# Convergence Problem

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April 10, 2012, 06:49
Convergence Problem
#1
New Member

Rob Hulme
Join Date: Jan 2012
Location: UK
Posts: 3
Rep Power: 6
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.
Attached Images
 Simulation.jpg (27.0 KB, 63 views)

 April 10, 2012, 13:04 Latest Run: 1000 Iteration Result #2 New Member     Rob Hulme Join Date: Jan 2012 Location: UK Posts: 3 Rep Power: 6 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?

 April 17, 2012, 11:47 #3 Senior Member   Julio Mendez Join Date: Apr 2009 Location: Greensboro, U.S.A Posts: 189 Rep Power: 9 It seems to be a boundary condition problem!!! why don`t you explain your problem in more details!!! Godd luck!

 April 19, 2012, 08:30 #4 New Member   Join Date: Apr 2012 Posts: 5 Rep Power: 6 Hi, 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.

 April 25, 2012, 23:52 #5 New Member   mj Join Date: Apr 2010 Posts: 5 Rep Power: 8 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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