Spatio-Temporal Turbulent Characterization of a Nuclear Reactor Fuel Assembly with Spacer Grid

Abstract

The present work will illustrate a series of numerical studies, performed to evaluate the predictive capabilities of various turbulence modeling approaches, applied to a typical pressurized water reactor spacer grid, with mixing vanes. Physical insight into the turbulent spatio-temporal structure of the flow will be addressed. Results will be taken as a reference for the explanation of the performances of the eddy viscosity-based turbulence models results already present in the scientific literature. Emphasis will be given to the predictive capabilities of the variable resolution (VR) turbulence models by the use of the partially averaged Navier-Stokes equations (PANS), Reynolds averaged Navier-Stokes equations (RANS) and large eddy simulation (LES). For the latter case an invariant analysis of the Reynolds stress anisotropy tensor will been conducted, based on the Lumley’s triangle. This has proven to be a powerful graphical representation of the second-order statistics collection provided by the Reynolds stress tensor. A numerical solution verification and validation (V&V) metric will be suggested for the application of turbulent PANS model in nuclear reactor applications. The aforementioned set of results will contribute to an invaluable resource to further refine RANS turbulence models, deepen the understanding of the physics in this class of flows and will have the potential to lead to a better understanding of the effects of the mixing vanes and their design optimization.