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-   -   Improve Mesh quality - airfoil simulation (http://www.cfd-online.com/Forums/star-ccm/77365-improve-mesh-quality-airfoil-simulation.html)

Lukas84 June 21, 2010 11:19

Improve Mesh quality - airfoil simulation
 
Hello everyone,

I'm working on a NACA 0012 airfoil analysis in 2D at low Reynolds-Number (Re=1.6e^5, chord length= 0,25m, v=10 m/s) at different angle of attack. I'm using k,omega-SST turbulence model with segregated flow, implicit unsteady with a time step around 1e^-4 s, velocity inlet and pressure outlet, ideal gas (incompressible).
My problem is when i start the simulation it doesn't converge at all. The residuals increase rapidly, so do velocity (http://yfrog.com/muvelj), temperature, pressure etc. until a floating point exception error occurs.
I assume it has something to do with the mesh quality at the (blunt) trailing edge. Star ccm+ retracts the prism layers at the trailing edge(s. http://yfrog.com/jnhinterkante1j ) and the mesh quality close to the trailing edge is very bad to ( http://yfrog.com/j9cellqualityj --> threshold of mesh quality between 0 and 0.1 of the volume mesh before converting to 2D).
Can anyone help me with improving the mesh quality? I tried a lot like mesh refinement etc. but it didn't work. Any suggestions? If the problem has nothing to do with the mesh quality, what else could it be? btw, i checked for negative volume cells: There aren't anyone.
I hope someone can help :o

http://yfrog.com/jnhinterkante1j

JBeilke June 21, 2010 18:53

http://www.beilke-cfd.de/naca_0012_5_degree.sim.gz

Lukas84 June 22, 2010 04:19

Hallo Joern,

thank you for your quick reply. Can you explain me how to create a structured mesh like the one in your .sim-file in star ccm+? Or do you need to use another program for creating it? Do you have any idea how to improve the mesh quality in my unstructured grid, using e.g. polyhedral model with prism layers?

JBeilke June 22, 2010 15:41

The mesh was created with GridPro. I never tried it with ccm+. Before using GridPro I did it with prostar (many years ago), but it was not very comfortable to do :-)

abdul099 July 6, 2010 10:07

You can try to play around with the prism layer options. Try to increase the layer reduction percentage (ccm+ will decrease the number of prism layers on the trailing edge where the thickness is reduced) and increase the minimum thickness percentage (if the thickness would fall below this value, prism layer thickness wil be set to zero in this area).

Also try to refne the mesh near the trailing edge.

Best regards


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