Evaluation of influence of wall roughness on wall turbulence using LES simulation with MSGD model for liquid Li flow inside two-staged contraction nozzle

Abstract

ABSTRACT Liquid lithium (Li) jet is planned as a beam target in fusion neutron sources (FNSs), such as IFMIF, A-FNS and IFMIF-DONES. For the safety and the efficiency of such FNSs, the high-speed Li jet need to be kept stable. For investigation of the detailed flow pattern inside the Li jet, numerical approaches using CFD simulation have been required to evaluate it because of its opacity. As one of issues about the inner flow structure, the influence of wall roughness on the vortex structure and surface variation is concerned in long-term operation of actual FNSs. In our previous simulation, in order to consider wall roughness in LES simulation, MSGD model was adopted to ANSYS Fluent using User-Defined Function, and CFD simulation in a simple parallel plate flow was conducted to confirm the performance of MSGD model. In this study, firstly, MSGD model was verified by LES simulation of Li flowing on smooth and rough plates. After that, LES simulation with MSGD model for two-staged contraction nozzle, installed into Li loop of Osaka University, was conducted. It was found that MSGD model was valid and spectrum of velocity in roughness wall cases clearly had different behavior from that in smooth wall case.