VOF model

[anna.tsitouridou]

Hi, I am simulating droplet formation using a VOF model in Fluent, but in microfluidic conditions where the flow is considered laminar. I have a question. Does it make sense to apply a SST k-omega viscous model instead of laminar? Because I have used it and it gives me more accurate predictions than the laminar model. Why?

[Rob]

Accurate compared to what? 

[anna.tsitouridou]

Accurate compared to experimental values (i.e of droplet size and droplet velocity). After the droplet is formed, I aim to quantify the intensity of internal recirculation within the droplet.For this reason, I implemente a k-omega model for the viscosity. However, I am not sure whether this choice is physically justified. Is the use of a k-omega model appropriate for capturing internal recirculation in this case? If not, how can I explain the fact that the simulation results appear reliable and consistent with experiments? Could you please advise me on that? 

[Rob]

I spent some time modelling micro-fluidics so need to be a little careful with what's public. Luckily most of it was published on paper. 

What do you think causes the internal flow in the droplet? How did you make the channels for the experiment, and measure the flow/stuff? 

 

[anna.tsitouridou]

When the droplet is formed, the velocity of the droplet interface is much lower than that of the surrounding phase, and thus the surrounding phase exerts viscous stresses at the interface, which results in the creation of recirculation within the droplet. As for the experiments, I used a commercial glass microfluidic cross-junction, and I measured the flow through micro-PIV experiments. 

[Rob]

So, laminar sub eddies probably linked to surface tension and wall contact? Ie not turbulent. How many cells have you got across the droplet? What aspect ratio on the near wall cells? How precise do you think the experiments are?