# Converge the numerical result

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• Last Post 14 December 2017
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José Mantovani posted this 08 December 2017

Gentlemen, I am trying to converge the value of the numerical result of the lift coefficient  for the experimental result of the airfoil S1223. I've tried it in several ways and am getting values between Cl = 0.95 and Cl = 0.98, but the experimental value is Cl = 2.23. This for conditions of approximately Re = 380000 and an angle of attack alpha= 10 degrees. In my opinion the problem is the mesh, particularly at the trailing edge of the airfoil ... How can I improve the mesh in this region? I think that if a simulation was done in the edX course for a validation case of the NACA0012 airfoil with a relatively simple mesh and cells similar, we can see in below image, in the trailing edge region, I can also obtain a numerical result close to the result experimental, performing knit procedure in the same way ...

Or does anyone know what can be done so that the value approaches the experimental value?

Gentlemans, thanks for help and attention!

peteroznewman posted this 08 December 2017

Mantovani,

If you slice the surface at the trailing edge, you can get good quality elements.

Regards,

Peter

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peteroznewman posted this 09 December 2017

Here is that technique applied to S1223.

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José Mantovani posted this 09 December 2017

Thank's so much Peter! Very nice!!!

peteroznewman posted this 14 December 2017

Mantovani,

I read Vishal's answer to your other question, and watched the video he recommended and learned how to calculate the first element thickness using a Y+ calculator. For your Reynolds number and the air properties in Fluent, I got a first layer thickness of 5.6e-2 mm. The video also used 60 layers of inflation. You should update your mesh to these values.

Regards,

Peter

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José Mantovani posted this 14 December 2017

But Peter, I need update my mesh ou the mesh you sent me by email?

peteroznewman posted this 14 December 2017

Yes, I just watched that video this morning, didn't you watch it last week?

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José Mantovani posted this 14 December 2017

I had seen yes, even tried to apply my meshes, the values that I obtained in this calculator of Y +. I run the simulations here and the value was close to the experimental one, it's acceptable, I'll change it and see it gets even closer. Many thanks for the help Peter! Really, thank you so hiper very much! Come here to Brazil for we drink some beer! hahahahaha

Hugs.

peteroznewman posted this 14 December 2017

I have been fighting with inflation and gave up. I am now doing face meshing with biased edge sizing. I have the first layer thickness < 0.05 mm.

I have a nice "inflation" layer manually created after slicing the geometry.

I extended the domain to the size recommended in the video.

I'll send you this file.

Cheers,

Peter