Verification and Validation of Nek 5000 for T - junction , Matis , SIBERIA , and Max Experiments

The turbulent mixing modeling for unsteady heat transfer problems in thermal-hydraulics has long been a focus in nuclear engineering community. One of the promising approaches that takes a full advantage of recent advances in HPC is the use of hierarchy of fidelity simulations that are cross-verified and validated in the regimes of interest. In particular, it is beneficial to have a higher fidelity reference simulation that could be used for benchmarking of the faster-turn-around lower-fidelity tools. This paper focuses on Nek5000 LES reference simulations for the OECD/NEA T-junction and Matis benchmarks and for the “SIBERIA” and MAX con-current validation experiments. The CFD capabilities to predict the unsteady heat transfer problems that are associated with nonisothermal flow mixing in pipe flows and related to thermal fatigue of nuclear power plant pipe system have been tested in the 2010 Vattenfall T-junction benchmark. The 2012 KAERI Matis experiment has tested the CFD predictions in a complex geometry of subchannel mixing flow behind a spacer grid. The Nek5000 LES submissions scored highly in the both blind benchmarks. The Novosibirsk’s “SIBERIA” experiment employs a novel electrochemical technique for accurate measurement of the wall mean shear and its fluctuations in an annular channel flow with a blockage. The ANL’s MAX experiment is designed to study thermal mixing in a wide mixing chamber where two out of a maximum of four adjacent differentially heated jets are injected to impinge on the top wall surface, leading to a thermal striping phenomenon. The resulting complex flow configuration is tracked by a high-resolution particle velocimetry method and thermal imaging. The high-quality benchmark data profiles and high-resolution MAX data provided are used for validating numerical simulation capabilities of Nek5000 for these types of flows and for benchmarking and improvement of lower-fidelity uRANS modeling as a part of hierarchical multi-fidelity approach.