Accurate fluid flow modeling of nuclear reactor rod bundles is essential and extremely challenging with exacting standards for the mesh to deal with the geometric complexity and near-wall physics. The tightly packed rods with wrapped wires, mainly used in liquid metal cooled systems, that contact the rods provide a challenging geometry into which well-defined boundary layers need to be inserted to capture the local physics accurately. Multiple Pointwise structured meshing techniques were used at the boundaries with hex-dominant unstructured meshing away from the boundaries to successfully meet the meshing challenge and produce accurate fluid flow modeling of a 19-rod bundle. 

Michael Böttcher of the Karlsruhe Institute of Technology used multiple Pointwise structured and unstructured meshing techniques to model the complex geometry of the rods and the wrapped wires that resulted in a highly accurate computational fluid dynamics (CFD) solution with ANSYS CFX.

The results computed with CFX for this highly turbulent, swirling flow yielded average rod Nusselt numbers well aligned with two empirical techniques.  

In a critical application such as nuclear power generation, getting the heat transfer right in the geometrically complex contact regions between rods and wires requires a mesh generator with the flexibility and breadth of techniques to allow accurate modeling, something that automatic, “free” meshing cannot achieve.

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