This tutorial demonstrates how you can use the full Hex-dominant parametric operation to create a mesh which supports the simulation of rotating systems. These meshes are required when you want to simulate a turbines, pumps and other systems which contain a rotor.
The geometry needs to be prepared in a special way so that a rotating zone mesh can be produced:
A cylinder needs to be placed around the rotor. All cells within the cylinder will later be treated as rotating.
As a first step we need to create a new simulation. To create a simulation left click under the Geometries and then on Create Simulation.
Geometry showing the rotating region with impeller inside
Select the simulation model. Click on Incompressible.
A cylinder has been put around the rotor to define the rotating zone.
One face of the cylinder is made invisible so that the rotor inside can be seen.
keep the default settings of the simulation the same.
Left click on the mesh icon to create a new mesh.
Choose the Hex-Dominant parametric (only CFD) Algorithm.
Select the number of cells in each direction for Bounding Box as shown in the figure below.
Scroll down to specify the Number of computing cores for the meshing operation (16 in this tutorial)
Background Mesh Box
An important parameter is the size of the base box, which is used as the surrounding fluid domain.
To change the size of the box click on Back ground mesh box expand geometry primitives under Mesh and change the coordinates of Back ground mesh box as shown below
Material point: This is the parameter the algorithm uses to determine wether the mesh is created inside a shape or outside. In this case this point therefore lies within the base mesh box but outside the body.
Select the Material Point and give the coordinates as below:
In order to resolve the features of the geometry accurately you can add a Feature Refinement under the Mesh Refinements.
Click on the ‘+’ icon next to Refinements and add an feature refinement and keep the default values as mentioned below.
A region refinement is used to refine the mesh within a volume.
The cylinder around the propeller will define a zone within the cells will be more refined than in the rest of the mesh.
Click on the ‘+’ icon next to Refinements and add an region refinement.
Select the refinement mode as ‘inside’ and the level of refinement as ‘2’.
select ‘solid_1’ by clicking on the top right corner.
In order to have a finer mesh over the surface of the body, we add surface refinement.
Click on Refinements to add a new refinement and select surface refinement. We use 2 surface refinements:
On the rotor to refine the cells near the blades and
On the cylinder to define the rotating zone.
Refinement for Blade surfaces
This refinement enforces that the cells near the propeller surface will get refined.
Select ‘solid_0’ and keep the minimum and maximum refinement levels at 3 and 4 respectively
Refinement for the rotating (MRF/AMI) zone:
This step is crucial to correctly define the cell zone which will rotate.
Add a surface refinement and set the ‘Cell Zone’ option to ‘With Cell Zone’
Keep the minimum and maximum levels at 1 and 2 respectively
Select ‘solid_1’ for this surface refinement.
Boundary Layer Refinement
Layer refinements are used to create boundary layers near solid walls.
When considering turbulent effects, boundary layer refinement is required in order to obtain a correct solution.
Create a new layer refinement and assign all faces of the propeller.
This can be done by hiding solid_1 and using Active box selection to select all the faces of solid_0
Select the Inflate Boundary layer setting and the below values.
Once the mesh is fully set up, the mesh generation can be started.
After the mesh is generated, use the mesh as the domain for simulation and click on reset the assignments when prompted.
Click on generate mesh clip to inspect the internal mesh. Adjust the settings of the normal. Click on generate mesh clip icon.
The region refinement in the rotating region is clearly visible.
On further zooming we can see the boundary layer refinement.
Hide all the bounding faces to view the surface refinement on our propeller.
Last updated: April 16th, 2019
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