Joint acoustic and wall-pressure measurements on a model A-pillar vortex

This study investigates the noise generation and radiation of a three-dimensional A-pillar vortex, which is a three-dimensional unsteady structure found on most automotive models. A small model is used to generate the vortex and is tested in an anechoic wind tunnel. The flow is validated against the literature using wall-pressure measurements: the maxima in the fluctuating pressure coefficient are found under the vortical structure. A 31-channel acoustic beamforming array is deployed to identify the noise sources on this model in 2 perpendicular planes. The A-pillar is identified to be the main noise mechanism over a wide range of frequency (between 1 and 8 kHz), with a monopolar radiation in a plane perpendicular to the flow. Some coherence between the fluctuating wall-pressure and the far-field radiation is found around 1 kHz, but only for wall-pressure sensors located in the area outside of the vortical structure, where the fluctuating pressure coefficient is low. An additional experiment with an external noise source is conducted and confirms that the wall-pressure fluctuations convected by the vortex structure mask the acoustic pressure fluctuations which result in a low coherence level in the area where the fluctuating pressure coefficient is the highest. This experiment shows that wall-pressure measurements need to be associated to microphone array measurements to carry out a thorough experimental aeroacoustic study of a complex 3D system such as the A-pillar vortex.