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-   -   Which Kind of Multiphase model? (http://www.cfd-online.com/Forums/fluent/109209-kind-multiphase-model.html)

fshak92 November 12, 2012 12:27

Which Kind of Multiphase model?
 
1 Attachment(s)
I'd like to model a "Fluid line" lied on a "solid plate".
An "air block" has been created to surround the "fluid line".
As you can see in the picture, the "fluid line" has been created like a solid block;but after running it should be deformed like a real fluid.
Therefore, i'm not sure which kind of multiphase model should be used for having the deformation of the "fluid line" IN the "air" and ON the "solid plate" after running.
(Or even if i should not use the multiphase mode...)

Big block (A) = Air
The thin block line (B) = a high viscous fluid
The violet block (C) = a solid plate

Thank you in advance.

fshak92 November 13, 2012 07:02

I guess Free Surface-VOF model should be used but i haven't been able to simulate yet.
e.g in cell zone conditions, when i set The "fluidline" as Phase2 , then the "AirBlock" is set to phase2 automatically and i cannot set 2 different phases to the different blocks(air and FluidLine)
I also doubt about having the AirBlock or remove it... .

Does anybody have any suggestion about the settings can be used?

ghost82 November 13, 2012 09:57

Quote:

Originally Posted by omid88 (Post 391826)
I guess Free Surface-VOF model should be used but i haven't been able to simulate yet.
e.g in cell zone conditions, when i set The "fluidline" as Phase2 , then the "AirBlock" is set to phase2 automatically and i cannot set 2 different phases to the different blocks(air and FluidLine)
I also doubt about having the AirBlock or remove it... .

Does anybody have any suggestion about the settings can be used?

Hi,
why do you want to create the solid domain?; you have to create the high viscous fluid domain and the air domain, then set as wall boundary conditions the surfaces of the solid plate
It seems also you can simulate it as 2D, instead of full 3d.
The VOF model seems ok to me; after initializing you have to patch the domain of the secondary phase, so you will have air domain with 100% air and high viscous fluid domain with 100% viscous fluid.
Then you can start your unsteady simulation.

Hope that helps

Daniele

fshak92 November 14, 2012 07:09

Quote:

Originally Posted by ghost82 (Post 391863)
Hi,
why do you want to create the solid domain?; you have to create the high viscous fluid domain and the air domain, then set as wall boundary conditions the surfaces of the solid plate
It seems also you can simulate it as 2D, instead of full 3d.
The VOF model seems ok to me; after initializing you have to patch the domain of the secondary phase, so you will have air domain with 100% air and high viscous fluid domain with 100% viscous fluid.
Then you can start your unsteady simulation.

Hope that helps

Daniele

Thank you for the reply.

I activate the VOF model(with default options).
Then i go to "cell zone conditions", when i set The "fluidline" as Phase2 , then the "AirBlock" is set to phase2 automatically(and vice versa) and i cannot set 2 different phases to the different blocks(air and FluidLine).
Instead, you mean setting the "mixture" for both blocks,then patching my second phase(fluid) to my first phase(air) with the volume fraction of 1? right?(i dont get any message when i patch fluid zone to the air zone)

Also i have some walls for the air block and the fluild block,Should i leave them with default values?
e.g in momentum field,all of them are set to "stationary wall". they shouldn't be changed to "moving wall" ... ?


Thank you in advance.

ghost82 November 15, 2012 09:37

1 Attachment(s)
Quote:

Originally Posted by omid88 (Post 392029)
Thank you for the reply.

I activate the VOF model(with default options).
Then i go to "cell zone conditions", when i set The "fluidline" as Phase2 , then the "AirBlock" is set to phase2 automatically(and vice versa) and i cannot set 2 different phases to the different blocks(air and FluidLine).
Instead, you mean setting the "mixture" for both blocks,then patching my second phase(fluid) to my first phase(air) with the volume fraction of 1? right?(i dont get any message when i patch fluid zone to the air zone)

Also i have some walls for the air block and the fluild block,Should i leave them with default values?
e.g in momentum field,all of them are set to "stationary wall". they shouldn't be changed to "moving wall" ... ?


Thank you in advance.


Hi,
I attached a picture to clarify my above comments: you should have 2 continuum zones (fluid 1 and fluid 2) and 2 boundary conditions (wall for the bottom solid plate and for example pressure outlet (?) for the other 3 edges) to define the volume of air.
Initialize your problem, then you have to patch the fluid 2 zone with your high viscous fluid.
Once you have patched the zone, plot the contour of phase-1 volume fraction to verify you have patched the zone.

As you can see I would model it in 2d; remember to specify reference values in your problem.

Daniele

fshak92 December 3, 2012 08:02

4 Attachment(s)
Thank you for your helpful suggestions.
I have some problems with the convergence of my simulation.
The courant number is very high and reversed flow at pressure outlet is occurred in my simulation.
I think coarsening the mesh (For decreasing courant number) decrease the accuracy of my simulation.and reducing the time step, can increase my computation time a lot.(i tested until the time step of 0.001s and still it had problem )
(By using the time step of 0.0001, i didnt get the error for courant number. But still there is reversed flow problem )

According to the mesh and details of the below pictures, what would you suggest for solving my problem?(high Courant number and reversed flow)
I also used a gauge pressure of 1000 pa and 3 kinds of backflow option, but still the same number of reversed flow faces can be seen.
Moreover,using the boundary conditions (outflow , outlet-vent and wall ) for the airOutlet , didn't give me a convergent solution.

First picture show the phase contour after simulation divergence for time step of 0.001.
Second one for the time step of 0.0001.
The contours for pressure and velocity are also shown in third and fourth pictures.
(Also,I dont know how the maximum velocity of 5 m/s has been generated in the air domain,because i dont have any initial velocity)

Thank you in advance

Kaixin December 5, 2012 21:08

heat exchange
 
Hello,all:
I want to know how to set the value of carbon dioxide scattering coefficient in the fluent button,who knows?thank you.


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