Tutorial: Hex Dominant Automated – Internal Flow Through an Angled Pipe

This short tutorial shows how to create a mesh using the automated Hex dominant operation for internal flow analysis.

hex dominant automated pipe mesh — Figure 1: Visualization of the mesh of the pipe with the hex-dominant algorithm.

Overview

This tutorial teaches how to:

Mesh with the SimScale Hex dominant meshing algorithm.
Inspect your mesh.

Be aware

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

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 import simscale workbench angled pipe — Figure 2: Imported CAD model of an angled pipe in the SimScale workbench.

1.1. Create the Simulation

As a first step, we need to create a new simulation. Therefore, left-click on the ‘Pipe-shape’ and then on the ‘Create Simulation’.

create simulation angled pipe — Figure 3: Creating a simulation for the pipe geometry.

This dialog box allows the user to select the simulation model. Click on the ‘Incompressible‘ option and then on the ‘Create Simulation’ one.

analysis type incompressible simscale — Figure 4: Choosing the incompressible analysis for the pipe simulation.

Did you know?

The Hex Dominant meshing algorithm can be used for any flow simulation that is not using the LBM solver, that means:

Incompressible
Compressible
Convective Heat Transfer
Conjugate Heat Transfer

2. Mesh

We will create five different meshes to demonstrate the differences between the main meshing features available:

Default Settings
Global Fineness
Region Refinement
Feature Refinement
Surface Refinement

To access the meshing options click on the ‘Mesh‘ in the simulation setup tree.

2.1 Mesh One: Default Settings

The following picture shows the global mesh settings:

hex dominant automated option settings panel internal pipe meshing coarse — Figure 5: Setting the Hex-dominant properties for an automated mesh generation.

Choose the ‘Hex-dominant ‘ Algorithm and leave the Meshing mode to its’ original state (‘Internal’).
Leave the Sizing and Fineness option to their default state.
The Automatic boundary layers generate layers automatically, based on the boundary conditions set by the user.

Warning

For the automatic boundary layer option, the physics of the simulation are taken into consideration. Click on the ‘Generate’ button on the mesh panel to create the mesh after all the properties and boundary conditions of the simulation are added.

In order to create a new mesh, click on the ‘Generate‘ option:

generate button for mesh hex dominant automatic — Figure 6: Generating a new mesh.

After 2 minutes, a mesh of 68,193 nodes will be generated. You can see more information about the mesh by clicking on the ‘Event Log‘:

mesh details event log — Figure 7: Checking the event log for information about the mesh.

Click on the ‘Mesh clip‘ to inspect the internal mesh. Adjust the settings of the normal. Click on the ‘Generate Mesh Clip‘ icon.

add mesh clip internal pipe meshing — Figure 8: Adding a cutting plane to inspect the internal mesh of the pipe.

This will appear then on your workbench:

final mesh cutting plane details pipe hex dominant mesh results coarse level — Figure 9: The internal mesh of the pipe, viewed from a cutting plane normal to the Y-axis for ‘Mesh One’.

2.2. Mesh Two: Changing Global Fineness

Did you know?

Often, large changes in the mesh’s cell sizes are only spotted in a few regions. Increasing the global mesh refinements rises the cells drastically.
You can also do this manually, by using one of the local refinement options, foremost being feature, surface and region refinements.

The settings for the second mesh will be the same, except for ‘Fineness‘.
Follow the steps below to create a new mesh:

Click on the current mesh in the main mesh panel.
Start a new mesh setup by clicking on the ‘+’ icon next to the Create new mesh.

Choose the ‘Hex-dominant‘ algorithm again, then simply change the ‘Fineness‘ level to ‘Fine‘ and ‘Generate‘ the second mesh.

hex dominant automated option settings panel internal pipe meshing fine — Figure 11: Setting the Hex-dominant properties for a fine automated mesh generation.

After 4 minutes, a mesh with 336,975 nodes will be created:

final mesh cutting plane details pipe hex dominant mesh results fine level — Figure 12: The internal mesh of the pipe, viewed from a cutting plane normal to the Y-axis for ‘Mesh Two’.

No refinements were added to the previous cases, but this time, the Region Refinement will be used. Region refinements are assigned to volumes and refine all the cells inside or outside that specific volume.
Depending on the user’s preference, it can refine all volume mesh cells inside the selected volumes up to the specified cell edge length, or the outside volume mesh cells up to the specified cell edge length.
There is also a third mode, accommodating different refinement levels at multiple distances, according to the distance to the surface of the assigned volumes.
Start by copying ‘Mesh Two‘. Click on the name of the mesh in the main mesh panel, then select the ‘Copy Mesh settings’. You can choose which already created mesh you want to duplicate by choosing it from a window that will appear.

copy mesh settings option — Figure 13: Creating a new mesh to add more refinements on it.

If you want to add any kind of refinements:

Select the ‘Mesh‘ in the simulation tree.
Click on the ‘+’ icon next to the Refinements
Pick the type of refinement you wish from the menu that will appear.

new mesh refinements add — Figure 14: Adding refinements to the mesh.

After you pick the ‘Region refinement’, proceed to set the maximum edge length to 0.02 \(m\). Make sure the Assignment is toggled on, and choose the whole part from the geometry tree.

featureregionlength — Figure 15: Setting a new region refinement.

The final mesh will be generated after 5 minutes and will consist of 419,287 nodes.

final mesh cutting plane details pipe hex dominant mesh results fine level region refinement — Figure 16: The internal mesh of the pipe, viewed from a cutting plane normal to the Y-axis for ‘Mesh Three’.

A feature refinement can be used to refine the geometry’s feature edges. Refinement settings include distance and length. The edge and surface mesh will then be refined up until the specified distance in all directions from the extracted edges. The length parameter determines the intended cell edge length.
After you copy the mesh settings from Mesh Three pick the ‘Feature refinement’, do the following:

Set the ‘Distance‘ to 0.05 \(m\) and the ‘Maximum edge length‘ to 0.005 \(m\)
Make sure the ‘Assignment’ is toggled on.
Apply the refinement on the whole part.

feature refinement maximum edge length — Figure 17: Setting a new feature refinement.

The mesh will be created after 8 minutes and consists of 1,028,364 elements.

final mesh cutting plane details pipe hex dominant mesh results fine level region refinement feature refinement — Figure 18: The internal mesh of the pipe, viewed from a cutting plane normal to the Y-axis for ‘Mesh Four’.

A surface refinement can be applied to refine cells on specific surfaces of the geometry. Both geometry faces and/or volumes can be selected for refinement. If a volume has been assigned, the refinement is applied to all surfaces of that volume.

It’s required to specify two refinement levels, the Minimum cell edge length, and the Maximum cell edge length. In a first step, a refinement up to the maximum length is applied across all of the assigned surfaces. Further refinement up to the minimum cell edge length is only applied to cells in areas where the normals form an angle greater than 30°. Therefore, in the following cases, only the first refinement step is applied:

A flat surface
A surface that has an angle between normals less than 30°

Copy the mesh settings from Mesh Four, and then choose the ‘Surface refinement‘. Before the Surface refinement is added, the pipe looks like this:

pipe mesh before surface refinement — Figure 19: The mesh of the pipe before any surface refinements are added.

Set the ‘Min length‘ to 0.0001 \(m\) and the ‘Max length‘ to 0.005 \(m\)
Make sure the Assignment is toggled on.
Apply the refinement on the three inlet and outlet faces.

surface refinement inlet and outlet of pipe — Figure 20: Setting a surface refinement for the faces of the inlets and outlets.

Proceed to creating another surface refinement, this time for the rest of the faces of the pipe:

Set the ‘Min length‘ to 0.0001 \(m\) and the ‘Max length‘ to 0.008 \(m\)
Make sure the Assignment is toggled on.
Select the four remaining faces of the pipe manually on the workbench.

surface refinement of pipe — Figure 21: Setting a surface refinement for the rest of the faces of the pipe.

This mesh took 31 minutes and consists of 4,173,190 nodes.

final mesh after surface refinement pipe hex dominant automatic — Figure 22: The mesh of the pipe after the two surface refinements were added.

3. Results

The boundary layer generation can easily be seen by zooming in on the mesh inlet.

details of hex dominant meshing for internal simulation of pipe — Figure 23: Details of the final mesh.

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.

mesh quality simulation tree inspection — Figure 24: Inspecting the mesh quality after the mesh is created.

Analyze your results with the SimScale post processor. Have a look at our post-processing guide to learn how to use the post-processor.

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: July 3rd, 2020

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Documentation

Tutorial: Hex Dominant Automated – Internal Flow Through an Angled Pipe

Overview