Direct and Large Eddy Simulation of three-dimensional non-Boussinesq gravity currents with a high order DG method

TL;DR

This paper conducts three-dimensional DNS and LES of turbulent gravity currents using a high-order DG method, providing new non-Boussinesq DNS data and evaluating LES models' performance in capturing turbulent structures.

Contribution

First non-Boussinesq 3D DNS data for gravity currents using a high-order DG method, and assessment of various LES models' effectiveness.

Findings

DNS captures loss of coherence in turbulence

Dynamic LES models outperform Smagorinsky model

Anisotropic dynamic model performs slightly better

Abstract

We present results of three-dimensional Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of turbulent gravity currents with a Discontinuous Galerkin (DG) Finite Elements method. In particular, we consider the three-dimensional lock-exchange test case as a typical benchmark for gravity currents. Since, to the best of our knowledge, non-Boussinesq three-dimensional reference DNS are not available in the literature for this test case, we first perform a DNS experiment. The three-dimensional DNS allows to correctly capture the loss of coherence of the three-dimensional turbulent structures, providing an accurate description of the turbulent phenomena taking place in gravity currents. The DNS is then employed to assess the performance of different LES models. In particular, we have considered the Smagorinsky model, the isotropic dynamic model and an anisotropic dynamic model. The LES results highlight the excessively dissipative nature of the Smagorinsky model with respect to the dynamic models and the fact that the anisotropic dynamic model performs slightly better with respect to its isotropic counterpart.