CFX Pre

ibadullah safdar · April 26, 2016, 13:00

Dear All,
I want to ask from anyone that when I decreased the time step size then the convergence becomes slow but if the RMS residuals does not change from 13 iterations then does it mean convergence have achieved or not or I have to wait for the specified convergence.
Answers will be appreciable
Thanks
Regard
Ibad

alirezame · April 27, 2016, 03:03

Hello,
what is your case? turbomachinery, nozzle, air foil, ... ?
it depends on the case, for example in compressor or turbine, constant efficiency and imbalance too close to zero are good criteria for convergence.
but for air foil constant LC and DC are important.

ibadullah safdar · April 27, 2016, 15:22

Thanks for reply. Actually its a venturi scrubber that consist of a converging, throat and a diverging section where air enters from converging section and the water enter from nozzle into throat area. I have attached the pic So what did you say about it now . Thanks
Regard
Ibadullah Safdar

-Maxim- · April 28, 2016, 02:44

Hi, your thread title is bad. Your question has nothing to do with CFX Pre. Please be more specific.

Read what I just wrote here about residuals and try that out too:
http://www.cfd-online.com/Forums/cfx...tml#post597054

Also as Ali wrote, have a look at the imbalances.

I would say that no changes in 13 iterations are not enough to tell if convergence is achieved.
How do your monitor points look like besides the residuals?

ibadullah safdar · April 28, 2016, 11:53

Thanks maxim for ur reply. i will try what you have said in your previous post.
Regards
Ibadullah safdar

April 26, 2016, 13:00	CFX Pre	#1
ibadullah safdar New Member Ibadullah Join Date: Jan 2016 Posts: 21 Rep Power: 10	Dear All, I want to ask from anyone that when I decreased the time step size then the convergence becomes slow but if the RMS residuals does not change from 13 iterations then does it mean convergence have achieved or not or I have to wait for the specified convergence. Answers will be appreciable Thanks Regard Ibad

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April 27, 2016, 03:03		#2
alirezame Member Join Date: Nov 2013 Posts: 57 Rep Power: 12	Hello, what is your case? turbomachinery, nozzle, air foil, ... ? it depends on the case, for example in compressor or turbine, constant efficiency and imbalance too close to zero are good criteria for convergence. but for air foil constant LC and DC are important.

April 28, 2016, 02:44		#4
-Maxim- Senior Member Maxim Join Date: Aug 2015 Location: Germany Posts: 415 Rep Power: 12	Hi, your thread title is bad. Your question has nothing to do with CFX Pre. Please be more specific. Read what I just wrote here about residuals and try that out too: http://www.cfd-online.com/Forums/cfx...tml#post597054 Also as Ali wrote, have a look at the imbalances. I would say that no changes in 13 iterations are not enough to tell if convergence is achieved. How do your monitor points look like besides the residuals?

April 28, 2016, 11:53		#5
ibadullah safdar New Member Ibadullah Join Date: Jan 2016 Posts: 21 Rep Power: 10	Thanks maxim for ur reply. i will try what you have said in your previous post. Regards Ibadullah safdar