Tutorial: Hex-Dominant Parametric Meshing of a Front Wing

This documentation 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:

Preparing the CAD model for the simulation
Setting up the simulation
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.

Please Note!

This is a tutorial purely about meshing. There will not be any simulation performed.
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.

Import tutorial into 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 $\mathrm{X}$ direction to ’20’.
Set the cells in the $\mathrm{Y}$ direction to ’10’.
Set the cells in the $\mathrm{Z}$ 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 cells that will be created initially at each direction. So, 20 cells will be generated across the $\mathrm{X}$-direction, and 10 across the other two. In total, 2000 cells will be generated before any refinements are added.

2.1. 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 extends 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 tutorial setup, the domain is sized with respect to the length of the wing L 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 $\mathrm{X}$-direction for example is then given as:

$$\displaystyle \mathrm{\frac{X_{max} – X_{min}}{N_x}}$$

where $\mathrm{X_{max}}$ is the maximum $\mathrm{X}$-coordinate, $\mathrm{X_{min}}$ is the minimum $\mathrm{X}$-coordinate of the Base Mesh Box and $\mathrm{N_x}$ is the number of cells in $\mathrm{X}$-direction.
Here, the dimensions of the domain, with 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 item 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

2.2. Create Geometrical Primitives

Before you add any refinements, create three cartesian boxes and some region refinements will be assigned to each of them afterwards.
Click on ‘+‘ 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, which 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

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.

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.

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.

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

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 ‘7’.
Set the maximum refinement level to ‘9’.
Toggle on the ‘Assignment’ option.
Assign the refinement to the whole Front Wing by clicking on ‘Select Volume’ on the top of the page and then on the part on the geometry tree at the right of the page or on the part itself.

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.

Leave the values in their default state, and assign this refinement to the front wing by activating the box selection, and then dragging it across the interface holding the left mouse button, so that the whole wing turns 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 ‘Min Z’, 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.

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. 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 Included 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

2.4. 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.

mesh box generation simscale platform tutorial — Figure 28: Generating a new mesh

3. Results

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

domain mesh final — Figure 29: The final mesh of the domain showing different levels of refinement

By toggling on the option to Show faces and hiding the faces of the bounding box domain from the 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

More details about the mesh can be found under Meshing Log. A quick look at the mesh metrics can be accessed under Event log:

mesh event log details hex dominant parametric

The mesh consists of approximately 4.2 million hexahedral cells, 0.12 million prism cells, 28 tetrahedral cells, and 2 pyramids.

You can check the quality of your mesh and improve it by clicking on the ‘Mesh quality’ in the simulation tree. This will take you to SimScale’s integrated post-processing environment. Use this article to help you visually examine the characteristics of your mesh.

mesh quality post processor non-orthogonality — Figure 32: Accessing the meshing quality post-processor. There are no cells lying with non-orthogonality beyond 72.

Congratulations! You finished the tutorial!

Have a look at the finished project

Note

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

Last updated: August 9th, 2024

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Tutorial: Hex-Dominant Parametric Meshing of a Front Wing

Overview