First layer thickness ignored

Hi all,

I am trying to set up a low speed aerodynamic simulation with the k-w STT turbulence model. I want to resolve the boundary layer fully, so I am inflating the no-slip walls. So far so good - I am very impressed by the user-friendliness of Simscale.

My estimated first layer thickness is 1.6e-5, I am using 20 layers, and the overall relative thickness of the inflations layer is 1.5, i.e. 150 mm according to the local mesh size. Now comes the interesting part: after running the first simulations, I noticed y+ was closer to 20. No problem, I adjust the first layer size with a factor of 20 - however, I get the same result: y+ is closer to 20.

Inspecting the mesh closer up, it appears that the meshing algorithm is ignoring the first layer thickness. All 20 layers show up, but for both settings, the first layer thickness is approximately 5e-4 (about a factor 20 too high, indeed…). I have been playing around with the mesh settings, but I have not been able to resolve this.

Things I have tried so far: using the ‘automatic boundary layer’ function, instead of the inflation layer under ‘refinements’, and reducing the overall thickness of the inflation layer. This does not resolve the problem, unfortunately.

Anyone run into this problem before? Seems like a minor glitch, but I can’t think of any solution. Thanks in advance!

Hello Arne
Thanks for reaching out to us here in the forum.
Can you please provide us with a link to your project so that we can have a look at it?

One idea that comes to me is that the free stream mesh at the layer might not be fine enough resulting in high volume ratio cells, and therefore the mesher cannot reach the lower limit.

Hi @SBlock,

Thanks for the quick reply! I actually found that the small feature repression was kicking in…

So for anyone else with this problem: small feature repression < initial layer thickness!

Great you found a solution. I therefore marked it as one.

Happy Simulation and good luck with your project.

Best regards Sebastian