Mean and Time-Varying Flow Measurements on the Surface of a Family of Idealised Road Vehicles

Aerodynamically generated noise in the A-pillar region of a passenger vehicle can make a significant contribution to interior noise and adversely affect passenger comfort. Modern vehicles experience strong surface pressure fluctuations on the side windows due to flow separation around the A-pillar. The objective of this work is to investigate how these fluctuations vary with speeds and also to study the effects of local A-pillar and windshield geometry and yaw angles on the nature of the fluctuations. Pressure fluctuations in cavities (where strong feedback mechanisms can occur) were not studied in this work. Investigations were performed to study the effects of the A-pillar and windshield effective corner radii on the local flow and its potential for noise generation using a group of idealized road vehicle models. Surface mean and fluctuating pressures were measured on the side window in the A-pillar region at different Reynolds numbers and yaw angles. Tests were carried out in the RMIT University Industrial Wind Tunnel. Flow structure was documented using flow visualization. The studies show that Reynolds number sensitivities (based on free-stream flow velocities and body width) in the range of 6.4×105-1.5×106 were minimal. Surface mean and fluctuating pressures scaled well with velocity head and Strouhal number. The magnitudes of the fluctuating pressure coefficients depend largely on local A-pillar radii and can be reduced significantly with the increase of local corner radii.