Abstract
Acoustic damping of a cylindrical chamber with open and closed ends is analytically and numerically investigated. In the analysis, based on the analytic solution of resonant acoustic modes inside cylinder, the damping from the open end is calculated by a simple acoustic source modeling for velocity fluctuation. The effect of viscosity is also considered as an attenuation mechanism. Acoustic damping calculated for first longitudinal and tangential modes are in good agreement with that obtained by numerical simulation. When a longitudinal mode exists, the directivity of radiation becomes like monopole and the damping is large. On the other hand, when a tangential mode exists, it is found that the dipole like directivity is obtained and the damping is small compared to that for the longitudinal mode. A configuration of the chamber and an injector installed off-centered is also investigated. Under non-resonant condition between injector and chamber acoustics, it is found that the acoustic radiation from the open end of the injector is negligible but the viscous effect becomes important. Finally we investigate the acoustic damping with hot gas injection numerically and semi-analytically. The obtained mode is found to be a spinning tangential mode due to the asymmetry of the mean flow field. The radiated wave has also a spinning feature and the damping is found to be much larger than that for symmetric dipole like radiation under uniform condition. The simple acoustic radiation modeling applied for the analysis also works well for this general non-uniform mean flow condition.
Published Version
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