Abstract
An experimental investigation into the production of high-frequency tones by a supersonic impinging jet using phase-locked shadowgraph photography and high-resolution digital particle image velocimetry (DPIV) is presented. High-frequency tones are often produced for nozzle-to-plate spacings less than two nozzle exit diameters and for nozzle pressure ratios (NPR) less than approximately 3.4, where NPR is equal to the stagnation pressure divided by the pressure at the nozzle lip. The high-frequency tones have lower amplitudes and less impulsive wavefronts than the more dominant low-frequency impinging tones and are presumably produced by a significantly different sound production mechanism. Periodic motion of the jet appears to be confined to the peripheral regions of the jet with no significant motion of the flow in the central regions of the jet behind the standoff shock wave. Unlike the jet motion associated with low-frequency impinging jet tones, recirculating regions are not formed and swept downstream behind the standoff shock wave and stationary stagnation regions are also not observed.
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