SimScale CAE Forum

Drag coefficient diverge after a while

Hello, I built these models in fusion 360 and was simulating them for CFD analysis. However, the drag coefficient and lift coefficient diverge, despite the mesh being fine and refined with all the models except the one named “Sidepod 4”. So could someone please tell me why this is happening and how I can improve

Link for the simulation:
https://www.simscale.com/workbench/?pid=632197329273536670&mi=spec%3Af40bc5ab-d742-4663-acc5-0c0a82d2dfe5%2Cservice%3AMESHING%2Cstrategy%3A17&sh=16

Photo of error:

Best Regards
Ishaan Agarwal

Hi Ishaan,

To help users identify and troubleshoot divergence in their simulations, SimScale has a divergence monitor. The following parameters are tracked: velocity, pressure, density, and temperature. Whenever a parameter reaches unrealistic levels in the domain, the simulation automatically stops with an error message:

The error message specifies which parameter diverged and also the exact location in the model. This information is valuable, and can be a starting point for the troubleshooting process.

To gain more insight into the causes of divergence, the following basic steps are useful:

  1. Create a ‘probe point‘ result control and input the coordinates displayed in the error message. In doing so, you will see exactly where the divergence occurred;
  2. If the point is close to one of the boundaries, double-check all boundary conditions, making sure they are correct;
  3. If the point is located inside the domain, inspect the mesh around the area. The ‘mesh quality‘ visualization feature is very useful in this step. Even just a few bad quality cells can create instabilities in the simulation, ultimately leading to divergence.

If you want to learn more, and have a look at some trouble-shooting examples too, make sure to read this article:

Best regards,
Fillia

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Hi @tsite, thanks for the response. I created a probe point and then checked the mesh quality there but the volume ration was less than 100 at the probed locations. So I am unable to identify the problem, if possible could you tell me the problem?

Best Regards.

Hi,

An excerpt from the article that Fillia linked: “Look for very small faces, very detailed topology, and small gaps.”

Having a quick look at the mesh, there is a face which becomes increasingly narrower, creating a problematic region, that ultimately causes the simulation to fail (it fails close to the arrow).

The article also gives you the solution:

In your case, applying more refinement won’t help, because this will only generate smaller cells and potentially worsen the problem. But the other two options are viable :slight_smile:

Good luck

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Oh alright, thanks for the help

Best Regards
Ishaan

1 Like