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High Frequency Residual Oscillation in Axisymmetric with Swirl Simulation

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Old   July 8, 2013, 08:25
Default High Frequency Residual Oscillation in Axisymmetric with Swirl Simulation
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I am simulating heat transfer of fluid flowing through two concentric cylinders, with the inner cylinder rotating (specified wall temperature and rotating speed) and outer cylinder stationary (adiabatic wall). I simulated the problem with 2D axisymmetric with swirl in FLUENT. I followed guidelines in FLUENT documentations for swirl flow as below.

1) Realizable k-e model with enhanced wall treatment
2) Use fine mesh (y+max<10)
3) Start simulation with axisymmetric solver with zero rotating speed.
4) Switch to axisymmetric with swirl and defining the rotating speed.
5) Solve turbulent and swirl velocity equations only.
6) Then solve turbulent and flow equations only.
7) Then solve all equations, e.g. energy, turbulent, swirl velocity, flow.

I also ran my simulation with lower rotating speed first and then increasing the rotating speed slowly by repeating step 5 to 7, as suggested in FLUENT documentations. I also used recommended relaxation factors by FLUENT documentation, e.g. 0.3 for pressure and 0.8 for swirl.

However, I still got high frequency high amplitude oscillation in residuals (continuity, velocities, etc) although the residuals are decreasing slowly. It seems that the solver is unstable. Is there other better way to get rid of this problem and have more stable simulation?

Thank you in advance.
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