High-fidelity numerical simulations of a standing-wave thermoacoustic engine

Thermoacoustic devices, in which heat fluxes and pressure waves are converted from one to the other, are a promising class of energy conversion, particularly as heat-driven heat pumps. However, accurate simulation and performance prediction of these devices is a major challenge on the path to better understanding and improved design. Herein, 2D simulations of a high-amplitude standing wave thermoacoustic engine are reported, based on the high-fidelity software PyFR. The performed simulations are validated against both computational and experimental results reported in the literature, exhibiting a deviation of less than 9% between the calculated and experimentally measured pressure amplitude, more than twice as accurate as previously reported calculations. Further, non-linear effects in the thermoacoustic engine are explored and discussed, including Rayleigh streaming, jet streaming and, importantly, higher-order harmonics. The influence of these effects on engine performance is gauged, with higher-order harmonics shown to cause the greatest reduction in engine performance. Harmonics suppression is then demonstrated, via a simple example, to improve performance and, in the present context, greatly reduce the deviation between the linear and non-linear model. This work demonstrates the utility of high-order CFD schemes for the analysis of thermoacoustics devices, providing useful insight on the importance of non-linear effects and highlighting the potential benefits of future work along similar lines.