STRUCTURED MESH CREATION FOR COMPLEX CONJUGATE HEAT TRANSFER PROBLEMS USING SWIFTBLOCK

In this study some new features are introduced for a structured meshing tool called SwiftBlock. SwiftBlock is an add-on to Blender [1] which was created by Nogenmyr [2]. Swiftblock uses the Blender as a 3D creation software that provides a graphical user interface (GUI) for creating the blocking structure in three dimensions. The blocks are automatically detected by using a automatic block detection algorithm by Gaither [3]. SwiftBlock exports the blocking structure in the input format of blockMesh (blockMeshDict) which is part of OpenFOAM software [4]. BlockMesh creates the unstructured OpenFOAM mesh from the input file.

First in the process of creating meshes with SwiftBlock one must create the multiblock blocking structure that topologically represent the fluid domain but also respects the required alignment of the cells. For a minimum possible numerical diffusion the faces of the cells should be perpendicular to the direction of the flow.

Because the edges of the blocks are straight lines, sometimes it is beneficial to add polylines that guide the edges of the blocks. This is important especially for round shapes in the mesh. When the blockMeshDict is ran with blockMesh, the mesh in the blocks will follow the polylines and this way round shapes can be created to the mesh as can be illustrated with paraview for example in figure 3 Since the last release of SwiftBlock several new features have been added to both Blender and blockMesh which have been used to improve SwiftBlock. A couple of them will be presented here. Firstly, Blender has released a new BMesh mesh system which allows to save unlimited amount of parameters to vertices, edges and faces. In SwiftBlock this feature allows to save the parameters more consistently than before and therefore new more advanced blocking parameters have been added. Also, a new feature to copy the blocking parameters to all aligned edges has been introduced. Secondly, the new multi-grading feature of blockMesh has also been added to SwiftBlock which is useful for channel flows that have several boundary layers. For instance, in a flow between two plates only one block is required in span wise direction instead of the three blocks that were required previously.

Most recently some new usability features are added to SwiftBlock such as control parameters to limit the maximum cell size in the whole domain and boundary layer definitions that can be changed globally from the interface. These new features are especially useful in the grid independence study workflow. Another important feature of this meshing style is that when the fluid mesh for example is ready, the interface between the fluid and solid region can be copied in Blender and then extruded so that the interface between the fluid and solid region stays identical. This is extremely beneficial in many multi region problems. For a conjugate heat transfer problem for example, this interface is used for interpolating the temperature field from the master to the slave patch. When the temperature fields are coupled properly the heat flux between the region is continuous.

The fin-and-tube heat exchanger geometry will be used as an example and an illustration is done with SwiftBlock, how a structured mesh can be created to these cases.

[1] B. O. Community, “Blender //www.blender.org a 3d modelling and rendering package,” 2017. [Online]. Available: http: [2] K. Nogenmyr, “Swiftblock,” 2017. [Online]. Available: https://openfoamwiki.net/index.php/Contrib/SwiftBlock [3] An Efficient Block Detection Algorithm For Structured Grid Generation, 1996. [4] OpenCFD, OpenFOAM: The Open Source CFD Toolbox. User Guide Version 1.4, OpenCFD Limited. Reading UK, Apr. 2007.