CFD Online Discussion Forums - [ICEM] 2D boundary layer growth with blayer

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2D boundary layer growth with blayer_2d

Hello all,

After having seen a lot of posts on this forum, I have managed to use the blayer2D tool to create a boundary layer on a multi element airfoil. The 2D geometry contains a slat, a main wing and a flap. I am making the mesh in a optimisation loop so I use a script to create the mesh.

I am facing a problem of mesh quality at the trailing edge of my airfoils. The boundary layer thickness doesn't decrease and I then obtain very large cells at trailing edges. See pictures below and code to generate the BL. I also need to use the check mesh tool to remove the overlapping elements.

Code:

ic_set_meshing_params prism 0 law exponential layers 21 height 8.0e-5 ratio 1.1 total_height 0.0134 prism_height_limit 0 max_prism_height_ratio {} stair_step 1 auto_reduction 1 min_prism_quality 0.2 max_prism_angle 140 fillet 0.5 tetra_smooth_limit 0.2000000 n_tetra_smoothing_steps 10 n_triangle_smoothing_steps 5

Code:

ic_run_prism Airfoil12508.tin temp_prism0.uns prism.uns params Airfoil12508.prism_params log prism_cmd.log n_processors 2 init_dir_from_prev 1 smoothing_steps 0 first_layer_smoothing_steps 1 blayer_2d 1 fillet 0.1 ortho_weight 0.1 max_prism_angle 140 min_prism_quality 0.2 tetra_smooth_limit 0.2000 family {SLAT height 8.0e-5 ratio 1.1 n_layers 18} family {MAIN height 8.0e-5 ratio 1.1 n_layers 31} family {FLAP height 8.0e-5 ratio 1.1 n_layers 22} family FLUID

Thanks,

Jean.

did you try suggestiong from simon's tips and tricks:
https://docs.google.com/file/d/0ByIL...nBqTXBQT3pQMjQ

Hi,

Thanks. I didn't know this best practices presentation. There is some very useful stuff inside. I will try to apply it tomorrow.
I think this might be useful:

Quote:

If Min Prism Quality is too high, it
may adjust Max Prism angle down to
keep quality up, this will result in
pyramids near sharp trailing edges.
–> Common mistake

However it seems to be mainly for 3D geometries, whereas mine is 2D.

it does work for both. good luck

Hello,
I tried some of the tips but I can't get any improvements. The improvements are visible on my local computer (icem 15.0). However, using the same script on my cluster (icem 14.0) I still have the mesh shown above.

Is there a way to tell the BL growth to stop at sharp angles (sharp trailing edges or sharp 90° turn), that is applicable to icem 14.0?
I use for my BL growth:
max prism of 140
min quality from 0.0001 to 0.2 but no improvements are made

Thanks,

Jean.

Hello again,

I am still struggling on my 2D mesh creation.

This is my procedure:
1. Import airfoil points
2. Create curves for airfoil and farfield
3. Create 1 surface on all domain
4. Split my surface with the curves created (build topology is modify my curves with no control (creates, split, change name, delete control point so that the resulting curves are wrong))
5. Delete the surfaces inside my airfoil
6. Set general mesh parameters (global and per parts)
7. Set curves bunching parameters
8. Creates the unstructured mesh
(9. Create a prism boundary layer) (I also tried without but it is worst and I don't know how to control the expansion ratio from the airfoil without prism BL)
10. Check and fix mesh
11. Smooth mesh
12. Extrude 1 cell to run on CFX

I don't need an extremely precise mesh but I need a robust one giving reliable results. What are the main steps and parameters to create a simple unstructured mesh around my multi element airfoil with Icemcfd?

Edit: I have also found this document which has proven to be very useful: https://docs.google.com/file/d/0ByIL...TnM/edit?pli=1
However, I have trouble, again, to set y+. It is advised to leave free the initial spacing so that transition between boundary layer and rest of the mesh is smoothen. However, it seems that the redistribute prism tool is ineffective in 2D. Any suggestion to obtain a good quality BL respecting boundary layer thickness and initial spacing to obtain y+ around 1?

Thanks a lot.

Jean.

Hello again!

I am still having troubles with my hybrid mesh. Can anyone tell me why I have those waves on my boundary layer prism on the pricture.

EDIT: This exactly what I want to achieve: http://grid-generation.blogspot.co.u...1_archive.html but no matter how I set up the parameters of 2dblayer, I always get bad BL.

If the prism layer is not possible, what is the method to specify a first cell spacing and expansion ratio using only tetra?

Thanks again,

Jean.

Anyone to help a lost soul on a problem with no tutorials all over internet?