ESTIMATION OF THE ACOUSTIC EMISSION SPECTRUM OF A BOUNDARY LAYER ON A ROUGH SURFACE.

Under engineering conditions the surfaces over which fluids flow are not usually hydraulically smooth. In this connection it is important to investigate the generation of sound by a turbulent boundary layer on a rough surface. Turbulent flow over a deformed surface creates dipole sources of sound, which may considerably increase the acoustic emission as compared with the quadrupole emission from a boundary layer on a smooth plate. In the case of sandy roughness estimates of the acoustic field are usually based on the energy summation of the fields generated by flow over the individual roughness elements. In the present study, in order to calculate the acoustic emission of a boundary layer on a surface with sandy roughness, it is proposed to employ the available experimental data on the cross of the surface pressure.