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-   -   Flows at High Angles of Attack (http://www.cfd-online.com/Forums/fluent/50846-flows-high-angles-attack.html)

Sarah C. March 12, 2009 05:59

Flows at High Angles of Attack
 
Hi,

I'm interested in flows around airfoils and wings at high angles of attack such as between -180 to +180.

I don't experience problems at normal angles (-10 to +20). At high angles, the flow is highly turbulent and the solution cannot converge at all. I use Rea-k and Spa-All turbulence models with Steady Density-Based Implicit Solver. I also tried Unsteady 2nd-Order Solver for airfoil at 50 degree angle of attack and got no converge. My grid is structured and created in Gridgen. It is sensitive to y+~1.

I would be happy for your suggestions about flows at high angles of attack.

Thanks,

Jason March 12, 2009 09:51

Re: Flows at High Angles of Attack
 
Well, what do you consider "converged"? At these high angles of attack you're going to have very large separation regions (this is now more of a bluff body problem than an airfoil problem). Separation is an unsteady phenomenon, and I would expect the forces and moments to bounce around rather wildly within a fixed range (something like a sphere or a flat plate would be better behaved because of the symmetry). The hard part would be running it long enough to ensure you've captured the full range of forces.

If you're looking for an "average" force then I would recommend monitoring the force each time step with an unsteady solver, run it for a LONG time and calculate the average from the output force monitor file.

Good luck, Jason

husker March 18, 2009 08:39

Hi,
 
You have explained what i need, very well.

Thanks for interest,


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