Tutorial: Hex-dominant parametric – Valve Geometry
- In this tutorial, the meshing process for a valve geometry is carried out using the “Hex-dominant parametric” approach.
- The “Hex-dominant parametric” is the semi-automatic meshing option that uses hexahedral cells and allows full flexibility in meshing parameters with all type of refinements options.
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.
Note: the STL geometry is pre-split to separate the faces for meshing and later assignment of boundary conditions.
- The Valve cane seen by hiding all the faces except face-3
- Select the simulation model. Click on Incompressible.
- 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)
Back Ground Mesh Box
- An important parameter is the size of the base box, which serves as the bounding coordinates for the mesh.
- To change the size of the box click on Back Ground Mesh Box expand geometry primitives under Mesh and change the coordinates of Base 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 geometry.
- Select the Material Point and give the coordinates as below:
- Now we create additional Geometry Primitives, to be used later for region refinements.
- Click Geometry primitives and ‘add new primitive’ of type Cylinder as shown in figures below.
- Specify the name ‘Cylinder-Valve’ and following values, then save to get the shown cylinder region.
- Similarly create 4 more primitives of ‘Type: Cylinder’ as detailed in the table below:
- These will be later used to refine the up/down stream regions, the opening gap between the valve and pipe, and hinge areas.
- The figure below illustrates the created primitives:
- Here we will add the necessary refinements for the surfaces, edges and regions to generate a fine mesh of optimum size.
- The refinement levels given are relative to the ‘baseMesh’ cell size with each level reducing the size to half.
- see Hex-dominant parametric documentation for details.
- 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.
- Re-name it to ‘Surf-pipe-inlet-outlet’ and select a Type ‘Surface refinement’ to specify the parameters as shown in figure below.
- This will refine the pipe, inlet and outlet surfaces. Select the shown faces and click save.
- Select the minimum and maximum level surface refinement as 2 and 3 respectively
- Create 1 more surface refinements for the valve surface as detailed in the figure below:
This refinement is important to resolve the feature edges of the geometry and produce a fine mesh at the edges.
- Add a new mesh refinement and select type ‘Feature refinement’ for refinement near edges. Re-name and enter the values as detailed in the figure below.
- This will now apply a level-5 refinement at a distance of 0.01m from the extracted edges in all directions.
Region refinements will refine the volume mesh cells based on the given refinement level. These are important to get a fine volume mesh in the vicinity, upstream and downstream of the valve.
- Now we add ‘Region refinements’ using the geometry primitives created before to refine the volume mesh.
- So add a new mesh refinement, rename to ‘Reg-hinge-1’, select Type ‘Region refinement’ and specify the settings as shown below and save.
- This will apply a level 7 refinement inside the selected region.
- Similarly, create 3 more ‘Region refinements’ as detailed in the table below:
- Lastly, add a ‘Layer refinement’ for resolving the viscous region of the boundary layer. Specify the settings as shown below.
- This will generate 3 layers based on relative size.
- Choose the inside physical walls and valve i.e the face_3 and face_4 from the assignment box and click save.
To generate a mesh of optimum quality, make sure the advance settings are set as shown in the figures below.
- For ‘Castellated mesh’ and ‘Span’ controls:
- For ‘Mesh Quality control’:
- After the mesh is generated, use the mesh as the domain for simulation and click on reset the assignments when prompted.
- The generated mesh with the mesh refinements is presented below:
- The Mesh generated on the valve can be seen by hiding the other faces.