On the nonlinear behaviour of oscillatory flow in a high pressure amplitude standing-wave thermoacoustic heat engine

Abstract

This article deals with the numerical study of the nonlinear features of oscillatory flow in a high pressure amplitude standing wave thermoacoustic heat engine. The overall performance of thermoacoustic devices can deteriorate due to nonlinearities caused by their operation at high pressure amplitudes. Acoustic mass streaming is one of these nonlinearities that can influence the performance of thermoacoustic systems by an undesirable convective heat transfer. Therefore, understanding the nonlinear phenomena within thermoacoustic devices is of fundamental and practical importance. The Navier‐Stokes and energy equations are solved on the structured meshes by resolving thermal and viscous boundary layers utilizing the open-source modelling software OpenFOAM. In particular, the paper looks in more detail at the causes of a non-uniform distribution of mean pressure along the resonator reported previously by both experimental and numerical studies. This is explained by an analogy to a “distributed fluidic pump” manifesting itself through the pumping effects of streaming patterns. Also, the non-linear regime of the mean dynamic pressure shows interesting start-up instabilities which can be influential on achievable efficiencies.