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Old   April 10, 2012, 06:49
Default Convergence Problem
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Rob Hulme
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Hi, I am simulating an induced air flow system where air from a compartment is drawn out using exhaust gases. The values for the inlet conditions (Mass flow rate Kg/s and density Kg/m3) have been determined using an experiment.

I have now ran numerous iterations but the model is not converging. An image of the model is attached.

I am guessing the probe position and number of iterations are the main factors. I am using a SARAH value of 0.001 to try and aid the convergence.

Any advice would be greatly appreciated.
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File Type: jpg Simulation.jpg (27.0 KB, 64 views)
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Old   April 10, 2012, 13:04
Default Latest Run: 1000 Iteration Result
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Hi, I have just ran a 1000 iteration simulation and again there is no sign of convergence.

I gather from the results the probe position needs to be changed as there is a fluctution in all the variables in this position.

The velocity values at the inlet are incorrect, the inlet condition is 0.04Kg/s but the model reads a velocity of 70,438m/s at the inlet where a value of around 10m/s is anticipated.

Would this error be caused due to the lack of convergence?
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Old   April 17, 2012, 11:47
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It seems to be a boundary condition problem!!! why don`t you explain your problem in more details!!!
Godd luck!
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Old   April 19, 2012, 08:30
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The cause of a convergence problem can be anything (grid problem, setting of underrelaxation parameters, etc. etc.). Sometimes it helps if
you make it a time dependent run with small time steps until the solution
is stable.
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Old   April 25, 2012, 23:52
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Try checking the flow pattern at the outlet, there might be a strong recirculation. If so, try to enlarge your domain. though, it is not easy to solve such a problem in phoenics.
And is this problem isothermal or not? If not, the relaxation factor is also one possible reason for divergence.
good luck
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