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November 10, 2010, 07:04 
gasliquid twophase flow in microchannel

#1 
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Hello everyone, I'm a newbie to the FLOW3D, and trying to setup a simplified 2D gasliquid twophase flow in microchannel to simulate the flow pattern. The channel is a Tshaped microchannel, its width is 0.5mm, the gas (air) and liquid (water) are introduced in the channel from the opposite inlets, the velocities of the gas and liquid are 0.7m/s and 0.5m/s, respectively. The channel for twophase flow is 0.01m in the length. The outlet is open to atmospheric conditions. And the finish time is set to 10 sec. But the simulation always terminate unexpectedly.
Does anyone can tell me what goes wrong or share some similar examples with me. 

November 15, 2010, 13:35 

#2 
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michael barkhudarov
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does it terminate with an error message? Does the solver run any distance or does it terminate right away?


November 15, 2010, 23:04 

#3 
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Yes the solver message is "excessive pressure iteration failures", the pressure iteration can't converge. I don't know where to find converge control options and how to control them. Could you please help me?


November 16, 2010, 23:09 

#4  
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michael barkhudarov
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Quote:
If the difference is relatively small, ~ 23, then you may be able to achieve convergence by introducing limited compressibility, or switching to a different pressure solver. Does it start failing right away? Have you talked to support? 

November 17, 2010, 00:13 

#5  
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Quote:
No, it doesn't start failing right away, and I haven't talked to support. 

November 17, 2010, 23:59 

#6  
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I found this in the help contents, "Twofluid problems may be composed of either two incompressible fluids or one incompressible and one compressible fluid". So I guess that's the problem I had. Thank you very much for your help. 

November 19, 2010, 01:36 

#7  
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michael barkhudarov
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Quote:
Limitted compressibility does not add the full equationofstate compressibility which the full gas model does (ICMPRS=1). Instead it adds, the acoustic compressibility, where the density changes are assumed small, and pressure changes is a linear function of density changes: dP/dt=c^2drho/dt, where c is the speed of sound. This is good for a) tracking acoustic waves, and b) softening stiff systems for better convergence. Looks like the latter worked out for you. 

February 3, 2011, 06:07 

#8 
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Dear LyngHoo
Please send me you email, maybe I can cooperte with you, regards Dr. M. Haghshenas haghshenas@cc.iut.ac.ir 

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