Experimental investigation of the wall dynamics of the A-pillar vortex flow

The influence of the A-pillar vortex on the wall flow of the side window of a car is investigated experimentally using a 30° dihedron model. The measurement of the unsteady pressure at the wall provides a map of the pressure fluctuation intensity, and a spectral analysis is performed to track the dominant frequencies of the wall pressure fluctuations. The wall flow generated by the vortex structure that develops parallel to the side-wall is characterised by means of particle image velocimetry (PIV). Its structure is analysed and compared to cross-sections of the A-pillar vortex in order to identify the different separation and reattachment lines. A comparison of the field of turbulent kinetic energy obtained by PIV with the map of the pressure fluctuations shows a correlation between the structure of the A-pillar vortex and the pressure fluctuations. It is found that the dominant wall pressure fluctuations are located at the secondary separation line, whereas the primary reattachment line does not show any significant pressure variations, that the A-pillar vortex will not naturally break down and that discrete vortices may be associated with the pressure fluctuations.