Practical Quality Measures for Large-Eddy Simulation

Abstract

Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES) and Scale-Adaptive Simulation (SAS) models are increasingly being used as engineering tools to predict complex flows where reference DNS or experimental data is not available. Frequently, the flow has not been studied previously and the required grid resolution is unknown. Industrial users studying these flows tend to be using commercial CFD codes and do not usually have access to high-performance computing facilities, making systematic grid-dependence studies unfeasible. There is a risk therefore that LES, DES and SAS simulations will be performed using overly coarse grids which may lead to unreliable predictions. The present work surveys a number of practical techniques that provide a means of assessing the quality of the grid resolution. To examine the usefulness of these techniques, a choked gas release in a ventilated room is examined using DES and SAS. The grid resolution measures indicate that overall the grids used are relatively coarse. Both DES and SAS models are found to be in poor agreement with experimental data and show greater grid sensitivity compared to RANS results using the SST model. The work highlights the need for grid-dependence studies and the dangers of using coarse grids.