Automatic Mesh Sizing includes several exciting improvements that further streamline the simulation meshing process. These improvements primarily affect four aspects of meshing: Mesh Adaptation, Volume-Based Autosizing, Mesh Enhancement, and the performance of Automatic Sizing.
Mesh Adaptation Improvements
Mesh Adaptation is a powerful tool for creating the best mesh for your model. For Simulation CFD 2014, Mesh Adaptation is faster, provides more feedback, and is more flexible.
Supported Material Devices
In its initial introduction, Mesh Adaptation could not be used with models that contained most material devices. This limitation has been removed, allowing Mesh Adaptation to be used for a much wider range of applications.
Mesh Adaptation now supports the following material devices:
- Internal Fan/Pump
- Centrifugal Pump/Blower
- Distributed Resistance
- Heat Exchanger
- Check Valve
- LED
- CTM
- TEC
Performance Improvements
- Mesh Adaptation now requires less time to compute the mesh distribution for each adaptation cycle.
- The adaptation error indicator uses an alternative method that more selectively refines the mesh. In many cases, the resultant mesh is smaller, which leads to reduced simulation times.
Boundary Layer Accuracy Improvements
In the prior version, Mesh Adaptation adapted enhancement layers only in the flow-wise direction. Because the thickness was unaffected, the effect of Adaptation within the boundary layer region was limited.
By allowing Mesh Adaptation to adapt both the thickness and in the flow-wise dimension of boundary layer elements, we can expect to see improvements in the solution accuracy along walls and fluid-solid interfaces.
Mesh Independence Indicators
When using Mesh Adaptation, it is important to know when the mesh is fine enough so that further refinements do not change the solution. When the solution no longer changes as the mesh is refined, the model is considered "mesh independent." With each adaptation step, Simulation CFD 2014 tells you how close your mesh is to a mesh independent solution.
Mesh Adaptation evaluates pressure, velocity, and temperature (for heat transfer simulations). At the conclusion of each adaptation step, Mesh Adaptation writes a message similar to the following in the Output bar:
Mesh Independence: Pressure: 85% Velocity 98% Temperature 97%
These values indicate how much of the solution from the previous mesh remained unchanged in the new mesh. Higher values mean that the value did not change over a greater amount of the model. Higher values indicate less sensitivity to the mesh, which means your solution is approaching mesh independence.
For best results, you should ensure that each adaptation cycle runs to convergence (or as close as possible). If your adaptation cycles only run for a small number of iterations, thus failing to reach convergence, the Mesh Independence indicators will not be accurate.
To learn more about Mesh Adaptation, click here.
Volume-Based Mesh Autosizing
In previous versions, Autosizing often produced a coarse mesh in regions that were not closely bounded by geometry. This was problematic because such a mesh could not accurately resolve flow activity such as circulation. To force a finer mesh in these regions, many users created "nested" internal volumes or used mesh regions to control the mesh within these regions.
Volume-Based Autosizing in Simulation CFD 2014 eliminates this need by better controlling how elements grow from the walls into large, open regions. While the resultant mesh count may be higher, the solution accuracy is generally improved.
To enable Volume-Based Autosizing, do the following:
- Change the value of the mesh_volume_autosize flag in the Flag Manager to 1.
- Click Autosize on the Automatic Sizing context panel.
- In the Automatic Sizing Refinement region, click Surface Refinement.
- Click Refine.
Volume-based autosizing grows the mesh by no more than 35% from the sizes prescribed at the surface and edges. To change this value, use this flag:
mesh_volume_autosize_growth
Set the growth rate within the domain (specified as integer percent). Default 135 (i.e. 1.35)
Example:
This is a mesh created without Volume-Based Autosizing:
Here is the mesh created with Volume-Based Autosizing:
To learn more about Volume-base Autosizing, click here.
Mesh Enhancement Modifications
User-defined Mesh Enhancement Layer Thickness Growth
This new setting provides a way to control how the enhancement layer thickness grows. In previous versions, the layer growth rate was not a user-defined quantity. As the number of enhancement layers increases, the layer thickness became more uniform. This control allows the layers nearest the wall to be smaller than those closest to the neighboring unstructured elements.
This control is useful for improving the accuracy of heat flux at the wall as well as for the new turbulence model.
The default growth value is 1.1. To change it, modify the Layer gradation setting on the Boundary Mesh Enhancement dialog. You can also modify the value for the flag called mesh_enhance_gradation in the Flag Manager.
Automatic Layer Adaptation Removed
The Mesh Enhancement dialog no longer contains the Automatic Layer Adaptation function. This conflicted with the Y+ Adaptation function located on the Adaptation tab of the Solve dialog. To automatically vary the mesh enhancement layer thickness to ensure proper Y+ value, enable Mesh Adaptation, and check Y+ Adaptation.
To learn more about Mesh Enhancement, click here.
Autosizing Performance Improvement
The Autosizing function was modified and refined to reduce the amount of time needed to compute the mesh distribution after you click the Autosize button. This improvement is most apparent for very large, geometrically complex models.
To learn more about Automatic Sizing, click here.