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suresh February 11, 2009 03:50

About run problem

I am using star CD for simulating compressible flow.I have two inlet and one outlet. Out of two inlets one is mass inlet while other is pressure inlet. Outlet is pressure outlet. I am not using stagnation or environmental pressure boundary for my problem.

I have defined ULR as given below: for u,v,w: 0.4

p: 0.12



den : 1 I am using density as function of pressure and temperature. For first 300 iterations I treated problem as incompressible later I converted density as fiunction of pressure and temperature.Then,I made star to perform 4000 iterations.But I am observing that my mass residual is continueously fluctuating around 6x10-3. while other residuals have gone below 10-4. Can anybody please answer following questions:

1) Do I have achieved convergence?

2)If I have not near the convegence then how to bring down mass residual below 10-4?

Any suggestions from expert is most welcome.Thanks in advance.

Andrea February 12, 2009 04:15

Re: About run problem
Try to monitor the mass flux, the pressure distribution and other charactheristics you may be interested in on your simulation (for example with boundary monitor option on). If they change a little or if they don't change appreciably with the progress of you calculation than you can argue that you've reached convergence.

If it is not as above then you may want to switch to a transient simulation to obtain a more realistic result from your model, involving transient phenomena you can't obtain in a steady state simulation.

Sometimes the geometry is not so simple so maybe in you model born some phenomena like vortex-shedding, recirculating region, etc...and you need a transient sim to describe them.

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