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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.

Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller

    Geometry showing the rotating region with impeller inside
  • Select the simulation model. Click on Incompressible.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Select the incompressible analysis
  • 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.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Image showing the impeller and the rotating geometry

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.
Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
Bounding box resolution settings for the mesh
  • Scroll down to specify the Number of computing cores for the meshing operation (16 in this tutorial)

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Selecting the number of processors for meshing

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

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    BASE MESH BOX Settings

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:

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Set up the coordinates of the material point

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.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Set up the feature refinement

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.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Select the rotating region for region refinement

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.

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

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Surface refinement settings for blade surfaces

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.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Surface refinement for rotating zones

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.
Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
Boundary layer refinement for impeller
  • 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.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Mesh clip showing the region refinement
  • The region refinement in the rotating region is clearly visible.
  • On further zooming we can see the boundary layer refinement.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Boundary layers on the mesh can be seen on zooming
  • Hide all the bounding faces to view the surface refinement on our propeller.

    Meshing, CFD, Simscale, External Flow Analsysis, Rotating Geometry, Fan, Propeller
    Surface refinement on the impeller

 

 

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