Broadband and Tonal Noise of Flow Excited Cavities

Abstract

Noise generation by low Mach number flow over a cavity is investigated. Prediction models for broadband noise and for tonal noise are compared with experimental data. The prediction model for broadband noise is based on the wavenumber-frequency spectrum of pressure fluctuations under a turbulent boundary layer. In the prediction method for tonal noise, the self-sustained flow oscillations in the cavity opening are represented by periodic shedding of discrete vortices. The shape of the frequency spectrum of the broadband noise data agrees with the prediction but the amplitude of the data is 20–25 dB higher than the predicted values. The Strouhal numbers for tonal noise are well predicted by the present model. It is shown that self-sustained oscillations occur in the experiment for conditions where linearized stability theory predicts that shear layer oscillations will not grow.