Numerical simulations of the low and acoustics of a wall jet through a gap using computational aeroacoustics methods are conducted to investigate possible sound generation mechanisms. It is found that discrete frequency sound or tone can be generated by the flow. The tone is produced by the periodic shedding of vortices at the nozzle lip. The vortex shedding process is linked to anacoustic feedback loop. The feedback process appears to begin with the shedding of a vortex at the nozzle lip. A byproduct of the vortex shedding process is the generation of an acoustic pulse. Part of the acoustic pulse propagates across the jet flow and impinges on the wall on the opposite side of the jet. Upon reflection and on propagating through the wall jet in the reversed direction, the sound pulse strikes the nozzle lip. This triggers the shedding of a new vortex accompanied by the generation of a new acoustic pulse. This process repeats itself, and in this way the feedback is closed. A tone frequency prediction formula is derived based on the observed feedback loop. This tone frequency formula appears to be able to provide predictions that are in reasonably good agreement with experimental measurements in a number of cases involving flows through the gaps of multielement high-lift systems.
Gap tones
Erzeugung von Tönen bei Durchströmung des Spaltes zwischen Tragfläche und Hilfsflügel
AIAA Journal ; 39 , 8 ; 1442-1448
2001
7 Seiten, 6 Bilder, 28 Quellen
Aufsatz (Zeitschrift)
Englisch
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