A high-order semi-explicit discontinuous Galerkin solver for 3D incompressible flow with application to DNS and LES of turbulent channel flow

TL;DR

This paper introduces a high-order semi-explicit discontinuous Galerkin solver for 3D incompressible flow, capable of large-scale DNS and LES of turbulent channel flow, with improved stability and scalability.

Contribution

The paper presents a novel semi-explicit high-order DG scheme with a divergence penalty for stable, scalable simulations of turbulent flows at high Reynolds numbers.

Findings

Successfully scaled to 34.4 billion degrees of freedom and 147,456 CPU cores.

Validated optimal convergence rates with laminar and turbulent flows.

Demonstrated applicability to DNS and LES of turbulent channel flow at high Reynolds numbers.

Abstract

We present an efficient discontinuous Galerkin scheme for simulation of the incompressible Navier-Stokes equations including laminar and turbulent flow. We consider a semi-explicit high-order velocity-correction method for time integration as well as nodal equal-order discretizations for velocity and pressure. The non-linear convective term is treated explicitly while a linear system is solved for the pressure Poisson equation and the viscous term. The key feature of our solver is a consistent penalty term reducing the local divergence error in order to overcome recently reported instabilities in spatially under-resolved high-Reynolds-number flows as well as small time steps. This penalty method is similar to the grad-div stabilization widely used in continuous finite elements. We further review and compare our method to several other techniques recently proposed in literature to stabilize the method for such flow configurations. The solver is specifically designed for large-scale computations through matrix-free linear solvers including efficient preconditioning strategies and tensor-product elements, which have allowed us to scale this code up to 34.4 billion degrees of freedom and 147,456 CPU cores. We validate our code and demonstrate optimal convergence rates with laminar flows present in a vortex problem and flow past a cylinder and show applicability of our solver to direct numerical simulation as well as implicit large-eddy simulation of turbulent channel flow at $Re_{\tau}=180$ as well as $590$.