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Steven March 10, 2008 12:11

Strange problem
 
Hi

Thanks to all response so far on this forum, especially the few regualr posters..

I have two idential simulations, both of an airfoil, both have exactly the same setup (mesh spacing etc)

There is one difference, in one simuaiton the airfoil it self is inclined to simulate AOA and on the other the incline is simlated by cartesian velocity components. In both cases the inlet is a half cylinder on the front of a rectangualr tube (aka windtunnel).

The inclined airfoil shows seperation (does not totally converge due to transient effects) and resonable lift and drag quantites. The cartesian simulation does not show seperation and also the drag value is negative ie the wing produces thrust?! The wind tunnel is much bigger than the model so wall effects should noot be an issue.

Ive been told the method of using cartesian velociies is fine but why is there this massive difference??

Thanks in advance (again!)

Steven

Glenn Horrocks March 10, 2008 17:47

Re: Strange problem
 
Hi,

Could it be that your simulation mesh is not big enough? How close are your inlet and outlets to the arifoil?

Glenn Horrocks

Steven March 11, 2008 05:23

Re: Strange problem
 
Hi

Thanks for the response, If you imagine a cylinder with radius 12.5 x the chord length around the leading edge for inlet and then a tube that comes of the cylinder at a tangent and stretches 12.5 times the chord downstream. Basically there is 12.5 x the chord lenght up/downstream and above/below.

Both simulations have this geometry and also have same space facings on the airfoil, defualt body space etc. It seems strange, the flow over hte wing in both cases should be relativly the same AOA but the result is not the same.....

Thanks

Steve


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