An investigation of LES and Hybrid LES/RANS models for predicting 3-D diffuser flow

In order to derive a possible path for developing a large eddy simulation (LES) applicable to high Reynolds-number complex turbulent flows, performance of an LES and a hybrid approach connecting LES with Reynolds-Averaged Navier-Stokes (RANS) modeling in the near-wall region (hybrid LES/RANS model, HLR model) was investigated. To discuss the model performance in detail, representative LES and HLR models were applied to a three-dimensional diffuser flow with massive separation. The HLR model gave considerable improvement of the prediction accuracy even with moderate grid resolution, while the LES returned earlier separation just downstream of the diffuser-inlet section. Furthermore, by processing the simulation data, useful knowledge was obtained for further development of this kind of turbulence model. In particular, it was elucidated that the non-linear eddy-viscosity model adopted in the HLR model was effective to reproduce the near-wall turbulence more correctly. This fact resulted in the suppression of an undesirable early separation.