Structure of a Supersonic Impinging Rectangular Jet via Real-Time Optical Diagnostics

A real-time imaging system is used to investigate the flow field of an impinging Mach 1.3 ideally expanded rectangular jet. Far field acoustic data show a variety of impingement tones. The most dominant tones occur for a Strouhal number (based on nozzle exit height) range between 0.2 and 0.25. Impingement plate locations of l = 70, 105, 115 and 356 mm were further analyzed as they characterize various states of the impingement flow. These locations were also investigated using the real-time flow visualization technique in order to correlate the dynamics of the flow’s mixing layer with its acoustic far field. There is a strong coupling between the organization of structures within the flow field and the degree of resonance observed in the acoustic far field. The most resonant case of l = 70 mm exhibited many high amplitude harmonics as well as a very organized asymmetric pattern of large-scale turbulence structures. No impingement tones above 110 dB were observed at l ll l = 105 mm, while a single tone greater than 125 dB was present at l = 115 mm. The flow fields of l = 105 and 115 mm were similar with l = 115 mm containing larger and more developed structures at the flow/plate interaction region.

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