The International Fusion Materials Irradiation Facility (IFMIF) is designated to generate a materials irradiation database for the future fusion reactors. The High Flux Test Module (HFTM) houses the test specimens which will be cooled with helium flows passing through several parallel narrow channels. The Reynolds numbers for individual sub-channels range from about 1000 to 8000. For most sub-channels the flow is in the transition region, which cannot be accurately predicted by using laminar or turbulence models. As a part of the HFTM validation activities, the thermo-hydraulic tests of a 1:1 single irradiation rig were carried out. The experiments also provide data for validating the CFD codes for using in the simulations of the whole HFTM. In this paper, the CFD simulations and experiments will be compared for helium flows at a Reynolds number between 3000 and 8000. The simulations were carried out with the commercial CFD code Ansys-CFX V14 using several turbulence models. It is found that, the CFX Gamma model with the transition onset Reynolds number of about 180 provides the best predictions for the transition flows.
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