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Tutorial: Hex-Dominant Parametric Meshing of a Front Wing

This article provides a step-by-step tutorial for a mesh creation of an F1 front wing model, using the “Hex-dominant parametric” approach. The “Hex-dominant parametric” (only for CFD) is the semi-automatic meshing option that uses hexahedral cells and allows full flexibility in meshing parameters with all types of refinement options. The objective is to get a high-quality mesh with sufficient resolution to capture key features in the model.
This tutorial will highlight some essential points of the meshing process that help users achieve better simulation results.

mesh results hex dominant parametric algorithm front wing f1
Figure 1: The mesh that was generated for the front wing using the hex-dominant parametric algorithm.

Overview

This tutorial teaches how to:

  • Use SimScale’s Geometry Operation features.
  • Get a new simulation started.
  • Mesh with the SimScale Hex-Dominant parametric algorithm.

We are following the typical SimScale workflow:

  1. Preparing the CAD model for the simulation
  2. Setting up the simulation
  3. Creating the mesh

If you want to learn more about the Hex-dominant parametric algorithm, take a look at this document: Main Settings for Hex-dominant parametric.

Be aware

  1. This is a tutorial purely about meshing. There will not be a simulation performed.
  2. The Hex Dominant algorithm is an advanced mesher. If you are new to SimScale and just getting started we highly recommend to use the standard mesher.

1. Prepare the CAD Model and Select the Analysis Type

1.1. Import the CAD Into Your Workbench

First of all click the button below. It will copy the tutorial project containing the geometry into your own workbench.

The following picture demonstrates what should be visible after importing the tutorial project.

cad model simscale workbench f1 front wing
Figure 2: The imported CAD model of the front wing in the workbench.

1.2. Create the Simulation

After the CAD is imported, click on the ‘Create Simulation‘ option.

creating simulation button
Figure 3: Creating a new simulation.

Choose ‘Incompressible fluid flow‘ as the analysis type.

analysis type incompressible fluid flow external aerodynamics
Figure 4: Choosing the analysis type to get the simulation set up started.

2. Mesh

Be Aware

The boundary conditions for cases where the mesh is created with the hex dominant parametric are assigned on the faces of the generated mesh. For the rest of the meshing algorithms, the assignment takes place on the faces of the model. As a result, for each new mesh with the hex dominant parametric, the user has to define the boundary conditions again.

The Hex Dominant parametric mesh does not take into consideration the physics of the simulation while being generated, so it can be set and created before the rest of the simulation settings are applied. Just click on the ‘Mesh‘ option in the simulation tree.

simulation tree mesh
Figure 5: The Mesh panel in the simulation tree.
  • Change the Algorithm to ‘Hex-dominant parametric’.
  • Set the cells in the X direction to ‘20‘.
  • Set the cells in the Y direction to ‘10‘.
  • Set the cells in the Z direction to ‘10‘.
cells in direction hex dominant parametric algorithm
Figure 6: Number of cells in each direction for the Hex-dominant parametric algorithm.

These settings indicate the number of the cells that will be created initially at each direction. So, 20 cells will be generated across the X-direction, and 10 across the other two. In total, 2000 cells will be generated before any refinements are added.

3.1. Background Mesh Box & Material Point

The Background Mesh Box represents the domain of the external simulation, and can be accessed from the simulation tree.

background mesh box simulation tree geometry primitives
Figure 7: The location of the background mesh box on the simulation tree.

It is recommended that it extents at least 3-5 times the reference length of the object, D, upstream, 8-10 times the D downstream and 3-5 times the D in the lateral directions. In this case, th domain is sized as you can see below, whereas L is the length of the wing in the direction of the wind:

domain dimensions external aerodynamics
Figure 8: The sizing of the domain.

For the creation of the base mesh the user previously specified the number of cells (for the Base Mesh Box) in each coordinate direction under Bounding box resolution.
The base mesh cell size in the X-direction for example is then given as:

(Xmax-Xmin)/(Nx)

where, Xmax is the maximum X-coordinate, Xmin is the minimum X-coordinate of the Base Mesh Box and Nx is the number of cells in X-direction.
Here, the dimensions of the domain, in respect to the chosen sizing seen in Figure 8 is as seen below:

  • Minimum x value: -3.73 m
  • Minimum y value: -2.725 m
  • Minimum z value: 0 m
  • Maximum x value: 5 m
  • Maximum y value: 0 m
  • Maximum z value: 2.725 m
background mesh box dimensions
Figure 9: The dimensions of the background mesh box.

The material point determines whether the resulting mesh is for an External flow simulation or Internal flow simulation. Set its’ coordinates to (1, -1, 1) after clicking on the ‘Material Point‘ under the Geometry Primitives option like below:

material point coordinates position on simulation tree
Figure 10: Setting the position of the material point.

Make sure the point is inside the Background Mesh Box by having them both visible on the geometry tree at the right of the page. It should also not intersect with any face of the model for an external aerodynamic simulation over a watertight geometry.

material point inside background mesh box outside the model
Figure 11: Examining the location of the material point regarding the background mesh box and the front wing.

2.1. Create Geometrical Primitives

Before you add any refinements , you will create three cartesian boxes and some region refinements will be assigned to each of them afterwards.
Click on the ‘+‘ next to the Geometry primitives, and choose the ‘Cartesian Box‘ option like below:

Cartesian box add new
Figure 12: Adding a new cartesian box.

The first cartesian box is the biggest of the three and has the following dimensions, that are set in the same way as the background mesh box, which is by having a maximum and minimum value for each direction:

  • Minimum x value: -2 m
  • Minimum y value: -1 m
  • Minimum z value: 0 m
  • Maximum x value: 3 m
  • Maximum y value: 0 m
  • Maximum z value: 1.5 m
cartesian box creation large box
Figure 13: The dimensions of the large box.

Then create a smaller box, with the following dimensions:

  • Minimum x value: -1.5 m
  • Minimum y value: -1 m
  • Minimum z value: 0 m
  • Maximum x value: 1.5 m
  • Maximum y value: 0 m
  • Maximum z value: 0.5 m
cartesian box creation medium box
Figure 14: The dimensions of the medium box.

Finally, the smallest box has the dimensions below:

  • Minimum x value: -1.2 m
  • Minimum y value: -0.85 m
  • Minimum z value: 0 m
  • Maximum x value: -0.15 m
  • Maximum y value: 0 m
  • Maximum z value: 0.3 m
cartesian box creation small box
Figure 15: The dimensions of the small box.

3.2 Add Refinements

For the hex-dominant parametric, several refinement options can be selected by the user to get the required mesh. These are all specified under the Mesh Refinement sub-tree.

Region Refinements

The region refinement is used to refine the volume mesh for one or more user-specified volume regions under Geometry primitives. Add a Region Refinement by clicking on the ‘+’ icon next to the Refinements, and then choosing the ‘Region Refinement’ option.

region refinement
Figure 16: Adding a region refinement.

The first region refinement that you will create is matched to the biggest cartesian box. The Refinement mode will be automatically set to Inside. This refines all volume mesh cells inside the surface up to the specified level. The surface needs to be closed for this to be possible.

  • Set the Level to ‘3′
  • Toggle on the ‘First Region‘ for the assignment.
large box region refinement assignment level
Figure 17: Refinement level and assignment to the large box.

Then add a second region refinement for the medium cartesian box. This time:

  • Set the Level to ‘4‘.
  • Toggle on the ‘Second Region‘ for the assignment.
medium box region refinement assignment level
Figure 18: Refinement level and assignment to the medium box.

Finally, create a last region refinement for the smallest Cartesian box like before:

  • Set the Level to ‘5‘.
  • Toggle on the ‘Third Region‘ for the assignment.
small box region refinement assignment level
Figure 19: Refinement level and assignment to the small box.

Surface Refinement

Add a Surface Refinement by clicking on the ‘+’ icon next to the ‘Refinements’, and then choosing the ‘Surface Refinement’ option.

surface refinement
Figure 20: Adding a surface refinement.

Specify two refinement levels, level min, and level max. The minimum level is applied first across all of the surfaces. The maximum level is only applied to cells in areas where the normals form an angle greater than the specified resolve feature angle (in Advanced Settings).

  • Set the minimum refinement level to ‘8‘.
  • Set the maximum refinement level to ‘10‘.
  • Toggle on the ‘Assignment‘ option.
  • Assign the refinement to the whole Front Wing by clicking on the part on the geometry tree at the right of the page.
surface refinement front wing assignment
Figure 21: Surface refinement levels and assignment to the wing.

Inflate Boundary Layer

The layer refinement adds a volume mesh with cells aligned to the surface. Add an Inflate boundary layer by clicking on the ‘+’ icon next to the ‘Refinements’, and then choosing the ‘Inflate boundary layer’ option.

inflate boundary layer mesh refinement
Figure 22: Adding an inflate boundary layer.

Leave the values at their default state, and assign it to the front wing by toggling on the ‘Assignment’, activating the box selection, and then dragging it across the interface, so that the whole wing turns into light blue. This means that all the faces are selected.

activate box selection inflate boundary layer f1 front wing
Figure 23: Inflate boundary layer assignment to the wing with box selection.

Bounding Box Layer Addition

The Bounding box layer addition refinement is similar to the Layer refinement but only applicable to the bounding box. This is mainly useful for external flow analysis where the box surface acts as a wall for the flow domain and must be refined with a layer mesh for accuracy. Add this by clicking on the ‘+’ icon next to the ‘Refinements’, and then choosing the ‘Bounding box layer addition’ option.

adding a bounding box layer refinement
Figure 24: Adding a bounding box layer.

Switch the Face to ‘Zmin‘, so that the layers are added to the ground, and keep the rest of the settings at their default state.

bounding box layer face assignment ground
Figure 25: Setting the ground as the face where the layers will be added.

Feature Refinement

This refinement type is specifically important as it is used to refine the geometry’s feature edges. The feature edges are extracted based on the Included angle under Surface Feature Extract. So, the edges whose adjacent surface normals form an angle less than the included angle are marked for extraction and refinement. Click on the ‘+’ icon next to the ‘Refinements’, and then choose the ‘Feature refinement’ option.

adding a feature refinement on mesh
Figure 26: Adding a feature refinement.

Change the Induced angle to ‘110’ degrees, the Distance to ‘0.01’ and the Level to ‘7’.
The edge and surface mesh will then be refined up until this Distance in all directions from the extracted edges.

feature refinement settings
Figure 27: Feature refinement level and included angle.

3.3. Generate Mesh

Go back to the Mesh panel, change the Numbers of the processors to ‘Automatic‘, for optimal usage of computational power, and click on the ‘Generate‘ button in order to start with the mesh creation.

Figure 28: Generating a new mesh.

4. Results

After the mesh is ready, the domain will look like this:

domain mesh final
Figure 29: The meshing of the domain.

And by hiding the faces of the domain on the geometry tree, you can visualize the final mesh of the front wing:

final mesh front wing visualization
Figure 30: The final mesh of the front wing.

Click on the ‘Meshing Log‘ for more details about your mesh:

mesh log details hex dominant parametric
Figure 31: Accessing the meshing log.

You can check the quality of your mesh and improve it by clicking on the ‘Mesh quality‘ on the simulation tree. Use this article to help you examine the characteristics of your mesh.

meshing quality post-processor
Figure 32: Accessing the meshing quality post-processor.

Congratulations! You finished the tutorial!

Note

If you have questions or suggestions, please reach out either via the forum or contact us directly.

Last updated: October 9th, 2020

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