Sound propagation through thermal turbulence near a convex surface

Abstract

Making use of an acoustic analogy, we study the sound propagation above a convex surface, to simulate the propagation of sound in an upward-refracting medium and to investigate the scattering of sound by turbulence into an acoustic shadow zone. An experimental study was achieved under well-controlled laboratory conditions. A heated grid is placed horizontally in a large anechoic room and the mixing of the free convection plumes above the grid generates a homogeneous isotropic random thermal field. The convex surface is simulated by a vertical cylinder. Experimental data are obtained by varying both the frequency of the acoustic source and the distance of propagation. Measurements will be presented for a rigid convex surface. In this paper, we concentrate on the mean sound-pressure levels and the intensity fluctuations. Experimental values will be compared with results of numerical simulations based on a wide-angle parabolic code.