Sound radiation from turbulent boundary layers over rough surfaces Seminar

Two distinctly different regimes will be considered. The first regime is characterized by hydrodynamically smooth surfaces for which the surface roughness does not impact the boundary layer turbulence. These surfaces have been shown experimentally and theoretically to radiate enhanced sound levels due to the scattering of the hydrodynamic pressure fluctuations into acoustic waves. The second regime considers large roughness elements that directly impact the boundary layer flow. Numerical calculations show that the flow separates around the large roughness elements and theoretically this implies that the roughness radiates sound in proportion to the unsteady force on each element. The paper will describe the theoretical approaches that have been used to predict roughness noise levels in each of these two regimes.