[MachZero]

Hello,

I am trying to simulate a flow in a relatively small device in which two fluids come into the device and exit together. The flow is laminar and the fluids flow parallel for most of the time in the device.

The two fluids in questions are technically miscible fluids, in that we can mix them together by stirring them together. I have run a species model with the appropriate diffusion constants and found that the fluids do not mix whatsoever by the time they exit the device.

I would like to examine if the fluid flow is stable or if instabilities form, and using a VOF method, I have found that this is very dependent on the interface tension used. I am at a bit of a problem though: The fluids are technically miscible, they just do not mix at all in this device. Is there therefore an interface tension between the fluids since they have not mixed? Or is that value technically zero? Would it be better to just use a transient species model and hope that the instabilities show up? According to the species model I have run thus far, there will be a clear interface. We could try and test the interface tension of the two fluids, but that experimentally involves an action that would simply mix them.

Any references or information anyone could provide would be very helpful!

Thanks in advance!

[eng_s_sadeghi]

I think you should first find a simple paper that shows all required equations for modeling this physic. Then compare equations with the species transport ant VOF equations of fluent. You can find it so easily.