A study of grid convergence issues for the simulation of the massively separated flow around a stalled airfoil using DES and related methods

Abstract

A systematic grid convergence study is conducted for the Detached-Eddy Simulation (DES) of the massively separated flow around a NACA0021 airfoil at high angle of attack. In order to study the convergence characteristics of DES/LES problems, velocity fields using a series of grids must be generated that demonstrate sufficient dynamic similarity to allow the assumption that the physics encapsulated within the solutions are similar. It is then possible to examine which characteristics of the fields can be used as indicators of some measure of grid convergence. The work detailed in this paper describes the methods that have been used to assess the level of convergence obtained on three grids by three partners using variations of the DES method implemented in different numerical solvers. In addition to recommendations on the methods employed for grid convergence assessment, information is provided concerning the computational expense and industrial feasibility of such studies. As an interesting secondary issue, the study provides opportunity for the direct cross-comparison of models and codes.