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CONVERGENCE (transient calculation)

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Old   March 7, 2004, 11:56
Default CONVERGENCE (transient calculation)
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Hi; I want to model an unsteady flow. In each time step many iterations(approximatly 400) must be done to reach convergence. On the otherhand the rate of convergency after some iterations become low in each time step. Should I increase each time step or decrease it? Note that I use PISO algorithm and now my time step is 5e-5 sec.

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Old   March 7, 2004, 14:49
Default Re: CONVERGENCE (transient calculation)
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Which model are your using? What equation doesn't converge?

Usually you can improve convergence reducing the underrelaxation factor of momentum equation to 0.5 or 0.4 and increasing a bit the underrelaxation factor of pressure (try 0.4 and, if this doesn't cause instability, 0.6).


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Old   March 8, 2004, 03:55
Default Re: CONVERGENCE (transient calculation)
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Hi; I want to model cavitation. Should I increase the mass fraction of non-condensable gas?
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