Aerodynamic noise of a body with separated and reattached flow by longitudinal vortices

Abstract

Flow around the front-pillar of an automobile is typical of flow field with separated and reattached flow by a longitudinal vortex system. In order to reduce aerodynamically generated noise by such a longitudinal vortex system, the present research studies generation mechanism of aerodynamic noise caused by the interference between a solid body and a longitudinal vortex system in a uniform flow with low Mach number less than 0.2. Noise radiated from the longitudinal vortex system show dipole feature. Reflecting the characteristics of the flow field, the surface pressure field has characteristics that negative pressure and pressure fluctuations have their maximum values close to tips of the longitudinal vortex system and decrease along the axial direction. The dipole noise distributions on the surface are evaluated by a new correlation area method which takes phase of noise source into consideration, based on Lighthill-Curie’s equation. The method reveals that noise level in the separated region is 10 10 20 dB greater than that in the reattached region. Noise generated in the separated region has features that low frequency components are dominant closer to tips of the longitudinal vortex system and the dominant frequency components tend to shift from low to high frequency components along the axial direction.