Engineering seminar on fluid acoustics lecture 3; broad band noise induced by flow turbulence

摘要

This is the third of a series of lectures for an engineering seminar on fluid acoustics which focuses on control and utilization of sound generated from unsteady flows. This third lecture presents the generation mechanisms and the controltechniques of broad band noise induced by flow turbulence. Boundary layer noise, separated flow noise, and jet noise are explained after explanations about frequency, wave-length, acoustic impedance, and the acoustic interference are presented. Thephenomena of bursts in the viscous transition layer under the turbulent boundary layer are seeds of boundary layer noise. The scale of flow separation controls the amplitude and the dominant frequency component of separated flow noise. The structure ofshear flow layer around the jet flow controls the jet noise and the span-wise non-uniformity of the shear flow decreases the jet noise.