Effects of under body diffuser on the aerodynamics of a generic car

Year 2018, Volume: 7 Issue: 2, 99 - 109, 03.09.2018

Seyfettin Bayraktar , Yilmaz Ogun Bilgili

https://doi.org/10.18245/ijaet.458901

Cited By: 3

Abstract

Flow structure and other aerodynamic properties such as drag and lift coefficients of one of the extensively investigated generic cars so-called Ahmed body are reported in the present numerical study for the fixed ground and upswept rear. For this purpose, Ahmed body with the slant angle of 25 degrees is considered and its rear bottom edge is upswept with various angles from 5 degrees to 30 degrees by 5-degree increments without any side plates. It is observed that the sizes of the upper and lower recirculation bubbles seen in the profile section are decreased compared with the classical Ahmed body, however, the existence of some additional recirculation bubbles are observed when the upswept angle increases. At the highest upswept angle, the upper and bottom vortices called counter-rotating vortices (CVP) become nearly symmetric in the near-far region however they merge and only one CVP forms behind the body in the far-field. Effects of the upswept angles on the drag and lift coefficients reveal that drag coefficient reduces the upswept angle to 15 degrees and then rises to 20 degrees while the lift coefficient increases after 25 degrees.

Keywords

Computational fluid dynamics (CFD), Ahmed body, Ground vehicles, Turbulence, Recirculation bubbles

References

• Hucho, W., Sovran, W.H., Aerodynamics of road vehicles, Annual Review of Fluid Mechanics, 25, 485-537, 1993
• Kang, S.O., Jun, S.O., Park, H.I., Song, K.S., Kee, J.D., Kim, K.H., Lee, D.., Actively translating a rear diffuser device for the aerodynamic drag reduction of a passenger car, International Journal of Automotive Technology, 13(4), 583-592, 2012.
• Ahmed, S.R., Ramm, G., Faltin, G., Some salient features of the time-averaged ground vehicle, SAE Technical paper 840300, 1-30, Society of Automotive Engineers, inc, Warrendale, PA, USA, 1984.
• Franck, G., Nigro, N., Storti, M., Delia, J., Numerical simulation of the flow around the Ahmed vehicle body, Latin American Applied Research, 39, 295-306, 2009.
• Beaudoin, J.F., Aider, J.L., Drag and lift reduction of a 3D bluff body using flaps, Experiments in Fluids, 44, 491-501, 2008.
• Gohlke, M., Beaudoin, J.f., Amieh, M., Anselmet, F., Shape influence on mean forces applied on a ground vehicle under steady cross-wind, Journal of Wind Engineering and Industrial Aerodynamics, 98, 386-391, 2010.
• Aider, J.L., Beaudoin, J.F., Wesfreid, J.E., Drag and lift reduction of a 3D bluff body using active vortex generators, Experiments in Fluids, 48, 771-789, 2010.
• Fourrie, G., Keirsbulck, L., Labraga, L., Gillieron, P., Bluff-body drag reduction using a deflector, Experiments in Fluids, 50, 385-395, 2011.
• Joseph, P., Amandolese, X., Aider, J.L., Drag reduction on the 25 slant angle Ahmed reference body using pulsed jets, Experiments in Fluids, 52, 1169-1185, 2012.
• Krajnovic, S., Large eddy simulation exploration of passive flow control around an Ahmed body, Trans. ASME: J. Fluid Engng., 136, 121103, 2014.
• Pujals, G., Depardon, S., Cossu, C., Drag reduction of a 3D bluff body using coherent streamwise streaks, Experiments in Fluids, 49, 1085-1094, 2010.
• Zhang, X., Senior, A., Ruhrmann, A., Vortices Behind A Bluff Body With An Upswept Aft Section In Ground Effect, International journal of Heat and Fluid Flow, 25, 1-9, 2004.
• Howard, R.J.A., Pourquie, M., Large eddy simulation of an Ahmed reference model, Journal of Turbulence, 3, n12, 2002.
• Andersson, B., Andersson, R., Hakansson, L., Mortensen, M., Sudiyo, R., Van Wachem, B., Computational Fluid Dynamics for Engineers, Cambridge University Press, 2012.
• Ansys Fluent 12.0 User`s Guide, 2012
• Bayraktar, I., Landman, D., Baysal, O., Experimental and Computational Investigation of Ahmed Body for Ground Vehicle Aerodynamics, SAE paper 2001-01-2742, 2001.
• Graysmith J.L., Baxendale A.J., Howell J.P., Haynes T., Comparisons between CFD and experimental results for the Ahmed reference model. RAeS conference on vehicle aerodynamics, Loughborough, pp 30.1–30.11, 1994.
• Muritala, A.O., Fatokun, H.A, Obayopo, S.O., Effect of an Add-On Device on the Aerodynamic Characteristics of a 3-Dimensional Ahmed Boyd, IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE), 14(6), 18-29, 2017.
• Lienhart, H., Stoots, C., Becker, S., Flow and Turbulence in the Wake of a Simplified Car Model (Ahmed Model). In Wagner, S., Rist, U., Heinemann, H.J., Hilbig, R. (ed.), New Results in Numerical and Experimental Fluid Mechanics III. Notes on Numerical Fluid Mechanics (NNFM), vol.77, Springer, Berlin. Heidelberg, 2002.
• Strachan, R.K., Knowles, K., Lawson, N.J., The vortex structure behind an Ahmed reference model in the presence of a moving ground plane, Exp. Fluids, 42, 659-669, 2007.
• Keogh, J., Barber, T., Diasinos, S., Doig, G., The Aerodynamic Effects on a Cornering Ahmed Body, J. of Wind Eng. Ind. Aerodyn., 154, 34-46, 2016.
• Ming, J., Raghu, M., David, T., Detection and Visualization of Vortices. The visual handbook. 10.1016/B978-012387582-2/50016-2, 2005
• Bayraktar, S., Yayla, S., Oztekin, A., Ma, H. Wall Proximity Effects on Flow over Cylinders with Different Cross Sections, Canadian Journal of Physics, 92, 141-148, 2014.