Approximation for Thin Boundary Layers in the Sheared Flow Duct Transmission Problem

An approximation based on an inner-expansion method is shown for obtaining an analytical solution for the problem of the transmission of sound in a duct containing a sheared flow in the case when the region of nonuniform flow is very thin. The method can be used with conventional uniform-flow transmission analysis to determine wavenumbers and mode shapes for acoustic propagation and attenuation