Unsteady pressure analysis of the near wall flow downstream of the front wheel of a passenger car under yaw conditions
Journal article, 2018
The flow around passenger cars is complex and is characterized by many different structures and interactions. The occurring flow phenomena around a car determine crucial vehicle properties such as the driving stability, the noise level, the aerodynamic performance and the vehicle contamination. Therefore, it is of high importance to increase the understanding of the developing flow phenomena. Generic models are widely used to investigate flow structures and their interactions, but cannot serve to derive a general flow field for detailed full-scale vehicle models. A particularly complex area is the flow around the wheels and its interaction with the vehicle geometry. Studies on wheel-wheelhouse flow focus mainly on the geometrical influence of the wheel size, rim and tyre on the aerodynamic drag and the flow field close to the wheel. The present work investigates the flow behind the front wheel arch of a full-scale passenger car. Time resolved surface pressure measurements were taken to study the near wall flow under different yaw conditions. Based on the data obtained, flow structures are identified and their propagation speed is calculated. Further, characteristic frequencies observed are discussed. It is found that coherent structures are present behind the front wheel arch, one above the wheel centre height and one below it. These remain even under large yaw angles, no matter if the vehicle is yawed to lee- or windward. The investigation further shows that two characteristic frequencies can be found, St=0.03 and St=0.2, whereby the latter is caused by the wheel rotation. The same frequencies also occur under yaw conditions, but yawing the measurement area to leeward results in less pronounced frequency peaks.