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Coarse‐Grid‐CFD for the Thermal Hydraulic Investigation of Rod‐Bundles
Author(s) -
Viellieber Mathias,
Class Andreas
Publication year - 2015
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/pamm.201510239
Subject(s) - computational fluid dynamics , parametrization (atmospheric modeling) , range (aeronautics) , grid , computer science , thermal hydraulics , scale (ratio) , closure (psychology) , mechanics , simulation , mathematics , geometry , heat transfer , engineering , physics , aerospace engineering , quantum mechanics , economics , market economy , radiative transfer
A nuclear reactor core, that is a few meters in height and diameter is composed of hundreds of fuel assemblies which are again composed of tenth of fuel rods with a diameter of about 10 mm. The relevant length scales for a Computational Fluid Dynamics (CFD) simulations range from the sub millimetre range, relevant for the sub channels up to several meters. Describing such a multi‐scale situation with CFD is extremely challenging and the traditional approach is to use integral methods. These are sub channel and sub assembly analyses codes requiring closure by empirical and experimental correlations. A CFD simulation of a complete nuclear reactor set up resolving all relevant scales requires exceedingly large computational resources. However, in many cases there exists repetitive geometrical assemblies and flow patterns. Based on this observation the general approach of creating a parametrized model for a single segment and composing many of these reduced models to obtain the entire reactor simulation becomes feasible. With the Coarse‐Grid‐CFD (CGCFD) ( [1], [2]), we propose to replace the experimental or empirical input with proper CFD data. Application of the methodology starts with a detailed, well‐resolved, and verified CFD simulation of a single representative segment. From this simulation we extract in tabular form so‐called volumetric forces which upon parametrization is assigned to all coarse cells. Repeating the fine simulation for multiple flow conditions parametrized data can be obtained or interpolated for all occurring conditions to the desired degree of accuracy. Note, that parametrized data is used to close an otherwise strongly under‐resolved, coarsely meshed model of a complete reactor set up. Implementation of volumetric forces are the method of choice to account for effects as long as dominant transport is still distinguishable on the coarse mesh. In cases where smaller scale effects become relevant the Anisotrop Porosity Formulation (APF) allows capturing transport phenomena occurring on the same or slightly smaller scale compared to the coarse mesh resolution. Within this work we present results of several fuel assemblies, that were investigated with our methodology. In particular, we show Coarse‐Grid‐CFD simulations including a 127 pin LBE cooled wire wrapped fuel assembly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)