On improving sound source localization in the wind tunnel

Abstract

When traveling in an open-jet wind tunnel, the path of an acoustic wave is affected by the flow causing a shift of source positions in acoustical maps of phased arrays outside the flow. In this paper, we start by comparing several well-known approaches to correct travel times between microphones and assumed sources, used, for example, by beamforming algorithms in such an environment. The methods under consideration include the original 1D-Amiet/Bahr formulation, a standard 2.5D-planar approach that assumes the constancy of angular frequency and wave-number-vector components along a plane, and finally, a 3D-ray-tracing method. Common to the former two of these methods is the assumption that the boundary layer of the flow, the so-called shear layer, is infinitely thin and refracts the acoustical ray, whereas, in principle, the latter algorithm allows for an arbitrary (but sufficiently smooth) vector field modeling the flow. Going through these methods, we discuss travel-time results relative to each other and in terms of differences in source localization using beamforming maps. In particular, we model the flow of an existing wind tunnel and discuss results of real-world measurements comparing the 2.5D-planar approach with the 3D-ray-tracing method.