Evaluation of the damping capacity according to the geometric and the number of resonator with thermal environment using a Rijke tube

Combustion instabilities are often-observed phenomena which take place in acoustically closed spaces such as combustion chambers in propulsion systems. These phenomena should be studied consistently because they can make considerable damage on the combustion chambers and even entire engine systems. Acoustic cavity has been widely used as a passive stabilization device to suppress these combustion instabilities. To elucidate damping capacity of acoustic cavity according to various geometric shapes, a well-known Rijke tube facility has been used to simply include the interaction of heat and acoustic field. The damping capacity has been evaluated quantitatively in terms of bandwidth and amplitude ratio. Present results showed that the acoustic cavities having large orifice area showed better damping capacity. But, in case of orifice length, the length above a certain value makes cavity volume and resultant acoustic stiffness too small, so the damping capacity was decreased above a threshold-like specific length. As for the number of cavities, the damping capacity increases with the number, but, in a certain number or more, the damping capacity has been attenuated and the significant increase of the capacity was not observed. In case of the acoustic cavities which were thought to have sufficient damping capacity, decay time has been measured to quantify the damping capability in time domain. The effect of orifice area on decay time was much higher than those of orifice length. These results from heat and acoustic field interaction through Rijke tube showed that the pure acoustic approach would be insufficient for the fine tuning of acoustic cavity, and further combustion tests would also be necessary to optimize the shapes of the cavity. (C) 2019 Elsevier Masson SAS. All rights reserved.