Experimental Investigations of Tonal Noise on a Vehicle Side Mirror

Abstract

Experimental investigations on an isolated vehicle side mirror model are performed in a low turbulence wind tunnel aiming at the identification of the acoustic source mechanism leading to tonal noise emission. A combination of acoustic measurements and Particle Image Velocimetry shows that the discrete frequency noise can be related to the presence of a laminar boundary layer separation extending up to the trailing edge on the mirror's side surface and upper side. In the vicinity of the trailing edge, the shear layer develops into a vortical structure, which impinges on the trailing edge. By utilization of Proper Orthogonal Decomposition on the ensembles of instantaneous velocity fields and application of a phase sorting method, the length scales of the vortical structures could be extracted and related to the acoustic radiation. Order of magnitude analyses show parallels to the acoustic feedback mechanism known from the NACA 0012 airfoil.

Application of LES combined with a wave equation for the simulation of noise induced by a flow past a generic side mirror

“…These phenomena were widely studied both experimentally and numerically. Real and simplified geometries of a side mirror were measured, for example, by Hartmann et al, 11 Werner et al, 12 and Siegert et al 13 Numerical simulations of these and other mirrors were done by Hartmann et al, 11 Frank and Munz, 14 Siegert et al, 13 and others. [15][16][17][18][19][20][21][22][23][24] In most of these works, authors applied hybrid approaches to aeroacoustics simulation.…”

“…[15][16][17][18][19][20][21][22][23][24] In most of these works, authors applied hybrid approaches to aeroacoustics simulation. An exception is a paper by Frank and Munz, 14 who directly computed the tonal whistling noise for a very special simplified mirror geometry, which was designed and experimentally studied by Werner et al 12 The tonal noise in that flow was generated by a significant feedback of acoustics on a flow over a mirror with the non-optimized sharp edges. Obviously, the standard hybrid approach with its one-way coupling of flow and acoustics is not applicable to analyze this phenomenon, which explains the application of the direct noise simulation using the compressible flow equations.…”