Variation of shock-spacing during screech stage-jumps

Flow visualization is used to investigate shock-spacings in a supersonic jet during stage-jumps associated with the screech phenomenon. Conventional schlieren and shadowgraphy techniques as well as a new projection focusing schlieren technique are employed. Both time-averaged and instantaneous snapshots of the flow field are analyzed for a 37.6 mm round convergent nozzle over the jet Mach number range of 1.0 < M j < 1.7. Shock-spacing is studied especially during hysteresis of the stage-jumps where two different screech frequencies could be realized at exactly the same M j depending on whether the latter variable was increased or decreased. The data follow a monotonic trend without any discontinuity at any M j . This establishes the fact that the stage-jumps in frequency are not associated with abrupt changes in the shock-spacing.