Fluctuating aerodynamic noise radiated from longitudinal vortex in the flow field with turbulence

Abstract

The paper focuses on fluctuating aerodynamic noise of automobiles, that is, time-varying wind noise which can significantly affect driver annoyance during at high cruising speed, independent of average loudness. One of the main aerodynamic noise sources is considered as longitudinal vortex behind the front pillar of a vehicle located near driver's ear. The mechanism of fluctuating aerodynamic noise was investigated from quantitative and qualitative viewpoints. Firstly, regarding quantitative noise level, wind-tunnel experiments and numerical simulations have been conducted for the longitudinal vortex around the delta wing subjected to the wake of a circular cylinder. The both results showed that the aerodynamic noise increases around the vortex-shedding frequency by 10 to 20 dB. Numerical analysis investigated the effect of the flow with turbulence on the generation of aerodynamic noise. Karman vortex emitted from the cylinder induces Aeolian tone with 58 Hz. The analysis revealed the noise sources with respect to time derivatives of both vorticity and surface pressure fluctuations, which lead to the increase in noise level around 58 Hz. Secondly, concerning noise quality, modulation spectrum analysis also clarified that the vortex-shedding frequency 58 Hz shifts to the lower frequency 10 Hz, which is considered as the fluctuating aerodynamic noise.