マルチスケールＬＥＳ解析コードＭＩＳＴＲＡＬによる旋回渦解析

Abstract

For numerical prediction of gas entrainment from a free surface in an upper plenum of a sodium-cooled fast breeder reactor (FBR), accurate computation of a swirling flow or vortices is one of the crucial ingredients. In this study, a multiscale large-eddy simulation (LES) code, MISTRAL, is applied to a swirl flow in a cylindrical vessel to examine the effects of the multiscale turbulence models on the accuracy of vortex prediction. The numerical results are compared with experimental results and another numerical results computed with a conventional LES code (SMART-fem). The comparison indicates that the multiscale LES code is able to resolve the fine vortex core structure more accurately than the conventional LES code. Especially, elimination of eddy viscosity in the large-scale equations (or introduction of eddy viscosity only in the small-scale equations) can improve the accuracy in computing a circumferential velocity around the vortex core. It has also turned out that a use of coarse mesh suppresses the peak value of circumferential velocity, which suggests us to employ an extrapolation method such as a vortex model in practice for quantitative estimate of unresolved vortex features.