Passive and active methods to control the aeroacoustic noise generated by elliptical cylinders for automotive applications

摘要

This work concerns control techniques employed to reduce the aeroacoustic noise radiated by crossbars installed on the roof of passenger vehicles. The Reynolds numbers analyzed range between 98,000 and 147,000 based on the crossbar chord. The methodology used in this work consists of measurements of the actual acoustic pressure near the source and at the receiver locations under real operational conditions. We first assess the effectiveness of existing noise control techniques and demonstrate that they do not completely eliminate the main tone generated by the crossbars but reduce its intensity instead. We adopt the elliptical cylinder as a reference profile and investigate the effectiveness of different two and three-dimensional boundary layer tripping configurations aiming tonal and broadband noise reduction. The effect of two-dimensional tripping is strongly dependent on the Reynolds number, and three-dimensional tripping shows a clear advantage over simple two-dimensional configurations. Next we assess new passive and active methods to control aeroacoustic noise, such as perforations and active blowing through different slot geometries. Both perforation and trailing edge blowing are effective in reducing tonal noise but present undesired side effects such as high frequency whistling.