A novel multi-scale domain overlapping CFD/STH coupling methodology for multi-dimensional flows relevant to nuclear applications

Abstract

A novel multi-scale domain overlapping coupling methodology designed to couple a computational fluid dynamics (CFD) code with a system thermal hydraulic (STH) code was developed and its performance was investigated. The methodology has been implemented in the coupling infrastructure code Janus, developed at the University of Michigan, providing methods for the on-the-fly data transfer through memory between the commercial CFD code STAR-CCM+ and the US NRC best-estimate thermal hydraulic system code TRACE. Coupling between these two software packages is motivated by the desire to extend the range of applicability of TRACE to scenarios in which local momentum and energy transfer are important, such as three-dimensional mixing of localized slugs of deborated or cold water in the downcomer and lower plenum of a reactor pressure vessel. The intra-fluid shear forces necessary to correctly capture these effects are neglected in the TRACE equations of motion, but are readily calculated from CFD solutions. CFD/STH coupling implementations therefore have applications in reactor transients such as boron dilution scenarios, Anticipated Transient Without Scram (ATWS) and Main Steam Line Break (MSLB). The proposed method is based on aliasing all spatial sources and sinks of momentum in the CFD domain as frictional losses in the system code domain. The internal velocity fields and, consequently, the inertial component of the pressure field are maintained consistent between the CFD and STH domains through a complementary velocity-matching interface. In this paper, coupled simulations are performed on Cartesian and cylindrical geometry with emphasis on consistency, convergence, and stability during transient scenarios. Results show that the presented domain overlapping coupling method is capable of adjusting pressure and velocity profiles of multi-dimensional system code solutions to match CFD solutions accurately. Important characteristics of transient simulations were found to include the background flow rate, specifically the stabilizing effect of viscous forces, as well as the time derivative of the flow rate. Under certain adverse conditions, the basic coupling method is found to produce unstable behavior. A stabilization method for adjusting CFD data is laid out and found to significantly improve the method's performance under the most challenging conditions. Recommendations are laid out for further improving the coupling via advanced time stepping methods.

The multiscale thermal‐hydraulic simulation for nuclear reactors: A classification of the coupling approaches and a review of the coupled codes

“…The updated boundary conditions of STAR‐CCM+ first come from a complete step of TRACE and then its fine fields are used to calculate the new closure coefficients for TRACE, forcing which produce CFD‐like TH distributions in the entire overlapped domain. This coupled pair works well for both 1D and 3D system models. And as a supplement to the correlation for convective and form‐friction pressure drops in RELAP5/FLUENT, the initial effect was also well‐examined and eliminated from the total pressure drop from STAR‐CCM+ to counteract the non‐erasable initial pressure drop in TRACE motion equation.…”

“…This new approach paved the way for new universal multiscale analysis tool for the nuclear reactor applications. It is able to handle both 1D and 3D cases . In connection with this work, the domain decomposition and overlapping methods are discussed in detail.…”

“…It is able to handle both 1D 102 and 3D 103 cases. 104 In connection with this work, the domain decomposition and overlapping methods 105 are discussed in detail.…”

Development of Integrated Thermal Fluids Modeling Capability for MSRs

“…It should be noted that this domain overlapping approach differs from the domain overlapping approach in the literature for system code and CFD code coupling, such as TRACE and STAR-CCM+ [26] or SAM and NekRS [27]. The key aspect of the overlapping-domain coupling is that for a given portion of the system that is modeled by both codes, i.e.…”

A coupling approach between resolved and coarse-grid sub-channel CFD

“…The concept of coupling different simulation packages/methodologies has been widely used in nuclear applications, an important example of which is the coupling between 1-D system/sub-channel codes and CFD (Aumiller et al, 2001;Bandini et al, 2015;Bavière et al, 2014;Bertolotto et al, 2009;Bury, 2013;Gibeling and Mahaffy, 2002;Grunloh and Manera, 2017, Papukchiev et al, 2009Pialla et al, 2015;Toti et al, 2017). In such approaches, the 1-D code, which has normally been validated against numerous engineering data and experiences, provides reasonable boundary conditions for the CFD models so that they can be used more efficiently to account for some key components/parts with complex 3-D phenomena and/or flow transients that cannot be well represented by the 1-D approaches.…”