Shock-induced flow resonance in supersonic jets of complex geometry

Jets with complex shock-cell structures exist in numerous technological app lications. This paper describes a fundamental study of shock-induced flow r esonance (commonly referred to as "jet screech") in supersonic jets with sp anwise nonuniform shock-cell structures. Experiments that involve flow visu alization and detailed mapping of the near field reveal unsteady aspects of shock-induced flow resonances, mode transitions, and directivity of the ra diated noise. The following important results about the role of spanwise no nuniform shock-cells emerged: (1) It is possible to have two coexisting, in dependent feedback loops at nonharmonically related frequencies and differe nt spanwise modes. (2) The same type of spanwise asymmetric mode was produc ed by two entirely different source configurations. (3) Nozzle geometry sig nificantly altered the intensity and directivity of screech and broadband s hock noise. The results presented here provide considerable insight into th e fluid dynamics and acoustics of jets with spanwise oblique shock-cell str uctures and provide grounds for believing that shock-induced noise can be c ontrolled by tailoring nozzle geometry. (C) 1999 American Institute of Phys ics. [S1070-6631(99)00103-8].