Experimental and numerical investigation of natural convection flows in two horizontal thermoacoustic cavities

This study aims at exploring the potential generation of natural convective flows in thermoacoustic devices. To this effect, two thermoacoustic setups are considered without acoustic oscillations, each setup thus constituting a cavity filled with air and comprising a porous medium heated on one of its ends. In the first configuration, the porous medium is a ceramic stack. In the second configuration, an ambient heat exchanger using circulating ambient water is placed on the other end of the porous medium (which is a regenerator). The wall temperature is measured in several points using thermocouples and natural convection flows developing in these cavities are measured in a vertical plane using Particle Image Velocimetry. Moreover numerical calculations are performed based on simplified 3D configurations, using immersed solid bodies at prescribed temperature to represent the heating or cooling elements and describing the porous media as homogeneous and either isotropic or anisotropic. Navier-Stokes equations under Boussinesq assumption are solved in the entire domain with the addition of a Darcy correction term in the porous media. Excellent qualitative and quantitative agreement on velocity fields is obtained between experimental and numerical simulation results for both configurations, which validates the model description. It is shown that the observed natural convection flows are fully three-dimensional and of significant magnitude so that they could potentially interfere with thermoacoustic effects. (C) 2019 Elsevier Ltd. All rights reserved.