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puzzling asymetrical flow seperation

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Old   January 20, 2025, 15:54
Default puzzling asymetrical flow seperation
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KTG
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Hello Foamers,


I would like to get some ideas on troubleshooting a simulation. I am using simpleFoam with a steady state, incompressible, K-Omega turbulence model to solve for flow around a round object on a flat surface. Its all pretty basic, and I made the case file by modifying the motorbike case to my geometry and adding log-layer ATM boundary conditions from another openFoam tutorial case. I ran the simulation out to 6000 iterations, which it more than enough to get the forces on the object to converge. Mesh quality passes all of openFoam's default checks on the motorbike case. The residuals look pretty good, though k is bounded:


Code:
smoothSolver:  Solving for Ux, Initial residual = 2.62633e-08, Final residual = 8.03931e-09, No Iterations 5
smoothSolver:  Solving for Uy, Initial residual = 4.63252e-06, Final residual = 4.03726e-07, No Iterations 11
smoothSolver:  Solving for Uz, Initial residual = 2.68199e-06, Final residual = 2.64187e-07, No Iterations 10
GAMG:  Solving for p, Initial residual = 0.000317136, Final residual = 2.32092e-06, No Iterations 5
GAMG:  Solving for p, Initial residual = 4.24504e-05, Final residual = 3.94228e-07, No Iterations 4
GAMG:  Solving for p, Initial residual = 3.67113e-06, Final residual = 6.8369e-08, No Iterations 4
GAMG:  Solving for p, Initial residual = 6.22585e-07, Final residual = 9.66498e-08, No Iterations 1
time step continuity errors : sum local = 8.47094e-09, global = 7.78326e-13, cumulative = 4.38872e-08
smoothSolver:  Solving for omega, Initial residual = 3.27349e-08, Final residual = 6.15804e-09, No Iterations 2
smoothSolver:  Solving for k, Initial residual = 5.14389e-08, Final residual = 5.92594e-09, No Iterations 3
bounding k, min: -2.33935e-09 max: 2.13351 average: 0.492268
ExecutionTime = 8278.28 s  ClockTime = 8558 s
K and Omega use upwinding.



As you can see in the attached figure (yplus and near-surface streamlines), flow separation is uneven with respect to the wake of the very round, symmetrical object.



I would like to hear what things other people would try checking first when they see this issue. I have re-run this simulation a number of times and am pretty stumped at the moment...


Thanks
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Old   January 20, 2025, 22:33
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And the winner is - the wrong sign on the top boundary condition. I knew if would figure it out as soon as I posted that. I wish there was a way to delete these...
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Old   January 21, 2025, 12:35
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Aaaah - but others can learn from our mistakes ... and our fixes! To err is human, I think someone said.
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Old   January 21, 2025, 17:01
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Haha, well hopefully no one is learning from my poorly written sentences...
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