[cwl6750084]

Hi, I appreciate if any experts can enlighten me somehow on VOF simulations.

I am simulating a water droplet in oil, flowing in a T-junction. However, for my simulations, the droplet tends to break at a much lower velocity threshold. (The one shown was done with inlet velocity of 0.03 m/s, width of channel is 30 micron. Our experiment shows that the droplet does not break. This observation is consistent from what is reported in the literature.)

I checked all my properties in the Fluent input and they are correct. The only remaining uncertainty that I could think of is contact angle (which I used 180 deg. as suggested by some papers) and the selection of "primary" and "secondary" phase. At this time, the primary phase is oil and secondary phase is "water". Does it really matter which fluid being selected as primary?
I am under the impression from the tutorial that the selection of primary phase does not affect the results.

Can anyone shed some suggestions of the probable cause of the droplets to seem prefer breaking?

Thanks.

[ksingh]

Hi Dear
Selection of primary and secondary phase does not affect results. Based on your pics, I can only suggest you to check how you are modelling surface tension.
In your current model you can reduce velocity and check whether your droplet is breaking or not. If it does, then definately you should check surface tension model and parameters associated with this.

[cwl6750084]

Originally Posted by ksingh

Hi Dear
Selection of primary and secondary phase does not affect results. Based on your pics, I can only suggest you to check how you are modelling surface tension.
In your current model you can reduce velocity and check whether your droplet is breaking or not. If it does, then definately you should check surface tension model and parameters associated with this.

Thanks for your suggestion. I tried varying the velocity and the droplet does not break when the velocity drops below a certain threshold. However, the current problem is that the threshold is too low.

There are not that much choices for surface tension model in Fluent. I used Continuum Surface Stress, Wall Adhesion, Constant for Surface Tension Coefficient (with value given in the literature and measurements in our lab).

Do you know the difference between Continuum Surface Stress and Continuum Surface Force models in Fluent? The help manual in our lab only describe Continuum Surface Force.

Thanks.

[kevinxichan]

How did you define the oil and droplet domain? Did you draw two bodies or you patch a region to the primary domain in FLUENT setup?

[cwl6750084]

Originally Posted by kevinxichan

How did you define the oil and droplet domain? Did you draw two bodies or you patch a region to the primary domain in FLUENT setup?

I created the channel as a single donain. It was then initialized with oil filling the whole space. The water droplet was then patched in the primary domain in FLUENT.

[kevinxichan]

Originally Posted by cwl6750084

I created the channel as a single donain. It was then initialized with oil filling the whole space. The water droplet was then patched in the primary domain in FLUENT.

im sooty that I can't solve ur problem but actually Im working on a problem similar to yours. Do u know if we can export the stress or force applied to the droplet if we patch to the primary domain. I found that we can only export shear stress or drag force applied to a wall. Apparently the patched region won't have a wall. Thanks.

[cwl6750084]

Originally Posted by kevinxichan

im sooty that I can't solve ur problem but actually Im working on a problem similar to yours. Do u know if we can export the stress or force applied to the droplet if we patch to the primary domain. I found that we can only export shear stress or drag force applied to a wall. Apparently the patched region won't have a wall. Thanks.

I am not sure if I understand your question. However, if you cannot export a stress data directly, you may try integrating based on the fluid data on the droplet surface.