COUPLING OF 1D AND 3D THERMAL-HYDRAULIC MODELS IN THE "KORSAR/CFD" COMPUTER CODE
Yu. V. Yudov, I. G. Danilov, S. S. Chepilko, D. S. Kasterin
VANT. Ser.: Mat. Mod. Fiz. Proc 2019. Вып.1. С. 57-68.
The paper presents a method for coupling 1D and 3D thermal-hydraulic models in the KORSAR/CFD system code. The KORSAR/CFD code is designed for safety analysis of pressurized water reactors. The one-dimensional approach is based on a two-fluid model. Conservation equations are discretized by the semi-implicit numerical scheme on a staggered grid. A single-phase liquid is modeled with a 3D approach using the immersed boundary method. Time integration is performed by the second-order accurate implicit scheme on the collocated grid. The models are coupled using the semi-implicit scheme. In the 1D model, mass and energy fluxes at the interface are written as sums of corresponding fluxes in the 3D model. The fluxes are expressed implicitly with respect to the velocities, thus ensuring the coupling of Poisson equation matrices in 1D and 3D domains when calculating the combined pressure field at each new time level. To improve the convergence of the iterative procedures for the Poisson equation, a multigrid method with a set of cells in the whole computational domain is used. The proposed coupling method was verified on a natural convection loop test problem in which parts of the natural convection loop were simulated using 1D and 3D approaches. The calculation of the loop heat-up dynamics and natural convection development has demonstrated the fulfillment of coolant mass and energy balance. Keywords: 1D model, 3D model, immersed boundary method, natural convection loop.
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