Self-sustained jet-flow oscillation induced by an organ pipe nozzle



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The phenomenon of self-sustained excitation of a 2.54 cm circular air jet by an organ pipe nozzle (OPN) was experimentally investigated by the application of hot-wire and flow visualization techniques. A sliding collar (collar 1) at the end of the OPN can generate pure acoustic tones as well as large velocity oscillations at the nozzle exit. The primary thrust of the study was to understand the excitation mechanism, derive empirical equations relating the controlling parameters, and document the near-field jet modification in the presence of the OPN excitation. Two stages of half-wave and one stage of full-wave excitation could be detected depending on the nozzle length and the collar length; at the peak tone situation, the exit centerline fluctuation intensity was at least an order of magnitude larger than that in the unexcited jet. Between the two stages of OPN excitation, another intermediate excitation was observed, which produces a very weak tone and almost no change in OPN exit centerline fluctuation intensity; this weak tone was not studied in detail. [...]