Dong Yang

Acoustic oscillations below 50 Hz are harmful in the occurrence of thermoacoustic instability and present a critical challenge issue in noise control due to their long spatial wavelengths and low attenuation efficiencies. This paper presents a solution by the employment of an elastic-wall Helmholtz resonator based on a loudspeaker, aiming at addressing the performance of noise suppression at low-frequency range. The resonant frequency and half-power bandwidth of acoustic absorption coefficient for the elastic wall resonator was evaluated and compared with a fixed-wall Helmholtz resonator of the same structure. The results indicate that the elastic-wall resonator effectively reduces the resonant frequency and achieves a reduction of the effective volume by 20-40 times as compared with the fixed-wall Helmholtz resonator. Additionally, the half-power bandwidth was narrower, indicating superior frequency selectivity for elastic-wall resonator. In conclusion, the proposed elastic-walled Helmholtz resonator offers an effective solution for noise suppression in the low-frequency range, with promising applications in noise control without requiring large cavity volumes.

Lean premixed combustion reduces NOx emissions but increases the risk of thermoacoustic instabilities. This study investigates the acoustic response of a turbulent premixed swirling flame using large eddy simulation (LES) in OpenFOAM, incorporating a modified reactingFoam solver and the partially stirred reactor model for C 2 H 4 /air combustion. The simulated flame transfer function (FTF) shows good agreement with experimental data. To further study the FTF shape, we employed the swirl flame transfer function framework, estimating directly five of the six independent parameters from the LES data and determining the tangential fluctuation coefficient by fitting the FTF dip from the LES. Key modulation factors—including fluctuations in the tangential velocity, spatial decay rates of perturbations, and the phase difference between axial and tangential perturbations—were systematically examined. The results demonstrate that the FTF characteristics can be effectively modulated through rational design of swirler geometry and flow parameters. This work provides valuable insights into the physical mechanisms governing flame dynamics, contributing to a better understanding of thermoacoustic instabilities.

Cavitation dynamics, such as cavitation surge and rotating cavitation, are natural performance limits for turbopump inducers and pose a significant risk to the development and operation of liquid rockets. In the last 63 years, progress has been made in understanding cavitation instabilities and their relationship to cavitation number, inlet flow coefficient, rotating speed, inducer size, and thermal effects. However, we are still unable to predict the cavitation behavior of a real inducer installed in rocket engines or contribute much to the design of a more cavitation-resistant machine. This paper comprehensively reviews findings from computational fluid dynamics simulations, reduced-order modeling, and experiments in cryogenic fluids and water, focusing on the effects of compressibility on multiphase flow calculations, the assessment of cavitation compliance and mass flow gain factor, and their influences on cavitation stability analysis, as well as the transfer function for cavitating inducers. This review will provide insights for future research to achieve more accurate performance predictions, improve flow modeling, and enhance the interpretation of experimental results.