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 blume83 August 23, 2011 05:38

starting vortex

Does anybody know, for starting vortex past an Airfoil, which BCs and also which strategies for time-dependent velocity should be used?

 cfdnewbie August 24, 2011 15:15

Are you talking about the starting vortex simulation wise (i.e. starting from a non-physical initial field) or about the physical starting vortex from an accelerated airfoil??

huge difference :)=

Cheers!

 blume83 August 25, 2011 03:59

I want to see what happend to the fluid past an Airfoil, if there is an acceleration in the fluid,
I do not know how I should increase the velocity and which BCs should I use?
Is special strategy necessary?

many Thanks!

 cfdnewbie August 25, 2011 07:09

so you are trying to simulate the flow from an airfoil at rest up to some given speed? like an airplane taking off?

I have seen that done a few times, almost always with a moving mesh approach, but I'm no expert on this...

What happens if you do sth like this: inflow BC: freestream, starting from u=0 to some u (of course, make sure your time discretization can handle this!!), outflow: extrapolation outflow. That would be my first try...

 blume83 August 25, 2011 09:00

I run this case with different BSc, but I could not get a good result. Do you think I should add a source term in NA-ST equations? or do you have another Idea?

 cfdnewbie August 25, 2011 10:18

Quote:
 Originally Posted by blume83 (Post 321558) I run this case with different BSc, but I could not get a good result. Do you think I should add a source term in NA-ST equations? or do you have another Idea?
could you describe what you mean by "not good results"?? with what did you compare your results? what scheme are you using?

 blume83 August 25, 2011 15:24

I compare my results with the experiment. I expect to have a vortex at the trailing edge (that agrees Helmholz theory too), but my results are the same as the results optained without the initial acceleration. I use DG (discontinous Galerkin) method.

 cfdnewbie August 25, 2011 15:41