residual oscillations

cfdgalaxy · February 23, 2011, 02:05

hi im relatively new to cfx, and im trying to model a can combustor flow with a mixture of propane and butane as the fuel. im getting steady residual oscillations in the solver after a 100 hundred iterations. im using EDM, k-e for turbulence. can anyone tell me why this is happening - i've tried changing to physical timescale, increasing the timestep, decreasing it,but nothing is working.

id be really grateful for any help. thanks.

ghorrocks · February 23, 2011, 16:45

http://www.cfd-online.com/Wiki/Ansys...gence_criteria

joey2007 · February 24, 2011, 13:43

Did it converge without combustion?
What does the mesh quality report in the outfile say?

cfdgalaxy · February 28, 2011, 01:34

@ghorrocks, i ve read through that already.. and though the timescale alteration works for some curves, the others are still steadily in a straight line. is it possible i have to change my boundary conditions? i have converged similar models with the same BCs.
@joey: i havent tried running it without combustion. i will do that now and see.

cfdgalaxy · February 28, 2011, 06:36

it doesnt converge without combustion either - what does that mean?

ghorrocks · February 28, 2011, 16:42

Quote:

and though the timescale alteration works for some curves

The page I referenced discusses a lot more than just the time scale. If the timescale does not work you have to consider the other approaches discussed there.

joey2007 · March 1, 2011, 14:25

If it does not converge without combustion, something basic is wrong. Follow the recommendation from Glenn.

February 23, 2011, 02:05	residual oscillations	#1
cfdgalaxy New Member Join Date: Feb 2011 Posts: 4 Rep Power: 15	hi im relatively new to cfx, and im trying to model a can combustor flow with a mixture of propane and butane as the fuel. im getting steady residual oscillations in the solver after a 100 hundred iterations. im using EDM, k-e for turbulence. can anyone tell me why this is happening - i've tried changing to physical timescale, increasing the timestep, decreasing it,but nothing is working. id be really grateful for any help. thanks.

February 24, 2011, 13:43		#3
joey2007 Senior Member Join Date: Mar 2009 Location: Europe Posts: 169 Rep Power: 17	Did it converge without combustion? What does the mesh quality report in the outfile say? __________________ - - - - - ------------------------------------------------------------------------ Please do not forget: I am not paid for answering your questions. Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."

March 1, 2011, 14:25		#7
joey2007 Senior Member Join Date: Mar 2009 Location: Europe Posts: 169 Rep Power: 17	If it does not converge without combustion, something basic is wrong. Follow the recommendation from Glenn. __________________ - - - - - ------------------------------------------------------------------------ Please do not forget: I am not paid for answering your questions. Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."

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February 23, 2011, 16:45		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	http://www.cfd-online.com/Wiki/Ansys...gence_criteria

February 28, 2011, 01:34		#4
cfdgalaxy New Member Join Date: Feb 2011 Posts: 4 Rep Power: 15	@ghorrocks, i ve read through that already.. and though the timescale alteration works for some curves, the others are still steadily in a straight line. is it possible i have to change my boundary conditions? i have converged similar models with the same BCs. @joey: i havent tried running it without combustion. i will do that now and see.

February 28, 2011, 06:36		#5
cfdgalaxy New Member Join Date: Feb 2011 Posts: 4 Rep Power: 15	it doesnt converge without combustion either - what does that mean?