Mesh
The mesh needs to be quite fine to ensure that the particle motion is accurate throughout the modeling domain. In this case, take care to ensure that the mesh is sufficiently fine close to the mixing blades.
1
In the Mesh toolbar, click Boundary  and choose Free Triangular .
2
Select Boundaries 5, 16–18, and 53–55 only. These boundaries include the leading edges of all three mixing blades.
3
Right-click Free Triangular 1 and choose Size .
4
In the Settings window for Size locate the Element Size section.
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From the Calibrate for list, choose Fluid dynamics.
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From the Predefined list, choose Extremely fine.
5
Click the Size node above the Free Triangular node.
6
In the Settings window for Size locate the Element Size section.
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From the Predefined list, choose Extremely fine.
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Click the Custom button. By first choosing the Extremely fine option and then switching to a Custom mesh, you can begin customizing the mesh with a reasonable set of default values.
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Locate the Element Size Parameters section. In the Curvature factor text field, type 0.15. The curvature factor is used to refine the mesh on curved surfaces while allowing the mesh to be somewhat coarser on planar surfaces.
7
In the Mesh toolbar, click Boundary  and choose Free Triangular .
8
Select Boundary 23, the Inlet boundary, only.
9
Right-click Free Triangular 2 and choose Size .
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In the Settings window for Size locate the Element Size section. From the Calibrate for list, choose Fluid dynamics.
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From the Predefined list, choose Extra fine.
10
Right-click Mesh 1 and choose Free Tetrahedral . Alternatively, select Free Tetrahedral  from the Mesh toolbar.
11
Click Build All .
The mesh should look like the following image. As for the geometry, some outer surfaces have been hidden from view so that the mesh on the mixing blades can be seen easily.