Observation of the waveguide propagation of sound in a turbulent boundary layer on a plate

The transition to the waveguide propagation of sound in a turbulent boundary layer on a plate is investigated experimentally and theoretically for low Mach numbers (much less than 1). Results of a theory for a boundary layer with a power-law velocity profile are compared with measurements of the acoustic field of a piston radiator in a wind tunnel. It is shown that acoustic energy concentration near the wall becomes substantial at distances from the radiator that exceed the refraction length.