Piecewise-spreading regime model for calculating effective gol'dberg numbers for supersonic jet noise

Abstract

A method for calculating the effective Gol'dberg number for diverging waveforms is presented, which leverages known features of a high-speed jet and its associated sound field. The approach employs a ray tube situated along the Mach wave angle where the sound field is not only most intense, but advances from undergoing cylindrical decay to spherical decay. Unlike other efforts, a "piecewise-spreading regime" model is employed, which yields, separately, effective Gol'dberg numbers for the cylindrically and spherically spreading regions in the far field. The new approach is applied to a plethora of experimental databases, encompassing both laboratory-and full-scale jet noise studies. The findings demonstrate how cumulative nonlinear distortion is expected to form in the acoustic near field of laboratoryscale round jets where pressure amplitudes decay cylindrically; waveformdistortion is not expected in the acoustic far field where waveform amplitudes diverge spherically. On the other hand, where full-scale jet studies are concerned, effective Gol'dberg number calculations demonstrate how cumulative waveform distortion is significant in both the cylindrical-and spherical-spreading regimes. The laboratory-scale studies also reveal a pronounced sensitivity to humidity conditions, relative to the full-scale counterpart.