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-   -   problem of modeling slug break-up in microchannel by interFoam (https://www.cfd-online.com/Forums/openfoam/202108-problem-modeling-slug-break-up-microchannel-interfoam.html)

shinri1217 May 21, 2018 14:53

problem of modeling slug break-up in microchannel by interFoam
 
Hi all,

I'm new to CFD and this forum.

Now I'm trying to model the slug break-up in microchannel by interFoam in OpenFOAM 4.1 or 5.0 and reproduce some simulation results from literature.

Currently, I used 2D meshes and same flow rate for inlet of two phases. When I'm using coarse meshes, I could successfully capture the break-up and the slug generated. However, when I use larger meshes, the slug could not formed.

I have tried to use 3D meshes, grading mesh near the wall, change the cAlpha, contact angle and Co number, but the results remain same.

Here are some results I obtained.

with ~6K cells

0.5s
https://i.imgur.com/rUJwq7q.png

0.7s
https://i.imgur.com/ZoJ7z7a.png


with ~300k cells

0.5s
https://i.imgur.com/4SPE2sK.png

0.7s
https://i.imgur.com/TYfLp0t.png


I also do simulation with mesh size from 6k to 300k and even higher (~1M cells), but once the mesh size is large enough, I could not obtain the slug break-up. Besides, I have examined whether the result is converge or not. The result is not yet converge, but I doubt that I would capture the break-up with even higher mesh size.

Does anyone know what's going on this or have any suggestion on solving this issue?

Thanks for your help.

Taataa May 21, 2018 19:46

The break-up may occurs when shear stress exceeds the surface tension, so you need to take a look at the parameters that influence these two such as surface tension, nu and turbulence. I would suggest to make sure that these parameters match the literature that the case is based on. You can also post BCs, schemes and solutions so we can provide more suggestions.

Cyp May 22, 2018 10:43

you clearly have a problem with the contact angle. It is 90 degrees in all your simulations (flat profile). My guess is that you are using a zeroGradient condition at the walls for alpha.

shinri1217 May 22, 2018 12:31

The question I most confused is that I could obtain the slug break-up with coarse mesh, which it would physically happen. However, when I use fine mesh, I could not see this phenomena. Would I again obtain the slug break-up when I use even finer mesh?

Quote:

Originally Posted by Taataa (Post 693099)
The break-up may occurs when shear stress exceeds the surface tension, so you need to take a look at the parameters that influence these two such as surface tension, nu and turbulence. I would suggest to make sure that these parameters match the literature that the case is based on. You can also post BCs, schemes and solutions so we can provide more suggestions.

Hi Taher,

Thanks for your reply.

Yeah, I have also read the literature about break-up mechanisms. By the way, I use same physical properties as the literature reported. I use default fvScheme from interFoam. The following is my BCs.

p_rgh:

inlet: zeroGradient
outlet: fixedValue
wall: zeroGradient
frontAndBack: empty (for 2D)

U:

inlet: fixedValue
outlet: zeroGradient
wall: noSlip
frontAndBack: empty (for 2D)

alpha.water:

inlet: inletOutlet
outlet: inletOutlet
wall: zeroGradient
frontAndBack: empty (for 2D)

Quote:

Originally Posted by Cyp (Post 693190)
you clearly have a problem with the contact angle. It is 90 degrees in all your simulations (flat profile). My guess is that you are using a zeroGradient condition at the walls for alpha.

Hi Cyprien,

Thanks for your reply.

Since the literature do not apply contact angle, I use zeroGradient for BC too. I have also changed contactAngle to less than 90 degree or higher than 90 degree. However, I still could not see the break-up with fine mesh. The result obtained from coarse mesh is actually very similar to the literature reported.

UKARUN September 29, 2019 09:54

Dear Shirini, I am new to OpenFoam, I want to generate air-water slug flow in microchannel. I have developed the T junction geometry in the '0' folder. I have the following files in the '0' folder, alpha, alpha.water, alpha.air, p, p.rgh, T.air, T.water, U.air, U.water and Theta. I wonder If I should have these three alpha files. Can you help me.


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