[Niicho]

Hi all,

I am new to Fluent. I am trying to mix water and oil and creat droplets from this. In the main channel there is a laminar water flow and in the two side pipes laminar oil flow. The simulation is transient of course and I have around 200K hexa elements as shown in one of the pictures. For the calculation I am using the VOF model, with a surface tension coefficient for the two fluids of 0.005 N/m.


So far so good, when I start the simulations, my residuals dont drop below 0.1 (even though I give an absolute value of 0.0001 criteria ). The other thing is that on the edges where the two fluidss first meet, there are some really strange gradients of pressure and velocity (100x bigger values from the average), which is unphysical. It also messes with the velocities and pressures in a whole domain. In my opinion the problem comes from the surface tension coefficient. When I turn it off or make it really small the gradients dissapear but the results are of course not what I want then, meaning no droplets. I have also tried to work with a tetra mesh but the results are not physical anymore, there are no droplets at all in that case. I also changed the boundary conditions, meaning either pressure outlet or a inlet with a negative velocity (this is the case shown in the pictures). But there are no differences!

So my qustion is, does anyone of you has an idea of how to deal with that, rather numerical problem?

Thank you Pressure.png

Pressure2.png

Mesh.png

VolFraction0.png