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Eulerian model theory

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Old   August 29, 2018, 09:39
Default Eulerian model theory
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Hamed Abdul Majeed
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Hi guys,

Can anybody recommend to me the source for the Eulerian model. Something that would help me to strengthen the theory of the Eulerian model. I've been trying to find this, if anybody can share, A Two-Fluid Model for Fluent, Flow Simulation Consultants, Ltd., Sheffield, England, Boysan, F.
, 1990.


I have the following questions:

1. Eulerian multiphase model allows for modeling of multiple separate yet interpenetrating phases! What does this statement mean??

2. If the secondary phase is a droplet (as we provide diameter in the model) how could a NS equation, which is continuous, be valid for it?

Thank you.

Best Wishes,
H.
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Old   August 29, 2018, 11:06
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1. Interpenetrating means you have several phases but you do not restrict a bulk region as having only 1 particular phase. I.e. you can have little droplets of phase 1 inside a region that is mostly phase 2.

2. You write down a (usually volume-fraction weighted) navier-stokes equations for each phase. There are several interphase terms that are added to this system (i.e. force of phase 1 acting on phase 2). A proper specification of these terms allows the phases to interact. So what you are solving is a set of coupled navier-stokes equations.
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Old   August 29, 2018, 12:13
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Quote:
Originally Posted by LuckyTran View Post
1. Interpenetrating means you have several phases but you do not restrict a bulk region as having only 1 particular phase. I.e. you can have little droplets of phase 1 inside a region that is mostly phase 2.
Thanks Lucky.

So interpenetrating is as opposed to separated flow.

Q. Eulerian multiphase model is fluent is as they refer in theory as "two-fluid model"? But is the model just used for dispersed flow then??

Thank you.
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Old   August 30, 2018, 00:46
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Far from dispersed. The size of these droplets can be as large as the surface tension supports. And whether or not you get any droplets at all is also dependent on these force interactions. I used the term "little droplets" just to illustrate that you can end up with phase 1 stuck inside phase 2. You can have big droplets or non-droplets or you can even end up with two immiscible flows.

Besides, if you were doing a dispersed phase, you wouldn't need two complete momentum equations because you'd have a dispersed phase and a carrier phase. Here you are solving a more-or-less homogeneous mixture with funny properties.
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Old   August 31, 2018, 13:00
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Far from dispersed. The size of these droplets can be as large as the surface tension supports. And whether or not you get any droplets at all is also dependent on these force interactions. I used the term "little droplets" just to illustrate that you can end up with phase 1 stuck inside phase 2. You can have big droplets or non-droplets or you can even end up with two immiscible flows.

Besides, if you were doing a dispersed phase, you wouldn't need two complete momentum equations because you'd have a dispersed phase and a carrier phase. Here you are solving a more-or-less homogeneous mixture with funny properties.
Dear Lucky,

This thing confuses me. Now in Eulerian multiphase model in Fluent I get a plot of volume fraction of phases. I see that there is a relationship between volume fraction and population number density of secondary phase.
So the plots are like bands of volume fraction!!

Is there a way to turn on the coalescence between the secondary phase particles...so that they eventually become continuous and I could get segregated flow!!
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Old   August 31, 2018, 21:13
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Quote:
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Is there a way to turn on the coalescence between the secondary phase particles...so that they eventually become continuous and I could get segregated flow!!

This is done in other non-interpenetrating models. But your problem is that your mesh is not fine enough to resolve the interface. And do you even want/need to resolve it?
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Old   August 31, 2018, 21:52
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This is done in other non-interpenetrating models. But your problem is that your mesh is not fine enough to resolve the interface. And do you even want/need to resolve it?
Yes I do need to resolve it. It is flashing of saturated liquid as it passes through a siphon. I need to see the formation of vapor bubbles in the flow!
Other option is to use VOF as it has refined interface, but it has a single momentum equation which is not accurate.

Is there any reference you could recommend me on this!
Thank you for your help!
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Old   September 4, 2018, 07:16
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This is done in other non-interpenetrating models. But your problem is that your mesh is not fine enough to resolve the interface. And do you even want/need to resolve it?
What are the other non-interpenetrating models?
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