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-   -   Convergence problem (http://www.cfd-online.com/Forums/fluent/111296-convergence-problem.html)

paudelrahul January 2, 2013 20:53

Convergence problem
 
Hello all,

I am trying to do simulation on a valve using steady state pressure based solver. I generated the mesh in Gambit and is structured with 270k cells. The CS area of the inlet is in the order of 1 mm^2. My velocity is 1m/s and the viscosity is 1E-3 for water. while doing the forward flow, it converges, however, the reverse flow doesn't converge. The continuity is in the order of 10^-4, along with the x,y and z velocity. The energy is in the order of 10^-16. And the flow is for Reynolds < 2000. The one I am doing right now is for Re=1000. So, it should be laminar flow.
I need to get the pressure in the inlet and outlet for the reverse flow and I am using area weighted average pressure. However even after 1000 iterations, the pressure at the inlet and outlet keeps changing. I don't know, what value I should take for the inlet and outlet surfaces?

Can anybody tell me how to get it to converge?
I tried using 0.3 for Pressure and 0.7 for momentum Under-Relaxation factors, as well as 0.7 for Pressure and 0.3 for Momentum, under - Relaxation factors.

Please help.

Sincerely,
Rahul Paudel

msaeedsadeghi January 3, 2013 02:46

I didn't understand. For reversing flow you should change boundary condition to get a reverse flow.

paudelrahul January 4, 2013 17:11

What I was saying is, for the reverse flow, I couldn't get the solution to converge. FYI: The setup is (for the reverse after switching boundary conditions), Velocity inlet and pressure outlet.

Also FYI: I noticed that theres a low pressure spot created in my valve which moves towards the outlet of the valve, which is giving me varying pressure at the outlet. Does that mean my outlet is at the unsteady condition instead of the steady flow (which I used to model)?


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