Numerical simulations have been performed to study the flowfield and near-field noise of a supersonic rectangular jet with two paddles inserted into the flow. The paddles cause a strong flapping motion to develop that enhances mixing of the jet with the surroundings. These simulations have been used to determine the flapping motion's frequency, the mixing enhancement, the near-field noise, and the thrust loss associated with the paddles and to study the acoustic feedback mechanism that modulates the flapping motion. The flapping frequency has been estimated using the pitot pressure distributions at a sequence of times and Fourier analysis of the local pressure and z component of velocity. For paddles located x/h = 7.3 from the nozzle, where h is the narrow dimension of the nozzle, a frequency of 4700 Hz (St(h) = 0.136) with an amplitude of 157.5 dB at the nozzle lip has been predicted and is in agreement with experimental results. The pitot pressure drop, the mass, and the x-momentum fluxes along the flow direction have been used as a measure of jet mixing for jets with and without paddles inserted into the flow. In our numerical simulations, a control volume approach was used to estimate the thrust loss caused by the insertion of the paddles. The computational value of 13 % is close to the experimental value of 14.4 %, considering that the physical support for the paddles in the experiments is not included in the simulations. A special sequence of local pressure distribution plots, which highlight the acoustic waves, has been used to study the feedback mechanism that modulates the flapping motion.
Numerical simulations of flow modification of supersonic rectangular jets
Numerische Simulation der Strömungsmodifizierung von Überschallströmungen mit Rechteckquerschnitt
AIAA Journal ; 34 , 5 ; 902-908
1996
7 Seiten, 13 Bilder, 1 Tabelle, 18 Quellen
Aufsatz (Zeitschrift)
Englisch
Flugzeug , Überschallgeschwindigkeit , Überschallströmung , Schallemission , Luftwiderstand , Abgasströmung , Schalldämpfung , Schallquelle , Druckwelle , Düse , Platte (Bauteil) , Simulationsmodell , Strömungsvorgang , Mischen (Feststoff) , Frequenz , Leistungsverlust , Druckmessung , Druckverteilung , Fourier-Analyse , Druckverlust , sichtbare Strömung , Variable , Druckänderung , Stromlinie , Strömungsgeschwindigkeit , Paddel
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