Natural convection in a porous layer bounded by impervious domains: from numerical approaches to experimental realization

Abstract

This work presents the results of a numerical and experimental study of free convection in a porous layer bounded by impervious domains subjected to a vertical temperature gradient. This configuration has been chosen as a reference for some geological structures. The main parameters of the experimental configuration are a slope of 15°, an aspect ratio of 10 for the porous layer and a thermal conductivity ratio (λ p⧹ λ np) of 0.7. For that case, a good coherence is found concerning the flow patterns observed through the different methods. In all results, an anti-clockwise unicellular flow (with a layer rising from left to right) is observed at low filtration Rayleigh numbers Ra∗. At higher Ra∗, the three-dimensional (3D) flow which develops is composed of seven transversal (horizontal ) rolls and five to seven longitudinal rolls. However, depending on the resolution method, the critical filtration Rayleigh numbers for the transition from 2D to 3D flows are significantly different. Moreover, the experimental temperature fields have some special features: a high amplitude of the unicellular flow and, for 3D flows, a low amplitude for the rolls in the central part of the layer and an even number of longitudinal rolls. Numerical resolutions taking into account the thermal heterogeneities of the experiment prove the significant influence of lateral thermal conditions on flow patterns and on the critical filtration Rayleigh number.