27 May How to spot low quality mesh zones
Is my mesh good enough? Will this grid allow me to obtain accurate results? These are common questions among CAE (and especially CFD) users. In this post, we present a particular feature provided by CONSELF that helps spotting problematic mesh regions.
Mesh problems can be roughly divided in two big families, depending on the relation they have with the iterative equation solution (that is the simulation itself):
1) Geometric problems. This first family groups all those mesh issues that can be identified without knowing how the mesh will be used in the simulation. This means that, to spot them, you don’t need to know how the different surfaces will behave, where the flow enters the domain, which boundary will act as a barrier and so on. This is the reason why we named them “Geometric problems”, since they are strictly related with measurable geometric properties of your grid.
We wrote a post in which we described the most typical geometric problems (“4 mesh issues causing poor CFD simulation accuracy”), so we will not describe them again here, it is not the scope of this article. An example of a typical mesh shortcoming is represented in the image on the right.
Common geometric problem: skewness.
One key aspect in flow-related mesh problems: turbulence and y+.
2) Flow-related problems. This second family is commonly recognized as the tricky one. In order to know if your mesh is good or not, you need to take into account many factors, all related with what will happen next, after the grid has been completed:
- surfaces role in the simulation (inlet, outlet, wall, periodicity, etc)
- flow regime (laminar, turbulent)
- boundaries relative position and their respective role (topological information, proximity, coupling, etc)
- variables distribution in the computational domain
To give just a few.
The last one listed is perhaps the biggest problem, since you typically first need the grid to run your simulation in order to be able to investigate variables distribution. So you should use an iterative algorithm going back and forth between meshing and simulation in order to obtain a proper computational grid. In fact, this is where experience plays a major role and consultants and simulation experts give their added value. They leverage on this very critical point to sell their professional activity.
Some of these aspects are treated in a previous post we wrote (“5 tips to improve your CFD simulation accuracy”).
“How to spot geometric problems in your mesh
with CONSELF Cloud Simulation Platform”
At CONSELF we firmly believe that in order to simplify our users life we have to tackle these two meshing issues families. That is the reason why in our recent releases you can find a very useful way to spot low quality mesh zones due to the first family group: geometric problems. As you probably already know, our simulation process is organized in consecutive steps to guide the user towards the correct completion of the entire analysis. At the end of the “Mesh 3D” step, when you are ready to start setting up your “Simulation” step, you are able to see where (if) your mesh has geometric problems.
To do so you have to follow the steps listed below. Take a look at the video on the right to see the guided procedure.
- Choose the mesh you want to use
- In the graphic window:
- open the menu clicking on the “Pipeline” button
- select the solution file “system.foam”
- apply the “Threshold” filter under the menu identified by a “+” sign
- in the filter properties choose the “meshQuality” variable as parameter (it is zero where the mesh is good, one where it presents problems)
- set the minimum and maximum threshold values as 0.5 and 1 and click on the small tick in the upper part of the filter property
- in the pipeline menu activate the visualization of the entire file “system.foam” and set “Opacity” value in its “Representation” property equal to 0.3
Completing these steps you are able to take a look at the whole file in transparency with low quality mesh zones highlighted in red.
Now it’s your turn! Create your case and find out if your are able to obtain a mesh free from geometric problems as the ones we talked about. Signup for the free WELCOME plan, you will be able to run simulation for free every month, forever!
Do you need advises, tutorials or just inspiration? Take a look at our webinars page, they allow every user to start from scratch and learn how to deal with CONSELF platform very quickly.
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