Abstract:

Explicit treatment of discrete, transitory, momentum-transporting features in boundary layers (bursts and sweeps) can generate acoustic models [e.g., J. M. Witting, ``A spectral model of pressure fluctuations at a rigid wall bounding an incompressible fluid, based on turbulent structures in the boundary layer,'' Noise Control Eng. J. 26, 28--43 (1986)]. This presentation addresses the following topics: (1) the relationships between the properties of the microscopic structures (such as their sizes, strengths, and durations) and the details of the wall-pressure spectrum; (2) estimating actual microscopic properties from measured data, either directly or from empirical models that have been compared to measured data; (3) extensions to more complex geometries; and (4) the role of the boundary-layer structures as direct sources of sound in the fluid.