Very different results for different mesh types

Hello everyone,

I was trying to calculate the drag experienced by an object and out of curiosity, I tried both standard and hex meshes. I knew both meshes might give different results but expected them to atleast be similar. Instead, the standard mesh with some refinements gives 2.72 N and the hex mesh gives 1.73 N. I used other meshes as well to check for convergence and these are the final values I am getting.

I tried searching online but could not find an explanation for why different meshes might give such different results. Can someone help me understand why the results are so different? I am observing similar behaviours in other projects as well. In such a situation, how do I determine which is the more accurate result?

The project is available here.
The runs in question are titled V23; Std 5.5; BL6; R0.05 for standard mesh and V23; hex_fine for the hex mesh.

Thanks in advance,

I’m no expert here but when I look at some of your convergence plots, there are still things like domain and walls that haven’t balanced out yet. I would run the simulation longer or play around with the mesh a little bit. you should try running them to 2400(what I do with my simulations) instead of only 1000. (also try to use the standard mesh if you can with your project)

hope that helps and have a great day,
frank Lucci

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I agree with @FrankTheTank :smiley: Adding some pages too:

Best regards,

Thanks for the links and suggestions. I looked through my other projects as well and found that Uy and Uz tend to fluctuate quite significantly in domain and outlet. Sometimes it is bad in the other plots as well. Are there any changes I can make to improve this? The flows all have an inlet velocity in the x direction only.

Hey @rsudhaharan

HERE is a good explination on how the meshing approach differs bwetween Standard and HEX.

You might also want to try and increaseing your bounding box size so there is less chance of the wing being infleuencedby the slip walls.

Good luck,