# Tutorial: Hex-dominant parametric – Rotating geometries

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.

### Geometry preparation

• 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.
• The cylinder needs to be defined as a solid body.

Import tutorial project into workbench

• 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.

## Mesh Generation

•  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

• 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:

## Feature Refinement

• 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.

## Region Refinement

• 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.

## Surface Refinement

• 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.

• 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.

## Mesh Inspection

• 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.