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Vortex Generator modelling, RANS, LES or DES?

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Old   December 4, 2022, 02:39
Question Vortex Generator modelling, RANS, LES or DES?
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My team and I are designing a plane and want to know the effects of VGs on lift and drag, but they are tricky to model, especially when combined with mild flow separation on the wing.

For what I've read general RANS doesn't work well on situations with flow separation and turbulence, even more so when you need to model it precisely. Despite that, I could find some literature saying that RST was a good model for the circulation on VG generated eddies.
I have ran one sim and convergence is nonexistent. Our model is 80M cells for an 18 ft wing. We are limited in terms of computational expense so we have to minimize the resources needed and maximize reliability of our results so that they can be referenceable in the future.

Would it be better to try and refine the mesh on the RST sim, or try DES or LES? How many orders of magnitude more expensive would it be to do DES or LES?
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Old   December 5, 2022, 17:04
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I presume that your wing flow calculation succeeds without vortex generators. If that is so, I would build a smaller model with just one of the vortex generators. This model could have much smaller cell counts. With this model, experiment with grid generation options as well as RST, DES and LES solution models.
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Old   December 5, 2022, 23:08
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Quote:
Originally Posted by wkernkamp View Post
I presume that your wing flow calculation succeeds without vortex generators.
It does with a Spalart-Allmaras steady sim, but not with unsteady RST. I don't think the scalability of turbulence is something we can rely on. I suppose the smaller test model is just to check validity and performance of the CFD and not the wing right? And then choose which model to use with the full-scale wing?
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Old   December 5, 2022, 23:17
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Quote:
Originally Posted by trans(sonic)_pride View Post
I suppose the smaller test model is just to check validity and performance of the CFD and not the wing right? And then choose which model to use with the full-scale wing?

Yes, to quickly check which grid and method works with your VG.


What does the steady calc look like with Vortex Generators? I have no idea what your VGs look like, but in general they are expected to create some steady vortex to sweep the boundary layer.
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