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-   -   Problem in the flow calculation around airfoil (https://www.cfd-online.com/Forums/openfoam-solving/59141-problem-flow-calculation-around-airfoil.html)

 swlee February 11, 2008 19:34

Dear all, I'm calculating l

Dear all,

I'm calculating lift and drag for 2d airfoil(aoa is 6 degree). I've already checked and followed the other posts. But, I didn't get a resonable result with icoFoam(or turbFoam) and potentialFoam. My problem was just successed with simpleFoam. Here are the image of my calculation domain and the results with strange velocity at the trailing edge.

http://www.cfd-online.com/OpenFOAM_D...ges/1/6651.jpg
http://www.cfd-online.com/OpenFOAM_D...ges/1/6650.jpg
http://www.cfd-online.com/OpenFOAM_D...ges/1/6652.jpg

This grid was combined by several multi-block sub domains and tested by "checkMesh" utility. checkMesh said like this,

Checking geometry...
Domain bounding box: (-0.5 -2 0) (0.75 1 0.01)
Boundary openness (-1.82318e-18 3.41252e-19 1.9459e-16) OK.
***High aspect ratio cells found, Max aspect ratio: 20349.8, number of cells 2204
<<Writing 2204 cells with high aspect ratio to set highAspectRatioCells
Minumum face area = 8.4915e-11. Maximum face area = 0.00210556. Face area magnitudes OK.
Min volume = 8.4915e-13. Max volume = 2.10556e-05. Total volume = 0.0374918. Cell volumes OK.
Mesh non-orthogonality Max: 85.8056 average: 17.6136
*Number of severely non-orthogonal faces: 176.
Non-orthogonality check OK.
<<Writing 176 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 3.21164 OK.
*Edges too small, min/max edge length = 1.14018e-06 0.0875403, number too small: 2014
<<Writing 2414 points on short edges to set shortEdges
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : average = 1 min = 1
All face flatness OK.

Failed 1 mesh checks.

Is there anyone can give me an avice for this problem?

Sung Wook

 swlee February 11, 2008 19:51

What is the problem in the abo

What is the problem in the above calculation?

Does anyone have some advice that I should check?

Sung Wook

 pbo February 12, 2008 01:25

Hey Sung, your mesh at the

Hey Sung,

your mesh at the trailing edge is kinda rough!
Only 2 cells on the trailing edge (TE) base is not enough. Try to have at least 10-ish cells there.
Also make sure the LE and TE spacings on the upper and lower surfaces are of the order of 0.001*chord or less. If it's not already the case, try as well to pack at least 100 cells on each of these surfaces (with the previous constraints at the TE and LE).
Also the quality of your mesh could easily be improved with a C-grid instead of a O-grid.
If you want to stick to the O grid, use some kind of laplacian smoothing during the grid generation to make it a bit more orthogonal, and/or use at least 3 non-Orthogonal correctors for the pressure equation. You'll get the computation started with 1st order upwind schemes for the convective terms and perhaps some limited laplacian schemes. Later on, if convergence settles in, switch to 2nd order.

Good Luck,

Patrick

 darioth September 9, 2010 11:51

Hello Sung, Did you fix your problem? I am trying a 0015 with potentialFoam and I have the same high velocities in the t.e.