Numerical investigation of thermoacoustic engine using Implicit Large Eddy Simulation

Abstract

Thermoacoustic engines are device that converts heat energy into work in the form of acoustic energy. The energy conversion using thermoacoustic techniques has the advantages of constructional simplicity, absence of moving parts, reliable operation, long service life and no environmental pollution. However, efficiency of thermoacoustic systems still needs to be improved (which is typically 40% of the Carnot coefficient of performance). To improve the efficiency of thermoacoustic engine, a thorough understanding of the flows in machines, onset temperature, acoustic velocity and streaming velocity is necessary. In this study, numerical simulation of a thermoacoustic heat engine is performed. The possibility of using Implicit Large Eddy Simulation (ILES) to simulate the flows in the thermoacoustic engine has been examined by using COMSOL Multiphysics. Unlike the Large Eddy Simulation (LES), ILES is neither explicit filtering nor explicit subgrid model: small-scale fluctuations are damped by the numerical diffusion, which acts both as an implicit filter and an implicit built-in subgrid model for a given grid. As the grid is refined, the simulation converges to a DNS. The results show that the ILES has predicted flows in the thermoacoustic engine and especially time-averaged flow called acoustic streaming, which can lead to undesired heat convection and loss of efficiency.