Reversed flow over airfoil in ANSYS

shoaib_aero · April 30, 2014, 11:29

I am simulating flow over an RAE2822 airfoil with forward sweep configuration.
After applying all boundary conditions, when I run the solver, everything is normal except in post processing, the lower pressure is on the lower camber of airfoil instead of upper camber. The values seem logical and correct except that they should be on opposite cambers. I am confused about this.

Any suggestions and advice would be really appreciated.

ghorrocks · April 30, 2014, 19:01

Are you sure you have the angle of attack right? The airfoil looks pitched down to me, and that would explain the low pressure on the bottom side.

shoaib_aero · May 1, 2014, 02:54

It is a twisted wing where the tip is at angle of 11 degree with the root. And the wing is kept at an angle of attack of 1.5 degrees.
Even if the wing is pitched down, the pressure has to be lower on the upper surface to produce lift.
The situation in the picture would mean that the wing will drop down more instead of lifting in this condition which makes no sense.

ghorrocks · May 1, 2014, 09:10

If the wing is twisted then one section of the wing can produce upwards lift and another produce downwards lift.

shoaib_aero · May 1, 2014, 21:43

I changed the angle of attack of the wing to 3 degree and still getting the same result.

Any advice

ghorrocks · May 1, 2014, 21:50

I still think what you are seeing is real.

But your question really is "I think my simulation is inaccurate". That is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

There are millions of benchmark results for flow over airfoils. You should do a validation that you can accurately produce the lift and drag of a foil you have good benchmark results on before attempting your configuration. Otherwise how do you know whether your result is accurate or not? And this is exactly the problem you are now in.

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April 30, 2014, 19:01		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Are you sure you have the angle of attack right? The airfoil looks pitched down to me, and that would explain the low pressure on the bottom side.

May 1, 2014, 02:54		#3
shoaib_aero New Member Shoaib Join Date: Apr 2014 Posts: 3 Rep Power: 12	It is a twisted wing where the tip is at angle of 11 degree with the root. And the wing is kept at an angle of attack of 1.5 degrees. Even if the wing is pitched down, the pressure has to be lower on the upper surface to produce lift. The situation in the picture would mean that the wing will drop down more instead of lifting in this condition which makes no sense.

May 1, 2014, 09:10		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If the wing is twisted then one section of the wing can produce upwards lift and another produce downwards lift.

May 1, 2014, 21:50		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I still think what you are seeing is real. But your question really is "I think my simulation is inaccurate". That is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F There are millions of benchmark results for flow over airfoils. You should do a validation that you can accurately produce the lift and drag of a foil you have good benchmark results on before attempting your configuration. Otherwise how do you know whether your result is accurate or not? And this is exactly the problem you are now in.