Measurements of the Scattering of Sound from Turbulence

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Abstract
An experiment was performed on the scattering of ultrasonic waves (25 65 kc/sec) from the turbulence produced by the flow through a grid in a 6×f-in. nozzle. The transmitter and receiver were of the solid dielectric, condenser type. The scattered signal was separated from the direct and reflected signals by a pulse technique. The intensity of scattered sound was measured at angles from 21.5° to 165° to obtain the differential scattering cross section. The 1-in. mesh grid was heated to obtain scattering from both the velocity and temperature fluctuations. The results were compared with the formulas derived by Lighthill, Kraichnan, and Batchelor. [Proc. Cambridge Phil. Soc. 49 531–551 (1953); J. Acoust. Soc. Am. 25, 1096–1104(1953); in Symposium on Naval Hydrodynamics, F. S. Sherman, Ed. (National Academy of Science-National Research Council, Washington, D.C., 1957), Publ. 515, pp. 409 430]. The general shapes of the curves predicted by the theory were obtained experimentally: the scattering was strongly in the forward angles, as was expected for high sound frequencies, with a minimum at 90°. The scattering from the velocity field displayed an additional minimum as 180° was approached, while the scalar field produced strong backscattering. Runs were taken at distances frown the grid to the center of the scattering volume of 5 and 22 in., and at Reynolds numbers of 4110–42 600, based on the grid mesh length.

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