Kinematic and Acoustic Similarities of Separated Turbulent Boundary Layers

Abstract

This Paper proposes a similarity model for separated turbulent boundary layers as a function of the outer flow parameters, the velocity associated with the maximum local mean shear , and the reduced wall-normal coordinate. By using this similarity model, the outer layer profiles are scaled for approximately 70–80% of the boundary layer height. A corresponding similarity model of the far-field sound pressure levels and surface pressure autospectrum was derived. The proposed scaling shows less variability than the canonical trailing-edge noise scaling within a range of the freestream velocity and airfoil’s angle of attack. The scaling of the surface pressure autospectrum reveals that the viscous and inertial time scales are of the same order of magnitude, which suggests strong turbulent dissipation in the separated turbulent boundary layer that results in the steep rolloff of the autospectrum in the midfrequency range.