[Cmaroline]

Hello everyone,

I'm new on Fluent, I must do a practical exercise. I need to simulate flow focusing from this microchip : exercice 1.png
I have flow rate of both inlets and maximal pressure of the system I have to find :
- InSheath q = 9 µL/s
- InSample q = 1 µL/s
- Pmax = 800 mbar
For this work I have set the following conditions :
-> Models : Viscous (Laminar) + Multiphase VOF (basics parameters, 2 Eulerian phases), Primary phase : sample, Secondary phase : sheath, liquid water both, no interaction between phases.
-> Boundary conditions :
- InSample, velocity inlet : 1,0e-4 m/s, gauge pressure 0, sheath volume fraction 0.
- InSheath, velocity inlet : 1,0e-3, gauge pressure 0, sheath volume fraction 1.
Basics conditons for the others.
-> Methods :
exercice 1.png
-> Initialization : Standard, compute from : all zones
-> Run calculation :
- Time stepsize : 1 s
- Number of time steps : 0
- Iterations : 100

I can not find the maximal pressure preticted. Please, could you tell me if something wrong on my setup, and why I can not find the good result!!

HELP PLEASE

[sina_mech]

Do you get any errors?! Can you for instance get the velocity magnitude contour working?

BTW, number of time steps = 0? It means that technically it doesn't run the simulation, does it?

[Cmaroline]

I don't have any error. Velocity magnitude is equal to 0, all the piece is blue.
I try with time step size = 1.0e-5s and number of time steps = 1 it is always the same result. I don't understand why.
I've been on this exercise for almost three weeks, I'm desperate.

[Mr.Tambourine]

The solution converges though ?
I am very unexperimented in transient simulation, but i do agree with sina_mech's point... Why do you have so few time steps ? Shouldn't there be much more ?
btw, we don't know much of the exercise in itself, so it'll be hard to get relevant help on it...

[sina_mech]

Originally Posted by Cmaroline

I don't have any error. Velocity magnitude is equal to 0, all the piece is blue.
I try with time step size = 1.0e-5s and number of time steps = 1 it is always the same result. I don't understand why.
I've been on this exercise for almost three weeks, I'm desperate.

Well, 1 time-step doesn't seem to be enough for a transient simulation, but it should at least give you some velocity profile. If you want, you can make a "Case+Data" file and share it with me so I can have a quick look on it.

[Cmaroline]

I'm an wondering! Would it be possible to use the discrete phases model?



sina_mech : How to make a file "Case+data"?

[sina_mech]

Originally Posted by Cmaroline

I'm an wondering! Would it be possible to use the discrete phases model?



sina_mech : How to make a file "Case+data"?

Well, I guess you need to watch few tutorials on YouTube, before moving forward with the current problem. It's always better to do some simpler cases before jumping into the main problem. Especially if you're new to a software.

For your second question: You have 2 different inlets, with 2 different materials. You need a multiphase model. You can't model the secondary phase inlet, just by DPM.

[Cmaroline]

I watched some tutorials on youtube, and I made tutorials and I succeeded. But when I come back on this exercise... I can't find similar tutorial...

I stay on VOF model, and I will see parameters of "Run calculation" like time of step and the others.


It is not really easy for beginner...

Someone told me about USD for materialize one of both phases. Can this help?