Cold flow and hot firing tests were conducted to findthe optimum design and positioning of an acoustic resonator fordamping high intensity pressure oscillations. The variables inthe cold flow tests were the position of the resonator and itsvolume. In the hot firings more than one resonator was used andthe gas properties were also varying. Pressure node or antinodelocations of the resonator were emphasized in the tests and theresonator cavity volume was varied from fully closed to threeand a half times the resonant volume calculated by the Helmholtzresonator theory. It was found that the resonator at the pressure nodeprovided little or no damping while when positioned at the pressureantinode the sound intensity in the cold flow duct was reducedto less than 50% of the undamped amplitude. The range ofdamping was found to be narrow and centered around the volume calculatedby the Helmholtz resonator theory. The results of thephase lag between the pressures in the cavity and duct and thevelocity in the orifice, connecting the cavity and the tube closelycorresponded to those predicted by Sirignano in Reference 14. Aninvestigation of the effective length of the orifice in the Helmholtzresonator indicated that a single end correction was appropriate(rather than the double end correction for conventionalacoustic amplitudes) - this also substantiated the jet flow model.
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