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How to get the volume from the volume fraction result

Posted 10 juin 2013, 22:35 UTC−4 Computational Fluid Dynamics (CFD) Version 4.3a 4 Replies

Dennis Wang
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I simulated a droplet falling and passed through the small gap between two solid balls. As the surface tension of the droplet, some part of liquid is kept between two balls. Now the result is the volume fraction figure which descrbe liqud by percentage, not real volume. anyone can help me find the volume between two solid balls( the volume of initial droplet already know) ?

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4 Replies Last Post 5 nov. 2013, 13:01 UTC−5
Duarte Albuquerque
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Posted: 1 decade ago 11 juin 2013, 06:41 UTC−4
Hi Dennis,

- I have done some studies with the two-phase flow physics with comsol v4.2, to create coupling with other physics.

- I think that the only way to compute the total volume of the liquid is to integrate in volume the function (tpf.Vf2>0.01), this function is 1 if tpf.Vf2 is greater than 0.01 and 0 otherwise. If there is another way to do this, I also would like to know.

- Do you have experiencied problems with the outlet boundary condition? I done many tests but its very difficult to eliminate any reflection from the boundary. I find that the best option is to use outletp option with a special constrain unidirectional, which appears in the advance physics.

Kind Regards,

Duarte Albuquerque
Hi Dennis, - I have done some studies with the two-phase flow physics with comsol v4.2, to create coupling with other physics. - I think that the only way to compute the total volume of the liquid is to integrate in volume the function (tpf.Vf2>0.01), this function is 1 if tpf.Vf2 is greater than 0.01 and 0 otherwise. If there is another way to do this, I also would like to know. - Do you have experiencied problems with the outlet boundary condition? I done many tests but its very difficult to eliminate any reflection from the boundary. I find that the best option is to use outletp option with a special constrain unidirectional, which appears in the advance physics. Kind Regards, Duarte Albuquerque
Dennis Wang
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Posted: 1 decade ago 11 juin 2013, 21:22 UTC−4
Hi, thanks for your suggestion. and I integrated the Tfv2 but the mass seem not conservation. some problem with that? I have not try outlet yet, but I really like to do it, and see how 's going!
Hi, thanks for your suggestion. and I integrated the Tfv2 but the mass seem not conservation. some problem with that? I have not try outlet yet, but I really like to do it, and see how 's going!
Duarte Albuquerque
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Posted: 1 decade ago 11 juin 2013, 22:05 UTC−4
- If you are computing the mass, you should make the integration (tpf.Vf2>0.01)*tpf.rho, the density changes in the zone between different phases.

- I noticed that comsol suffer of some numerical diffusion in the solution. In a 3D case I have more severe mass losses. I can only convergence cases with triangle or tethaedral meshes, which is very strange to me since any CFD code with FV method can use cartesian grid. Refining the grid or using the adaptive refinement option reduces this mass losses.

- If you are computing the mass, you should make the integration (tpf.Vf2>0.01)*tpf.rho, the density changes in the zone between different phases. - I noticed that comsol suffer of some numerical diffusion in the solution. In a 3D case I have more severe mass losses. I can only convergence cases with triangle or tethaedral meshes, which is very strange to me since any CFD code with FV method can use cartesian grid. Refining the grid or using the adaptive refinement option reduces this mass losses.
Reza Safi
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Posted: 1 decade ago 5 nov. 2013, 13:01 UTC−5
Hi

I faced the same problem. I have a droplet of water floated in air and dropped on the surface. After the droplet hits the surface, the volume fraction of droplet (water) converges to zero.
Did you solve your problem? Can you help me through this?

Best regards,
Safi
Hi I faced the same problem. I have a droplet of water floated in air and dropped on the surface. After the droplet hits the surface, the volume fraction of droplet (water) converges to zero. Did you solve your problem? Can you help me through this? Best regards, Safi

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