Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 07, 2019 - November 08, 2019
The longitudinal vortex generated around the front pillar driving is one of the main noise sources of a car. It is very important to clarify the generation mechanism of aerodynamic noise caused by longitudinal vortices. There have been some studies on the aerodynamic noise of the longitudinal vortex, but there still remain sound generation mechanisms to be solved. It was experimentally found that there exist sound sources at the apex and the rear end of delta wing in our previous study. The paper aims to clarify the relationship between frequency characteristics and sound sources. This study employed RANS (Reynolds Averaged Navier-Stokes Simulation) for steady analysis. Unsteady numerical analysis was conducted, based on initial values obtained by RANS. For the accurate simulation, eddy viscosity model is employed as Menter SST k-ω model and turbulent model is LES (Large Eddy Simulation). Total grid number used is 120 million. As a result, the predicted values quite agree with experimented ones in the far field, which means that the analytical method is valid. To identify the sound source of the broadband sound, the time derivatives of pressure fluctuations on the delta wing surface were calculated. The time derivatives of pressure fluctuation are high around the apex of the delta wing in each frequency band, and the broadband sound source is considered to be around the apex of the delta wing. To identify the narrow band sound sources, the coherence between far field sound and time derivatives of pressure fluctuations around the rear end of the wing was conducted. Strong coherence was found at a frequency of 100 Hz very close to the narrowband peak frequency. Narrow-band sound source is considered to be around the rear end of a delta wing.
