Problem with 2-phase flow in Fluent

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  • Last Post 15 February 2019
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Peace posted this 08 February 2019

Hello all,

I am trying to create a Oscillating water column simulation 2D. I am using the Academic Ansys 19.1

I am creating my surface which consists of 4 parts and meshing it. But when I load Ansys I get a wall at the boundaries between my parts.

Also I noticed from many tutorials that I am supposed to get shadow walls but I don't get any shadows (I don't know if that matters but figured better to say it). 

I tried to make a single domain but then when I am loading the mesh in Fluent I get a single domain so I can't define seperate cell zone conditions.

Can someone help me on what should I do to avoid getting the wall but still getting the 4 seperate cell zones that I need?

Thanks in advance.

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mdfaizan444 posted this 15 February 2019

these are the formula's they have used..

 

mdfaizan444 posted this 15 February 2019

Actually i am validating one of the paper in which they have used mixture model so i have to take this model only. 

I am doing nano fluid flow inside a channel by TWO PHASE MIXTURE MODEL.
Actually i am trying to validate one of the paper, in which i am getting over predicted results but i am not able to find where i am doing wrong. Its a water AL2O3 nanofluid with AL2O3 volume fraction 4%.
Queries..
1) Do i need to on the gravity for slip equation?
2) There is a slip between phases, but do i need to specifies if yes where is the option for that in TWO PHASE MIXTURE MODEL or ansys calculated it itself.
3)I am getting the result at lower Re (250) but at heigher Re(1050) i am getting 8% deviation from the reference paper.
What could be the changes that i need to do?


Thanks in advance

rwoolhou posted this 15 February 2019

Depends: does gravity change the flow?  If the phases are separating try using the Eulerian model as Mixture has a shared velocity field so can struggle if the phases separate too quickly. 

mdfaizan444 posted this 15 February 2019

I am validating one of mixture model paper, in which mess is exactly same as taken by others. I have a problem in mixture model physics.

Do i need to on gravity option and put -9.81 in mixture model? As by doing this my problem is not converging but without  gravity its converging with overpredict results. (8% overpredict)

rwoolhou posted this 14 February 2019

How slight is slight? Errors can be caused by poor meshing, lack of convergence, incorrect use of models and unintentional differences from the physical model: this assumes the physical data is also correct. 

mdfaizan444 posted this 14 February 2019

so now i am getting slightly over-estimated result, what could be the reason for this?

 

abenhadj posted this 09 February 2019

Residual monitoring is not enough. Create report definitions for holdups or other important quantities and monitor them. You residuals are ok. Read documentation on judging convergence.

Best regards,

Amine

mdfaizan444 posted this 09 February 2019

i am giving volume fraction criteria as e^-5 but in residual graph it starts from e^-15 and stop at nearly e^-10. But the solution is converge. Also continuity and x velocity stops before e^-5 criteria. Why it is happening? My solution is right or i have done some mistake in input? 

abenhadj posted this 08 February 2019

Just click and read the documentation thoroughly. I guess this solves this thread and you can mark it as resolved.

Best regards,

Amine

mdfaizan444 posted this 08 February 2019

My query is do i need to calculate the drift and slip velocity or just tick the slip velocity.

abenhadj posted this 08 February 2019

And if you account for slip it is what you shared under Drift Flux.

Best regards,

Amine

abenhadj posted this 08 February 2019

Do you need to account for binary particle collisions? If not switch off "Granular". If yes stick to the default.

Best regards,

Amine

abenhadj posted this 08 February 2019

Create a fluid material for your nano-particles and assign phase-2 to that new material.

Best regards,

Amine

mdfaizan444 posted this 08 February 2019

 in mixture model, in phase 2, what will be mine phase material and if i considered granular what i will have to put in granular viscosity?

Also i need to specify the AL2O3 properties like density, thermal conductivity specific heat etc. where i have to put it? 

Do i need to calculate average properties of nano fluid, if yes where i have to put it? Or these equations is for homogeneous model?

also where i have specify volume fraction of solid particle?

mdfaizan444 posted this 08 February 2019

Actually i am validating one of the paper in which they have used mixture model for nanofluid transport.

i am using water as a base fluid and Al2O3 as nanoparticle. in mixture model primary phase i am giving water and what will be my secondary phase?, as in secondary phase option only liquid material is showing in the option. 

Also in mixture model do i need to calculate drift velocity, slip velocity mean viscosity or ANSYS take it by default?, As in ANSYS guide manual these formula's are given.

 

abenhadj posted this 08 February 2019

If my post answers your question, please mark Is Solution to show that the discussion is Solved, or ask a follow-up question.

Best regards,

Amine

Peace posted this 08 February 2019

Thank you for your reply. Will try and revert

abenhadj posted this 08 February 2019

Have you put your parts under a single multibody part?

You can put all parts under single part, in ANSYS Meshing you give for fluid surface a dedicated name and name for the contact line between the surfaces. This would result in conformal mesh with 4 cell zones and dedicated names for the contact between the cell zones (internal boundary).

Best regards,

Amine

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