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Convergence: doesn't converged after 800k iterations

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Old   February 19, 2016, 11:22
Default Convergence: doesn't converged after 800k iterations
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Reza Rohani
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Hi

I try to simulate a dual throat nozzle in 2D. I reached flow pattern but my case doesn't converged after 800k iterations. Which part of my solution is wrong?

here is my cas & data files:
https://drive.google.com/file/d/0By1...ew?usp=sharing

my solution setup:
Density based, steady, planar
Energy: on

material: Air, ideal gas, viscosity; Sutherland

viscous model:
k-epsilon(2eqn) Realizable
wall treatment:
scalable wall function

solution methods:
Implicit, Roe-FDS, Least square cell based, flow;second order upwind, Turbulent kinetic energy;second order upwind, Turbulent dissipation rate;second order upwind,


Thanks in advance
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Last edited by rohani; February 19, 2016 at 11:40. Reason: adding files links
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Old   February 21, 2016, 01:23
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arshia
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hi ,
what problem you have during convergency??
what accuracy you want??
how is your residuals now??
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Old   February 25, 2016, 16:52
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Reza Rohani
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residuals oscillate, they are under e-3 but solution isn't converged
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Old   February 26, 2016, 05:55
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Cees Haringa
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On what basis did you conclude lack of convergence?
That something doesn't converge doesn't mean it's wrong. It means that the set of equations cannot be properly solved.
You can try a denser mesh, might help. Or try to improve on mesh quality (I don't know what the quality is now, so maybe this is irrelevant).

The setup you have is quite complex, including quite a lot of physics, so I can very well imagine it is hard to converge. For stability, it may help to run transient instead of steady. If your problem is steady, the transient solver will still converge to that steady state, but it may do so in a more stable way.

Also, maybe it helps to start with regular k-e (in my experience, REA is more accurate but less stable), and with first order discretization first - once that converged, switch to 2nd order.
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2d flow, convergence, fluent 15.0, nozzle simulation

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