Noise Predictions for Rectangular Jets Using a Conformal Mapping Method

Abstract

An acoustic analogy approach is used to predict the turbulent mixing noise emitted by cold, subsonic, rectangular jets of aspect ratios 2, 4, and 8. Mean flow interaction effects are accounted for in terms of a Green’s function under the locally parallel mean flow approximation. The problem for the Green’s function is reduced to a set of coupled ordinary differential equations by modeling the mean flow as having level surfaces in crossflow planes coinciding with one coordinate in a cylindrical elliptical coordinate system and using a conformal mapping method. The Green’s function is combined with a previously developed hybrid source model to complete the prediction method. Source model coefficients are chosen based on the results of low-speed flow surveys in the nozzles considered. Results are compared with acoustic data, and it is found that the method is generally capable of predicting the measured azimuthal directivity characteristics of the sound field.