Based essentially on the numerical approach a different modelling method for wind gusts was proposed. Using this method significant unsteady effects regarding the yaw moment were found and the underlying phenomena in the flow field were analyzed. The lateral deviation of the leeward airflow at the rear end of the vehicle and the two relating vortices develop with a time delay of approximately a quarter of a second to a change of the incoming flow of 1 Hz. This explains the pressure differences between the unsteady and the quasi-stationary solution which cause the difference in yaw moment. The detection of the unsteady phenomena in the flow field now allows investigating the correlation between the shape of the car and these unsteady effects and eventually optimizing cars regarding side-wind sensitivity. The two different methods applied during this study are considering slightly different gust perturbations, which both exhibit the same unsteady flow characteristics. Further studies will have to show which method is suitable to simulate the real phenomena more accurately. Finally, it has to be pointed out that the numerical investigations presented in this paper can only give a qualitative understanding of the flow phenomena under timedependent flow conditions. The results still show a significant variation which is mainly caused by the turbulent flow especially at the rear end of the vehicle. Depending on which state the flow field around the rear end of the vehicle has when the gust reaches the car, different unsteady peak values are obtained. Furthermore, comparability with realistic situations remains a problem until verified input parameters are available.
Unsteady phenomena in vehicle aerodynamics under time-dependent flow conditions
2010
21 Seiten, 25 Bilder, 14 Quellen
Conference paper
English
Unsteady phenomena in vehicle aerodynamics under time-dependent flow conditions
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