Hydrodynamic and acoustic wavelet-based separation of the near-field pressure of a compressible jet

An experimental study of the pressure fluctuations generated by a single-stream subsonic isothermal jet has been carried out. Measurements were performed for two jet Mach numbers in an anechoic wind tunnel using a linear microphone array in the near field and a polar microphone array in the far field. The main focus of the present investigation was the analysis of the near-field pressure data. Three novel decomposition techniques for the separation of the hydrodynamic and acoustic pressures in the near field based on wavelet transform are presented. The innovative techniques were validated by the comparison with separation procedures found in the literature. Hydrodynamic and acoustic pressures were characterized in terms of spectral content and statistical quantities, establishing a direct link between acoustic pressure in the near field and noise measured in the far field. The effect of the stream-wise position of the near-field microphone as well as of the jet Mach number were clearly addressed. The analysis shed light on the intermittent/nearly Gaussian nature of the hydrodynamic/acoustic component.