convergence criteria

 Register Blogs Members List Search Today's Posts Mark Forums Read

 February 4, 2011, 05:16 convergence criteria #1 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 hi all users, i am running an unsteady case of Cascade T106A. It is a bounded flow. i want to ask what convergence criteria i have to used? Mass flow rate will be ok or not? any guide line for me please? Regards: Aqib

 February 4, 2011, 05:36 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 I would uncheck convergence criteria Just let iterate and monitor any quantity yu are interested (for instance massfow) __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 4, 2011, 08:24 #3 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 thanks for replying.... i am interested in the co-efficient of loss pressure in which i have to compared my case with some other case..... should i iterate both cases to the same number of iterations? secondly, in "the co-efficient of loss pressure" formula there is a quantity of "inlet stagnation pressure" which varied after every 500 iterations.... so what does it means? which value i have to be used?

 February 4, 2011, 08:41 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 what is co-efficient of loss pressure? __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 4, 2011, 09:13 #5 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 The total pressure loss coefficient ω=(Pt(inlet)-Pt(outlet))/q(inlet) inlet where ω is the total pressure loss coefficient, Pt is the stagnation pressure, and q(inlet) is the dynamic pressure at the inlet

 February 4, 2011, 09:14 #6 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 in my case dynamic pressure at inlet(q) remains same but both the stagnation pressure at inlet and outlet varied with number of iterations

 February 4, 2011, 09:44 #7 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 Then you didn't reach convergence. Let iterate untill you get constant values __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 7, 2011, 02:32 #8 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 thanks for replying.... my solution is converged but it is periodically converged....that's why the values are varying with the iterations.....

 February 7, 2011, 03:08 #9 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 Sorry I just checked, that you are working with unsteady solver. Is your monitoring x-axis iterations or time step? (post a picture) I cannot remember if you can choose between iterations and time step in the monitoring panel (for unsteady solver). __________________ In memory of my friend Hervé: CFD engineer & freerider

February 7, 2011, 08:37
#10
Member

Join Date: Nov 2010
Posts: 50
Rep Power: 8
attaching the picture of inlet and outlet stagnation pressure
Attached Images
 inlet and outlet stagnaation.jpg (67.3 KB, 52 views)

 February 8, 2011, 02:05 #11 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 I don't think this is an absolute convergence monitoring, but unsteady monitoring. If I am right you can see, the "convergence" (especially in the left chart), it looks like stairs. Each stair represents a convergence loop. To be sure, just increase the max iterations per time step, and replot: the stairs should be stretched. __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 8, 2011, 05:25 #12 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 so its mean my solution is converged?

 February 8, 2011, 05:49 #13 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 if the "stairs" are stretched while you increased the max iteration/time step, then your solution converged for each time step __________________ In memory of my friend Hervé: CFD engineer & freerider

 February 8, 2011, 06:30 #14 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 8 thanks yes it is visualize to me.... solution is converged....

 March 7, 2012, 05:41 Divergence detected in AMG solver: temperature #15 Member   Arun Join Date: Mar 2012 Location: Vellore,TN,India Posts: 43 Rep Power: 7 Hi, I doing the cascade and i'm new to CFD. I like to know what are the input values i need to have with me before i start fluent. I just finished the gambit and now waiting for solution. My case is 2D. I using K-omega SST. I'm pleased if some one help me about the steps i need to follow to solve. (I had the same problem "Divergence detected in AMG solver: omega" i changed URF to F-cycle.)

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post steventay CFX 7 May 14, 2010 12:44 PrandtlGlawert Main CFD Forum 1 August 13, 2009 17:13 edwin FLUENT 1 February 14, 2008 20:24 asaha OpenFOAM Running, Solving & CFD 0 December 9, 2007 10:53 ROOZBEH FLUENT 1 October 6, 2003 09:32

All times are GMT -4. The time now is 01:25.