Experimental study of flight effects on screech in underexpanded jets

Flight effects on screech from an underexpanded supersonic jet have been experimentally investigated in a free jet facility. Screech frequency prediction is addressed, and some conclusions about the convection velocity under flight conditions are drawn. An azimuthal near field acoustic antenna is used to investigate the modal behaviour of screech with forward flight effects. Several mode switchings are identified as the flight velocity is increased but none can be related to a change in the screech azimuthal mode content. Screech is enhanced by flight at high fully expanded Mach number Mj. This conclusion, established from acoustic far field measurements, is supported by the analysis of schlieren visualizations.