This work was motivated by the effect of screech tone noise on fuel-oxidizer mixing and the noise of jets associated with high speed civil transport (HSCT). Previous studies include both theoretical and experimental investigations for axisymmetric and asymmetric (elliptical and rectangular) supersonic jets (E. Gutmark, K.C. Schadow, K.J. Wilson, and C.J. Bicker 1988 Physics of Fluids 31, 2524-2532; E. Gutmark, K.C. Schow, and C.J. Bicker 1989 Physics of Fluids A1, 868-873; A. Krothapolli, Y. Hasi, D. Baganoff, and K. Karamchiti 1986 Journal of Sound and Vibration 106, 119-143). It was revealed that noise associated with shock structure and having well defined frequencies (screech tone) could enhance mixing. The frequencies and amplitudes of these discrete noise tones can also be theoretically predicted given the jet nozzle geometry and pressure ratio. A recent review that concentrated on cicular jets (C.K.W. Tam 1995 Annual Review of Fluid Mechanics 27, 17-43) summarizes the important aspects of supersonic jet noise and outlines the challenges of further studies on asymmetric jets. Future generations of HSCT are likely to have a non-circular nozzle geometry. For the purpose of varying, or possibly modifying or extending, the existing theories, this letter is aimed at underexpanded square jets. The following conclusions can be drawn from the results of this study. (1) Switching between the toroidal and helical screech modes were observed for the fully expanded Mach number greater than 1.48. The frequencies of both the toroidal and helical modes scale with pressure ratio following St is nearly equal R(exp-0.6). The amplitude of the helical mode reaches a maximum at Mj is nearly equal 1.58(R=4.13), in the similar range of Mj and R as circular jets and rectangular jets with large aspect ratios. (2) Tams theory for large aspect ratio rectangular jets predicts the shock spacing and the toroidal mode Strouhal number of the present square jets within 10 % and 6 %, respectively. His circular jet theory predicts the helical mode Strouhal number within 5 % when the hydraulic diameter of the square nozzle is used.
An experimental study of underexpanded square jet noise
Zur experimentellen Untersuchung einer schrill tönenden nicht gänzlich expandierten Strömung in einem quadratischen Kanal
Journal of Sound and Vibration ; 197 , 2 ; 255-261
1996
7 Seiten, 4 Bilder, 2 Tabellen, 7 Quellen
Aufsatz (Zeitschrift)
Englisch
An experimental study of underexpanded square jet noise
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