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Old   April 3, 2015, 06:15
Default CFD_external aero problems
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Argyris Apost
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Hi everyone,
i am new to ANSA and i am interested in making a CFD study of a simple car.
In order to correctly predict separation regions i am using K-w SST model. For this to work i choose y+ 11 so the first height is 0.25mm. But when i create the layers all the cells of the road violate the aspect ratio criterion, even when i make it 100, and non orthogonality.

Surface mesh of the car: min 5mm max 20mm
Windtunnel: 5mm-300mm
Sizebox_around_car: max surf:30 max vol:30
Sizebox_wake:max surf:40 max vol:40

I've tried many things such as making different layers for the road with first height cell 2.5mm but then i had skewed elements between the layers of the car and that of the road.
I 'm interested in a 6-8 million cell mesh. Any advice about how to solve these problems and what are the best sizing for the mesh would be helpful.

Thanks in advance,
Argyris
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Old   July 31, 2015, 10:43
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Lefteris
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Hi Argyris.

Late reply, you've probably already solved the issue which I think doesn't have to do with ANSA.

I think that the Aspect Ratio of the cells inside the boundary layer could be in the order of 10^3 not just 100. You can live with that I guess. If not, you can increase the number of points in the longitudinal direction but you'll end up with a massive cell count.

Out of curiosity, why y+=11? It seems quite odd. I mean, if you are to use such a small value, why not go down to 1 as Menter suggests for his model? (even though the formulation in Fluent is supposed to be y+ insensitive. And also the underlying assumption is that you use fluent, right?)


Best Regards,
Lefteris


Quote:
Originally Posted by Argyris View Post
Hi everyone,
i am new to ANSA and i am interested in making a CFD study of a simple car.
In order to correctly predict separation regions i am using K-w SST model. For this to work i choose y+ 11 so the first height is 0.25mm. But when i create the layers all the cells of the road violate the aspect ratio criterion, even when i make it 100, and non orthogonality.

Surface mesh of the car: min 5mm max 20mm
Windtunnel: 5mm-300mm
Sizebox_around_car: max surf:30 max vol:30
Sizebox_wake:max surf:40 max vol:40

I've tried many things such as making different layers for the road with first height cell 2.5mm but then i had skewed elements between the layers of the car and that of the road.
I 'm interested in a 6-8 million cell mesh. Any advice about how to solve these problems and what are the best sizing for the mesh would be helpful.

Thanks in advance,
Argyris
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