### ASA 125th Meeting Ottawa 1993 May

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

**Scott Morgan
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*Dept. of Phys., Southeastern Louisiana Univ., P.O. Box 878 SLU, Hammond,
LA 70402
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**Richard Raspet
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*Univ. of Mississippi, University, MS 38677
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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.