Numerical study of the effects of natural convection in a thermoacoustic configuration

This study focuses on natural convection flows within a cylindrical guide containing a porous medium. This configuration is applicable to standing-wave thermoacoustic engines, usually composed of an acoustic resonator where a (short) stack (or porous medium) is inserted, with a heat exchanger placed at one of its ends. The resulting horizontal temperature gradient, when high enough, triggers the onset of an acoustic wave. Natural convection effects are usually neglected in thermoacoustics so that axisymmetry is often assumed. Here a 3D numerical study of natural convection flow is performed using a finite volume code for solving mixed Navier-Stokes and Darcy-Brinkman equations under Boussinesq approximation. The influence of the porous medium’s physical characteristics (permeability, thermal conductivity, anisotropy) on the flow and temperature fields is investigated. It is shown that such flows are fully three-dimensional and therefore can modify significantly starting as well as steady operating conditions of the thermoacoustic engine.