Simultaneous Density Gradient and Far-Field Pressure Measurements on a Cold Jet

Kurzfassung

The aeroacoustic sound generation process on a cold jet at a Mach-number M = 0.9 has been investigated by means of simultaneous Background Oriented Schlieren (BOS) measurements in the near-field and microphone measurements in the far-field. 20 000 BOS snapshots in the field of view have been recorded. Both measurements were conducted in a synchronized manner so as to enable the calculation of the cross-correlation between the acoustic pressure and the measured density gradients. The main idea of the concept presented here was to use the coefficient matrix obtained from the aforementioned correlation to identify regularities in the near-field fluctuations that are related to the radiated sound field. A second approach is presented, correlating the deformed image patterns resulting from the BOS measurement directly with the far-field pressure signal. By this the averaged pixel-shift weighted with the pressure signal is obtained.