Experiments characterizing nonlinear shear layer dynamics in a supersonic rectangular jet undergoing screech

Jet screech is the result of a resonant aeroacoustic feedback loop. In modern high performance aircraft jet screech has given rise to in-flight sonic fatigue failure of nozzle components. For this reason, jet screech has been the focus of numerous investigations. However, the prediction of screech amplitude still remains a very elusive goal. A primary objective of the work to be reported is to experimentally characterize the nonlinear instability wave development in the shear layer of a rectangular supersonic jet undergoing screech. Hot-film probes are used to measure the instability wave development in the jet shear layers along a constant Mach number ray. Higher order polyspectral and wavelet analysis techniques are employed to determine resonant nonlinear phase locking between multiple instability modes and to investigate unsteady aspects of the screech feedback loop. A detailed comparison of the "inner loop" hot-film measurements with the "outer loop" acoustic measurements is made. Such a comparison reveals the importance of incorporating nonlinear effects into a jet screech amplitude prediction method.