A Dual-Mesh Hybrid Rans-Les Simulation Of The Buoyant Flow In A Differentially Heated Square Cavity With An Improved Resolution Criterion

In this work, the dual-mesh hybrid RANS-LES approach was applied for the first time to a natural convection flow, namely a high Rayleigh number differentially heated square cavity flow. This approach involves running an unsteady Reynolds Averaged Navier-Stokes (RANS) simulation and a coarse Large Eddy Simulation (LES) simultaneously using two different grids that overlap each other (typically, a highly wall-refined grid is used for the RANS, whereas a more homogenous and isotropic mesh is used for the LES). The two simulations correct each other using a switching criterion that determines the driving and the driven simulations at every point in space. It is demonstrated that the flow unsteadiness and the coexistence of laminar and turbulent regions in the square cavity complicate the task of choosing a suitable switching criterion. Accordingly, a new criterion based on comparing the turbulence lengthscales to the grid size was developed to account for the presence of the aforementioned complex flow features. The behaviour of this criterion and comparisons of the dual-mesh predictions against pure RANS, pure coarse LES and Direct Numerical Simulation (DNS) results are also presented in the current paper. (C) 2021 Published by Elsevier Ltd.