Simplified VOF Model

gulbenkian · June 10, 2010, 16:57

Hello

I am trying to solve a transient simplified model in 2D. Air is flowing from a source at 200000 Pa and get into contact with a pool of water of 2mm X 4mm before expands to atmospheric conditions see Figure 1.

I want to see the deformation of the water (droplet formation if any) due to the air flow. I am having problems to get convergence in the model. I am using a VOF model using air as primary phase and the water as secondary phase. As boundary conditions I am using a pressure inlet and pressure oulet conditions. I am patching the water at the beginning. I have used a k-e model and a simplified laminar model for the air and a time step size of 0.0001, however, after I begin the iterative process, it quickly diverge.

I highly appreciate if someone can give me some ideas.

Thanks in advance

pranab_jha · June 10, 2010, 17:52

Hi,
What error message does Fluent give you?
I am also using VOF and facing some issues with divergence. I am modeling two-phase flow in pipe. I got the error msg: "divergence detected in AMG solver: pressure correction" when I initialized the whole pipe domain with VF =1 or even with VF = 0.5. But for low phase velocities, I was able to 'avoid' divergence by lowering the relaxation factors for pressure from 1 to 0.5. But I am not able to get around it for higher velocities (air and water ~ 1.5 m/s, pipe dia = 50 mm) by lowering the value further.
I guess you can try it. Maybe it works for you. If you come across any useful tip, do let me know.
Thanks,
Pranab

June 10, 2010, 16:57	Simplified VOF Model	#1
gulbenkian New Member Join Date: Jun 2010 Posts: 2 Rep Power: 0	Hello I am trying to solve a transient simplified model in 2D. Air is flowing from a source at 200000 Pa and get into contact with a pool of water of 2mm X 4mm before expands to atmospheric conditions see Figure 1. I want to see the deformation of the water (droplet formation if any) due to the air flow. I am having problems to get convergence in the model. I am using a VOF model using air as primary phase and the water as secondary phase. As boundary conditions I am using a pressure inlet and pressure oulet conditions. I am patching the water at the beginning. I have used a k-e model and a simplified laminar model for the air and a time step size of 0.0001, however, after I begin the iterative process, it quickly diverge. I highly appreciate if someone can give me some ideas. Thanks in advance

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June 10, 2010, 17:52		#2
pranab_jha Member Pranab N Jha Join Date: Nov 2009 Location: Houston, TX Posts: 86 Rep Power: 17	Hi, What error message does Fluent give you? I am also using VOF and facing some issues with divergence. I am modeling two-phase flow in pipe. I got the error msg: "divergence detected in AMG solver: pressure correction" when I initialized the whole pipe domain with VF =1 or even with VF = 0.5. But for low phase velocities, I was able to 'avoid' divergence by lowering the relaxation factors for pressure from 1 to 0.5. But I am not able to get around it for higher velocities (air and water ~ 1.5 m/s, pipe dia = 50 mm) by lowering the value further. I guess you can try it. Maybe it works for you. If you come across any useful tip, do let me know. Thanks, Pranab