Prediction of low-frequency tones produced by flow through a duct with a gap

A method is presented for predicting the frequencies of tones produced by h igh Reynolds number, subsonic flow through a duct with a gap. An inviscid, linear model of the fluid motion is developed in which the shear layer deli miting the jet formed between the inlet and exit of the duct gap is modelle d as a vortex sheet. The linear analysis is used to calculate the Rayleigh conductivity parameter which is then analyzed to find the frequency depende nce of the shear layer behavior. The calculations for the case when an exte rnal load is applied across the shear layer have been carried out for Strou hal numbers from 0 to 10, Mach numbers from 0.001 to 0.5, and a gap length- to-diameter ratio of 0.5 to 2.0. The resonant frequencies have been calcula ted for Mach numbers ranging from 0.001 to 0.8 at a length-to-diameter rati o of 1.0. The results for the forced motion in the low Mach number limit co mpare well with previous incompressible predictions for flow past wall aper tures. The resonant frequency predictions have been validated at the Mach n umber of 0.52 through comparison with experimental data. (C) 2000 Academic Press.