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-   -   X-Foil Airfoil with gurney? (https://www.cfd-online.com/Forums/main/91926-x-foil-airfoil-gurney.html)

 Yur August 26, 2011 11:33

X-Foil Airfoil with gurney?

Dear forum members,

I'm working on a double element wing, and I would like to know if there is a way to get reliable results for a wing with a gurney?

As I know that it's not possible to simulate multi element airfoils in X-Foil, I separate them and also simulate separatly, but on some way, X-Foil doesn't get the right chord lenght. So the simulation totally fails.

I organize all coordinates in Excel, so maybe there are some tricks to do it better.

Thanks.

 truffaldino August 26, 2011 13:32

Why do not you fix the chord lenghth of each airfoil and change reynolds number instead?

What problem are you solving exactly? Is it a gurney flap which is separated from main airfoil? X-foil could be not a good choise for such kind of problems.

Truffaldino

 Yur August 27, 2011 04:23

Well is there a way to change the chord length in X-Foil? The gurney is attached to the foil, so there are no gaps.

The problem is that X-Foil thinks that the gurney flap, is the chord length and doesn't recognize the LE.
The thing I would like to know is, if there's a proper way to put in the coordinates in Excel to let X-Foil recognize the right LE and TE.

Thanks.

 truffaldino August 27, 2011 05:26

1 Attachment(s)
Quote:
 Originally Posted by Yur (Post 321875) The problem is that X-Foil thinks that the gurney flap, is the chord length and doesn't recognize the LE. Thanks.
I have just added a 2% gurney flap to naca0012 and loaded it to x-foil: everything seems to work. Xfoil recognizes LE and TE.

Bad panelling coul be also eliminated by tiny rounding the right angle.

For sure, your coordinate loading problem can be easily fixed, but it is not the main problem with x-foil. The real problem is more fundamental: the methods X-foil uses are not fitted for analyzing gurney flaps, and results you will get could have nothing to do with reality.

X-foil is based on integral boundary methods that do not handle vorticity regions that you have at gurney flaps, corners, steps etc.

Truffaldino

 jemo January 17, 2014 06:32

Quote:
 Originally Posted by truffaldino (Post 321884) I have just added a 2% gurney flap to naca0012 and loaded it to x-foil: everything seems to work. Xfoil recognizes LE and TE. Bad panelling coul be also eliminated by tiny rounding the right angle. For sure, your coordinate loading problem can be easily fixed, but it is not the main problem with x-foil. The real problem is more fundamental: the methods X-foil uses are not fitted for analyzing gurney flaps, and results you will get could have nothing to do with reality. X-foil is based on integral boundary methods that do not handle vorticity regions that you have at gurney flaps, corners, steps etc. Truffaldino
Can you share the dat file?

 truffaldino January 17, 2014 14:44

1 Attachment(s)
Quote:
 Originally Posted by jemo (Post 470481) Can you share the dat file?
Here it is. you could do fine repanelling (using standard x-foil/xflr procedures) closer to the flap

 lovecraft22 January 17, 2014 15:13

I agree with truffaldino, what you are doing cannot be done with x-foil for two reasons:

1. It cannot handle multi element wings and the behavior of a main plane + flap all together is totally different from the behavior of each one of them alone since they influence each other.
2. A gurney tab works because of the flow separation it creates and this is not handled by X-foil

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