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-   -   Extreme WIG simulation-reality results divergence (http://www.cfd-online.com/Forums/main/101542-extreme-wig-simulation-reality-results-divergence.html)

 Jeb51 May 7, 2012 07:44

Extreme WIG simulation-reality results divergence

Hello everyone,
I've been doing a project on modelling the Ground Effect with a NACA0012 aerofoil for my final year and have found that at a h/c value of 0.1 the numbers simply don't make sense. Between 1.0 and 0.2 they match the experimentally established values well but at 0.1 things go horribly wrong. I've checked my boundary conditions and they're the same as all the others and I can't explain why this has occurred.

Here are the numbers from 0.2:
Angle of attack: 4 degrees
Lift: 113.31N
Drag: 17.71N
Cl: 0.43525
Cd: 0.06803

h/c = 0.1
Angle of attack: 4 degrees
Lift: -22891.56N
Drag: -239.04
Cl: -87.9323
Cd: -0.918214

Does anyone know anything that might be able to explain what's happened here?

Thanks,
Jake

 alireza_b May 9, 2012 06:01

Hello
when h/c=0.1, (extreme ground effect) negative lift can be found.
if you increases your angle of attack, you will see positive lift.
albeit:
in many of papers reported different data.for example positive lift in Ahmed paper and negative lift in moore papre. (for symmetrical airfoil)

 Jeb51 May 9, 2012 06:48

The issue here isn't that it's negative, I expected that from looking at published data. The problem is the magnitude of it. I'm getting aerodynamic efficiencies of 90 upwards. I can't explain how the simulation has diverged so far from the expected values as given by the material I'm comparing to.

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