|June 17, 2015, 15:00||
Gas-liquid pipe flow
Join Date: Dec 2014
Posts: 12Rep Power: 2
Hi guys, im new in CFX and im trying to simulate a gas liquid multiphase flow but im getting weird results, i just want to be able to identify some horizontal pipe flow patterns (wave, stratified, etc) but i reallt dont know very well how to set the bc and multiphase models, i have read some tutorial and i have done this.
i set a simple horizontal pipe 3 m lenght and 0.20 m diameter
at inlet i set 0.5 of gas and 0.5 of water
1 m/s both
a simple outlet with av pressure 0 atm
im starting with laminar flow, both continuos phases, inhomogeneuos. fluid pair with mixing model, and drag coefficient.
i just want to know what best settings i have to usea to model stratified flow
as i run the model i get some waves but at some time i have "picks" in convergence and i see like suddenly "explosions" in the flow. i know i have alotof things wrong.
In simple words what a have to do to set a stable model.
|June 17, 2015, 19:13||
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,053Rep Power: 86
For free surface flows - they are quite sensitive to time step size. I would recommend you use adaptive time stepping so it can automatically find a good time step.
Use adaptive time stepping, homing in on 3-5 coeff loops per iteration. Make sure the max and min time step size are wide enough that you do not hit them, and give it a sensible starting time step size.
|June 18, 2015, 10:13||
Join Date: Jun 2012
Posts: 292Rep Power: 6
Curious question for the knowledgeable:
Can you run this problem in steady state, with a small physical time step (e.g. t = 0.001 s) for 10000 iterations?
This will give you a pseudo simulation time of 0.001 * 10000 = 10 s.
Then use the steady state results as the initial guess for a transient run, but setting the initial start time as 10 s?
|gas, liquid, multiphase flow|
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