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Oscillating residual, lift and drag values

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Old   July 8, 2015, 13:16
Default Oscillating residual, lift and drag values
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Aidan
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Hi,
I'm just wondering if anyone knows what is going on here (see attached)? and how I may go about resolving it? (note, this is in Ansys Fluent)

I'm trying to calculate Coefficient of lift for a NACA 0012 airfoil.
Details: Mach Number 0.26, Angle of attack 8 degrees, Wind speed= 87.64m/s, airfoil length 1m, Ideal gas, Y+=30,
BCs: Inlet = velocity inlet, Upper surface = Pressure Far-field, Lower surface = Pressure Far-field, Outlet = Pressure Far-field.

The program worked fine when I used 17000 nodes, but when I increased the node number, I left the program running for hours expecting it to converge and came home to find that the residual, lift and drag values are oscillating wildly (see "oscillating" attached). The attached "oscillating1" shows a more detailed look at the first 150 iterations, before the oscillations really took off. Whilst the attached shows the oscillations for 54,000 nodes, similar graphs were present at 25,000 and 35,000 nodes.

I really appreciate any assistance you can offer
Aidan
Attached Images
File Type: jpg oscillating.jpg (34.5 KB, 11 views)
File Type: jpg oscillating1.jpg (59.4 KB, 6 views)

Last edited by aptahaney; July 8, 2015 at 15:27.
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