Flow/acoustic coupling in heated and unheated free and ducted jets

The major goal of this research was to explore the flow/acoustic coupling in free and ducted heated and unheated jets.;For the free jets, it was shown that the frequency of the screech tones could be predicted quite accurately. Modal decomposition experiments and convection speed measurements were conducted that allowed modifications to the present screech frequency prediction scheme that improved the accuracy of the predictions. The modal decomposition work also showed that the screech frequencies were associated with several types of instability waves. The convection speed measurements showed that different types of instability waves had slightly different non dimensional convection speeds, and that there was only a slight dependence of the convection speed upon Mach number and temperature.;The modal decomposition work showed that the overall increase in the screech amplitude with Mach number was a result of a more complicated trend involving the growth and decline in amplitude of the screech tones associated with the different instability wave modes. The directivity of the screech tones was found to be independent of both Mach number and temperature.;The results on the free jet led to a better understanding of the phenomena associated with the coupling of the jet and duct. Tonal amplitudes greater than 170 dB were measured inside the ejector under conditions where the jet/duct coupling was occurring. It was found that such high acoustic amplitudes were produced when the frequency of the most preferred mode of the jet instability waves matched the frequency of two particular duct resonance modes. These two modes were found to be the (0,0,4) and the (0,1,1) modes, both of which occur at nearly the same frequency.;Jet/duct coupling produced marked changes in the ejector exhaust profile, increased ejector pumping, and a sharp drop in the test cell pressure. Jet/duct coupling was found for all temperature ratios tested. It was also found that the severity of this coupling was mostly independent of the jet temperature ratio of the jet. Increasing the temperature of the jet was found to increase both the Mach number and frequency at which the coupling occurred. It was shown that both the Mach number and the frequency at which the coupling occurred could be accurately predicted.