Aeroacoustic study on roof bow. CFD generation of input data for hybrid approach.

Abstract

Aeroacoustics means noise induced by ow, which is a growing field of interest in todays automotive industry. This study was carried out at Volvo Group Trucks Technology with the purpose to learn about the aeroacoustics around a roof bow in combination with cavities as well as looking into methodologies. This Master's thesis is focused on the first part of a two step hybrid approach for noise simulation, meaning to simulate the ow using computational uid dynamics (CFD). Both stationary and transient simulations with aeroacoustic treatment were performed. Different turbulence models such as large eddy simulations (LES), detached eddy simulations (DES) and unsteady Reynolds averaged Navier Stokes (URANS) were tested. Acoustic sources were looked upon with help of acoustical analogies such as Curle and Proudman, both derived from Lighthill's analogies. It was realized that the bow studied introduces broad banded noise, which could be related to its shedding frequency. Also the cavities seemed to produce broad banded noise, particularly at higher frequencies. The results reveals that LES is costly and requires approximately twice the computation time of DES and a considerably denser mesh.