URANS and LES analysis of turbulent swirling flows

Abstract

URANS and LES analysis of confined, incompressible turbulent swirling flows exhibiting vortex breakdown are presented, employing a RSM closure in conjunction with the former. Emphasis is placed upon the predictability of the sub-and supercritical vortex core states. Results are assessed by comparisons with experiments. It is observed that significantly better results are obtained by the RSM based URANS approach, compared to the RANS or turbulent viscosity based URANS. This indicates the importance of transient phenomena such as the precessing vortex core and vortex shedding, along with the unsuitability of the turbulent viscosity based approaches in this bracket of flows. LES did not perform as well as expected. This is possibly due to inaccuracies in formulating the boundary conditions, or to too coarse a filter width for the simple subgrid model adopted. Although the present work shows that remarkable improvements can be achieved over RANS approaches, comparisons with measurements reveal that further research and model improvements are still necessary.