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-   -   Farfield Boundary Problems (http://www.cfd-online.com/Forums/fluent/111996-farfield-boundary-problems.html)

Tam January 19, 2013 10:45

Farfield Boundary Problems
 
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I was wondering if someone could answer a problem I've been having within Fluent for the last two weeks.

I've spent far too long playing with the setting to try to get a convergence, and was wondering if someone would know what was going on.

I built a mesh in ICEM to fit around a NACA0012 airfoil in order to simulate a low-reynolds number wind tunnel test. It followed the advice given in the 2D Hexa meshing Youtube video, generating a Farfield BC. After numerous attempts, the solution wouldn't converge. I attempted adapting the under-relaxation factors but to no avail, as the residuals kept oscillating.

The conditions of the test are as such:
Farfield BC: Velocity 10m/s (Mach Number 0.0303)
If I'm correct, FF deals with absolute pressures, so the operating conditions was set to 0Pa and the FF BC had a gauge pressure of 1 bar.

Turbulence model being used was k-omega SST. Therefore, I was aiming for a y+ of around 1 and hence the cell spacing out of the airfoil was around 0.00003 (as stated by the pointwise y+ calculator).
I used both least squares and green node based solution methods, neither were successful.

On investigation I found some peculiar results. There was no stagnation point and no recognisable pressure gradient around the airfoil. The temperature at exit had shot up to 5000K and the velocity at inlet was not as expected, see picture attached.

I've taken this to three different people with Fluent experience, but none could explain what was happening with my set-up. I am hoping for someone to be kind enough to lend a hand.

Cheers.


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