Boundary layer flow noise—The direct radiation

Abstract

The farfield sound radiation due to the transitional and turbulent boundary layer flow over a rigid, finite body of revolution is addressed quantitatively. Three statistically independent sources of flow noise are analyzed; namely, the intermittent laminar-to-turbulent transition zone that occurs near the nose, the fully developed turbulent boundary layer that covers nearly all of the body surface, and the unsteady trailing edge flow that occurs on the body stabilizer fins. The modeling is used to predict the radiated noise spectra measured in a deep lake along the trajectory of a test body that was released from the bottom and propelled by buoyancy. These experimental data are from the Huddle and Skudrzyk [J. Acoust. Soc. Am. 46, 130–157 (1969)] flow noise experiments. In these experiments the radiated noise was found to be independent of the body composition (both metal and wooden units were used) and the authors concluded that flow unsteadyness was the primary source of farfield radiation. The predictions presented here support that conclusion in that the transition zone and trailing edge flows are very unsteady and their acoustic emissions are significantly more intense than those from the relatively stable turbulent boundary layer flow. [ Work supported by Applied Research Laboratory under contract with U. S. Navy.]