Turbulent Velocity and Pressure Fields in Boundary-Layer Flows Over Rough Surfaces

This paper is a discussion of recent measurements of the statistics of the turbulent velocity and wall pressure fields in rough-wall boundary layers. These measurements, made in part by the author, have been performed over a variety of walls covering a wide range of roughness sizes and configurations. The various measurements are compared in order to determine the structure and scaling parameters of the turblulent field convected at speeds near the mean velocity of the boundary layer. The mean square turbulent velocities, their one-dimensional spectral densities, and their longitudinal and vertical microscales are compared for different walls. The velocity fields are shown to be similar when described in terms of local mean velocity, friction velocity, and displacement thickness. Turbulent production and dissipation rates, which are derived from the measurements, are also discussed. Recent measurements of wall pressure fluctuations are also reviewed. The wall pressure spectrum levels on rough walls are shown to increase with local mean wall shear through a dependence on the vertical component of turbulent velocity by a mean shear-turbulence interaction. Finally, the dependence of the high frequency convected pressure field on the insitu roughness size is discussed in terms of the mean shear-turbulence interaction