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Computational Investigations on the Aerodynamics of a Generic Car Model in Proximity to a Side-Wall
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 03, 2018 by SAE International in United States
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This paper discusses a realistic approach of simulating a generic idealized car model (Ahmed body) moving in close proximity to a Side-wall using transient CFD. This phenomenon is very important in motorsports where racing very close to the safety barrier is very common. Driving in close proximity to a Side-wall alters the aerodynamic characteristics of the vehicle significantly, however, only a handful of published work exists in this area. Additionally, the experimental studies conducted in the past suffer from certain inadequacies especially in properly emulating the Side-wall, which cast some uncertainty as to their applicability to the real world. As such, the present study attempted to imitate the real world flow phenomenon by taking a non-traditional CFD approach in which the body is translated relative to the stationary surrounding fluid and Side-wall instead of the classical method of flowing air over a stationary object. This was achieved by using a newer meshing technique for overlapping grids called the “Overset” or “Chimera” mesh. The initial challenging task was to predict accurately the flow over the rear slant of the 25o slant angle Ahmed body model where previous studies struggled to achieve accurate enough predictions using the eddy-viscosity turbulence models. In the present study, the SST turbulence model with modified closure coefficients is utilized to accurately predict flow characteristics in the initial separated shear layer and, as well as, the flow reattachment over the rear slant. Compared to the eddy viscosity CFD simulations of an isolated 25-degree slant angle Ahmed body seen in existing literature, the results presented in this paper show significantly better correlations with the experiments in terms of overall aerodynamic characteristics, like drag and lift, and flow characteristics like pressure and velocity in the wake region. The wall proximity studies show a strong influence of the presence of the wall on the overall aerodynamic characteristics of vehicle body. When compared with the experimental studies, although both show similar trends, however, there exist significant differences between the experimental and CFD predicted results, which tend to worsen as one approaches the wall. These differences can be attributed to the fact that the CFD emulation of the flow around the side-wall is more realistic compared to the experimental implementation.
CitationUddin, M., Mallapragada, S., and Misar, A., "Computational Investigations on the Aerodynamics of a Generic Car Model in Proximity to a Side-Wall," SAE Technical Paper 2018-01-0704, 2018, https://doi.org/10.4271/2018-01-0704.
Data Sets - Support Documents
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- Wallis, S. and Quinlan, W., “A Discussion of Aerodynamic Interference Effects between a Race Car and a Race Track Retaining Wall (A Wind Tunnel NASCAR Case Study),” SAE Technical Paper 880458, 1988, doi:10.4271/880458.
- Advantage CFD, “A CFD NASCAR Case Study into the Effects of Wall Proximity,” Race Car Engineering, Jun 2001, pp 48-54, 2001.
- Brown, J., “Racecar Aerodynamics in Close Proximity to a Retaining Wall,” MSc Thesis, Cranfield University, Cranfield, Bedfordshire, UK, 2005.
- Strachan, R., Knowles, K., Lawson, N.J., and Finnis, M.V., “Force and Moment Measurements for a Generic Car Model in Proximity to a Side Wall,” Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 226(10):1352-1364, 2012.
- Strachan, R.K., “The Aerodynamic Interference Effects of Side Wall Proximity on a Generic Car Model,” PhD Thesis, Cranfield University, Cranfield, Bedfordshire, UK, 2006.
- Ahmed, S., Ramm, G., and Faltin, G., “Some Salient Features of the Time-Averaged Ground Vehicle Wake,” SAE Technical Paper 840300, 1984, doi:10.4271/840300.
- Guilmineau, E., Deng, G.B., Leroyer, A., Queutey, P. et al., “Assessment of Hybrid RANS-LES Formulations for Flow Simulation around the Ahmed Body,” Computers & Fluids, 2017.
- Maduta, R. and Jakirlic, S. “Improved RANS Computations of Flow over the 25°-Slant-Angle Ahmed Body,” SAE Int. J. Passenger Cars Mech. Syst., 10(2), pp.649-661, 201710.4271/2017-01-1523.
- Graysmith, J., Baxendale, A., Howell, J., and Haynes, T., “Comparisons between CFD and Experimental Results for the Ahmed Reference Model,” 1994.
- Lienhart, H., and Becker, S., “LDA Measurements of the Flow and Turbulence Structures in the Wake of a Simplified Car Model,” Institute of Fluid Mechanics (LSTM) University Erlangen-Nuremberg, 2000.
- Lienhart, H., Stoots, C., and Becker, S., “Flow and Turbulence Structures in the Wake of a Simplified Car Model,” (Berlin, Heidelberg, Springer Berlin Heidelberg, 2002), 323-330.
- Lienhart, H. and Becker, S., “Flow and Turbulence Structure in the Wake of a Simplified Car Model,” SAE Technical Paper 2003-01-0656, 2003, doi:10.4271/2003-01-0656.
- Strachan, R., Knowles, R., and Lawson, N., “The Vortex Structure Behind an Ahmed Reference Model in the Presence of a Moving Ground Plane,” Experiments in Fluids 42(5):659-669, 2007.
- Krajnovic, S., and Davidson, L., “Flow Around a Simplified Car, Part 1: Large Eddy Simulation”, 127(5):907-918. Journal of Fluids Engineering, 2005. Berlin, Heidelberg: ASME.
- Minguez, M., Pasquetti, R., and Serre, E., “High-Order Large-Eddy Simulation of Flow over the “Ahmed Body” Car Model,” Physics of Fluids 20(9):095101, 2008.
- Kapadia, S., Roy, S., Vallero, M., Wurtzler, K. et al., “Detached-Eddy Simulation over a Reference Ahmed Car Model,” ERCOFTAC Series 9:481-488, 2004.
- Serre, E., Minguez, M., Pasquetti, R., Guilmineau, E. et al., “On Simulating the Turbulent Flow Around the Ahmed Body: A French-German Collaborative Evaluation of LES and DES,” Computers & Fluids 78:10-23, 2013 LES of Turbulence Aeroacoustics and Combustion.
- Guilmineau, E., “Computational Study of Flow Around a Simplified Car Body,” Journal of Wind Engineering and Industrial Aerodynamics 96(6):1207-1217, 2008 5th International Colloquium on Bluff Body Aerodynamics and Applications.
- Ashton, N., West, A., Lardeau, S., and Revell, A., “Assessment of RANS and DES Methods for Realistic Automotive Models,” Computers & Fluids 128:1-15, 2016.
- Argyropoulos, C. and Markatos, N., “Recent Advances on the Numerical Modelling of Turbulent Flows,” Applied Mathematical Modelling 39(2):693-732, 2015.
- Menter, F.R., “Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications,” AIAA Journal 32(8):1598-1605, 1994.
- Bredberg, J., Peng, S.H., and Davidson, L., “An Improved k − ω Turbulence Model Applied to Recirculating Flows,” International Journal of Heat and Fluid Flow 23(6):731-743, 2002.
- Wilcox, D. C. et al., “Turbulence Modeling for CFD,” DCW Industries La Canada, CA, 1998.
- Launder, B.E. and Spalding, D.B., “The Numerical Computation of Turbulent Flows,” Computer Methods in Applied Mechanics and Engineering 3(2):269-289, 1974.
- Menter, F.R., Langtry, R.B., Likki, S., Suzen, Y. et al., “A Correlation-Based Transition Model Using Local Variables - Part I: Model Formulation,” Journal of Turbomachinery 128(3):413-422, 2006.
- Suluksna, K., Dechaumphai, P., and Juntasaro, E., “Correlations for Modeling Transitional Boundary Layers Under Influences of Freestream Turbulence and Pressure Gradient,” International Journal of Heat and Fluid Flow 30(1):66-75, 2009.
- Malan, P., Suluksna, K., and Juntasaro, E., “Calibrating the γ − Reθ Transition Model for Commercial CFD,” 47th AIAA Aerospace Sciences Meeting, pp. 5-8, 2009.
- Abe, K., Kondoh, T., and Nagano, Y., “A New Turbulence Model for Predicting Fluid Flow and Heat Transfer in Separating and Reattaching Flows-I. Flow Field Calculations,” International Journal of Heat and Mass Transfer 37(1):139-151, 1994.
- Fu, C., Uddin, M., Robinson, C., Guzman, A., and Bailey, D., “Turbulence Models and Model Closure Coefficients Sensitivity of NASCAR Racecar RANS CFD Aerodynamic Predictions,” SAE Int. J. Passeng. Cars - Mech. Syst. 10(1):330-344, 2017, doi:10.4271/2017-01-1547.
- Nagano, Y., Tagawa, M., and Niimi, M., “An Improvement of the k-e Turbulence Model (the Limiting Behavior of Wall and Free Turbulence, and the Effect of Adverse Pressure Gradient),” Trans. Jpn. Soc. Mech. Eng. B 55(512):1008-1015, 1989.
- Barlow, J.B., Rae, W.H., and Pope, A., “Low-Speed Wind Tunnel Testing,” (Canada, John Wiley & Sons, 1999).
- Cooper, K., Bertenyi, T., Dutil, G., Syms, J. et al., “The Aerodynamic Performance of Automotive Underbody Diffusers,” SAE Technical Paper 980030, 1998, doi:10.4271/980030.