MULTISCALE OVERLAPPING DOMAIN COUPLING FOR THERMAL HYDRAULICS SIMULATIONS WITHIN THE BLUECRAB CODE SUITE

Enabling multiple approaches for modeling and simulating fluid flow and heat transfer for analyzing nuclear systems has been a research topic of great interest over the past decades. Such an effort is motivated by the broad spectrum of scales existing in both time and space that manifest in reactor core analysis, for which different numerical methods can have their own set of advantages. The present work introduces a novel overlapping domain method that enable coupling between system thermal hydraulics (STH) and computational fluid dynamics (CFD) codes. Our research group implement and validate the proposed approach within the Comprehensive Reactor Analysis Bundle (BlueCRAB), a code suite in active development at Idaho National Laboratory for tailored for multi-physics analysis of advanced reactors. Different from previous approaches, BlueCRAB supports an agnostic interface between STH - CFD while its coupling formulation can address arbitrary flow geometries with varying inlets/outlets in coupled components. Here, we detail the implementation for incompressible flows. Results of an experiment that involves mixing between two systems connected by a double tee component demonstrate the accuracy of the developed approach. This setup is particularly interesting to validate the methodology while the three-dimensional flow pattern in the connecting component dictates the split of scalars between the systems. Further, the reference experiment includes multiple inlets and outlets in the coupled section, which imposes non-trivial constraints to achieve stability while conserving the governing equations across the simulations. Ultimately, this work is the first to successfully couple both the Navier-Stokes and scalar transport equations in this problem class.