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How to reduce the value of "Cell Non-Orthogonality" when creating the boundary layer

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Old   October 29, 2021, 08:38
Post How to reduce the value of "Cell Non-Orthogonality" when creating the boundary layer
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hirota tomohiro
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Hello, everyone.

I am currently trying to create a calculation grid using Pointwise for the case where fins are added to a hull.

But the problem is that
I am trying to create a boundary layer grid around the hull and fins using T-Rex, but the problem is that when I try to initialize the grid, it stops. The problem is that when I try to create a boundary layer grid around the hull and fins using T-Rex, it stops at initialize, and when I then check the created grid, the Cell Non-Orthogonality values are very high (88 or 89), so I am not able to create a grid that can be used for calculations.

The attached photo is a photo of the fin area when the Cell Non-Orthogonality value is high.
If we make Δs smaller, the T-Rex will not be stopped and the Cell Non-Orthogonality value will be less than 80, but this is not enough for the desired boundary layer thickness.

If anyone knows how to create a smooth boundary layer between the fin and the hull, could you please let me know?
Any advice would be appreciated.
Best regards.

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Old   December 30, 2021, 09:59
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Ali İhsan İşgüder
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Hi Hirota,

This can be the most common issue probably for the creating boundary layer on the acute angle between hub and blade.

If you're mentioning cells on the acute angle between hub and blade, Imho;

Firstly, u can decrease spacing on the root connector of the blade. (or can be increased dimension, you know.). By this way, while T-Rex algorithm is running, cells that come from the root connector, earlier switch to isotropic.
And another my own solution parameter is CollisionBuffer. I give 4 or 6 to this parameter to avoid non-orthogonal cells. Generally, 4 is enough for me.
Of course, the edge lengths ratio on adjacent surfaces must be acceptable. Because, layers coming from bigger cells on the surface superimpose over the little ones, on running T-Rex.

Otherwise, If you're mentioning the blade surface. I had a problem like this too;

Sometimes, when ı run Trex, Trex stops at the first layer as soon as it starts. And it then goes on processing. And when I check the cell quality at end of the process, I m see "splitted trex cells". I fixed this problem by changing global tolerance values on the properties tab.

I hope I could help. Good luck!

Quote:
Originally Posted by hirota View Post
Hello, everyone.

I am currently trying to create a calculation grid using Pointwise for the case where fins are added to a hull.

But the problem is that
I am trying to create a boundary layer grid around the hull and fins using T-Rex, but the problem is that when I try to initialize the grid, it stops. The problem is that when I try to create a boundary layer grid around the hull and fins using T-Rex, it stops at initialize, and when I then check the created grid, the Cell Non-Orthogonality values are very high (88 or 89), so I am not able to create a grid that can be used for calculations.

The attached photo is a photo of the fin area when the Cell Non-Orthogonality value is high.
If we make Δs smaller, the T-Rex will not be stopped and the Cell Non-Orthogonality value will be less than 80, but this is not enough for the desired boundary layer thickness.

If anyone knows how to create a smooth boundary layer between the fin and the hull, could you please let me know?
Any advice would be appreciated.
Best regards.

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