Nonlinear effects on sound in nearly sonic duct flows

A nonlinear theory for sound propagation in nearly sonic flows in variable area ducts is outlined. The theory is based on a quasi-one-dimensional model and the use of matched asymptotic expansions. The problem of an acoustic source located in the throat region of a duct with a converging section is treated. It is shown that the near-sonic region has a marked nonlinear effect on sound propagation in the duct.