Incompressible aerodynamics of a complete car

Hello guys
I am completly new on simscale or CFD and I am on the proccess of figuring it out.
I was doing the tutorial of incompressible aerodynamics of the simulation of a complete car.
I think I followed the instructions step by step but I get two problems:
1) Lower quality mesh than the already done project from simscale.
2) Can not start the simulation due to the following problem : “Multiple boundary condition assignments for the following entities: NONE@Flow region, NONE@Flow region, NONE@Flow region, more …
(click to select)”.

The problem with the bad quality mesh has happened to me before with other projects/tutorials, in particular with the formula student simulation and I have not found the answer to that.

The link to the project is :
SimScale Login

Any help is greatly appreciated as it is very frustating to find the mistake.
In any case, thank you for your help and time

Hello apiergili

To your second question please have a look at this article here:

To your first question, we are always improving and updating the settings of our standard meshing algorithm to improve the stability and quality of the mesh, so changes can be possible,
However, what do you mean by lower quality of the mesh in comparison to the tutorial one?

Best regards
Sebastian

Hello Sebastian

Regarding the problem of the lower quality mesh, below there is the screenshot of the meshing log of the Final Project (The final project you can find at the end of the tutorial, which has all the tutorial steps done by simscale):

Now, following the same steps, I get a much worse mesh ( just looking at the non-orthogonality, overall mesh quality,…):

I understand the algorithm may change and get updated, but I think that the values shouldn’t change as much as it does.
Strangely, this difference in mesh quality between my own projects and the given tutorial projects (already done by simscale) is always present.
Which means that I am making a systematic error.
I have checked all the steps between both projects and I can not find any difference.

Thank you
Alvaro

Hi apiergili,

The mesh quality is a bit misleading since the values are calculated differently.

Before multiple factors calculated it:
nonOthogonalty - Skweness -Aspect Ratio

Now it’s just calculated by the Non-Othogonaltiy.

when comparing directly we can see that no major difference between the meshes can be found.

Thanks and best regards
Sebastian

Thank you, Sebastian.
Now I understand that the way the quality is measured is different, therefore different results.
But now, I have some additional questions:

I was reading that in order to have a good quality mesh and therefore an excellent valid simulation, there are some factors from the meshing log-in.

To sump it up :

  • tetAspectRatio: ≪ 100
  • Non-orthogonality: ≪ 75
  • tetEdgeRatio: ≪ 100
  • VolumeRatio: ≪ 100

Now, when I check these parameters for all the available tutorials for incompressible aerodynamics, I can see that they do not follow the previous list 100%.

For example, In the previous model of the car, the mesh from simscale had a max non-orthogonality of 87.
And for other examples they had a volume ratio larger than 100%.

Now, what should I do next?
Ignore the previous table that I found in this article : How to Check and Improve Mesh Quality | SimScale ?

Or if these parameters are important, how can I reduce them? (For example the volumeRatio, Non-orthogonality,… ) ( I know that cleaning the CAD model would help, but the models of the tutorials are already clean )
Also on the previous link, I found some steps to reduce the volume ratio. I tried to somewhat use it without any visible change.

In any case, what steps would you advise to follow to try to have a good quality mesh to have representative simulations?

Thank you very much
Alvaro

Hello apiergili,

with mesh quality, it’s always a trade of mesh quality to simulation run time.
For our tutorials, we lean towards fast simulation run time, then accuracy and higher quality mesh, since the focus is more on how to set up the whole simulation.

As you have seen in the KBA ISO volumes can be found, for which the mesh quality is not ideal.
here we can either work with a region or surface refinements of the mesh or defeature the geometry. But this will increase the overall cell count, which comes with the cost of a longer simulation run time.

The best practice is to perform a mesh sensitivity study starting from a low-quality mesh to find the sweet spot of mesh quality and simulation runtime(cell count). More on mesh sensitivity studies can be found here:

Best regards
Sebastian