Nek5000: improvements in the available RANS models, meshing, tutorials, and training

Abstract

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Updates to Nek5000: RANS wall functions, NRC support, and documentation

“…In our prior work, we implemented and tested several wall-resolved RANS approaches in Nek5000, including a regularized version of k − ω model [4]. The k -τ model, however, is especially conducive to the framework of high order spectral element methods [3] owing to boundedness of the τ equation source terms, the wall boundary condition of zero for τ [12] and its asymptotically vanishing near wall gradient. Wall functions for k -τ model, as a consequence, are also bounded, as opposed to the k -ω model [13].…”

“…Validation of the PWF and SWF results is performed for all test cases by comparison against wall-resolved k -τ simulation results and experimental data, where available. Prior efforts dedicated towards increasing the robustness of wall-resolved k -τ model implementation in Nek5000 [3] also percolate to wall function simulations, while using a significantly larger time step size owing to elimination of the need for resolution of high near-wall gradients. As a consequence, great enhancements in time-to-solution are recorded for all cases as compared to corresponding wall resolved simulations, while the solution times for SWF and PWF were found to be comparable.…”

“…Leveraging the material prepared for last year's training session [3], three training sessions were held in FY22. These sessions were held in response to a request from a partner organization in the UK, as part of a workshop at the NURETH-19 conference, and as a webinar hosted by the American Nuclear Society.…”

“…The collaboration with the NRC is a continuing exercise that has been ongoing for multiple years [2,3]. As part of this collaboration, we are performing simulations of a long transient hydrogen mitigation benchmark experiment.…”

“…The expansion of the code documentation has been an ongoing effort over the past few years to address feedback from the various stakeholders. Improvements last year focused on the development of training and tutorials [3]. This effort was increased through this year with additional training sessions offered to the broader nuclear community and expanded documentation focused on bridging identified gaps.…”