A novel domain overlapping strategy for the multiscale coupling of CFD with 1D system codes with applications to transient flows

Abstract

A novel multiscale coupling methodology based on a domain overlapping approach has been developed to couple a computational fluid dynamics code with a best-estimate thermal hydraulic code. The methodology has been implemented in the coupling infrastructure code Janus, developed at the University of Michigan, providing methods for the online data transfer between the commercial computational fluid dynamics 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. These types of flows are relevant, for example, in the simulation of passive safety systems including large containment pools, or for flow mixing in the reactor pressure vessel downcomer of current light water reactors and integral small modular reactors. The intrafluid shear forces neglected by TRACE equations of motion are readily calculated from computational fluid dynamics solutions. Consequently, the coupling methods used in this study are built around correcting TRACE solutions with data from a corresponding STAR-CCM+ solution. Two coupling strategies are discussed in the paper: one based on a novel domain overlapping approach specifically designed for transient operation, and a second based on the well-known domain decomposition approach. In the present paper, we discuss the application of the two coupling methods to the simulation of open and closed loops in both steady state and transient operation. The objective of this study is to examine the performance of each coupling method in terms of convergence, consistency, and numerical stability. As expected, the results produced by the two methods were found to be identical, once numerical convergence is achieved, and consistent with the standalone STAR-CCM+ solution in both steady state and transient cases. However, the domain overlapping method was found to achieve convergence at larger integration time steps than the domain decomposition approach and exhibited superior convergence and numerical stability characteristics in both steady state and transient scenarios.

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

“…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.…”

STH-CFD Codes Coupled Calculations Applied to HLM Loop and Pool Systems

“…First developments and applications of coupling methodology can be found in Korea, in the works of Jeong et al [2,3], and in USA, in the works of Aumiller et al [4,5]. More recent works on coupled calculation applied to water systems can be found in literature [6][7][8][9]. Moreover, coupling methodologies found wide application in GEN-IV systems thermalhydraulic analysis, as in [10] where coupled simulation was performed on a gas-cooled reactor.…”

A multiscale numerical algorithm for heat transfer simulation between multidimensional CFD and monodimensional system codes

“…Above all, the imposition of a uniform flat profile is the easiest method since it doesn't require the solution of an additional equation or a modification of the numerical code. Sometimes in the case of the Navier Stokes equation this method can lead to an overestimation of the pressure losses inside the CFD component as in the region near the inlet boundary strong velocity gradients take place [2].…”

“…The CFD solution is then used to improve the system code one: this can be performed by calculating some source terms that are then imposed in the system code equations or by modifying some system code parameters [1], [2], [3], [4]. Some performances of domain decomposition and domain overlapping methods are evaluated in [2]. These papers show that the convergence of the decomposed domain strongly depends on the physics of the simulation.…”

“…In this case the coupling between the two codes is obtained with appropriate boundary conditions when information are passed from the system code to the CFD one. The CFD solution is then used to improve the system code one: this can be performed by calculating some source terms that are then imposed in the system code equations or by modifying some system code parameters [1], [2], [3], [4]. Some performances of domain decomposition and domain overlapping methods are evaluated in [2].…”