Abrupt amplification of self-excited acoustic oscillations in a thermoacoustic engine with non-zero mean flow

In this study, we conducted experiments on a quarter-wavelength standing-wave thermoacoustic engine (TAE) and unexpectedly observed self-excited acoustic oscillations even when the left end was partially closed (with a central orifice connected to a tube). Remarkably, when suction was applied to the tube, the acoustic oscillations exhibited a sudden increase followed by gradual attenuation. Motivated by these phenomenological observations, we systematically explored the influence of control parameters including flow rates, lengths, and outlet distance of suction tubes on the performance of the TAE. Results reveal that nonlinear effects play a significant role in the abrupt amplification of acoustic oscillations (while the stack temperature difference increases by less than 1%) in the presence of a non-zero mean flow. There are optimal values of control parameters at which the thermoacoustic amplification is maximized. Under optimal conditions, the maximum pressure amplitude increased by a factor of 2.8. This study has successfully demonstrated the feasibility of using a non-zero mean flow to amplify acoustic oscillations in TAEs, offering great value in promoting the application of thermoacoustic technology in the fields of thermal power generation and energy harvesting.