Convergence problem with axial pump simulation!

cnchilavert · October 4, 2011, 16:35

Hello, everyone,

now I am suffering a convergence problem with my simulation of axial pump. In my case, only one blade section is simulated, and mass flow rate BC is used in the inlet, zero pressure is used in the outlet.

But I am not quite sure about the physical timescale. Now I am using 1/ω as the timescale as suggested in the tutorial. Actually I have ever used a larger value, e.g. 2π/ω when the convergence was not achieved with 1/ω, but this change was not helpful.

So here I am asking you guys who can recommend me a better solution. I even noticed here that somebody mentioned "residence time". Is it the time for the water to flow through the whole domain? Is it suitable for the simulation with a long inlet pipe and a long outlet pipe? Does anybody here have a similar experience?

Thank you for your attention!

ghorrocks · October 4, 2011, 18:43

The timescales are just guides to start from. If that is not converging then use a smaller time step and forget about physical significance.

bhatiadinesh · October 5, 2011, 05:23

Try Automatic timescales

October 4, 2011, 16:35	Convergence problem with axial pump simulation!	#1
cnchilavert New Member Join Date: Jul 2011 Posts: 2 Rep Power: 0	Hello, everyone, now I am suffering a convergence problem with my simulation of axial pump. In my case, only one blade section is simulated, and mass flow rate BC is used in the inlet, zero pressure is used in the outlet. But I am not quite sure about the physical timescale. Now I am using 1/ω as the timescale as suggested in the tutorial. Actually I have ever used a larger value, e.g. 2π/ω when the convergence was not achieved with 1/ω, but this change was not helpful. So here I am asking you guys who can recommend me a better solution. I even noticed here that somebody mentioned "residence time". Is it the time for the water to flow through the whole domain? Is it suitable for the simulation with a long inlet pipe and a long outlet pipe? Does anybody here have a similar experience? Thank you for your attention!

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October 4, 2011, 18:43		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	The timescales are just guides to start from. If that is not converging then use a smaller time step and forget about physical significance.

October 5, 2011, 05:23		#3
bhatiadinesh Member D Join Date: Nov 2010 Posts: 50 Rep Power: 16	Try Automatic timescales