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Investigation of Aerodynamic Drag in Turbulent Flow Conditions
Abstract:
In this paper the influence of different turbulent flow conditions on the aerodynamic drag of a quarter scale model with notchback and estate back rear ends is investigated. FKFS swing® (Side Wind Generator) is used to generate a turbulent flow field in the test section of the IVK model scale wind tunnel.
In order to investigate the increase in drag with increasing yaw, a steady state yaw sweep is performed for both vehicle models. The shape of the drag curves vary for each vehicle model. The notchback model shows a more pronounced drag minimum at 0° yaw angle and experiences a more severe increase in drag at increasing yaw when compared to the estate back model.
Unsteady time averaged aerodynamic drag values are obtained at two flow situations with different turbulent length scales, turbulence intensities, and yaw angle amplitudes. While the first one is representing light wind, the second one is recreating the presence of strong gusty wind. The results are compared to a quasi-steady averaged aerodynamic drag value derived from steady state yaw sweep measurements in the low turbulence environment of the standard wind tunnel setup. It can be shown that aerodynamic drag at 0° yaw angle is not representative of the drag found under real onroad wind conditions. Furthermore, the results show that a quasi-steady analysis under predicts forces occurring under turbulent flow conditions. Additionally, aerodynamic modifications changing aerodynamic drag at 0° yaw angle are presented, and their potential under turbulent flow conditions is discussed. The method presented here does not only take the presence of yaw under different wind conditions into account, but also contains the unsteadiness inherent in the flow found on the road.