Automobile design optimisation using adjoin ...

Kingston University

Faculty of Computing, Engineering and Science BSc Mechanical Engineering

Automobile design optimisation using adjoin method By

Hamid Eskandari 22/04/2016

Module Leader: DR Konstantin Volkov Supervisor: Dr Ali Heidari

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Abstract The prime aim in automotive aerodynamic on the roads is to minimise drag on alongside of unwanted lift force to maximise fuel efficiency and lower air pollution and C02 emission, this includes sound emission as well. Without the implementation of aerodynamic forces known as lift and drag components, flying for aircrafts would not be a possibility for instance, wind turbine would not be able to spin, and many other applications would not function. According to Levi & Hart, (2010), the fluid decomposes on the body as a force, which leads to lift and drag forces. The force normal to velocity of the free-stream is known as the lift component and the force velocity in free-stream direction is known as the drag. Aerodynamic force consists of friction force as well which is dependent on vehicle speed. It was 1920s that the investigation of aerodynamic resulted into reduction of drag by altering the aerodynamic shape of a vehicle. This discovery was initiated by British and German engineers and the influence of drag on higher performing vehicles were analysed in 1950s and in 1960s the investigation went in more details with sound emission at significantly effects drag at high speed (Cebeci, et al., 2005). The initial approach in this project is to produce a CAD design from an existing VAN which is Ford Transit, and modify it to gain reduction in drag through aerodynamic improvement based on literature review to find and pinpoint high drag acting on the shape of the car and refining it to minimise the drag further. Since CFD simulations are the main aspect of the project, to have a reliable results then domain size sensitivity, mesh quality of the domain and van sensitivity along with inflation layers through calculations should be worked out. This enables the domain size to be big enough so it does not influence the results and it is not bigger than required to influence the time intervals of the simulations. The mesh quality means the smaller the mesh cells the higher the accuracy of the results, however this increase the time interval of the simulation running, mesh sensitivity can be used to find the right balance. Inflation layers influence the streamline from near the wall; this increases the sensitivity of the drag along the van itself. In second part if the project the modification of the van begins. Based on the literature review the aerodynamic performance is analysed and is optimised. Using different sections of the car which are adding different angles to the top roof at the rear end, front windshield and bumper, adding angles to underneath the car both front and back at separate simulation and the lowest drag are added to the final optimised version. The final overall optimisation of the above named type modification came to 12.8%. This aligns with the aim of the project that a significant reduction of drag has been achieved.

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Acknowledgements

I need to thank my friends and family for their patience and guidance throughout my studies. I have to sincerely thank my wife and kids for their understandings and love and support, without them this project and study would have never been possible. My supervisor Dr Ali Heidari supported me with this project and I need to thank him dearly.

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Contents Abstract ................................................................................................................................................... 2 Acknowledgements................................................................................................................................. 3 1.

Introduction .................................................................................................................................. 10 1.1History of Aerodynamic ............................................................................................................... 10

2.

1.2

Friction, Drag Force and Down Force in vehicles .................................................................. 11

1.3

Typical drag coefficients ....................................................................................................... 12

1.4

Breakthrough of the Streamline effect ................................................................................. 15

Project outlook:............................................................................................................................. 16 2.1 Aim and Objective: ...................................................................................................................... 16

3.

Literature Review .......................................................................................................................... 18

4.

Turbulence Model studies: ........................................................................................................... 22 4.1.1 K-epsilon............................................................................................................................... 22 4.1.2 K-omega ............................................................................................................................... 22 4.1.3 Baseline (BSL) ....................................................................................................................... 22 4.1.4 Shear Stress Transport (SST) ................................................................................................ 23 4.2 Turbulent study of Ford Transit .................................................................................................. 23

5.

Problem solving............................................................................................................................. 24 5.1. Ford transit CAD Designing ........................................................................................................ 24 5.2. Simulation parameter ................................................................................................................ 25 5.2.1. Domain simulation study .................................................................................................... 25 5.2.2. Domain mash ...................................................................................................................... 27 5.2.3. Van mash study. .................................................................................................................. 29 5.2.4. Inflation layer ...................................................................................................................... 30 5.3. Ford Transit Setup ...................................................................................................................... 33 5.4. Ford Transit simulation Results.................................................................................................. 33

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Design Optimisation ...................................................................................................................... 35 6.1

Angle of the back bumper..................................................................................................... 36

6.1.1 6.2

Results ........................................................................................................................... 37

Angle of the top roof............................................................................................................. 38

6.2.1 Results .................................................................................................................................. 39 6.3

Angle of the front bumper .................................................................................................... 42

6.3.1 Results .................................................................................................................................. 42 6.4

Windshield angle reduction .................................................................................................. 43 4

6.4.1 7.

Results ........................................................................................................................... 44

Final Modification CAD design ...................................................................................................... 46 7.1

Final Optimisation Design Simulation ................................................................................... 46

8.

Discussion and Conclusion ............................................................................................................ 49

9.

Reference ...................................................................................................................................... 53

10.

Appendix ................................................................................................................................... 55

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Figure 1 : Downforce, Lift and Drag, (Miniuy, 2015)............................................................................. 12 Figure 2: highest drag coefficient (Physics Stack Exchange, 2016) ....................................................... 13 Figure 3: Time history of Aerodynamic drag of cars in comparison with change in geometry of streamlined bodies (medlibrary, 2015) ....................................................................................... 14 Figure 4: La Jamais contente (1899) ..................................................................................................... 15 Figure 5 drag in each section of a car ................................................................................................... 15 Figure 6 : the vortex created behind the vehicle B.Abdi, (2013) .......................................................... 19 Figure 7 : design Front Bonnet Duct, Wing, Ahmad Haseeb & CHACKO, Sibi, (2012) .......................... 20 Figure 8 : Dimension and shape of diffuser Akshay Parab, Ammar Sakarwala, (2013) ........................ 20 Figure 9 : design variables K. S. SONG, S. O. KANG, S. O. JUN, (2012) .................................................. 21 Figure 10 Ford Transit CAD design Measurement Specification (H.eskandari) .................................... 24 Figure 11 Ford Transit CAD design (H.Eskandari) ................................................................................. 25 Figure 12 sketch of the domain aound the imported van (H.Eskandari) .............................................. 26 Figure 13 : the result for medium mesh quality (H.Eskandari) ............................................................. 28 Figure 14 : Van mesh with inflation layers(H.Eskandari) ...................................................................... 30 Figure 15 : Boundary Layers - Wall Functions (LEAP CFD Team, 2012) ................................................ 31 Figure 16 : van with 32 inflation layers for Speed 70mph= 31.293 m/s ............................................... 33 Figure 17 : Setup of the Ford Transit .................................................................................................... 33 Figure 18 Ford Transit Velocity Contour ............................................................................................... 34 Figure 19 Ford Transit pressure Contour .............................................................................................. 34 Figure 20 Ford Transit Streamline ........................................................................................................ 34 Figure 21 optimisation of Ford Transit ................................................................................................. 35 Figure 22 angle of the back bumper ..................................................................................................... 36 Figure 23 : the angles behind of the vehicle, back of the car with A) at 9.08, B) at 12.08, C) at 15.08 36 Figure 24 streamline resize 3 degree back of the van (12.08 degree).................................................. 37 Figure 25 : 6 degree from the original (15.08 degree).......................................................................... 37 Figure 26 Angle of Top Roof.................................................................................................................. 38 Figure 27 : roof angle 1 to 4 degree ...................................................................................................... 38 Figure 28 1 degree modification ........................................................................................................... 39 Figure 29 2 degrees modification ......................................................................................................... 39 Figure 30 3 degrees modification ......................................................................................................... 40 Figure 31 4 degrees modification ......................................................................................................... 40 Figure 32 Original and optimised top roof angle comparison .............................................................. 41 Figure 33 Front bumper ........................................................................................................................ 42 Figure 34 : front of car angles (A) Original angle, (B) modified angle................................................... 42 Figure 35 modification of the front bumper ......................................................................................... 43 Figure 36 Front windshield of Ford Transit ........................................................................................... 43 Figure 37 Modified version of the windshield ...................................................................................... 44 Figure 38 Streamline of windshield modification ................................................................................. 44 Figure 39 Final improved CAD design ................................................................................................... 46 Figure 40 : final design streamlines at 31.293 m/s (70 miles per hour) .............................................. 47 Figure 41 : final design streamlines at 15.626 m/s (35 miles per hour) ............................................... 47 Figure 42 Original and optimised top roof angle comparison .............................................................. 51 6

Figure 43 : Pressure contour Van optimisation back 3 degree ............................................................. 55 Figure 44 : velocity contour Van optimisation back 3 degree .............................................................. 55 Figure 45 : Pressure contour Optimisation top roof 1 degree .............................................................. 55 Figure 46 : velocity contour Optimisation top roof 1 degree ............................................................... 56 Figure 47 : Pressure contour Optimisation top roof 2 degree .............................................................. 56 Figure 48 : velocity contour Optimisation top roof 2 degree ............................................................... 56 Figure 49 : Pressure contour Optimisation top roof 3 degree .............................................................. 57 Figure 50 : velocity contour Optimisation top roof 3 degree ............................................................... 57 Figure 51 : Pressure contour Optimisation top roof 4 degree .............................................................. 57 Figure 52 : velocity contour Optimisation top roof 4 degree ............................................................... 58 Figure 53 : top roof CD graph................................................................................................................ 58 Figure 54 : top roof CL graph ................................................................................................................ 58 Figure 55: top roof Velocity graph ........................................................................................................ 59 Figure 56 : top roof Pressure graph ...................................................................................................... 59 Figure 57 : Pressure contour, Van final optimise speed 15.626m/s ..................................................... 60 Figure 58 : velocity contour, Van final optimise speed 15.626m/s ...................................................... 60 Figure 59 : Pressure Final operation van .............................................................................................. 60 Figure 60 : velocity Final operation van ............................................................................................... 61 Figure 61 : velocity contour Angle of front bumper 3 Degree .............................................................. 61 Figure 62 : pressure contour Angle of front bumper 3 Degree ............................................................ 61 Figure 63 : Van final optimisation speed 31.293 m/s ........................................................................... 62 Figure 64 : Van final optimisation speed 31.293 m/s ........................................................................... 62 Figure 65 : Van final optimisation speed 15.656 m/s ........................................................................... 62 Figure 66 : Van final optimisation speed 15.656 m/s ........................................................................... 63

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Table 1 CD and CD A values for various vehicle, (Mercedes-Benz, 2016), (Barnard, R.H., 2001), (ecomodder, 2016) ............................................................................................................................... 12 Table 2 Turbulent model study using Drag ........................................................................................... 23 Table 3 domain size study ..................................................................................................................... 26 Table 4 final domain size study ............................................................................................................. 27 Table 5 : The effect of mesh quality on output parameters ................................................................. 28 Table 6 : minimum domain mesh studies ............................................................................................. 28 Table 7 : maximum domain mesh studies ............................................................................................ 29 Table 8 : Van mesh study ...................................................................................................................... 30 Table 9 Drag reduction by changing the angle of back bumper ........................................................... 38 Table 10 Drag reduction by changing the top roof angle ..................................................................... 41 Table 11 Drag reduction by changing the bumper angle...................................................................... 43 Table 12 Modification of front windshield. .......................................................................................... 45 Table 13 final optimisation results........................................................................................................ 47

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Nomenclature m2

A

Area (Frontal area unless otherwise stated)

CD

Coefficient of Drag

CL

Coefficient of Lift

-

CP

Coefficient of Pressure

-

D

Drag Force

N

DF

Downforce

N

F

Force (Aerodynamic)

N

g

Gravity Constant

m/s2

h

Height

m

L

Lift, Characteristic Length

N, m

P

Pressure

N/m2

Re

Reynolds Number

-

U

Free-stream Velocity

m/s

V

Velocity

m/s

x

Horizontal distance from origin

m

y

Vertical distance from origin

m

δ

Velocity Boundary Layer Thickness

-

𝛍

Dynamic Viscosity

kg/ms

𝛒

Density

kg/m2

∞

Denotes Free-stream conditions

-

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1. Introduction In order to have low drag on a car engineers design cars based on aerodynamic principle of smooth body shape. Designing and optimising automobile aerodynamic shape is the industry’s main aspect of focus. Using initiatives the efficiency of a car can be optimised, less air drag for instance and higher aerodynamic flow can be obtained. This enables the reduction of fuel consumption which improves fuel efficiency that results into improvement of C02 emission and air pollution. In recent years automotive industry is paying more attention to this factor as fuel is limited and pollution is worsens by day. By controlling and optimising the shape of a car then the drag minimises and results into the named factors of improvements. The government has also put pressure on automotive industries to use green fuel and produce lower C02. The government in the UK has also produced a Band width based on C02 production of a car that is based on that, the road tax is given. Below 99 g/km the road tax becomes £0 per year. In this project the design of Ford Transit is used for optimisation purposes. A CAD design using SolidWorks based on the van is produced and using domain size sensitivity, Domain mesh sensitivity, van mesh sensitivity and adding inflation layers by calculations, the original van is simulated based on its drag components and contours of pressure and velocity with streamline is taken using ANSYS. Then using the output of the data, the optimisation based on literature review is added to the van using separate selection of the van itself and optimising each section individually then the best modification of each part selection is added to the final van design and a final simulation is taken into account. The selections adding different angles to the top roof at the rear end, front windshield and bumper, adding angles to underneath the car both front and back.

1.1History of Aerodynamic Aerodynamic drag according to Barned (2001) is a force due to distribution of pressure surrounding the vehicle and partially due to shear force of the surface airflow. In normal vehicles design for cities and roads the main factors for aerodynamic is the drag force that consists of forward motion resistance within a vehicle. Every dynamic vehicle opposes a force of motion. Generally the mechanical force is known as the drag. This is caused and generate by solid body interaction with a fluid or liquid gas. Drag is not due to a force field of gravity or electromagnetic where an object affects another without a physical contact. If there is no contact between a fluid and solid body then no drag is produced, this is because drag is generated by a velocity difference of solid body and the fluid, so there must be a motion between the two. It makes no difference whether the object is stationary and the fluid is dynamic or vice versa. 10

Since drag is force and subsequently is a vector with both magnitude and direction. Lift acts in perpendicular to the motion where drag acts in opposite direction of the motion. Many factors can affect drag and also some factors affect lift as well. Drag can be defined as aerodynamic friction with one of the main factors being skin friction. In any CFD simulation or wind tunnel testing the first few layers, however small, the air velocity is zero due to skin friction, which is a friction between the solid body and air molecules. This is due to an interaction of a solid and a gas that the skin friction’s magnitude is dependent on both gas and solid properties. Slick and smooth surface of a solid influences the improvement of skin friction, and a rough and high viscous surface makes skin friction to be high, which increases drag. In gas property, the viscosity of the air and viscosity of the forces in respect to the flow motion is expressed as Reynold number. Across the solid surface a low energy boundary layer is generated that the magnitude of skin friction is dependent on the condition of this boundary layer. Another aspect of aerodynamic is the resistance of the object motion in fluid. This is a drag dependent on the shape of the vehicle known as form drag. Airflow motion influences a change of local velocity and pressure. Pressure is a measurement of momentum in molecules of gas and change in momentum results into generating force, and various pressure distributions will produce a force on the body. By integrating or adding the local pressure times by the entire body’s surface area, the magnitude can be determined (NASA, 2016).

1.2

Friction, Drag Force and Down Force in vehicles

Drag force is a common problem in cars that occur while the vehicle is moving. The air is pushing the and brushes the body of the car and this causes friction, along with this the air resistance is also acting upon the car that requires the car to overcome the resistance in order to move forward to backward. These common forces are known as drag. In aerodynamic of cars, drag plays a big role in having a fuel efficient vehicle. By modification and optimising the aerodynamic shape of the vehicle, the drag force acting upon the vehicle is lowered and this causes the vehicle to use less fuel in order to travel the same distance. Subsequently the fuel consumption is minimised by the aerodynamic efficiency and also this influences the C02 emission and air pollution. Down force in cars are a magnitude of drag components and the definition of the forces in the resultant of the total aerodynamic drag on a moving body at velocity of the x direction on a fluid that is also the net effect of all pressures acting upon the body of the vehicle. The formula to calculate total aerodynamic forces on a body using static pressure at various areas across the body is given below:

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1 𝐹 = ∁𝑃 × 𝜌𝑉12 × 𝐴 [𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐴𝑒𝑟𝑜𝑑𝑎𝑦𝑛𝑎𝑚𝑖𝑐 𝐹𝑜𝑟𝑐𝑒 2 The components of Lift and Drag are given below on a simple equation. 1 L = ∁𝐿 × 𝜌𝑉12 × 𝐴 [𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐿𝑖𝑓𝑡] 2 1 D = ∁𝑃 × 𝜌𝑉12 × 𝐴 [𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐷𝑟𝑎𝑔] 2 The Figure below illustrates the forces acting upon the body of a car. This includes the Drag force acting backwards. Lift force is acting upwards and the down force is acting downwards.

Figure 1 : Downforce, Lift and Drag, (Miniuy, 2015)

1.3

Typical drag coefficients

From 1920 the aerodynamic design of vehicles has been improving and this has changed blunt body shape into a more aerodynamic in respect to airflow, to maximise streamline to reduce air drag from 0.95 to 0.30, which is effectively less than one third. The following table shows the evolvement of crag coefficient from 1933 to recent.

Vehicle Bugatti type 51 (1933) Jaguar D-type (1955) VW Microbus (1958) Honda Civic,(1988) Audi,A8,(2002 Chevrolet ,Astro Van(2005) Dodge RAM 1500 QC Aptera ,2e prototype (2011) Toyota Prius, (2012) Mercedes-Benz at the CES® 2015

∁𝐷 0.74 0.49 0.45 0.34 0.28 0.49 0.52 0.15 0.26 0.19

∁𝐷 A 0.96 0.59 1.04 0.65 0.63 1.55 1.69 0.27 0.15 0.22

Table 1 CD and CD A values for various vehicle, (Mercedes-Benz, 2016), (Barnard, R.H., 2001), (ecomodder, 2016)

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Drag Area represented by (CDA) is the efficiency of power into forward speed and the lower the value, the better the drag area, and CD is the coefficient of drag and A is the frontal area of the vehicle. A also is exposed to the incoming air, while moving forward. In comparison from the table above, the only van from the table has higher CDA value at 1.55. The comparison shows the evolving of drag area reduction is normal vehicles compared to a van which is highlighted. In Table 1, the most recent cars have a CDA of as low as 0.15, although in vans this value is way higher due to the purpose design of the vehicle and this causes drag to be significantly higher. Just to demonstrate the drag improvement of recent years the table above shows how gradually from 1933 this has been taken in account and a significant reduction is shown. Figure 1 below illustrates the drag coefficient against the shape and geometry. The sphere shape has a drag coefficient of 0.47 and as it progresses in respect to aerodynamic principles. The highest drag coefficient is obtained by short cylinder with 1.15 followed by cube with 1.05. Using an elliptical shape and extended mid-section give a better drag coefficient, similarly to streamlined body that has a drag coefficient of 0.04.

Figure 2: highest drag coefficient (Physics Stack Exchange, 2016)

Drag coefficient varies at various velocities and Reynolds number represents that. In most cases drag coefficients can be considered as constant in constant velocities. Average cruising speed on vehicles is kept constant to minimise any changes to CD due to CD being sensitive and could drastically change.

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The higher the CD (drag coefficient) the higher the drag force and the lower the drag force the lower the CD value becomes. CAFE short for Corporate Average Fuel Economy was established in 1975, and influenced cars to be more fuel efficient and in 2016 the model vehicles are at the best fuel consumption configurations with minimum of 34.1 miles per gallon of up to 83 per gallon. A combination of Figure 1 is demonstrated in Figure 2. From 1920 the cars had an average drag coefficient of 0.8 with plate body type and as the time passed and the study of aerodynamic improved in 1940s it reached 0.4 with body type of cylinder, which is half of what is use to be 20 year in prior to that. In 1970 the oval was introduced that is decreased CD even further to half of what it used to be at 0.4. In current studies of CD of vehicles in 2015 and 2016 it reach an average of 0.16 which is less than half of what used to be in 1970s.

Figure 3: Time history of Aerodynamic drag of cars in comparison with change in geometry of streamlined bodies (medlibrary, 2015)

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1.4

Breakthrough of the Streamline effect

Figure 3, illustrates the aerodynamic car that broke 100km/h known as the Land Speed Record (LSR) in 1899. This was achieved by La Jamais Contente that implemented a body type of aluminium streamlined body

Figure 4: La Jamais contente (1899)

The focused areas for optimisation based on study as illustrated in figure 4 the areas with the most drag acting upon are marked, top of the car has 45% of total drag, 30% the airflow underneath the car and 25% the tyres and the back of the car. Based on this the modifications began. At first step to begin our optimisation was to design the van accurately and effectively. Identification of these areas results into identification and paying more attention on what exactly needs to be carried out on the original van design. This leads to better understanding of what and where needs the most attention for optimisation.

Figure 5 drag in each section of a car

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2. Project outlook: In this section of the project many aspect of the planning process will be illustrated. The initial approach is to expand on the aim and the objectives that the project is targeting to achieve and also its details in objectives.

2.1 Aim and Objective: The aim is to understand and review aerodynamic principles in vehicles and to consider various methods of generating downforce and reducing drag, and using an existing van apply modification to optimise drag, so simply the aim of the project is to study the aerodynamic principle to maximise fuel efficiency subsequently lowering drag using an existing Ford Transit van. The initial approach is to analyse different methods to reduce drag and also generate downforce, applying aerodynamic principles, using SolidWorks a CAD design of an existing van which is considered to be Ford Transit. Series of simulations needs to be carried out in order to find the optimum conditions for the following. 

Domain size sensitivity study



Domain Mesh sensitivity study



Van mesh sensitivity study

Using the above parameters enables the accuracy of the results to be in precision. The number of inflation layer is calculated to maximise the near-wall sensitivity. In order to achieve the aim of the project then flow control, active and passive control should also be studied and understood. In consideration of the objectives, the tools of SolidWorks and ANSYS to incorporate design modification and run appropriate simulations in regards to the sensitivity study and final study of the design along with the design optimisations. Lift and drag components needs to be recorded along with pressure, velocity contours and also streamline of the original CAD design of Ford Transit and each modification made. The areas of modification selected based on literature review and the relevant sources of drag are identified from the contours and the drag component itself. The final design contains the best drag component gained from the part modified. The followings are the step by step procedures: 1. Review and understand the principles of aerodynamic in vehicles 2. Choose an appropriate existing (Ford Transit) 3. Produce a CAD design based on Ford Transit using SolidWorks 4. Using ANSYS and the CAD design to carry out the following studies: a. Domain size sensitivity study 16

b. Domain Mesh sensitivity study c. Van mesh sensitivity study 5. Obtain drag component, pressure and velocity contour, and lastly streamline from the midsection of the van. 6. Based on the literature review and studies of the above contours apply modifications. In this case the front of the van has been modified and improved. The circled locations are the focus to lower drag. The front of the van along with the windshield, which needs to be smoothed out as you can see the modification has been already carried out on this picture. The corners of underneath of the van needs angle adjustment and top roof of the van needs angle adjustment as well. 7. Then after analysis of each point of modification, the lowest combination is chosen and added to the final CAD design. 8. The final drag reduction is compared with the original Ford Transit results.

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3. Literature Review To reduce drag, utilising exhaust gas alternatively to fill the low pressure generated behind a vehicle. At velocity change the outlet fume channel is caused due to exhaust gas flown out. Low pressure attracts the flow towards itself, which is generated behind the vehicle and it reduces the negative pressure i.e. increase the pressure to reduce drag force. On numerical study on drag reduction of aerodynamics of racing cars according to a study conducted by Rakibul Hassan (2013), windward van can reduce up to 12.5% energy consumption; this reduction of drag generates a deflector on the top of the van. Any dynamic object has to overcome some air resistance and in moving vehicles this also applies. Many procedure tactics are implemented in automotive industry to reduce drag within the design stage of the vehicle by carrying out series of CFD simulations and later on when this is optimised in its full potential it goes through wind tunnel testing analysis. Force of drag reduction has many encounters of factors in relations to drag coefficient. 1. Skin friction, which is caused by the material used on the surface of the body of a vehicle and this, could reduce skin friction and the total drag implied. 2.

The guide lines on the vehicle to cause air split known as vehicle body lines.

3. The aerodynamic shape of the vehicle to be at optimum to encounter the lowest drag possible. In vehicle design procedure the turbulent flow reduction is of the main factors that need a lot of attention. Laminar flow has less drag due to intact air flow with minimum or no turbulent flows. The air separation causes a lot of drag, which leads to higher fuel consumption and it takes more energy to overcome the air resistance than required. This turbulent flow in worse cases consists of mini or full vortices that indicate high turbulent flow. In design of a vehicle the aerodynamic issue is of the main concerns. Novelty in some cases have outstanding results, Mercedes Benz’s new conceptual designs (Concept IAA) is among these cases. The aerodynamic of the car alters with velocity to minimise drag, at 80 km/h. This transforms the captivity of eight segments at the rear end of the vehicle to extend that increases the length by 390 millimetres. The front flap located at the front bumper also extends by 25 millimetres and 20 millimetres to the rear; this improves the airflow around the wheel arches and front end. An alteration in cupping is taken place by Active Rims from 55 millimetres to zero. Louvre located at the front bumper moves 60 millimetres to the rear which improves the underbody airflow. This resolves the aims of functionality and aesthetics. Similar concept is applied to small cars and vans in general with some alterations and both have the relation of velocity and fuel consumption. The upper surface of a vehicle has lower velocity and the 18

lower surface has higher pressure due to air resistance. This causes the vehicle to be implied with suction to the ground known as the downforce. Different type of pressure acting on a vehicle is as follow: 1. The front of the car with high pressure 2. The rear has a little pressure The vehicles streamline represents the airflow around the vehicle and the air separation as illustrated in the Figure below, represents turbulent flow. The intact flow of air means the flow is laminar which gives lower drag. The front vehicle is responsible to cut through air and pass through, whereas the rear end is responsible for minimising the streamline gaps to avoid added drag. This results into less vortices and turbulent flow.

Figure 6 : the vortex created behind the vehicle B.Abdi, (2013)

Using a flat plate underneath the car results into drag reduction force, generating a assemble body like the wheels to smooths the lower surface of the body in terms of airflow and this improves in significance of drag reduction due to backflow in empty spaces causing sharp edge assemblies wheel. This effect of flow on a horizontal surface eliminates until a circle in a vertical plane to spin. This influences the flow of the wheels and helps to reduce the exposure of the front to the airflow, according to Abdi (2010). Vehicle aerodynamic computational optimisations according to a study conducted by Ahmad Haseeb & CHACKO, (2012), two main modifications were studied. Part one was based on the bonnet duct and the other was adding a wing to the rear end of the vehicle. The added wing caused a rise in drag coefficient due to its presence, although the performance improved with the downforce created, which is a prime factor of the performance. The Figure below illustrates the streamline shown on the improvement of the streamline with the added wing that caused air to be smooth on the upper surface of the vehicle along with having a better intact flow. In respect to the turbulent flow at the rear end of the vehicle adding a wing also got rid of it and this indicates a better flow overall. In regards to the

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downforce it has also improved its performance and in comparison the flow is significantly improved by the added wing, with also reduced overall drag.

Figure 7 : design Front Bonnet Duct, Wing, Ahmad Haseeb & CHACKO, Sibi, (2012)

Using ANSYS according to Akshay Parab and Ammar Sakarwala, (2013), an advance method on drag reduction and downforce aspect of the vehicle geometry can be modified and diffused to add in the rear end of the vehicle. In this study the angle implied has to be tested in order to find the optimum angle. The aim of this is to reduce the wake area generated by the airflow behind the car and reenergising the air upwards to reduce lift coefficient. The figure below illustrates the angle implementation using SolidWorks.

Figure 8 : Dimension and shape of diffuser Akshay Parab, Ammar Sakarwala, (2013)

In a similar study of above another study investigated on the aerodynamic optimisation in regards to drag reduction, by modification of reshaping the rear component. According to K. S. SONG, S. O. KANG, S. O. JUN, (2012), the modification of aerodynamic of the rear shape influences the drag reduction.

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Figure 9 : design variables K. S. SONG, S. O. KANG, S. O. JUN, (2012)

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4. Turbulence Model studies: Using ANSYS and FLUENT or CFX solvers enables the usage of different types of model studies. Depending on the applications and the purposes different models can be used. Each has its own advantages and disadvantages. In order to understand the functionality the main model solvers are chosen to expand upon in order to use the right solvers in consideration of using turbulent model studies. The relevant solvers that can perform on a turbulent model within fluid boundary conditions are k-epsilon, SST, and Baseline Reynolds stress.

4.1.1 K-epsilon According to Menter, (1992), K-epsilon turbulent model is used in industry for its turbulent model capability to solve. The disadvantages are low sensitivity to adverse-pressure gradient. This results into imprecision or inaccuracy of the flow simulations and this the uses two equations as follow, 𝜕𝜌𝑘 𝜕𝜌𝑢𝑗 𝑘 𝜕 𝜕𝑘 + = 𝑃𝑘 − 𝛽 ∗ 𝜌𝜔𝑘 + [(𝜇 + 𝜎𝑘1𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝜌𝜔 𝜕𝜌𝑢𝑗 𝜔 𝜕 𝜕𝜔 + = 𝛾1 𝑃𝜔 − 𝛽1 𝜌𝜔2 + [(𝜇 + 𝜎𝜔1𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗

4.1.2 K-omega According to Menter, (1992), k-omega is sensitive towards flow separation prediction unlike k-epsilon. The disadvantage that k-omega has lays in inaccuracy prediction of complex flow due to free-stream dependency. K-omega is sensitive to adverse-pressure gradient. In boundary layer this model is ideal. This model uses two equations as follow.

𝜕𝜌𝑘 𝜕𝜌𝑢𝑗 𝑘 𝜕 𝜕𝑘 + = 𝑃𝑘 − 𝛽 ∗ 𝜌𝜔𝑘 + [(𝜇 + 𝜎𝑘2𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝜌𝜔 𝜕𝜌𝑢𝑗 𝜔 1 𝜕𝑘 𝜕𝜔 𝜕 𝜕𝜔 + = 𝛾2 𝑃𝜔 − 𝛽2 𝜌𝜔2 + 2𝜌𝜎𝜔2 + [(𝜇 + 𝜎𝜔2𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜔 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗

4.1.3 Baseline (BSL) According to Menter, (1992), BSL (Baseline) forms a new equation by a combination of k-omega and k-epsilon formulas which increases the sensitivity of the boundary layer F1 function. The following is the two equations used. 𝜕𝜌𝑘 𝜕𝜌𝑢𝑗 𝑘 𝜕 𝜕𝑘 + = 𝑃𝑘 − 𝛽 ∗ 𝜌𝜔𝑘 + [(𝜇 + 𝜎𝑘𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝜌𝜔 𝜕𝜌𝑢𝑗 𝜔 1 𝜕𝑘 𝜕𝜔 𝜕 𝜕𝜔 + = 𝛾𝑃𝜔 − 𝛽𝜌𝜔2 + 2𝜌(1 − 𝐹1 )𝜎𝜔2 + [(𝜇 + 𝜎𝜔𝜇𝑡 ) ] 𝜕𝑡 𝜕𝑥𝑗 𝜔 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 𝜕𝑥𝑗 22

4.1.4 Shear Stress Transport (SST) SST which stands short for Shear Stress Transport according to to Menter, (1992) is a combination of both k-omega which is used in the inner part of the boundary layer that is known to be very sensitive within that region of the wall and k-omega in free-stream which is known to perform best in that region. This avoids the common error made by k-omega to be too sensitive in the region of inlet freestream turbulent. This model has high precision is adverse pressure gradient that detect flow separation. 𝜏 = 𝜌𝑎1 𝑘 The formula above represent SST model with high accuracy at the near wall flow, a1 represents a value, and this value is known to be set at 0.3 although Menter has stated that higher value means higher accuracy in the results. SST enables switching between the two models of between k-omega and kepsilon equations within the boundary layer.

4.2 Turbulent study of Ford Transit The chosen three models to be used in this project are K-omega and k-epsilon and also SST. The Ford Transit, which is designed in section 5 of the report, is used to demonstrate the differences in sensitivity of the three models. The model used is shown in the table below and k-omega and k-epsilon are showing to be significantly higher than SST. Both of the models with two equations gave similar pattern results, with 2889N and 2648N, k-omega and k-epsilon respectively. SST gave the best result with 2058N.

Ford Transit

Turbulence Model study of Drag K-omega K-epsilon 2889N 2648N

SST 2058 N

Table 2 Turbulent model study using Drag

23

5. Problem solving In this section, a CAD design of Ford Transit is is produced based on the parameters available on their website and available blue prints. These parameters then were used to produce a CAD model. The initial approach in this project is to produce a CAD design from an existing VAN which is Ford Transit, and modify it to gain reduction in drag through aerodynamic improvement based on literature review to find and pinpoint high drag acting on the shape of the car and refining it to minimise the drag further. Since CFD simulations are the main aspect of the project, to have a reliable results then domain size sensitivity, mesh quality of the domain and van sensitivity along with inflation layers through calculations should be worked out. This enables the domain size to be big enough so it does not influence the results and it is not bigger than required to influence the time intervals of the simulations. The mesh quality means the smaller the mesh cells the higher the accuracy of the results, however this increase the time interval of the simulation running, mesh sensitivity can be used to find the right balance. Inflation layers influence the streamline from near the wall; this increases the sensitivity of the drag along the van itself. Each section has its own introduction for ease of understanding.

5.1. Ford transit CAD Designing Based on available data online from a reliable source, the van was re-designed using SolidWorks with the showing parameters. The dimensions are perfectly aligns with the data on Ford’s website and also their blueprint of the car available also on their website.

Figure 10 Ford Transit CAD design Measurement Specification (H.eskandari)

The following figure is the CAD design, which is same one from above without the numbering and the precise measurements.

24

Figure 11 Ford Transit CAD design (H.Eskandari)

5.2. Simulation parameter In this section the studies of domain and mesh are carried out. In order to import the CAD design from SolidWorks to ANSYS the files were saved as IGS format, any other format gives one or two of the solid bodies contained by the assembly as surface body which ANSYS recognises as just surface and no simulation on the part can be performed. An example of the format save is IGS that the tyres of the van were saved as surface bodies along with the parts of the back of the van. Saving as IGS also influences the size of the file, but in this study IGS file is used with 700kb file, (which with STEP file is around 2mb).

5.2.1. Domain simulation study In flow domain size study the initial approach is to find the best domain shape which by research is rectangular for vehicle simulations whereas in wings and aerofoils, this shape is changed to C-type shape, so it depends on the application and purpose. The domain size influences two main factors of the simulations. It is crucial to find the right size for the application before moving on to the next part. The two factors are, one it influences the time intervals, which effect the time taken of the simulations as it needs more mesh cells and more time at each millisecond to work out the results and the flow distribution. And the other is its influence on the results itself; if the domain size is small then most likely the results will be influence by a ‘Backflow’. Backflow is a term used to indicate the return flow from the outlet back to inlet which effect the results in a major way and the results will be unrealistic and unreliable. In domain study various sizes were tested against drag component with two constant variables. The main problem to avoid was the flow back and this is the reason why more attention was given to the x direction. Each simulation took around 2 hours to be solved with 500 interactions and 20 inflation layers; Physical Timescale was calculated based on flow boundary domain size and Residual Target of 1e-5.

25

Figure 12 sketch of the domain aound the imported van (H.Eskandari)

The file was imported and the domain was sketched on ANSYS, the time below illustrates the number of different sizes of domain with two constants at a time to work out the influence of that specific sizing. The table shows the alteration in x, y and z direction. And the best sizing is chosen based on the results below.

n

Size(x, y, z) (m)

Lift(N)

Drag (N)

1

(15 , 6 , 4)

-2433

2600

2

(20 , 6 , 4)

-629

1832

3

(25 , 6 , 4)

-2178

2573

4

(35 , 6 , 4)

-2081

2733

5

(40 , 6 , 4)

-2352

2991

6

(15 , 8, 4)

-2878

3063

7

(15 , 10 , 4)

-2365

2620

8

(15 , 6 , 6)

-1991

2160

9

(15 , 6 , 8)

-2781

2865

10

(15 , 6 , 10)

-3825

3394

Table 3 domain size study

The table above represents the various boundary domains against drag component from the simulations carried out. The first size 15, 6,4m in dire3ction of x, y, and z respectively were used and is the minimum size of the domain used in this case. With increase of the x direction the drag was at minimum at 35m. In x direction also the lift and drag components were dramatically effected with the length from 15 to 25m but were gradual changes after that. In Y direction the components of lift and

26

drag were not affected and in Z direction at 8m the results were the same as 6m, and sue to time intervals 6m was selected.

n

Size(x, y, z) (m)

Lift(N)

Drag (N)

1

(25 , 6 , 6)

-247.81

1464.10

2

(35 , 6 , 6)

-337.21

1540.08

3

(35 , 8 , 6)

-377.30

1545.89

4

(40 , 10 , 8)

-504.01

1454.34

Table 4 final domain size study

The data above represents the four final nominees of the dimensions for the flow domain size. The x direction influences the results in a major way unlike Y and Z direction. The drag which is what the aim of the project, and based on that the size of (25, 6, 6) is chosen. This gave a lift of -247.81N and Drag of 1464.10N. the drag of the other sizes were higher, although in larger size of (40, 10, 8) the drag is slightly lower than the chosen dimensions but it took four 6 hours for the simulations to run unlike the chosen one that the simulations were over in less than two hours, and because in CFD the time interval or the time taken for the simulations is one of the important factors, and also the differences are minimal.

5.2.2. Domain mash In domain mesh studies the quality of the mesh will be investigated in order to maximise the efficiency of the simulations in respect to the time intervals and the influence of it on the drag component. Same concept applies for mesh as domain size study. Large mesh means too many unnecessary mesh cells; this increases the accuracy of the results; however this also increases the time taken for the simulations. A balance should be considered using time and also the influence of the mesh on drag. In general, more mesh cells are used, the better the results, and this also increases the reliability of the results but the time interval increases as well so taken both parameters into account, to have a balance of a good reliable mesh in consideration of the time interval and also the result of the drag component within that chosen mesh size. Starting from coarse mesh to fine mesh and adjusting the mesh size in respect to drag and time taken. The followings are found to be as optimum for this case of study.

27

n

Maximum velocity (m/s)

Maximum pressure (pa)

1942.27

70.57

680.2

2:04:35

Medium

1937.67

69.58

679.6

2:24:21

Fine

1935.08

68.10

679

3:40:30

1

Relevance mesh centre quality Coarse

2 3

Drag (N)

Time spent for simulation

Table 5 : The effect of mesh quality on output parameters

Based on the above figures the drag from the fine mesh is optimum, however the time taken from is 3 hours and 40 minutes. The follow up drag results with only 2N difference is the medium mesh size that resulted into having the time intervals of 2 hours and 24 minutes, which is a significant figure in comparison with fine mesh. So the chosen mesh is medium, however in more details the mesh size should be considered. The following figure represents the inlet flow and better quality mesh that affected the results.

Better quality of back flow in back of van compare to coarse mesh

Figure 13 : the result for medium mesh quality (H.Eskandari)

The mesh size has to components, minimum and maximum. The following tables are representing the mesh sizes similarly to the above table, in respect to drag and time intervals

Domain Mesh studies minimum size Mesh size(m) Drag (N) Time Interval (m) 0.0020 1934.25 3:54:27 0.0025

1935.59

3:40:48

0.0030

1936.57

3:25:08

0.0035

1937.15

2:42:35

0.0040

1939.61

2:25:15

Table 6 : minimum domain mesh studies

Based on the table above the minimum mesh size has been studied. The extract of the results are illustrated on the above table. At 0.0035 minimum mesh size has the lower time interval and the drag component is also worked out to be the best.

28

Domain Mesh Studies maximum size Mesh size (m)

Drag (N)

Time Interval (m)

0.2

1934.48

5:49:23

0.4

1935.14

5:30:12

0.6

1936.43

4:47:16

0.8

1936.74

3:38:58

1.0

1937.28

2:34:42

1.2

1942.59

2:29:31

Table 7 : maximum domain mesh studies

The table above represents the maximum size for the mesh were analysed and it illustrates that it potentially influences the time interval is a major way and it does not influence drag as SST is used for a turbulent model and the sizes are made based on the wall rather than the input mesh size. It increases the time interval but not potentially the drag component, however based on the results the mesh size with 0.8m is chosen as the maximum size in respect to the time intervals and drag component.

5.2.3. Van mash study. The van mesh similarly to domain mesh has the same principle. The van mesh has to be studied based on its sensitivity. The sensitivity of the van mesh influences the results. Starting from 0.005m of mesh cells to 0.030m, even though this is an extract of the range covered. The trend of the table below shows the time interval being in correlation with the mesh size. The smallest size is 0.005m gave 1982.18N with 4 hours and 17 minutes. The lowest time interval was off course from the biggest mesh size of 0.03m that was 2 hours and 5 minutes. The drag from the range was slightly different, although this is in consideration of both time intervals and the mesh size. The chosen mesh size is 0.02m due to its close drag component value and also the low time intervals. The difference of its drag is 4N with close to 2 hours of time intervals difference. The figure below is the final mesh with the inflation layers of 32.

29

Figure 14 : Van mesh with inflation layers(H.Eskandari)

The table below as mentioned above consists of the mesh size along with the time interval that in this case similarly to the mesh sensitivity carried out throughout this project, influenced the time intervals in a major way. The difference of the time interval is more than 2 hours and the chosen mesh size of 2m to the smallest size is significantly spaced. However, the drag component which is the main factor is at minimal difference.

1

0.005

1980.18

Time spent for simulation 4:17:53

2

0.010

1982.34

3:24:35

3

0.015

1983.03

2:58:21

4

0.020

1984.15

2:18:10

5

0.025

2027.61

2:12:12

6

0.030

2089.87

2:05:12

n

mesh size (m)

Drag (N)

Table 8 : Van mesh study

5.2.4. Inflation layer The boundary layer thickness needs to be calculated in mesh control in order to maximise the sensitivity and this is achieved through wall function. The Figure 13 represents the wall function being optimised. This means the number of nodes required is optimised within the mesh and this affects the time interval or in other words the computational time is reduced. However, this function of wall function should only be applied to ample flow separation. The distance of non-dimensional from the first node of the inflation layer and the wall is known as Y+ value. This is function of delta y, (Δy), this is the distance between the first node and the wall. This is calculated by the following function. 30

∆𝑦 = 𝐿𝑦 + √74𝑅𝑒𝑥 -13/14 And, 𝛿

= 0.37 × (𝑅𝑒𝑥 )-0.2

Also,𝛿

=

∆𝑦(1−𝑟 𝑛 (1−𝑟)

Figure 15 : Boundary Layers - Wall Functions (LEAP CFD Team, 2012)

In SST model which is the chosen solver based on the comparison simulations made, the chosen Y + value is 2. In this section the effect of inflation layers will also be investigated. The number of inflation layer on van’s surface with the parameters of 70mph = 31.293 m/s and T = 20 C°.

𝑅𝑒 = 𝜌𝑣𝐿/𝜇 =

1.225 × 31.293 × 2.4 = 5.145 × 106 1.7879 × 10−5

In consideration of Reynolds number if it is more than 4000, this is an indication of it being turbulent. The follow up to this, is to find the number of inflation layers for this particular Reynolds number. The quality of the flow within the domain is directly proportional to the Y+. 1

𝛿 = 0.37𝑥𝑅𝑒 − 5 1

𝛿 = 0.37 × 2.4 × (5.145 × 106 )−5 = 0.40 (m) The first layer thickness will be calculated as follow:

∆𝑦 =

13 − 𝐿𝑦√74𝑅𝑒𝚤 14 −

13

∆𝑦 = 2.4 × 2 × √74 × (5.145 × 106 )𝚤 14 = 2.4 × 10−5 (m) δ is found based on the equation below and the inflation layer is estimated,

∆𝑦(1 − 𝑟 𝑛 ) 𝛿= 1−𝑟 31

400 = 2.4 × 10−5 ×

1 − 1.2𝑛 1 − 1.2

𝑛 ≅ 32 Reynolds number for SST is considered based on the parameters of the velocity being of 35mph = 15.656 m/s and T = 20 C°.

𝑅𝑒 = 𝜌𝑣𝐿/𝜇 =

1.225 × 15.656 × 2.4 = 2.574 × 106 1.7879 × 10−5

Y+ = 2, therefore: 1

𝛿 = 0.37𝑥𝑅𝑒 − 5 1

𝛿 = 0.37 × 2.4 × (2.57 × 106 )−5 = 0.046 (m) The first layer thickness will be calculated as follow:

∆𝑦 =

13 − 𝐿𝑦√74𝑅𝑒𝚤 14

∆𝑦 = 2.4 × 2 × √74 × (5.145 ×

13 − 6 ) 14 10 𝚤

= 2.4 × 10−5 (m)

δ is found based on the equation below and the inflation layer is estimated,

𝛿=

∆𝑦(1 − 𝑟 𝑛 ) 1−𝑟

46 = 2.4 × 10

−5

1 − 1.2𝑛 × 1 − 1.2

𝑛 ≅ 71 The following Figure represents the inflation layers at the wall. The following figure is the at 70mph which equals to 31.293 m/s. the number of the inflation layers on the following Figure is 32.

32

Figure 16 : van with 32 inflation layers for Speed 70mph= 31.293 m/s

5.3. Ford Transit Setup The setup parameter consists of defining the inlet, outlet and the walls. This involves defining the fluid, and the pressure in the inlet and the outlet.

Figure 17 : Setup of the Ford Transit

5.4. Ford Transit simulation Results Pressure contour and velocity contours are taken from the results with the lift and drag coefficient. This will be compared with the improved and optimised model. This shows the effect of the aerodynamic principle on the car and how and where the car needs modification. Lift component was -475 and drag component was 1948.3.

33



Contour velocity: overall skin friction of the van, 0 meters per second, and the front of the van has a velocity of 17 meters per second; the front of the car has a general velocity of 23.8 meters per second. The top roof of the van generally has 44.1m/s with higher velocity at the both ends of the top with velocity of 47.5m/s. at the back of the van at some region 0 m/s is shown with overall velocity of 10.2 m/s. under the car the velocity is pretty constant with 27 m/s.



Contour pressure: the front of the van has the highest pressure with 695 pascal, and with overall pressure of 322 pascal. The top of the van shows -423 pascal similarly to underneath the car. The back of the van has various pressures with high and low pressures. Ranging from 508 pascal to -50.7 pascal.



Then we have the streamlines along the van. The back of the van clearly shows air disturbance.

Figure 18 Ford Transit Velocity Contour

Figure 19 Ford Transit pressure Contour

Figure 20 Ford Transit Streamline

34

6. Design Optimisation In vehicles in general the pressure drag is considered to be a critical factor and due to the exposure of the surface (wetted area), of the flow direction in vans, the drag components is higher due to more exposure to friction drag. In van sue to its functionality the importance of ability to transfer heavily items, the aerodynamic aspect was never considered greatly and this has caused higher drag by the aerodynamics. Since air pollution and C02 emission along with fuel consumption is becoming more and more important, more attention is given to less aerodynamically friendly vehicles including vans. Overall drag of back and at the top of the van producing is less than 10% and it is not considered to be a strong candidate in respect to drag reduction technology according to McCallen (2000). Aerodynamic drag associated with the van is a combination of different locational parts. The resistance of movement in the body through a fluid medium increases the drag component significantly. Various parts have been studied from the original van simulation in the last chapter to allocate the drag acting upon the van and by modification, a drag reduction is gained. In this case the front of the van has been modified and improved. The circled locations are the focus to lower drag. The front of the van along with the windshield, which needs to be smoothed out as you can see the modification has been already carried out on the Figure below. The corners of underneath of the van needs angle adjustment and top roof of the van needs angle adjustment as well.

Figure 21 optimisation of Ford Transit

35

6.1

Angle of the back bumper

The original angle of the back bumper was 9.08 degrees and two modifications were considered to be applied on the can. The modifications were 12 degrees and 15 degrees. These were selected to the optimum; these angles go up by 3. The figure below circles the modification area of the van.

Figure 22 angle of the back bumper

The original implementation of the angles is as follow; this figure represents the modifications on the angles.

Figure 23 : the angles behind of the vehicle, back of the car with A) at 9.08, B) at 12.08, C) at 15.08

36

6.1.1 Results In this section of the report the simulations of the streamlines at the increased angled are shown. The comparison from the original van design which had 9 degrees to 12 degrees has shown a significant improvement on the flow being intact. However, once the angle reaches 15 degree, the flow becomes much laminar and it becomes stable along with a decrease on velocity speed at the back which was due to turbulent flow. This has shown that the flow at the back of the van has significantly improved.

Figure 24 streamline resize 3 degree back of the van (12.08 degree)

From the original 9 degrees to 12 degrees, the flow improved significantly, however, at 12 degrees the flow as shown on Figure 24 is still turbulent as disturbed at the back. The improvement from 12 degrees to 15 degrees makes the improved turbulent flow to laminar and intact flow.

Figure 25 : 6 degree from the original (15.08 degree)

The Table below represents the drag improvement of the two angles added as the modification. The Original van had an angle of 9 degrees and this was changed to 12 degrees, which resulted into 0.93% improvement in drag reduction. Increasing the angle to 15 degrees gave laminar flow and also an improvement in drag reduction of 1.456%.This is a reduction of 28.4N by just changing the angle.

37

Angle 9O (original Ford Transit) 12O 15O

Drag Component (N) 1948.3 1930.2 1919.9

Reduction of Drag 0% 0.929% 1.456%

Table 9 Drag reduction by changing the angle of back bumper

6.2

Angle of the top roof

The selection of this part of the report is the top roof angle as the following Figure shows. The original had zero degree angle. Starting from 1 degrees to 4 degrees the van was simulated.

Figure 26 Angle of Top Roof

The selection was from the mid-top of the van to the rear end from the top, adding 1 degrees at a time to 4 degrees. The following Figure represents the added angles using SolidWorks. Based on the studies this intact the airflow at the back of the van and causes further drag reduction.

Figure 27 : roof angle 1 to 4 degree

38

6.2.1 Results Increasing the angle influences the flow over the upper surface of the vehicle. The gradual increase in the angle at the top of the van influences the air flow the back which results into high turbulent flow if this angle is at 0 degrees, which in the original design was. In Figure 28, the angle has been increased from 0 to 1 degrees. The flow separation at the back of the van indicates that the flow is turbulent. Increasing the angle has influences the upper surface velocity from 65m/s to 68 m/s.

Figure 28 1 degree modification

Figure 29 the angle is modified from 1 degrees is increased to 2 degrees. The influence of the angle of the flow at the back of the van can be seen clearly from 1 to 2 degrees. The flow has been optimised from the separated flow to turbulent flow with laminar flow as well. The velocity of at the upper surface of the van has now increased from 68 m/s to 68.5m/s.

Figure 29 2 degrees modification

In Figure 30, the angle is changed to 3 degrees and the density of the flow separation has now significantly reduced. The flow at the back has been improved from the full separation to a better and a smaller region of turbulent flow. The various velocity encounters within 3 degrees are significantly higher than 0, 1 and 2 degrees which indicate the flow is less turbulent as turbulent flows are known to have 0 velocity at the inner sections.

39


Figure 31 similarly to the previous figures of this section has the final increased angle. This angle at 4 degrees represent the flow separation at which has to be within the modification of better flow intact or having a better turbulent to laminar flow. The back of the van due to the height difference can never reach a full intact flow, but this flow separation can be minimised to reduce the implied drag, to face the total drag reduction. In the Figure below, the streamline at the upper surface indicate high velocity and this velocity has now been increased further to 78.3m/s and the flow separation is at minimal. A better representation of the final drag reduction can be seen the table below.


The following are optimisation on the top roof of the van, from 1 to 4 degrees. As the angle increases the velocity at the top roof also increases and also the differences at the end were the original streamline of the van and the modified version is shown, it is clear that at 4 degrees the vortex at the back is re-energised and also the smoothness of the lines are increased. The original van in this case had 1948.3N of drag and the improved version of just the top roof modification this was reduced by 3.25% to 1886.9N.

Angle

Drag Component (N)

Reduction of Drag 40

0O (original Ford Transit) 1O 2O 3O 4O

1948.3 1932.1 1915.9 1903.1 1886.9

0% 0.8314% 1.663% 2.32% 3.25%

Table 10 Drag reduction by changing the top roof angle

Table 10 shows the modification of the angle on the top roof by altering angle at 1 degrees at a time. The results are clearly show an improvement at each declination at the angle. At 1 degrees the drag reduction was 0.83% and this drag reduction increased by the increase of the angle. At 2 degrees, the drag reduction was 1.663% and at 3 degrees is increased to 2.32%. At final angle of 4 degrees, 3.25% of drag reduction was achieved. This is a drag reduction of 61.4N at angle of 4 degrees. The following figure represent the flow difference from the original zero degree angle compared to 4 degrees. This enables the ease of understanding the flow direction with the added top roof angle and also the streamline improvement. The table above shows an improvement of 3.25% in drag reduction.

Figure 32 Original and optimised top roof angle comparison

41

6.3

Angle of the front bumper

The Font of the car is responsible for cutting through air. The front bumper modification enables the airflow to smoothly travel to the rear end of the vehicle. The Figure below shows the exact location of the modification that will be made in this section.

Figure 33 Front bumper

The original angle used on Ford Transit as shown on Figure 33 part A, was 51.54 degrees and this was reduced to 35 degrees. The implementation of the angle reduction is based on the literature review that at lower angles at 35 degrees, the flow can be directed to underneath the car, it produces the ability to have an intact lamina flow.

Figure 34 : front of car angles (A) Original angle, (B) modified angle

6.3.1 Results The Figure below represent the front bumper modification. The overall performance of the front bumper lays in the guidance line by the changed angle. The velocity of the streamline within the region is a re-energising flow at the lower surface of the van which in the original had higher pressure along with disturbed and with no linear flow at some point.

42

Figure 35 modification of the front bumper

The drag comparison of the original van and the improvements are represented in the table below. Angle 51.54O (original Ford Transit) 35O

Drag Component (N) 1948.3

Reduction of Drag 0%

1919.9

1.456%

Table 11 Drag reduction by changing the bumper angle

The table above represents the influence of the angle drag. The original angle was 51.54 degrees and this gave a drag component of 1948.3N. By reducing the angle, the direction of the airflow changes, and this leads to a potential drag reduction. However, the results are representing that this in fact was the case and an improvement in drag reduction was made. At 35 degrees the drag component was reduced to 1919.9N with 1.456% improvement in drag. This gives an additional 28.1N reduction in drag by altering the angle.

6.4

Windshield angle reduction

The windshield similarly to the front bumper since it needs to cut through the air in order to move the vehicle forward in high speed, then it needs to be highly aerodynamically friendly. The front shape of the Ford Transit has an angle that causes the air to trap and cause a significant rise in the drag. The following Figure represent the angle of trap, and the area that needs attention in order to reduce drag within that particular area.

Figure 36 Front windshield of Ford Transit

43

The modifications made was getting rid of the trap angle to reduce drag and also the angle of the windshield needed more attention in order to achieve the aim of the task. The following Figure represent the modifications made on the windshield.

Figure 37 Modified version of the windshield

6.4.1 Results The results from the original streamline and contours that are available in section 5.4 of this project are showing higher velocity with high pressure around the areas of the angle being steep. In this modification the angle was removed and the angle of windshield was adjusted for better lamina flow. The Figure below represents the streamline at the windshield along with the smoothness of the flow at the named region.

Figure 38 Streamline of windshield modification

The most important aspect of the project is to face reduction in drag. The drag reduction of this modification that increased the laminar flow behaviour and also having a better interaction with the 44

flow at the front bumper in respect to flow separations. The Table below represents the drag reduction in this modification. Front windshield Original Ford Transit Modified

Drag Component (N) 1948.3 1827

Reduction of Drag 0% 6.255%

Table 12 Modification of front windshield.

The drag reduction in windshield is more than any other components or parts. This is due to its purpose of cutting through air. The modification of the windshield resulted into 6.255% drag reduction and also this is mainly due to guidance of the air to have a lamina flow and also to have an intact flow close to the body. The drag reduction from the original van is 121.3N.

45

7. Final Modification CAD design In this section the combination of the best performing parts of the previous section is combined into one CAD design and is simulated accordingly using the same parameters of setup and mesh as previously mentioned. However, the following Figure represent the final CAD design. The CAD design is based on the results as mentioned previously is important to combine the best performing part on to this CAD design in order to optimise the drag reduction. The aim of the project was to produce a CAD design based on Ford Transit that has lower drag component.

Figure 39 Final improved CAD design

In this CAD design none of the parameters were changed but the angles and aerodynamics of the car. Everything else is kept the same. The modifications were front and rear end bumper angle modifications, top roof angle declination modifications, and the windshield. Based on the combinations of the modifications the CAD design similar to the previous section was simulated.

7.1

Final Optimisation Design Simulation

The final CAD design was simulated based on two velocities. 70 miles and 35 miles per hours, which is 31.293 m/s and 15.626 m/s respectively. The parameters were kept the same and the following figures represent the Streamlines of the modified version of Ford Transit in two different velocities. The Figure 40 represents the streamline at high velocity of 70 miles per hour. The flow compared to original van has significantly improved and flow is now intact and more defined. The back of the van faces the turbulent flow and this is a major improvement of what is was at this speed with the original shape. There are some rooms for improvement off course but the main aspect of the project was to demonstrate drag reduction, which this design has clearly achieved to show. The Velocity is at

46

72.73m/s and the upper and lower surface of the van has shown significant improvement in lamina flow.

Figure 40 : final design streamlines at 31.293 m/s (70 miles per hour)

Figure 41 represents a similar format of the van from the above Figure, with only a velocity difference of half. The velocity is changed to 35 miles per hour (15.626 m/s). Similar pattern is shown is both simulations and similar improvements are demonstrated by both streamlines compared to the original van design.

Figure 41 : final design streamlines at 15.626 m/s (35 miles per hour)

The table below shows the final drag reduction based on all of the modifications and their effects on the drag and total drag reduction.

Type of modification

Drag component (N)

Original Top Roof Front Windshield and Bumper Underneath Front Underneath Back Overall Optimisation

1948.3 1886.9 1927

Improvement in Percentage 0% 3.25% 6.225%

1919.9 1912.3 1698.92

1.456% 1.848% 12.8%

Table 13 final optimisation results

47

The breakdown of the results are individually shown on the above table. This represents the ability of each section and their effects and influences on drag and total drag itself The improvement and optimisations based on the original van design is shown in the above Table. The original van has a drag component of 1948.3 newton, the regions that were improved are top roof, front bumper and windshield, both ends of the underneath the car, front and back, and lastly all of the improvements at once. This shows the impact of each case and as overall. Each case consists of different parameters. The overall optimisation gave an outstanding drag reduction of 12.8% which is nearly 250N.

48

8. Discussion and Conclusion The aim of the project which was to understand and review aerodynamic principles in vehicles and to consider various methods of generating downforce and reducing drag, and using an existing van apply modification to optimise drag, so simply the aim of the project is to study the aerodynamic principle to maximise fuel efficiency subsequently lowering drag using an existing Ford Transit van. The First approach was to produce a CAD design based on Ford Transit which is an existing van in industry. The next analysis was carried out on the turbulent model study and three chosen models were k-omega, k-epsilon and SST. Three simulations were carried out to find out the most sensitive turbulent models and the SST gave the most feasible results. Based on using SST then other calculations were carried out, such as the inflation layers, which were 72 and 35. In ANSYS or any other simulating software, the study of domain and mesh are the most important factors. This influences the results directly and without this the results are meaningless or cannot be used. In order to find a suitable domain size, series of simulations needed to be carried out in order to find the right size. The size of the domain should be big enough so it has no effect on the reading or the results, having said that, bigger domain size than required means more time for the simulation to take place. Flow back is one of the issues that affects the results due to small domain size. So the size of the domain should be simulated at different sizes in respect to time taken and in this case drag. Starting from small to big, keeping 2 parameters constant at a time to find the right size for this geometry. Same concept applies for mesh size. Large mesh means too many cells. This increases the accuracy of the results; however this also increases the time taken for the simulations. A balance should be considered using time and also the influence of the mesh on drag. In general, more mesh cells are used, the better the results. Starting from coarse mesh to fine mesh and adjusting the mesh size in respect to drag and time taken. Then another two studies were carried out based on the medium which was the chosen mech. This encounters with the maximum and minimum mesh size that were simulated and worked out to maximise the precision of the results. After setting up the original van was simulated with its pressure and velocity counters being taken along with its drag component and streamline. Based on the parameters of the results and a combination of it with literature review then the modification aspect of the project began. Four parts were taken into account with all influencing the drag component. The initial modification was based on the angle of the back bumper that was modified. The original angle of the back bumper was 9.08 degrees on the Ford Transit and two modifications were considered to be applied on the can. 49

The modifications were 12 degrees and 15 degrees. These were selected to the optimum; these angles go up by 3. The streamlines at the increased angled are shown. The comparison from the original van design which had 9 degrees to 12 degrees has shown a significant improvement on the flow being intact. However, once the angle reaches 15 degree, the flow becomes much laminar and it becomes stable along with a decrease on velocity speed at the back which was due to turbulent flow. This has shown that the flow at the back of the van has significantly improved. This had a significant improvement on the drag reduction. Increasing the angle to 15 degrees gave laminar flow and also an improvement in drag reduction of 1.456%. This is a reduction of 28.4N by just changing the angle. The next modification was based on the top roof angle. The original had zero degree angle. Starting from 1 degrees to 4 degrees the van was simulated, by adding 1 degrees at a time to 4 degrees. This resulted that increasing the angle influences the flow over the upper surface of the vehicle. The gradual increase in the angle at the top of the van influences the air flow at the back which results into high turbulent flow if this angle is at 0 degrees, which in the original design was. The flow separation at the back of the van indicated that the flow is turbulent at 1 degrees. As the angle increased the flow started to become more lamina than turbulent at the back of the van. From 1 degrees is increased to 2 degrees. The influence of the angle of the flow at the back of the van has been optimised from the separated flow to turbulent flow with laminar flow as well. When angle changed from 2 to 3 degrees the density of the flow separation were significantly reduced. The flow at the back has been improved from the full separation to a better and a smaller region of turbulent flow. At angle of 4 degrees, the flow separation at which has to be within the modification of better flow intact or having a better turbulent to laminar flow. The back of the van due to the height difference can never reach a full intact flow, but this flow separation can be minimised to reduce the implied drag, to face the total drag reduction. As the angle increases the velocity at the top roof also increases and also the differences at the end were the original streamline of the van and the modified version is shown, it is clear that at 4 degrees the vortex at the back is re-energised and also the smoothness of the lines are increased. At 1 degrees the drag reduction was 0.83% and this drag reduction increased by the increase of the angle. At 2 degrees, the drag reduction was 1.663% and at 3 degrees is increased to 2.32%. At final angle of 4 degrees, 3.25% of drag reduction was achieved. This is a drag reduction of 61.4N at angle of 4 degrees. The following figure represent the flow difference from the original zero degree angle compared to 4 degrees. This enables the ease of understanding the flow direction with the added top roof angle and also the streamline improvement. The table above shows an improvement of 3.25% in drag reduction.

50

Figure 42 Original and optimised top roof angle comparison

The next modification was based on the angle pf the front bumper, which is responsible for cutting through the air. The front bumper modification enables the airflow to smoothly travel to the rear end of the vehicle. The original angle used on Ford Transit as shown on was 51.54 degrees and this was reduced to 35 degrees. The implementation of the angle reduction is based on the literature review that at lower angles at 35 degrees, the flow can be directed to underneath the car, it produces the ability to have an intact lamina flow. The overall performance of the front bumper lays in the guidance line by the changed angle. The velocity of the streamline within the region is a re-energising flow at the lower surface of the van which in the original had higher pressure along with disturbed and with no linear flow at some point. The original angle gave a drag component of 1948.3N. By reducing the angle, the direction of the airflow changed, and this led to a potential drag reduction. However, the results are representing that this in fact was the case and an improvement in drag reduction was made. At 35 degrees the drag component was reduced to 1919.9N with 1.456% improvement in drag. This gives an additional 28.1N reduction in drag by altering the angle. The last and the most important aspect of this modification laid in windshield modifications. This part is mainly responsible to cut through the air in order to move the vehicle forward in high speed, then it needs to be highly aerodynamically friendly. The front shape of the Ford Transit has an angle that causes the air to trap and cause a significant rise in the drag. The modifications made was getting rid

51

of the trap angle to reduce drag and also the angle of the windshield needed more attention in order to achieve the aim of the task. In this modification the angle was removed and the angle of windshield was adjusted for better lamina flow. The Figure below represents the streamline at the windshield along with the smoothness of the flow at the named region. The drag reduction in windshield is more than any other components or parts. This is due to its purpose of cutting through air and its ability to redirect the airflow and being able to keeping the flow lamina. The modification of the windshield resulted into 6.255% drag reduction and also this is mainly due to guidance of the air to have a lamina flow and also to have an intact flow close to the body. The drag reduction from the original van is 121.3N. The aim of the project has been achieved as previously mentioned and the CAD design of which it was improve upon Ford Transit van gave 12.8% drag reduction. The purpose of which this can be used lays on fuel consumption at initial state. Fuel consumption is one the most important factors that automotive industry is paying more attention to. As fuel consumption affect the CO2 mission and therefore air pollution increases. Although in secondary aspect a fuel efficient vehicle the running costs are cheaper along with the implementation of the recent governmental decisions that attacks more people into keeping a vehicle to be fuel efficient.

52

9. Reference David Levin and Dan Hart, (2010). [Online]Availableat:http://www.pbs.org/wgbh/nova/space/lift-drag.html

pbs.

Drag, NASA, (2016). [Online]. https://www.grc.nasa.gov/www/k-12/airplane/drag1.html. (Accessed 4 .4.2016) Landman, D., Wood, R., Saey, W. & Bledsoe, J., 2009. Understanding Practical Limits to Heavy Truck Drag Reduction, SAE International. Levi, D. & Hart, D., 2010. pbs. [Online] Available http://www.pbs.org/wgbh/nova/space/lift-drag.html [Accessed 30 12 2015].

at:

M. Wood, R. & X. S. Bauer, S. X., 2003. Simple and Low-Cost Aerodynamic Drag Reduction Devices for Tractor-Trailer Trucks. SAE International, p. 3377. McCallen, R., 2000. Aerodynamic Drag of Heavy Vehicles Simulation and Benchmarking. Washington: SAE international. Transport, P. f. A. R., 2015. part20.eu. [Online] http://www.part20.eu/en/applications/trailer/ [Accessed 9 01 2016].

Available

at:

Kambiz salari, 2013,” DOE’s Effort to improve heavy vehicle Aerodynamics through joint Experiments and computations” Project ID: VSS006 The Concord Consortium. (2012). the Reynolds Number. [Online]. Available at: http://www.grc.nasa.gov/WWW/BGH/reynolds.html. (Accessed 4 .4.2016) Physics Stack Exchange, 2016,” highest drag coefficient” http://physics.stackexchange.com/questions/201633/what-shape-has-the-highest-dragcoefficient Mercedes-Benz at the CES® (2016), [Online]. Available at:https://www.mercedesbenz.com/en/mercedes-benz/design/mercedes-benz-design/concept-cars/concept-iaaintelligent-aerodynamic-automobile/ [Accessed 07 04 2016]. FDA Approved Medication Information, (2015). http://medlibrary.org/medwiki/Drag_coefficient. (Accessed 4 .4.2016)

[Online].

Vehicle Coefficient of Drag List, (2016), [Online]. http://ecomodder.com/wiki/index.php/Vehicle_Coefficient_of_Drag_List. (Accessed 4 .4.2016). M. Beccaria et al. / Future Generation Computer Systems 15 (1999) 323–332

53

Miniuy, North American, Motoring.com, (2015) http://www.northamericanmotoring.com/forums/r56-hatch-talk-2007/285802-roof-airintake-aerodinamic-spoiler.html LEAP CFD Team, 2012, [Online] http://www.computationalfluiddynamics.com.au/author/leap-support-team/ Accessed 4 .4.2016).

54

10.

Appendix

Figure 43 : Pressure contour Van optimisation back 3 degree

Figure 44 : velocity contour Van optimisation back 3 degree

Figure 45 : Pressure contour Optimisation top roof 1 degree

55

Figure 46 : velocity contour Optimisation top roof 1 degree



56




57


Figure 53 : top roof CD graph

Figure 54 : top roof CL graph

58

Figure 55: top roof Velocity graph

Figure 56 : top roof Pressure graph

59

Figure 57 : Pressure contour, Van final optimise speed 15.626m/s

Figure 58 : velocity contour, Van final optimise speed 15.626m/s

Figure 59 : Pressure Final operation van

60

Figure 60 : velocity Final operation van

Figure 61 : velocity contour Angle of front bumper 3 Degree

Figure 62 : pressure contour Angle of front bumper 3 Degree

61

Figure 63 : Van final optimisation speed 31.293 m/s



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