Pressure-density gradient correlations in the near-field of a transonic jet

Abstract

The relation between pressure fluctuations and density gradients in the near-field of a jet at M=0.9 is studied in this paper. For this purpose, an experiment was performed where the density gradients were acquired with the Background Oriented Schlieren technique. This optical technique measures virtual displacements of a background pattern when seen through the compressible flow. Simultaneously, pressure fluctuations were measured with two microphones at 2D away from the shear layer. These signals were decomposed in sound and pseudo-sound using a wavelet based separation technique. The objective is to study the degree of correlation between these three quantities: density gradient, sound and pseudo-sound. Moreover, a cross-conditional analysis is done in order to relate intermittency events in the pressure signal with variations in the density gradient field. The results of the cross-correlation indicate that only the hydrodynamic component is correlated with the density gradients. Furthermore, the correlation is located after the potential core. In addition, the results of the cross-condtional analysis show that fluctuations of the density gradient related with intermittent events in the pressure signal are mainly after the potential core.