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Old   July 9, 2007, 09:13
Default steady state solution
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cfxdude
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Hi,

Does steady state solution depends on your initial guess?

cfxdude
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Old   July 9, 2007, 09:35
Default Re: steady state solution
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Gert-Jan
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A complete converged solution (i.e. constant values in monitoring points, imbalances=0, RMS residuals < 1e-6) should not depend on initial guess.

Gert-Jan
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Old   July 9, 2007, 09:57
Default Re: steady state solution
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cfxdude
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Hi,

What you are saying is that If 1e-5 < RMS residuals (pressure and velocities) <1e-4 and 1e-6 < RMS residual (k-e turb) < 1e-3 is not a steady state solution, or the solution depends on the initial guess?

In my case the velocity of the monitored point is fluctuating between 0.25 - 0.35 m/s (11000 iteration), but the volume average velocity is constant. which one is the correct steady state indication.

Thanks.

cfxdude
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Old   July 9, 2007, 10:31
Default Re: steady state solution
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Gert-Jan
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When your monitoring values are fluctuating, you won't have a steady state situation. Looks like your problem is time dependent.

Gert-Jan

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Old   July 9, 2007, 10:38
Default Re: steady state solution
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cfxdude
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So constant volume average velocity is not the steady state indication.

Is there any book or paper about these, I am looking for some thing written.

Thanks for your time.

A.A.
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Old   July 9, 2007, 18:20
Default Re: steady state solution
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Glenn Horrocks
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Hi,

For a small number of situations the steady state solution does depend on the initial guess. I have seen some flows were the Coanda effect caused a jet to stick to one wall or the other depending, then settle down to a steady state solution. Which wall the jet stuck to depended on the initial guess.

In general, however, a fully converged solution is independent of initial guess.

Glenn Horrocks
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Old   July 9, 2007, 18:28
Default Re: steady state solution
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Italy
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If the velocity of the monitored point is fluctuating between 0.25 - 0.35 m/s after 11000 iteration, try to increase gradually the timescale. In this way you should obtain a non fluctuating velocity value.

Probably now you are reading some fluctuations of your domain; increasing the timescale works as a filter for this numerical fluctuations.

Bye

Alberto
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Old   July 10, 2007, 05:43
Default Re: steady state solution
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Helge
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Numerical fluctuations? You may damp out physical fluctuations by numerics. If you increase the time step you may stabilize the solution but you will not get a fully converged (grid independant and time step independant) solution.

I agree with Gert-Jan and Glenn
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