High-order implicit large-eddy simulation for transitional aerodynamics flows

Abstract

This thesis presents a high-order Implicit Large-Eddy Simulation (ILES) approach for simulating transitional aerodynamic flows. The approach consists of a hybridized Discontinuous Galerkin (DG) method for the discretization of the Navier-Stokes (NS) equations and a parallel preconditioned Newton-GMRES solver for the resulting nonlinear system of equations. The combination of hybridized DG methods with an efficient solution procedure leads to a high-order accurate NS solver that is competitive to alternative approaches, such as finite volume and finite difference codes, in terms of computational cost. The proposed approach is applied to transitional turbulent flows over a NACA 65-(18)10 compressor cascade and the Eppler 387 wing at Reynolds numbers up to 460,000. Grid convergence studies are presented and the required resolution to capture transition at different Reynolds numbers is investigated. Numerical results show rapid grid convergence and excellent agreement with experimental data. Focus is also placed on analyzing the structure of the boundary layer and the mechanism that causes transition to turbulence. Two-dimensional unstable modes in the form of Tollmien-Schlichting and Kevin-Helmholtz instabilities are found to be responsible for natural transition to turbulence through a laminar separation bubble. In short, this thesis aims to demonstrate the potential of high-order ILES for simulating transitional aerodynamic flows. This will be illustrated through numerical results and supported by theoretical considerations.