Enhancing energy conversion performances in standing-wave thermoacoustic engine with externally forcing periodic oscillations

Abstract

The present work focuses on enhancing thermo-acoustics energy conversion performance and nonlinear dynamics of heat-driven acoustics oscillations in standing-wave thermoacoustic engines (SWTAE) in the presence of externally forcing perturbations. Such perturbations could be applied in either pressure or velocity fluctuations. 2D numerical SWTAE models are developed and validated, and then applied to examine the effects of 1) the forcing perturbation frequencies, 2) its amplitudes, and 3) the inlet diameter of applying such perturbations on heat-driven acoustics behavior. Our results show that pressure perturbations attenuate heat-driven acoustic limit cycles, while forcing velocity perturbations at a specific frequency range can enhance the thermo-acoustics conversion in the SWTAEs. Our results also show that frequency lock-in is observed, when the ratio of the forcing velocity perturbations' energy to the self-excited acoustical energy is ranged from 0.11 to 0.66. Furthermore, Hopf supercritical bifurcations are observed, resulting in transitions from steady state to quasi-periodic and limit cycle oscillations. As the forcing perturbation frequency is approaching to that of the self-excited heat-driven acoustic oscillations (i.e. the ratio of the forcing frequency to that of self-excited oscillations is ranged from 0.89 to 1.11), apparent improvements are observed on the output heat-driven acoustic power and thermo-acoustic energy conversion efficiency, especially when the two frequencies are coincided (i.e. ∼180 Hz). Increasing the forcing perturbation's energy or enlarging the inlet diameter of applying such perturbations further enhances these improvements. Overall, the developed numerical model may serve as a valuable tool for predicting the heat-driven acoustic power output from a SWTAE in the presence of externally forcing perturbations.