This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Unsteady Vehicle Aerodynamics during a Dynamic Steering Action: 1st Report, On-Road Analysis
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 16, 2012 by SAE International in United States
Annotation ability available
Relationships between vehicle's high speed stability during a steering action and following aerodynamic coefficients have already been reported in the past: coefficients for time-averaged aerodynamic lift, yawing moment, side force and rolling moment. In terms of the relationships, however, we have occasionally experienced different high speed stability during steering input even with identical suspension property and almost the same aerodynamic coefficients. A vehicle during high speed cornering shows complex behavior due to unsteady air flow around the vehicle and unintentional steering input from a driver. So it is supposed that the behavior is too complex to be fully described only with those aerodynamic coefficients.
Through on-road test  and CFD analysis [2,3,4], we have studied unsteady aerodynamic characteristics around a vehicle for pitching motion during straight-line high speed driving. As a result, the existence of aerodynamic damping to stabilize the pitching motion was confirmed. The result also showed that unsteady aerodynamic characteristics had a substantial influence on the vehicle stability during straight-line high speed driving. The unsteady characteristics are assumed to affect lateral and yawing vehicle motions during cornering as well. In recent years, several studies on unsteady aerodynamic characteristics for a yawing vehicle have been conducted in wind tunnel [5,6], but not yet enough for on-road test.
In this study, we attempted to clarify how the unsteady air flow around a steered vehicle influenced on the vehicle during high speed cornering on road. In the first report of the two for this time, we examined vehicle motions and aerodynamic forces loaded on the vehicle.
The results of analysis on the vehicle motion and its surface pressure fluctuation indicated that unsteady aerodynamic forces to hold back the vehicle cornering motion were created there. It was also confirmed, in a comparison of two vehicles having different high speed stability during steering input, that the more stable vehicle had greater aerodynamic forces to hold back the cornering force. Thus it was suggested that the unsteady aerodynamic forces swayed the vehicle stability during high speed cornering.
CitationOkada, Y., Nouzawa, T., Okamoto, S., Fujita, T. et al., "Unsteady Vehicle Aerodynamics during a Dynamic Steering Action: 1st Report, On-Road Analysis," SAE Technical Paper 2012-01-0446, 2012, https://doi.org/10.4271/2012-01-0446.
Vehicle Aerodynamics, 2012
Number: SP-2333; Published: 2012-04-24
Number: SP-2333; Published: 2012-04-24
- Okada, Y. Nouzawa, T. Nakamura, T. Okamoto, S. “Flow Structures above the Trunk Deck of Sedan- Type Vehicles and Their Influence on High-Speed Vehicle Stability 1st Report: On-Road and Wind-Tunnel Studies on Unsteady Flow Characteristics that Stabilize Vehicle Behavior,” SAE Int. J. Passeng. Cars - Mech. Syst. 2 1 138 156 2009 10.4271/2009-01-0004
- Nakashima, T. Tsubokura, M. Nouzawa, T. Nakamura, T. et al. “Flow Structures above the Trunk Deck of Sedan-Type Vehicles and Their Influence on High-Speed Vehicle Stability 2nd Report: Numerical Investigation on Simplified Vehicle Models using Large-Eddy Simulation,” SAE Int. J. Passeng. Cars - Mech. Syst. 2 1 157 167 2009 10.4271/2009-01-0006
- Tsubokura, M. Cheng, S. Nakashima, T. Okada, Y. et al. “Simulation and Analysis of Effects of Dynamic Pitching for Idealized Sedan-Type Vehicle Models,” SAE Technical Paper 2011-01-0153 2011 10.4271/2011-01-0153
- Cheng, S. Y. et al. “A Numerical Analysis of Transient Flow Past Road Vehicles Subjected to Pitching Oscillation.” Journal of Wind Engineering and Industrial Aerodynamics 99 511 522 2011
- Theissen, P. Wojciak, J. Heuler, K. Demuth, R. et al. “Experimental Investigation of Unsteady Vehicle Aerodynamics under Time-Dependent Flow Conditions - Part 1,” SAE Technical Paper 2011-01-0177 2011 10.4271/2011-01-0177
- Wojciak, J. Theissen, P. Heuler, K. Indinger, T. et al. “Experimental Investigation of Unsteady Vehicle Aerodynamics under Time-Dependent Flow Conditions - Part 2,” SAE Technical Paper 2011-01-0164 2011 10.4271/2011-01-0164
- Buchheim, R. Maretzke, J. Piatek, R. “The Control of Aerodynamic Parameters Influencing Vehicle Dynamics,” SAE Technical Paper 850279 1985 10.4271/850279
- Howell, J. Le Good, G. “The Influence of Aerodynamic Lift on High Speed Stability,” SAE Technical Paper 1999-01-0651 1999 10.4271/1999-01-0651
- Howell, J. Baden Fuller, J. “A Relationship between Lift and Lateral Aerodynamic Characteristics for Passenger Cars,” SAE Technical Paper 2010-01-1025 2010 10.4271/2010-01-1025
- Mayer, J. Schrefl, M. Demuth, R. “On Various Aspects of the Unsteady Aerodynamic Effects on Cars Under Crosswind Conditions,” SAE Technical Paper 2007-01-1548 2007 10.4271/2007-01-1548
- Wijciak, J. et al. “Experimental Study of On-Road Aerodynamics during Crosswind Gusts.” 8 th MIRE International Aerodynamics Conference 311 321 2010
- Sims-Williams, D. “Cross Winds and Transients: Reality, Simulation and Effects,” SAE Int. J. of Passeng. Cars - Mech. Syst. 4 1 172 183 2011 10.4271/2011-01-0172
- Carlino, G. Cardano, D. Cogotti, A. “A New Technique to Measure the Aerodynamic Response of Passenger Cars by a Continuous Flow Yawing,” SAE Technical Paper 2007-01-0902 2007 10.4271/2007-01-0902
- Schroeck, D. Krantz, W. Widdecke, N. Wiedemann, J. “Unsteady Aerodynamic Properties of a Vehicle Model and their Effect on Driver and Vehicle under Side Wind Conditions,” SAE Int. J. of Passeng. Cars - Mech. Syst. 4 1 108 119 2011 10.4271/2011-01-0154
- Theissen, P. et al. “Unsteady Aerodynamic Phenomena under Time-Dependent Flow Conditions for Different Vehicle Shapes.” 8 th MIRE International Aerodynamics Conference 184 195 2010
- Tsubokura, M. Ikawa, Y. Nakashima, T. Okada, Y. et al. “Unsteady Vehicle Aerodynamics during a Dynamic Steering Action: 2nd Report, Numerical Analysis,” SAE Technical Paper 2012-01-0448 2012 10.4271/2012-01- 0448
- Norman, K. “Objective Evaluation of On-Center Handling Performance,” SAE Technical Paper 840069 1984 10.4271/840069
- “Road vehicles - Test method for the quantification of on-centre handling- Part 1: Weave test” ISO13674-1 2010
- Hashimoto, T. et al. “MAZDA New Wind Tunnel.” Journal of Automotive Technology 39 7 822 826 1985
- Hino, M. “Spectral Analysis.” Asakura Shoten 1977