The recommended approach to hexahedral mesh generation is as follows:
Generate a mesh using Ansys Icepak’s default parameters for a coarse mesh (see Creating a Minimum-Count Hexahedral Mesh), using the Hexa unstructured mesher. The resulting mesh (called the minimum-count mesh) contains the minimum number of elements required to adequately represent the model geometry and satisfy the default meshing rules.
You can compute an approximate solution on this initial mesh to determine quickly if the calculation runs properly and the results seem reasonable, before proceeding to refine the mesh and compute a more accurate solution. This initial calculation will also enable you to estimate the total computation cost.
Set the Max X size, Max Y size, and Max Z size values to about 1/20 of the cabinet dimensions in the corresponding directions.
Select the Normal mesh resolution.
Generate the mesh.
If the mesh is invalid, an error dialog box will be displayed indicating where the error occurred.
See Global Refinement for a Hexahedral Mesh for details.
Examine the mesh, using plane cuts and diagnostics (as described in Displaying the Mesh and Checking the Mesh), to see if it satisfies the following requirements:
The number of elements between solid faces should be at least 2.
There should be at least 4 or 5 elements on each flow object (openings, grilles, resistances, fans).
The mesh quality should satisfy the requirements outlined in Mesh Quality and Type.
If the mesh does not satisfy these requirements, use the object-specific meshing controls to refine the mesh locally and improve the mesh quality. Suggestions are listed below:
Refine the mesh around objects where the temperature and velocity gradients are expected to be high (for example, heated blocks and plates, objects blocking or diverting the flow, fans).
If the element count on the face of an object is low, use the X, Y, or Z count (or the corresponding parameter) to change it.
Use high and low element size and ratio to refine the mesh around objects. You can also use the inward/outward size and ratio to refine the mesh.
See Refining the Mesh Locally for details.
Additional options for improving the mesh are as follows:
If your model includes a small number of objects, and the element count or spacing on all of them is low, you can use the Init element height option to turn on O-grid cocooning (Hexa unstructured and Mesher-HD only) and place graded elements on the faces of all objects. This option should be used only when the number of objects is not too large; otherwise, the mesh count can become very large. See Global Refinement for a Hexahedral Mesh for details.
In some cases, setting the Max O-grid height to a small enough value relative to the object size will yield better mesh quality by localizing the cocooning action of the mesher. Note that the value of Max O-grid height should be higher than that of Init element height, and that a value of 0 for Max O-grid height leaves the O-grid height unbounded. See Global Refinement for a Hexahedral Mesh for details.
Aligning faces that are nearly aligned (see Figure 35.4: Aligning Nearly-Aligned Faces) will generally reduce the overall mesh size and result in better convergence (due to the improved aspect ratio of the elements). You can align faces by modifying the coordinates of the appropriate object(s), or by using the alignment tools (see The Object modification Toolbar).
Rectangular objects are generally easier to mesh than circular objects. In some cases, you may be able to improve the mesh quality without affecting the solution by replacing circular objects (fans, openings, and so on) with rectangular objects of the same type. For models with circular objects you may also want to consider using the hex-dominant mesher described in Hex-Dominant Meshing Procedure instead of the hexahedral mesher.
You can use fluid blocks to refine or otherwise improve the mesh locally. Unless you change their material properties, fluid blocks do not alter the flow or temperature distribution inside the cabinet because they are, by default, made of air, which is the material inside the rest of the cabinet as well.
Calculate a solution on the refined mesh.
For optimal accuracy, refine the mesh further, calculate a solution, and compare it with the solution for the previous mesh. Repeat until the solution is grid-independent (that is, until it no longer changes with each new mesh).
