Book Description

A comparison of the noise generation of air jets and turbojet engines has been made from data obtained under similar free-field conditions. At jet pressure ratios below or only slightly above that for choked flow, the over-all sound power is well represented by the Lighthill parameter, but the results obtained with the afterburning data are somewhat low. Application of a correction to the directional data using nozzle area ratio and jet veloctiy ratio to the 8th power gave good correlation between air-jet and engine data. Air-jet and engine spectral data were dissimilar because of a dip in the engine noise spectrum, which was probably caused by a combination of ground-reflection effects and additions to portions of the spectrum by compressor and combustion noise.