This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Experimental Investigation of Unsteady Vehicle Aerodynamics under Time-Dependent Flow Conditions - Part2
Technical Paper
2011-01-0164
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Language:
English
Abstract
Unsteady aerodynamic flow phenomena are investigated in a wind tunnel by oscillating a realistic 50% scale model around the vertical axis. Thus the model is exposed to time-dependent flow conditions at realistic Reynolds and Strouhal numbers. Using this setup unsteady aerodynamic loads are observed to differ significantly from quasi steady loads. In particular, the unsteady yaw moment exceeds the quasi steady approximation significantly. On the other hand, side force and roll moment are over predicted by quasi steady approximation but exhibit a significant time delay.
Part 2 of this study proves that a delayed and enhanced response of the surface pressures at the rear side of the vehicle is responsible for the differences between unsteady and quasi steady loads. The pressure changes at the vehicle front, however, are shown to have similar amplitudes and almost no phase shift compared to quasi steady flow conditions. The difference between unsteady and quasi steady yaw moment proves to be independent of oscillation amplitudes between 2deg and 4deg. It is assumed that the intensity of the unsteady flow phenomena is determined by the interaction of the time scale of the model rotation and the time scale of the delayed wake flow, described by the Strouhal number. The largest magnification factors for the yaw moment are found at 140kph and 2Hz for the notchback geometry, which results in a Strouhal number of Sr=0.12. It is finally shown that the yaw moment overshoot is less pronounced for a fastback and especially for a fullback geometry, which is explained by smaller unsteady pressure variations at the rear side of the fullback.
Recommended Content
Authors
Citation
Wojciak, J., Theissen, P., Heuler, K., Indinger, T. et al., "Experimental Investigation of Unsteady Vehicle Aerodynamics under Time-Dependent Flow Conditions - Part2," SAE Technical Paper 2011-01-0164, 2011, https://doi.org/10.4271/2011-01-0164.Also In
References
- Wojciak, J. Theissen, P. Indinger, T. Adams, N.A. Demuth, R. “Experimental Study of On-Road Aerodynamics during Crosswind Gusts” MIRA International Vehicle Aerodynamics Conference UK October 13 14 2010
- Tsubokura, M. Nakashima, T. Kitoh, K. Sasaki, Y. “Development of unsteady aerodynamic simulator using large-eddy simulation” 7th FKFS Conference Germany October 6 7 2009
- Tsubokura, M. Nakashima, T. “Unsteady Aerodynamic Simulator for Road Vehicles based on Large-Eddy Simulation” MIRA International Vehicle Aerodynamics Conference UK October 13 14 2010
- Favre, T. Efraimson, G. “Numerical Study of Design Alterations Affecting the Crosswind Characteristics of a Generic Road Vehicle Model” MIRA International Vehicle Aerodynamics Conference UK October 13 14 2010
- Theissen, P. Demuth, R. Adams, N.A. “Unsteady phenomena in vehicle aerodynamic under time-dependent flow conditions” 10th Stuttgart International Symposium Germany March 16 17 2010
- Theissen, P. Wojciak, J. Demuth, R. Indinger, T. Adams, N.A. “Unsteady Aerodynamic Phenomena under Time-Dependent Flow Conditions for Different Vehicle Shapes” MIRA International Vehicle Aerodynamics Conference UK October 13 14 2010
- Gohlke, M. Beaudoin, J.F. Amielh, M. Anselmet, F. “Experimental analysis of flow structures and forces on a 3D-bluff-body in constant cross-wind” Experiments in Fluids 43 579 594 2007
- Lemke, T. “Untersuchung der Fahrzeugumströmung bei Seitenwind für die Frühphase der PKW-Entwicklung” PhD Thesis Universität Siegen 2006
- Guilmineau, E. Chometon, F. “Numerical and Experimental Analysis of Unsteady Separated Flow behind an Oscillating Car Model,” SAE Int. J. Passeng. Cars - Mech. Syst. 1 1 646 657 2008 10.4271/2008-01-0738
- Mullarkey, S.P. “Aerodynamic stability of road vehicles in side winds and gusts” PhD thesis University of London 1990
- Bearman, P.W. Mullarkey, S.P. “Aerodynamic Forces on Road Vehicles due to Steady Side Winds and Gusts” RAeS, Vehicle Aerodynamics Conference Loughborough 1994
- Passmore, M.A. Richardson, S. Imam, A. “An experimental study of unsteady vehicle aerodynamics” Proceedings of the Institution of Mechanical Engineers 215 Journal of Automobile Engineering 2001
- Schröck, D. Widdecke, N. Wiedemann, J. “Aerodynamic Response of a Vehicle Model to Turbulent Wind” 7th FKFS Conference Germany October 6 7 2009
- Garry, K.P. Cooper, K.R. “Comparison of Quasi-Static and Dynamic Wind Tunnel Measurements of Simplified Tractor-Trailer Models” Journal of Wind Engineering and Industrial Aerodynamics 22 1986
- Passmore, M.A. Mansor, S. “The Measurement of Transient Aerodynamics Using an Oscillating Model Facility,” SAE Technical Paper 2006-01-0338 2006 10.4271/2006-01-0338
- Heft, A.I. Indinger, T. Adams, N.A. “Investigation of Unsteady Flow Structures in the Wake of a Realistic Generic Car Model” 29th AIAA Applied Aerodynamics Conference June 27 30 2011 Honolulu, Hawaii, USA
- Kulite Semiconductor Products Inc., Leonia, New Jersey, USA Kulite Miniature Ruggedized IS Pressure Transducers XT-190 (M) Series 2009
- Mansor, S. Passmore, M.A. “Estimation of bluff body transient aerodynamics using an oscillating model rig” Journal of Wind Engineering and Industrial Aerodynamics 96 1218 1231 2008