International Review of Mechanical Engineering (I.RE.M.E.), Vol. 10, N. 6 ISSN 1970 - 8734 September 2016
Numerical Comparison of Drag Coefficient between Nacelle Lip-Skin with and without Bias Acoustic Liner Qummare Azam1, Mohd Azmi Ismail2, Nurul Musfirah Mazlan3, Musavir Bashir4 Abstract – The paper demonstrates the drag coefficient on the nacelle lip skin with and without bias acoustic liner. It is acknowledged that bias acoustic liner potentially reduces the drag coefficient and enhances the fuel efficiency of the aircraft. In the present study,the geometric mesh modelling of nacelle lip-skin has been developed using GAMBIT pre-processor, and FLUENT 14.0 CFD code is employed to obtain the numerical results. According to the results, drag coefficient of nacelle lip reduces by 90.5% with bias acoustic liner as compared to drag coefficient of nacelle lip-skin without bias acoustic liner. Therefore, bias acoustic liner with bias flow has potential to reduce the drag coefficient apart from being utilized in hot air anti-icing. Copyright © 2016 Praise Worthy Prize S.r.l. - All rights reserved.
Keywords: Drag Coefficient, Efficiency, Nacelle Lip-Skin, Acoustic Liner, Bias Acoustic Liner
I.
Introduction
II.
The research approach on the safety regulations of the aircraft is significantly important. The aviation research centers are increasing the awareness about the environmental issues. Today, one of the intention of aircraft industry is to achieve more efficient, safe and cost reliable aircrafts [1], [2]. Much of the study is focused on the aerodynamic performance of the aircraft, because it has a significant effect on the atmospheric conditions and civil transportation. Aerodynamic drag comprises of pressure drag, viscous drag, and skin friction drag [3]. Except for helicopters and military aircraft, operational cruise drag for most commercial aircraft consists of friction drag and drag due to lift[4]. More recently, optimization-based approaches such as those of Knapp [5], the WINGOP code of Wakayama [6], and in particular the PASS program of Kroo [6] perform tradeoffs in a much more detailed geometry parameter space, but still rely on simple drag and engine performance models. Engine nacelle is used as a housing that holds engine, fuel and other equipment’s of the aircraft. Besides, nacelle also reduces the noise from the engine. According to Federal Aviation Administration (FAA), aircraft noise is a serious cause of environmental noise pollution and the only way to achieve clean aircrafts is to mitigate these noises [3], [4], [7]. Also, the radiating noises coming from the different aircraft components cause adverse effect on the performance of the aircraft [4]. Therefore, FAA has developed a program named, Continuous Lower Energy, Emissions and Noise (CLEEN), to make it advance in technologies for further noise reduction [8].
Noise Abatement System
Nowadays acoustic liner is one of the excellent noise abatement tools [9]. Honeycomb structure of the acoustic liner takes responsibility by higher impedance conditions to optimize the high dissipation of noise [10]. The computational method can set a standard process to resolve the problem with the help of model analysis, but the numerical analysis shows the impedance instability for feasible conditions [11], [12]. Finally the shape of the acoustic liner has proven from researchers with optimal features [13]. Basically acoustic liner placed at the inlet section of the aircraft engine. The single layer acoustic liner assembled, hexagonal shape cell honeycomb structure with perforated sheet (punched metal sheet). Figure 1 shows the example of noise abatement for commercial aircraft. The bias acoustic liner is another noise abatement tool. One of the advantages of bias acoustic liner is that it has much higher heat transfer rate than acoustic liner. Distinct from acoustic liner, bias acoustic liner is installed in nacelle D-chamber. Also, perforated plate is applied on upper plate in case of bias acoustic liner. Thereby, the hot air from Dchamber enables the flow to move inside bias acoustic liner, then exit to ambient. As a result, bias acoustic liner has higher heat transfer rate than acoustic liner. Another advantage of bias acoustic liner is that it produces bias flow, and then reduces drag force on the nacelle lip. Bias flow exits from bias acoustic liner and develops slip condition on the nacelle lip, thus reduces velocity gradient, shear stress and drag force on the nacelle lip as shown in Fig. 2. As a result, enhances the efficiency of aircraft with eminent fuel saving.
Copyright © 2016 Praise Worthy Prize S.r.l. - All rights reserved
DOI: 10.15866/ireme.v10i6.9427
390
A. Qummare Azam et al.
Fig. 1. Types of acoustic liners which are using in aero engines
Hot air anti-icing is famous anti icing system and widely used among commercial aircraft [16]. Since hot air anti-icing is used in nacelle lip, acoustic liner (one of the famous noise abatement tool) is not applicable for hot air anti-icing due it is not a good thermal conduction. As consequences, bias acoustic liner invented. It allows hot air flows through the holes and keep nacelle lip-skin warm and free from ice accumulation problem. However, the effect of bias acoustic liner to drag coefficient is still not study by the researchers yet [14]. Also, the computational methods have been used to simulate the nacelle, pylon and wing interference effects and Euler codes have been developed [17]. Later, the viscous corrections were made to study the drag calculation more accurately [18]. In recent years Reynolds Averaged Navier Stokes (RANS) calculations have been performed [19]. Now, our study aims to conduct numerical evaluation of effect of bias acoustic liner on drag coefficient for nacelle lip-skin application.
IV.
The Bias Flow
The objective of the bias acoustic liner is emphasized on identifying the flow control system and its effect on the aerodynamics features of specific aircraft parts [16]. The bias flow mechanism follows the flat plate liner wall with simple configuration for alternate flow of fluid by pores with micro blowing technique. The reduction of drag and effect of bias flow problem is highly complex with multi scale interaction [20]. The mixing of arrays of micro flow as sketched in Fig. 2 can be assumed as a flow over the body by channels. Flow shows the typical structure of boundary layer characteristics by thickness for the mass diffusion through the wall layer [12]. The interaction of the body surface and fluid flow results in both the friction drag and pressure difference, so the bias flow is employed to reduce these wall effects.
Fig. 2. The Bias flow diagram [1]
III. Drag Effect on Nacelle Surface: The problem statement Nowadays many investigations are being carried out to enhance the efficiency of aircrafts. Ismail [14] placed noise abatement system on the nacelle lip-skin; however it is compulsory to ensure that this area should free from ice accumulation [15]. Therefore, they have to combine noise abatement system with ice protection system.
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International Review of Mechanical Engineering, Vol. 10, N. 6
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A. Qummare Azam et al.
V.
3
Geometry Modeling and Boundary Condition Setup
2,5 drag coeff.
GAMBIT pre-processor has been used to develop geometry modelling and mesh of the nacelle lip. In order to obtain reliable numerical results, quad type mesh was employed and very fine mesh was used in nacelle wall vicinity as illustrated in Fig. 3.
2 1,5 1 0,5 0 5
10 15 20 free stream velocity in m/s
25
drag coeff. Without bias flow drag coeff. With bias flow Fig. 4. Drag Coefficient for Velocity Inlet v/s Bias Flow Fig. 3. Boundary Condition on Meshed model
As shown in figure, velocity inlet is used to supply free stream velocity to the nacelle lip. Both top and bottom lines were set as wall. Finally, pressure outlet is employed to let air velocity flows crossing nacelle lip. Afterwards, ANSYS fluent 14.0 was used to obtain simulation result. k-ω/SST turbulent model was utilized in the study[14]. The flow was assumed as incompressible as the Mach number lower than 0.1. Six difference free stream velocities between 1.5 m/s to 25 m/s were investigated.
VI.
Results and Discussion
Fig. 5. Velocity profile with bias flow
Fig. 4 depicts the free stream velocity on the nacelle lip skin surface with and without bias flow. The bias flow is channelized with micro blowing controlling techniques but do not control in real case condition. In case of drag coefficient without bias flow, the graph increases gradually with the grazing effect along with the surface showing smooth functionality. The drag coefficient as depicted, shows the bias flow control as the graph increases sharply between 15 m/s to 20 m/s according to the bias flow due to the pores of the liner by imposing the wall friction. As shown in the figure, the drag coefficient for bias flow is about 1.304 as the free stream velocity increases from 5 m/s to 25 m/s. Also in Table I, the optimum ratio of flow velocity to free stream velocity decreases with free stream velocity, and results in the increment of drag coefficient with the free stream velocity. The highest percentage difference of drag coefficient of nacelle lip with and without liner is 90% at free stream velocity of 5 m/s. The bias flow with liner introduces this difference in the model and velocity profile with and without bias flow has shown in Figs. 5 and 6. Drag force is generated by the effect of shear stress with the variation of the boundary layer thickness.
Fig. 6. Velocity profile without bias flow
The boundary layer moves away from the wall significantly by the presence of the liner, thereby reducing the drag effect on the surface with the help of bias flow. The thickness of the boundary layer with bias flow is about 0.12 mm and without bias flow is 10.12 mm. The local shear stress between these two conditions is about to 4.5×10-3 Pa and 4.4×105 Pa, and it shows the significant effect of the bias flow at 25m/s.
Copyright © 2016 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Mechanical Engineering, Vol. 10, N. 6
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A. Qummare Azam et al.
Fig. 7. Pressure contour of the model without liner and with liner TABLE I MODIFIED MODEL OF NACELLE BIAS FLOW Velocity inlet (m/s) Bias Flow Inlet (m/s) 25 7.154 20 5.700 15 4.050 11 2.700 10 2.652
Fig. 7 shows the velocity profile of the model with bias flow and without bias flow, the Spalart-Allmaras (SA) turbulence model [21] is used, solving only one equation for the calculations, which is equal to the eddy viscosity far from walls. The transport equation has been generated empirically to recreate the flows to increase complexity [22]: = +
− 1
VII.
+
([ + ] +
(1)
)+
The present work investigates the effect of bias flow on drag coefficient of nacelle lip skin surface. The investigation has been done by using Fluent CFD code in 2D. Very fine mesh was employed in nacelle lip vicinity in order to obtain reliable simulation results. According to the simulation results, bias flow helps in reducing the drag coefficient of nacelle lip. The highest percentage difference in drag coefficient occurs at free stream velocity of 5 m/s. However, the percentage difference of drag coefficient decreases as the free stream velocity is increased. The lowest percentage difference of drag coefficient was generated at free stream velocity of 25 m/s.
∙
where d is the distance to the closest wall and the model has been modifying so that close to solid surfaces but outside the viscous region which fits the logarithmic region, i.e.: = where
,
=
(2)
is the friction velocity based upon the wall =
friction
and
and the turbulent viscosity variable by: =
1 ,
1=
the Von Karman constant is linked to the transported
Acknowledgements +
,
=
is linked to the vorticity S (which reduces to
Many thanks to Grant code 304/PAERO/60313022 from University Sains Malaysia due to sponsored this paper.
(3) in
thin shear flows), by: =
+
Conclusion
References 2,
2=1−
1+
1
[1]
(4)
Finally, is a function of the ratio ≡ ⁄( ), and both equal unity in the log layer. Eq. (1) is in balance provided = + (1 + )/ .
[2]
Copyright © 2016 Praise Worthy Prize S.r.l. - All rights reserved
J. Li, C.-H. Lee, L. Jia, and X. Li, "Numerical study on flow control by micro-blowing," in Proc. of 47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, Florida (USA), 2009, pp. 1-19. A. Kempton, "Acoustic liners for modern aero-engines," in 15th CEAS-ASC Workshop and 1st Scientific Workshop of X-Noise EV, 2011.
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Authors’ information 1
Research Student (M.Sc.), School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia. E-mail:
[email protected] 2
Senior lecturer, School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, 14300Nibong Tebal, Penang, Malaysia. E-mail:
[email protected] 3
Lecturer, School of Aerospace Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia. E-mail:
[email protected] 4
Research Student (M.Sc.), School of Aerospace Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia. E-mail:
[email protected] Qummare Azam received Bachelor degree in mechanical engineering from the ICFAI University, Dehradun in 2014 India. He is currently pursuing a Master degree by research in Mechanical Engineering at Universiti Sains Malaysia, Engineering campus, Nebong Tebal, Penang, Malaysia. His areas of interest include Nacelle Drag optimization, Bias Acoustic Liner, CFD Simulation and finite element modelling. Mohd Azmi Ismail received BachelorDegree and Master Degree in mechanical engineeringfrom the Universiti Sains Malaysia, Engineering campus, Nebong Tebal, Penang, Malaysia. He obtained Doctoral Degree from Kingston University, United KingdomHe received fundsunder research grants from various research organizations. He has published few articles innational and international level journals andconference proceedings. He is professional member of BEM (Board of Engineering Malaysia). His areas of expertise electronic cooling, Anti-Icing, Spillway dam, CFD and Air-Conditioning. Nurul Musfirah Mazlan received a M.Sc. in Thermal Power Aerospace and Doctoral Degree in Aerospace Propulsion Engineering from Cranfield University, U.K. She is currently working as a Lecturer in the Department of Aerospace Engineering, Universiti Sains Malaysia, Engineering campus, Nebong Tebal, Penang, Malaysia. Her expertise in Bio-fuel, Aircraft engine performance and Aircraft combustion. Musavir Bashir received a Bachelor Degree in Aerospace engineering from the Aerospace Engineering and Research Organization, Pune, in 2014, India. He is currently pursuing a Master degree by research in Aerospace engineering at Universiti Sains Malaysia, Engineering campus, Nebong Tebal, Penang, Malaysia.
Copyright © 2016 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Mechanical Engineering, Vol. 10, N. 6
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