Shock noise from single and twin supersonic jets of complex geometry

Abstract

This paper represents a fundamental study of shock noise from nozzles of non-uniform exit geometry. An earlier paper (Raman (1997)) studied the basic features of screech tones from such nozzles. The present paper addresses numerous issues that have arisen since then such as details of unsteady aspects of shock noise, screech mode transitions, directivity, and finally the coupling of twin jets of complex geometry. The following important results emerged: (1) It was found that it is possible to have two independent feedback loops at non-harmonically related frequencies and different spanwise modes—a finding consistent with linear theory. (2) The spanwise antisymmetric mode could be produced by two entirely different source configurations. (3) Nozzle geometry changes could significantly alter the directivity of screech on the azimuthal plane. (4) The intensity of broadband shock noise depended significantly on the nozzle exit geometry at a constant nozzle pressure ratio. (5) Finally it is shown that screech tones from twin jets of complex geometry can couple. Unlike coupling of twin rectangular jets of uniform geometry, the coupling here is more intricate and occurs at a frequency that is lower than the screech frequency of either jet. The data presented provide grounds for believing that the shock noise problem can be controlled by tailoring nozzle geometry.