Learning Forum

[SV]

Greetings

I am trying to model injection of air into water to see the formation of bubble from a nozzle 3D and symmetric. When inlet velocity is below 0.2 m/s, the air does not come out and formation of bubble is not possible and when velocity is more than 0.25 m/s, air will be injected into the water but formation of bubble is missing. Following figures might help to figure out the issue. Please let me know if you know the problem. I see formation of bubble 2D.

Inlet velocity=0.25 m/s

 

Inlet velocity=0.7 m/s

Geometry

[SRP]

Hi,

Which model are you using for the simulation of multiphase flow?

Thank you

[SV]

VOF

[SRP]

Hi,

With VOF you're fully resolving the bubbles, is your mesh fine enough? Bubbles can be patched into the domain (covered under initialisation). You will need a very good quality and well resolved mesh, small time steps and time.

Since you want to create bubble, You can try Multi VOF.

please check ansys forum disscusion:Simulating bubble formation in water container (ansys.com)

Thank you.

[SV]

 

Greetings
2D modeling from nozzle is fine and I can see a reasonable prediction for given mesh size and time step. There is a problem when I try to model 3D. Mesh size is 0.1 mm and time step is 0.00005. They are small enough. 
Look at following picture. This is the picture after 4500 time steps and inlet velocity 0.15 m/s.

 

 

[SRP]

Hi,

Can you please share your mesh screenshot and corresponding statistics?

Thank you.

[SV]

Greetings

Please look at following figures.

[SRP]

Hi,

The mesh appears coarser. I suggest you to refine the mesh so that it will help to capture interface.

Thank you.

[SV]

Greetings

How small you would like me to go? Would you like 0.05 mm or smaller? We can see a good result in 2D modeling with 0.1 mm mesh size.

Thank you

 

[SRP]

Hi,

Make it small, so that it can capture your bubble diameter.

Thank you.

[SV]

 

Greetings

Mesh size is reduced to 0.03 mm. please look at following figures:

Inlet velocity=0.7 m/s

 

Inlet veloocity=0.1 m/s

Please look at following figure. How can I save the clip in a specific file

 

[SRP]

Hi,

You can check fluent user's guide: 39.9. Animating Graphics (ansys.com)

Thank you.

[Abhishek Shingala]

I dont know how to do it in ansys, but you may use high resolution interface capturing scheme, 3rd order would be nice in order to have sharp interface, in addition you can use adaptive mesh and implicit time step method, theses is how you can use bigger possible timestep automatically and can also use big coarser cells wherever possible automaticaly.