ASA 125th Meeting Ottawa 1993 May

5aPA9. Noise production by turbulent flow over an unscreened measurement microphone.

Scott Morgan

Dept. of Phys., Southeastern Louisiana Univ., P.O. Box 878 SLU, Hammond, LA 70402

Richard Raspet

Univ. of Mississippi, University, MS 38677

In previous work, it has been shown that the wind noise in an unscreened microphone placed in a low-speed turbulent flow is caused by the turbulence intrinsic in the flow [S. Morgan and R. Raspet, J. Acoust. Soc. Am. 92, 1180--1183 (1992)]. The theory of pressure fluctuations in a turbulent flow as related to wind noise in an unscreened measurement microphone is discussed in this paper. A Poisson's equation for fluctuation pressure in terms of mean and fluctuation velocity derivatives with respect to spatial dimensions results from the theory. This implies that the mean and fluctuation velocities must be known at every point in space in order to solve for the fluctuation pressure at a given point; however, through comparison of theory with experimental data, it is shown that the fluctuations in the boundary layer near the microphone where velocity gradients are very large provide the major source of wind noise. An approximation method for estimating the contribution of this ``local interaction'' is also discussed.