Learning Forum

[Vidya Muthulakshmi M]

I have completed a multiphase simulation (VOF) - Free surface type and obtained converged solution. The two phases are air and water. Now I am introducing three species in water phase within the same case setup. After defining the materials, I patched the mass fraction of species 1, 2 and 3 in all zones. I expected that the profile of mass fraction of the species to be same as that of the volume fraction of water in all grids of the mesh. But I am not getting the same profile. I request you to kindly help me out on finding the possible reason for the same. 

[Rob]

Please can you post some images? You should be patching species to phase, but if the air space has 0.0001 volume fraction of water you'll still see the species fraction. 

Run a time step as it may clear out when the solver updates. 

[DrAmine]

Yes, Screenshots are helpful. The post-processor will clip any values to zero below certain cut-off.

[Vidya Muthulakshmi M]

Thank you Rob and DrAmine for your replies. I am attaching two screenshots below. 

This is the volume fraction of water contour plot I have obtained after solving the multiphase simulation. Now I am additionally adding sucrose as a species in water phase.  I would like to resume the simulation from converged flow state (freezing flow equations and solving only species transport equation with user defined rates). For that, I clicked patch in initialisation window. I clicked phase water. Variable -> Sucrose, Value 0.5.

I patched the the cell zone with the value of sucrose as 0.5. I expected that sucrose will be patched proportional to the volume fraction of water. But I got profile as seen in the figure below.

I checked the ascii file. I saw that wherever there is non-zero value for water, the mass fraction of sucrose is 0.5. But I would like it to be say I have volume fraction of water to be 0.4 in a computational cell, sucrose mass fraction should be 0.2 and rest water (which is part of my mixture model - mixture model consists of sucrose and water).

 

Please let me know where I am making a mistake.

[Rob]

Turn off node values and replot. If you set sucrose as 0.5 it ought to be 0.5 in the water phase. Note, you're displaying the fraction on the phase, so it can be a little misleading. 

To better understand I suggest using a small model and patching species onto various levels of water. Trying to explain this is difficult face to face, via the Forum is going to be nigh on impossible. 

[DrAmine]

Please understand that whenver there is water phase even with small volume fraction the mass fraction will be just as you set it won't be set relative to the volume fraction of the phase.