Effects of Vehicle A-pillar Shape on Local Mean and Time-Varying Flow Properties

Separated flow is the main generator of aerodynamic noise in passenger vehicles. The flow around the A-pillar is central to the wind noise as many modern vehicles still have high fluctuating pressures due to flow separations in this region. Current production vehicle geometry is restricted due to the amount of three dimensionality possible in laminated windscreen glass (and door opening etc). New materials (e.g., polycarbonate) offer the possibility of more streamlined shapes which allow less or no flow separation. Therefore, a series of experimental investigations have been conducted to study the effects of the A-pillar and windshield geometry and yaw angles on the local flow and noise using a group of idealised road vehicle models. Surface mean and fluctuating pressures were measured on the side window in the A-pillar regions of all models at different Reynolds numbers and yaw angles. Flow visualisation was also used to see the flow structure and supplement the surface mean and fluctuating pressure data. Frequency based analysis was conducted. The studies show that depending upon the curvatures of A-pillar and windshield, the fluctuating pressure coefficients can be reduced significantly. Reynolds number sensitivities were minimal and the surface mean and fluctuating pressures can be scaled if no feedback mechanism is present. A relationship between the surface fluctuating pressure coefficients and local A-pillar radii was established.