[esol]

Hello everyone,
This is my first time asking a question here, so I may be unfamiliar with it.

I want to simulate for bubble behavior in air-water system of 2D domain.
Domain is just rectangular and nozzle is plate type).

The gas inlet was velocity inlet and outlet was pressure outlet. Gas inlet(Mixture) was set the same velocity per seconds. As I want to inject air gas, so I set the air volume fraction to 1 in the gas inlet. And I set the initialization of the air volume fraction to 0 to fill the domain with water, and the rest of the values ​​were set to default.

When simulating this boundary condition, the simulation result is different from the experimental result. The bubble diameter is much larger than the actual experimental result, and the rising velocity is also much slower than the actual experimental result.

1)What values ​​can I adjust to match the experimental results with the simulation results? I tried increasing the contact angle to match the diameter, but the results are different each time.
I cannot set the drag coefficient because I am using a VOF model.

2) Whenever I simulate this condition, it always goes for 3 s (time step: 1e-04) and then stops with an error message like "turbulent viscosity or floating point exception". Is this most likely a mesh issue? If so, how should I set up the mesh?

Kindly help.
Im new to fluent, so I may not know much. Thank you.

[lolno]

Did you enable gravity in your simulation?

[esol]

Yes, I set the gravity based on the Y axis.

[lolno]

And whats your velocity inlet magnitude? And can you screenshot your domain and sim setting so we can have better grasps about your simulation?

https://ansyshelp.ansys.com/public//...d_settings.png

And in your experiment setup, how do you control your air inlet velocity? Using some kind of pump with constant flow rate? Does your experiment inlet area is the same as your sim inlet?

[esol]

Originally Posted by lolno

And whats your velocity inlet magnitude? And can you screenshot your domain and sim setting so we can have better grasps about your simulation?

https://ansyshelp.ansys.com/public//...d_settings.png

And in your experiment setup, how do you control your air inlet velocity? Using some kind of pump with constant flow rate? Does your experiment inlet area is the same as your sim inlet?

attached file is domain. (Sorry the drawing is rough).

I can't capture the simulation setup settings, so I'll explain it in words. Sorry.
The gas inlet velocity of simulation 0.11m/s (mixture). - air volume fraction of gas inlet was 1 and remainder filled water (initialized - air volume fraction was 0).
At this time, the experimental nozzle is cylindrical and injects 0.2 ml/min of gas, but the simulation calculated the flow rate by assuming that the area of ​​gas sprayed from the nozzle area is a circle in a 2D shape.

In the experiment, a flow control device is used to inject a constant flow rate.

The experimental results and simulation results do not match well, some bubbles keep rising and some bubbles spread out.
Is it a mesh problem?
I don't know how to configure the mesh.

I tried dividing the inlet nozzle by 4 or more and adjusting the bias coefficient for the remainder. If the AR is not large, the total number of cells will exceed a million. how should I do?

[lolno]

Just to confirm is your velocity inlet value is correct? Cause it’s not the same as your experiment value
IMG_2218.jpg

[esol]

Originally Posted by lolno

Just to confirm is your velocity inlet value is correct? Cause it’s not the same as your experiment value
Attachment 103339

When going from 1 to 2, if I convert the units (mm->m), wouldn't the velocity values ​​for the experiment and simulation become the same?

[lolno]

Oh yeah you’re right, sorry my mistakeIMG_2219.jpg

[lolno]

just wondering what's your operating density?

https://ansyshelp.ansys.com/public//...ase_body_force