INFLUENCE OF LOW MACH NUMBER SHEAR FLOW ON ACOUSTIC PROPAGATION IN DUCTS

An experimental and theoretical investigation of the influence of a parallel shear flow on the sound propagation in a circular duct is described. The theoretical model is based on a perturbation expansion at low Mach number of the modal equation for parallel shear flows (Pridmore-Brown equation). In this model one assumes a rigid wall and no viscous or thermal effects. The experimental study was performed at low Mach number (M<0·05) with two propagating acoustic modes, and the Reynolds number range (0<Re<8500) allowed various profiles for the mean flow. Measurement of the pressure gave the behaviour of the axial wavenumber of modes 0 and 1 that were propagating in our experiment. A good agreement between experimental and theoretical results was obtained.