Analysis of circumferentially coherent pressure fluctuations relevant to jet noise

Power spectra of the lower-order azimuthal constituents of the fluctuating jet pressure field are presented. They result from a Fourier decomposition of narrowband circumferential space correlations employing static pressure probes. The relevance of the pressure cross spectra to the noise from turbulence mean shear interactions was worked out from Michalke's expansion scheme. It is shown that the m = 0,1,2,3 constituents dominate in the turbulent pressure field in the range of Strouhal numbers between 0.1 to 1.0 where the bulk of the acoustic energy is known to be radiated. The variation of these lower order azimuthal constituents with radial distance from the jet axis and with axial distance from the nozzle exit was determined throughout the conjectural source region for jet noise.