ASSESSMENT AND DEVELOPMENT OF METHODS OF ACOUSTIC PERFORMANCE PREDICTION FOR JET NOISE SUPPRESSORS

The acoustical behavior of certain nozzles designed to reduce the exhaust noise from turbo-jet engines has usually been established by direct measurement. The need for a simple yet adequate method of prediction of such behavior is clear. The paper reviews the quasi-empirical approaches which have been adopted in the past, and paying particular attention to methods suggested by Eldred to deal with the power spectral density and Lee for deriving directivity patterns, develops these for application to axisymmetric nozzles where the elements are not all of the same size. The measure of agreement between predicted levels and typical results quoted in the literature is generally reasonably good. Some implications of the theory are discussed. Additionally, a mathematical model is presented to calculate the noise reduction due to the interference of adjacent twin round jets.