SimScale CAE Forum

Boundary layer inflation thickness


#1

Hello

i m doing simulation in which i need to set minimum thickness of boundary layer at lets say 6mm. Its absolutely neccesary to do this for me. But when i try to add layer inflation i cant set total thickness as i can in other cfd softwares.
I can only set minimum thickness - this is minimum thickness of 1 layer or all of them combined ?
Final layer thickness - this is thickness of layer that is furthest from surface right ?

So i m supposed to calculate total thickness by diving final layer thickness by expansion ratio 10 times ( in case i add 10 layers) ?

Thanks for help


#2

Hi @AnetaNovak!

To my knowledge the minimum length describes the overall thickness of all layers and the final layer thickness is the one furthest from the wall. Feel free to share your project here so that we can make some comments on it and give you some suggestions. Inviting @DaleKramer, @Retsam, @anirudh2821998 as well as @Get_Barried!

Best,

Jousef


#3

Hi @AnetaNovak

@jousefm is perfectly right regarding the minimum thickness of boundary layer and minimum thickness. If you want to have a total layer thickness of 6mm here are following steps that you should perform-

  1. Decide the thickness of the farthest layer(first layer thickness) and use the expansion ratio to calculate the size of cells nearest to the boundary(the thickness of each layer will be in geometric progression). You can get the thickness of each layer which you can simply add to check if the sum of thickness is 6mm or not.
    inflation%20layer

  2. The minimum thickness is just a limit that will determine if the inflation layer will form or not. If the overall thickness goes below this value then the layer addition step will stop and no boundary layers are added. So there is no need to change this value as it will not go below Zero :rofl:. You should focus on the number of layers, the expansion ratio and first layer thickness to generate a successful inflation layer.

Thanks
Ani


Mesh study external aerodynamics problem
#4

Great ! this works … but
when i create inflation layer look what happens


Boundary layer sort of collapses. What i can do with this ?

https://www.simscale.com/projects/Novak_Ondrej/183034_copy_copy/ (wing_F6 mesh)


Mesh study external aerodynamics problem
#5

Hi @AnetaNovak

If you look carefully at the regions where inflation layers were not formed completely, then you will realize that in these area your radius of curvature is very small and the normal vector of an element on the surface changes its direction rapidly at a very short distance along the wall surface. This cannot be solved completely but you can give a try by adjusting the mesh features that are related to cell concavity and other such angles.

Inkedimage%20(1)_LI


#6

@AnetaNovak Here is my method to do that, but be careful about my final mesh quality warnings…


#7

Tryed it and its not helping in my case … i will work on and let u know if it works


#8

Hi @AnetaNovak,

A suggestion would be to add a small round to the trailing edge of the aerofoil. That will better allow the layers to conform without significantly compromising your results.

Cheers.

Regards,
Barry