinal vortices there are two re-circulatory vortices which is formed and situated one over the other.

- 52 -

It is clear from the above figure that the high number of drag area is reduced now with the result of increased slant angle. Still there are two re-circulatory regions are formed as it is clear from the above stream line with the drag figure.53.

When the angle reaches to the 20o . The value of Drag and the coefficient of drag are 14.519 miles/h and 0.066 respectively. In this the time averaged flow shows the strong and massive three-dimensional behaviour.

Figure 55: Pressure trajectories (back

Figure 54: Pressure trajectories

view)

(back side view)

Figure 56: Pressure trajectories (complete view from left back)

- 53 -

In this case the bubble boundary is increased because the angle is larger. The side longitudinal vortices are stronger and obvious than any other previous cases. As it can be seen in the middle the separation point was created between the two longitudinal vortices.

Figure 57: Max and Min drag areas As it is clear that the high point area is becoming lower as the slant angle goes on increasing. The flowing pattern is showing more streamlines than any other previous. The Lowest drag force and the drag coefficient on the 30o slant angle. The respective values are 8.263 miles/h and 0.0377. The flow trajectories are as follows:

Figure 59: Pressure trajectories (back side

Figure 58: Pressure trajectories (back

view)

view)

- 54 -

Figure 60: Max and Min drag areas In this case the longitudinal vortices are stronger at the back from the sides of the body and going to the surface of the road. It is clear that this model has the least number of drag acting on the back of the body. The last angle which was test is 40 degrees. As the graph and the table are showing that the both the drag force and the coefficient of drag are increasing after the 30 degrees.

Figure 62 : Pressure trajectories (back

Figure 61: Pressure trajectories (side

view)

back view)

- 55 -

Figure 63: Pressure trajectories (complete view from left back)

In this case flow is again going to the two dimensional phase. Like the other flow less than 20o. In this case the re-circulatory regions starting to generate over the surface of the slant and it also has the same flow pattern near the bottom wake. So as soon as the angled goes on increasing the body will be become more square shape which means the drag will go on increasing.

Figure 64: Max and Min drag areas

- 56 -

Figure 65: Maximum drag areas on different backlight angles

Ahmed model with the 30o. This was due to that the time-averaged flow in this case was massively separated 3d. Another factor which contributes to this because the upper surface flow is no longer attached which is mostly around the sharp top surface , rear corners and the flow returns to a structure more like to that of the initial square back. (HAPPIAN-SMITH, 2004). So from the recent years the rear shape of the car are advised to be more hatch back than the square which can be responsible of reducing the drag. From all the results it is clear that now a days in the new car design it is almost necessary for all the medium or large saloon car design to raise the boot lid. In the saloon cars the trailing vortices are formed which are responsible for the low pressure drag. Which makes the saloon and the hatch back design good aerodynamics shape of now days.

- 57 -

5.3 Discussion on the Lift coefficient CL for different Ahmed model: In simple words the pressure difference between the up and down of the car, foil or any streamline object is known as the lift force or the lift coefficient of the object. In this the most important factor which effect the lift of any object is the angle of attack and the camber of the curvature of the body. (Barnard, 1996)

Increasing any of the components will result in increasing the lift of the object. Mostly the lift is depending on the air flow underneath the car and the pressure distribution. Following are the resutls gatthed from the Solidworks simulation:

Backlight angle (degrees) Drag (mile/h) Coefficient of lift (no units)

0 38.058 0.1738

5 38.177 0.17444

12.5

20

30

40

38.049

38.186

38.182

38.177

0.17383

0.1744

0.1743

0.1743

Table 7: Lift force and the Coefficient of lift

Lift force miles/h

Backlight angle Vs Lift force 38.22 38.2 38.18 38.16 38.14 38.12 38.1 38.08 38.06 38.04 0

10

20

30

40

Backlight angle

Graph 3: Backlight angle against lift force

- 58 -

50

Backlight angle Vs Coefficent of lift CL 0.1745

Coeffiecient of lift

0.1744 0.1743 0.1742 0.1741 0.174 0.1739 0.1738 0.1737 0

10

20

30

40

50

Backlight angle

Graph 4: Backlight angle against Lift coefficient

It is clear from the above graph and tables that in this case of Ahmed model with different backlight angle the lift coefficient or the lift force does not affect much on it. All the values are the same with some minor effect or slightly changes.

Figure 66: Lift distribution over different backlight angle of the Ahmed model

The lift force shown over the different Ahmed models. The square back or 0 degree back all have the blue line almost similar which indicates the values for the all models are almost the same with slightly change due to the back angle. This could be because the bottom of the body is the same throughout the tests and the flow domain size is the same as well throughout the tests. This could only be changed when almost there is no gap between the bottom of the model and the flow domain, or there is any deal at the - 59 -

bottom front or the back of the model. This could leads to the big change in the lift of the body. 5.4 Discussion on Pressure areas on different backlight angle:

Figure 67: Pressure distribution over different backlight angles of the Ahmad model Above picture shows the pressure distribution over the different backlight angle. As it is clear that when the angle was 0 degrees which is almost the square back the pressure is distributed over the all the back of the where the 2 re-circulatory vortices are made. This shows that the square back have minimum pressure along all the back from top to bottom. As the backlight angle is increasing the minimum pressure area is going over to the top of the slant angle and as it can be clearly seen that the pressure area on the 30 degrees has the very larger area as compared to the others.

- 60 -

CHAPTER 6: Conclusions

- 61 -

CONCLUSIONS 6.1 Conclusions As summarized by R Stone, “The aerodynamic drag of a vehicle will depend on both the overall shape of the vehicle (e.g., whether it is a notchback or a hatchback), and body details such as the gutters at the edge of the windshield or the wheel trim. In hatchback cars, the angle of inclination of the rear window determines whether separation occurs at the top or bottom of the rear window.” (R Stone, 2004). “When considering vehicle drag results, care should be taken in making comparisons among different tests. The drag coefficient will depend on how the area is defined, the nature of any turbulence, the Reynolds number, the velocity distribution of the incident flow, the accuracy of anybody details (especially on a reduced-scale model), the internal flows, and the presence of the ground. Remember also that vehicles usually are subject to a cross wind and that drag coefficients rise markedly for non-zero yaw angles.” (R Stone,2004) From the results of the simulation which was conducted on the Ahmed body (bluff body). This is concluded that the rear angle for the car is very important and all the aerodynamics forces such as lift and the drag or coefficient of drag and the coefficient of lift all depends on these changes in shape. The findings could suggest ways in which air flow controls the water and dirt deposition patterns on the glass surfaces to aid in vehicle design process.

From the results and discussion it is clear that the back light angle of the model is below than 20o or above 30o the time-averaged flow is almost two dimensional attached. On the other hand if the angle is from 20o to 30o the time-averaged flow is massively three dimensional separated. All the aerodynamics is explained.

The first analysis of this project was on the drag force and the drag coefficient of the bluff body. It explains all the detail which is responsible for the high drag or the low drag. On the basis of results the best up to date design were proposed.

- 62 -

The second analysis of this project is on the lift coefficient or the lift force on the Ahmed model. It was clear from all the results almost all the lift coefficients are the same with some slightly change in the values. This was due to no change in the underneath of the model was taken. It is discussed that the how the lift can be changed the proposed model was discussed.

6.2 Recommendations / Future work

The three-dimensional flow around a vehicle is highly complex, and complete numerical solutions have yet to be achieved. Consequently, the wind tunnel testing of models and full-size vehicles remains a vital part of their aerodynamic development. (R Stone,2004) At first there was wind tunnel testing were also including in the project. This couldn’t be done because of some limitation of the available wind tunnel at Teesside University. The main problem was with the smoke machine and also there was nothing to calculate the pressure, drag or lift forces. So for the future work it is recommended that the wind tunnel tests must be conducted and the results can be compared with the CFD simulation results and then the better discussion can be made, on the other hand the comparison can be done on both the values. For this project as the CFD simulation SolidWorks were used to study the nature of aerodynamics over the bluff body. The results which were obtained were good to some extent as the flow trajectories don’t have many details on them, that’s why there is some point where results cannot be explained properly. For this ANSYS software can be used to study the flow over the bluff body, because it gives the better results in determining the separation points as indicated by literature findings, and supported by the authors study. For this project Ahmed model were used. In the future work some modification can be done to study the lift force and then on the basis of that also can see the variation on the drag force. Then comparison can be done with the original results.

- 63 -

Reference Ahmed, S.R., Ramm, G., Faltin, G., 1984. Some salient features of the time-averaged ground vehicle wake, SAE Technical Paper 840300 AudiAG. (1999, December 14). New Audi Wind Tunnel Centre in Ingolstadt. Retrieved February 05, 2014, from Audi World: http://www.audiworld.com/news/99/wind/content.shtml Barnard, R. H. (1996). Road vehicle aerodynamic design: An introduction. In R. H. Barnard, Road vehicle aerodynamic design: An introduction (pp. 264-265). St Albans: MechAero. Brennan, J. (2011, 06 10). Hooniverse Fastback Friday. Retrieved 03 17, 2014, from Hooniverse: http://hooniverse.com/2011/06/10/hooniverse-fastback-friday-what-is-yourdefinition-of-a-fastback/ Centurion Magazine online. (2011, September 12). Classic Cars. Retrieved April 03, 2014, from Centurion Magazine online. cfdanalysisservices. (2014). SIGNIFICANCE OF CFD ANALYSIS IN MODERN INDUSTRY. Retrieved 03 26, 2014, from CFD Analysis Services: http://cfdanalysisservices.net/cfd-analysis-services-significance-of-cfd-analysis-in-modernindustry/

Emmanuel Guilmineau, 2007, Computational study of flow around a simplified car body, Available online 6 August 2007, date accessed November 2013 E.L, H., A.P, C., H, C. S., & T, V. D. (2013). Navier-Stokes Equations. In H. E.L, C. A.P, C. S. H, & V. D. T, Aerodyanamics for Engineering students (pp. 113-115). Kidlington : Elsevier. FENTON J 1999, Advances in Vehicle Design, ISBN-10: 1860581811 G.Franck, N.Nigro, M., & D'elia, J. (2009). Numertical Simulation of the flow around the ahemd vehicle model. Latin American Applied Research 39, 295-306. Genta, G. (2008). Road Vehicle Derodynamics. In G. Genta, Motor Vehicle Dynamics Modeling and Simulation (pp. 89-90). Toh Tuck, Singapore : World Scientific Publishing Co .Pte. Ltd. Guilmineau, E. (2008). Computational Study of flow around a simplified car body. Journal of wind Engineering and Industrial Aerodynamics 96, 1207-1217. Hall, J. (2013, 02 14). 'Ground Effect'. Its history and Theory explained. Retrieved 03 15, 2014, from The Judge 13. HAPPIAN-SMITH, J. (2004). An introduction to Moden Vehicle Design. Warrendale: SAE International . Huerta, J. D. (2003). Finite Element Methods for Flow Problems. Sussex: John and Wiley & Sons.

- 64 -

Institution of Mecanical Engineering. (2013, 10 10). C1385 - 2014 International Vehicle Aerodynamics Conference. Retrieved 03 01, 2014, from Institution of Mecanical Engineering. Joseph, K. (1995). In K. Joseph, Race Car Aerodynamics: Designing for speed (pp. 94-95). Cambridge: Bentley Pubishers. Nasira, R. E., Mohamada, F., Kasirana, R., Adenana, M. S., Mohamed, M. F., Mata, M. H., & Ghania, A. R. (2012). Aerodynamics of ARTeC’s PEC 2011 EMo-C Car. Procedia Engineering 41, 1775-1780. National Aeronautics and Space Administration. (2012). Factors That Affect Aerodynamics. Retrieved 03 15, 2014, from Exploration NASA: http://exploration.grc.nasa.gov/education/rocket/factord.html

R Stone and J K Ball, "Automotive Engineering Fundamentals", SAE 2004 Ringis, V. (2013, February 16). Mercedes-Benz Aerodynamics. Retrieved March 10, 2014, from Mecdes-Benz Digest News. Scott, J. (2005, 02 13). Golf Ball Dimples & Drag. Retrieved 03 26, 2014, from Aero space web: http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml SolidWorks. (2014). Element Types. Retrieved 03 10, 2014, from Help. Solidworks: http://help.solidworks.com/2012/English/SolidWorks/cworks/Mesh_Types.htm?id=5600bd 43ae334ceb9f0521de4f3b09e5 W.Slater, J. (2008, 06 17). CFD Analysis Process. Retrieved 03 18, 2014, from NASA: http://www.grc.nasa.gov/WWW/wind/valid/tutorial/process.html Watkins, S., & Vino, G. (2008). The effect of vehcile spacing on the aerodynamics of a representative car shape. Journal of Wind Engineering and Industirial Aerodynamics 96, 1232-1239.

- 65 -

APPENDICES

- 66 -

APPENDIX A

- 67 -

Solid works report: 0 degree

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 MHz

General Info Model

U:\3rd year\project\tests\0\AHMED MODEL 0.SLDPRT Ahmed model U:\3rd year\project\tests\0\3 SI (m-kg-s) External (exclude internal spaces) On Global coordinate system X

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow

None - 68 -

At X min At X max At Y min At Y max At Z min At Z max

Default Default Default Default Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals Drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

Equation Goals Drag Coefficient Type Formula

Equation Goal Drag/(0.5*1.2922*55^2*0.112032) - 69 -

Dimensionality Use in convergence

No units On

Lift Cofficient Type Formula Dimensionality Use in convergence

Equation Goal Lift/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 123 CPU time: 487 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 122 Goals are converged 122 Calculation finished 123

17:55:00 , Apr 19 17:55:25 , Apr 19 18:03:16 , Apr 19

18:04:51 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells

101520 98392 1912 - 70 -

Partial cells Irregular cells Trimmed cells

1216 0 0

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Drag Lift Lift Coefficient Drag Coefficient

mile/h mile/h

20.323 38.058 0.1738132

100 100 100

Use in convergence On On On

0.0928156

100

On

Delta

Criteria

0.908273201 0.0137368797 6.27365866e005 0.00414810071

0.931433449 0.0546892793 0.000249766962

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100932.09 292.95 1.20 0 -36.777 -39.157 -67.277 292.95 0 0.038 0 -392.91 0

Maximum 101694.72 293.50 1.21 71.213 36.928 36.896 20.356 293.50 0.09 339.339 1.85 369.72 0

0

0

- 71 -

0.00425387399

5 degrees

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 MHz

General Info Model

U:\3rd year\project\tests\5\AHMED MODEL 5.SLDPRT Ahmed model (2) U:\3rd year\project\tests\5\2 SI (m-kg-s) External (exclude internal spaces) On Global coordinate system X

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow At X min At X max

None Default Default - 72 -

At Y min At Y max At Z min At Z max

Default Default Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals Drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

Equation Goals Drag Cofficient Type Formula Dimensionality Use in convergence

Equation Goal Drag/(0.5*1.2922*55^2*0.112032) No units On - 73 -

lift Cofficient Type Formula Dimensionality Use in convergence

Equation Goal Lift/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 110 CPU time: 421 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 109 Goals are converged 109 Calculation finished 110

18:16:15 , Apr 19 18:16:27 , Apr 19 18:23:20 , Apr 19

18:26:13 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells Partial cells Irregular cells

101520 98440 1872 1208 0 - 74 -

Trimmed cells

0

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Delta

Criteria

100 100 100

Use in convergence On On On

Drag Lift lift Coefficient Drag Coefficient

mile/h mile/h

16.454 38.050 0.1737749

0.518039245 0.0517874752 0.000236514368

0.711705581 0.0572636863 0.000261524327

0.0751448

100

On

0.00236589493

0.0032503727

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100931.56 292.95 1.20 0 -36.834 -39.064 -67.450 292.95 0 0.033 0 -393.44 0

Maximum 101694.69 293.50 1.21 71.186 36.901 36.889 16.615 293.50 0.09 340.112 1.85 369.69 0

0

0

- 75 -

12.5 degrees

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 MHz

General Info Model

U:\3rd year\project\tests\12.5\New folder\AHMED MODEL 12.5.SLDPRT Project (1) U:\3rd year\project\tests\12.5\New folder\2 SI (m-kg-s) External (not exclude internal spaces) Off Global coordinate system Z

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow At X min At X max At Y min At Y max

None Default Default Default Default - 76 -

At Z min At Z max

Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Equation Goals Cofficient of lift Type Formula Dimensionality Use in convergence

Equation Goal lift/(0.5*1.2922*55^2*0.112032) No units On

Coficient of drag - 77 -

Type Formula Dimensionality Use in convergence

Equation Goal drag/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 131 CPU time: 487 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 130 Goals are converged 130 Calculation finished 131

18:30:59 , Apr 19 18:31:42 , Apr 19 18:39:19 , Apr 19

18:40:12 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells Partial cells Irregular cells Trimmed cells

101520 98452 1862 1206 0 0

- 78 -

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Delta

Criteria

100 100 100

Use in convergence On On On

lift drag Coficient of drag Cofficient of lift

mile/h mile/h

38.177 13.844 0.0632248

0.0177759906 0.482626477 0.00220416415

0.0573083696 0.50676727 0.0023144156

0.1743537

100

On

8.11832818e005

0.000261728396

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100929.47 292.95 1.20 0 -36.847 -39.110 -67.493 292.95 0 0.033 0 -395.53 0

Maximum 101694.65 293.50 1.21 71.198 36.881 37.012 13.952 293.50 0.09 348.583 1.85 369.65 0

0

0

- 79 -

20 degrees

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 MHz

General Info Model

U:\3rd year\project\tests\20\AHMED MODEL 20.SLDPRT Ahmed model U:\3rd year\project\tests\20\3 SI (m-kg-s) External (exclude internal spaces) On Global coordinate system X

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow At X min

None Default

- 80 -

At X max At Y min At Y max At Z min At Z max

Default Default Default Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals Drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

Equation Goals Drag Coefficient Type Formula Dimensionality

Equation Goal Drag/(0.5*1.2922*55^2*0.112032) No units - 81 -

Use in convergence

On

Lift Coefficient Type Formula Dimensionality Use in convergence

Equation Goal Lift/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 112 CPU time: 435 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 111 Goals are converged 111 Calculation finished 112

18:45:00 , Apr 19 18:45:22 , Apr 19 18:52:23 , Apr 19

18:53:54 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells Partial cells

101520 98476 1842 1202 - 82 -

Irregular cells Trimmed cells

0 0

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Delta

Criteria

100 100 100

Use in convergence On On On

Drag Lift Lift Coefficient Drag Coefficeint

mile/h mile/h

14.518 38.186 0.1743960

0.462990754 0.050056881 0.000228610712

0.494643439 0.058269208 0.000266116563

0.0663047

100

On

0.00211448744

0.00225904584

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100930.07 292.95 1.20 0 -36.767 -39.108 -67.547 292.95 0 0.034 0 -394.93 0

Maximum 101694.63 293.50 1.21 71.225 37.019 37.018 14.798 293.50 0.09 353.640 1.85 369.63 0

0

0

- 83 -

30 degrees

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 (3094) MHz

General Info Model

U:\3rd year\project\tests\30\New folder\AHMED MODEL 30.SLDPRT Ahmed model U:\3rd year\project\tests\30\New folder\3 SI (m-kg-s) External (exclude internal spaces) On Global coordinate system X

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow At X min At X max At Y min

None Default Default Default - 84 -

At Y max At Z min At Z max

Default Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals Drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

Equation Goals Drag Coefficient Type Formula Dimensionality Use in convergence

Equation Goal Drag/(0.5*1.2922*55^2*0.112032) No units On

- 85 -

Lift Coefficients Type Formula Dimensionality Use in convergence

Equation Goal Lift/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 140 CPU time: 533 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 139 Goals are converged 139 Calculation finished 140

19:00:46 , Apr 19 19:01:17 , Apr 19 19:09:44 , Apr 19

19:10:40 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells Partial cells Irregular cells Trimmed cells

101520 98476 1842 1202 0 0 - 86 -

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Drag Lift Lift Coefficients Drag Coefficient

mile/h mile/h

8.263 38.182 0.1743789

100 100 100

Use in convergence On On On

0.0377366

100

On

Delta

Criteria

0.320967027 0.0115949958 5.29545627e005 0.00146586242

0.323879149 0.0580110528 0.000264937564

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100818.36 292.95 1.20 0 -36.757 -39.098 -67.440 292.95 0 0.035 0 -506.64 0

Maximum 101694.59 293.50 1.21 71.231 37.073 37.016 9.167 293.50 0.09 509.752 1.85 369.59 0

0

0

- 87 -

0.00147916213

40 degrees

FULL REPORT System Info Product Computer name User name Processors Memory Operating system CAD version CPU speed

Flow Simulation 2013 SP4.0. Build: 2401 SSE-172-78821 j9112108 Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz 16334 MB / 8388607 MB Windows 7 Service Pack 1 (Build 7601) SolidWorks 2013 SP4.0 3401 (2992) MHz

General Info Model

U:\3rd year\project\tests\40\AHMED MODEL 40.SLDPRT Ahmed model U:\3rd year\project\tests\40\3 SI (m-kg-s) External (exclude internal spaces) On Global coordinate system X

Project name Project path Units system Analysis type Exclude cavities without flow conditions Coordinate system Reference axis

INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 4 Advanced narrow channel refinement: Off Refinement in solid region: Off

Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic

Computational Domain Size X min X max Y min Y max Z min Z max

-1.000 m 1.000 m -0.200 m 1.000 m -6.000 m 0.800 m

Boundary Conditions 2D plane flow At X min At X max At Y min

None Default Default Default - 88 -

At Y max At Z min At Z max

Default Default Default

Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent High Mach number flow: Off Humidity: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall

Ambient Conditions Thermodynamic parameters

Static Pressure: 101325.00 Pa Temperature: 293.20 K Velocity vector Velocity in X direction: 0 mile/h Velocity in Y direction: 0 mile/h Velocity in Z direction: -55.000 mile/h Turbulence intensity and length Intensity: 0.10 % Length: 0.003 m

Velocity parameters

Turbulence parameters

Material Settings Fluids Air

Goals Global Goals Drag Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Z) Maximum value Global coordinate system On

Lift Type Goal type Calculate Coordinate system Use in convergence

Global Goal Velocity (Y) Maximum value Global coordinate system On

Equation Goals Drag Coefficient Type Formula Dimensionality Use in convergence

Equation Goal Drag/(0.5*1.2922*55^2*0.112032) No units On

- 89 -

Lift Coefficient Type Formula Dimensionality Use in convergence

Equation Goal Lift/(0.5*1.2922*55^2*0.112032) No units On

Calculation Control Options Finish Conditions Finish conditions Maximum travels Goals convergence

If one is satisfied 4 Analysis interval: 5e-001

Solver Refinement Refinement: Disabled

Results Saving Save before refinement

On

Advanced Control Options Flow Freezing Flow freezing strategy

Disabled

RESULTS General Info Iterations: 163 CPU time: 462 s

Log Preparing data for calculation Calculation started 0 Calculation has converged since the following criteria are satisfied: 162 Goals are converged 162 Calculation finished 163

19:16:56 , Apr 19 19:17:37 , Apr 19 19:24:50 , Apr 19

19:25:11 , Apr 19

Calculation Mesh Basic Mesh Dimensions Number of cells in X Number of cells in Y Number of cells in Z

40 27 94

Number Of Cells Total cells Fluid cells Solid cells Partial cells Irregular cells Trimmed cells

101520 98476 1842 1202 0 0 - 90 -

Maximum refinement level: 0

Goals Name

Unit

Value

Progress

Drag Lift Lift Coefficient Drag Coefficient

mile/h mile/h

9.776 38.178 0.1743590

100 100 100

Use in convergence On On On

0.0446456

100

On

Delta

Criteria

0.379564393 0.00869277748 3.97000774e005 0.00173347769

0.380563273 0.0570436175 0.000260519268

Min/Max Table Name Pressure [Pa] Temperature [K] Density (Fluid) [kg/m^3] Velocity [mile/h] Velocity (X) [mile/h] Velocity (Y) [mile/h] Velocity (Z) [mile/h] Temperature (Fluid) [K] Mach Number [ ] Vorticity [1/s] Shear Stress [Pa] Relative Pressure [Pa] Heat Transfer Coefficient [W/m^2/K] Surface Heat Flux [W/m^2]

Minimum 100687.91 292.95 1.20 0 -36.844 -39.112 -67.384 292.95 0 0.016 0 -637.09 0

Maximum 101694.70 293.50 1.21 71.190 36.872 37.014 9.818 293.50 0.09 699.850 1.85 369.70 0

0

0

- 91 -

0.00173803959