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Question about Implicit Unsteady Solver and Maximum Inner Iterations

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Old   June 28, 2016, 05:55
Default Question about Implicit Unsteady Solver and Maximum Inner Iterations
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Greetings,

I am working on a Simulation of a Injection Nozzle Flow with Cavitation. Right now I've got:
  • Stagnation Inlet Boundary and an Outlet Pressure Boundary
  • Eulerian Multiphase (Fuel and Gas, for now both constant density) with VOF-VOF Phase Interaction and Cavitation
  • Solver: Implicit unsteady Solver
I've a question how i can identify the right time steps and maximum inner Iterations? Right now the residuals are swinging highly.


Another question: Is it possible to simulate a cavitating flow with the steady Solver? Because there i get convergence and the results are reasonable.


Thanks!
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Old   June 28, 2016, 06:01
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The time step can be deduced from your cfl number, reference velocity and minimum cell size i think; as for the inner iterations you should monitor a parameter and plot it as a function of iterations to see if it converges; if you give e.g 20 inner iterations but it converges after 10, decrease it to 10
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Old   June 28, 2016, 06:11
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If I understand you right, i can get identify the maximum inner iterations by an monitor plot. Is this possible with the residuals? Or can you give me an example how to.
Right now I'm testing it with max inner iterat. = 50 and the residuals aren't converging in the timesteps (see below attachment).

Thanks.
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Old   June 28, 2016, 07:05
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Yes you can simulate cavitation assuming the flow is steady,

sometimes you start with a steady solver and if you see vapor produced and remains constant and if the vapor is expanding/collapsing than you know to switch to the unsteady solver, and look for frequency or something else,
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Old   June 28, 2016, 08:57
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Another question: Is a third phase called "Air" needed in a Cavitation modelling?
Thanks!
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