Volume 4: Innovative Solutions for Energy Transitions: Part III

Large Eddy Simulation of Self-Excited Acoustic Oscillations in a Thermoacoustic Engine Geng Chen , Yufan Wang , Lihua Tang*, Kai Wang , Brian R Mace

Abstract

In this paper, we present three-dimensional (3-D) large eddy simulations (LES) of the thermally-induced oscillatory flow inside a full-scale quarter-wavelength standing-wave thermoacoustic engine (TAE). The TAE comprises a hot buffer, a stack and a resonator. Compressible nonlinear governing equations together with the equation of state are solved by the computational fluid dynamic (CFD) solver with the optimal node number and time step size. Numerical results show that self-excited acoustic oscillations occur inside the TAE, undergoing exponential growth, saturation and limit-cycle processes. It is also found that fundamental-mode standing-waves dominate the limitcycle acoustic oscillations while higher-order harmonics coexist. The velocity profiles in the radial direction are highly affected by the Stokes number, displaying Poiseuille flow patterns in the stack channels and Richardson’s annular effects in the resonator. The vortex shedding at the stack ends contributes to kinetic energy and heat losses as presented by the three-dimensional vorticity and time-averaged mass flux contours. The developed 3-D LES framework in this study provides high-fidelity simulations of thermoacoustic oscillations, deepening the understanding of multi-dimensional thermoacoustic effect and various nonlinear phenomena in the large-amplitude regime.

Keywords thermoacoustic engine, large eddy simulation, self-excited acoustic oscillations, vortex shedding.