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Thermal Two Fluid (Not Interacting with Each Other) in CFX

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Old   December 17, 2019, 12:09
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Quote:
Originally Posted by Opaque View Post
If you follow Glenn's suggestion of using multicomponent approach (which is limited and you will find out later if you need additional functionality) be certain you set the material components as algebraic; therefore, no need to solve any equations nor boundary conditions.

You must initialize these expressions to be 1 in the domain the material exists, and 0 in the other. Similarly for the second material component. How do you do it?

COMPONENT: Material 1
Mass Fraction = inside()@Domain 1

COMPONENT: Material 2
Mass Fraction = inside()@Domain 2

Done!!
Hi. I have the same modeling problem like this guy above and I've decided to go with path, that you suggested, but when I use these expressions modified to my case solver is going to crash. Can you tell me where do you put this expressions? And should I use Pure Substance, Fixed Composition Mixture or Variable Composition Mixture? Thanks in advance
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Old   December 17, 2019, 12:58
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You set up those expressions within each Domain/Fluid Models/Component Details.
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Old   December 17, 2019, 13:09
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Originally Posted by Opaque View Post
You set up those expressions within each Domain/Fluid Models/Component Details.
I've put it as expressions: inside()@Air and inside()@Oil, but it still going to crash. The problem is certainly with this expression, because when I put numerical values e.g. 0.5 for each components, the case start pretty nice. And when I try to evaluate expression Expressions/Evaluate for command that you've proposed, the evaluated value shows [ERROR]. Seems like unit error.. Did you try this work around for any of your analysis with 2 different fluid domains?
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Old   December 17, 2019, 13:32
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Is Air the name of the CFX domain, or the name of a material?
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Old   December 17, 2019, 13:34
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Originally Posted by Opaque View Post
Is Air the name of the CFX domain, or the name of a material?
It's the name of domain, the same for oil. I put in these expressions names of domains.
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Old   December 17, 2019, 14:38
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How are your materials and fluid named?

It is probably best if you can post the error message you are getting.
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Old   December 18, 2019, 04:12
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Originally Posted by Opaque View Post
How are your materials and fluid named?

It is probably best if you can post the error message you are getting.
So the fluid, that I'm using is based on your approach with multi-component material (air + oil) named "Air Ideal Gas and Oil". And I just use this material for for air and oil domains simultaneously. When I open one of this domains and go to Fluid Models/Component Models/Component I can put expression, that you have suggested for each material component (with Algebraic Equation option). Is that right?

Here is that error message I get:
Attached Images
File Type: png Error_01.PNG (24.7 KB, 6 views)
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Old   December 18, 2019, 08:09
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Can you post the definition of the materials being used? Not only the pure substances, but the mixture as well.

It seems the density of one of them is missing something
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Old   December 18, 2019, 09:05
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Originally Posted by Opaque View Post
Can you post the definition of the materials being used? Not only the pure substances, but the mixture as well.

It seems the density of one of them is missing something
Images Error_02 and Error_03 relate to mixture definition and Error_04, Error_05 relate to Pure substance definition of oil - you can see, that density, heat capacity, viscosity and thermal conductivity are defined by User Functions. These functions are correct, because were used many time in previous models.
Air properties comes from Air Ideal Gas CFX material library.
Attached Images
File Type: png Error_02.PNG (8.6 KB, 1 views)
File Type: png Error_03.PNG (10.1 KB, 1 views)
File Type: png Error_04.PNG (6.7 KB, 2 views)
File Type: png Error_05.PNG (22.1 KB, 1 views)
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Old   December 18, 2019, 10:51
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I think (just a guess) that once Non Ideal Mixture is selected you must provide the Equation of State.

My advice, since you are not mixing the materials anyways, is to use Ideal Mixture.

Equation of State defines density implicitly or explicitly as a function of temperature, pressure and composition in this case.

My guess: you have not defined the density, and the software failed to find it
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Old   December 18, 2019, 11:16
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Originally Posted by Opaque View Post
I think (just a guess) that once Non Ideal Mixture is selected you must provide the Equation of State.

My advice, since you are not mixing the materials anyways, is to use Ideal Mixture.

Equation of State defines density implicitly or explicitly as a function of temperature, pressure and composition in this case.

My guess: you have not defined the density, and the software failed to find it
I did it already.. And it doesn't matter.. It's interesting issue, ins't it?
And what about User Functions? Don't you think that material properties for mixture component comprising constant values and from User functions can be too difficult for CFX solver to calculate? That's exactly like in my case..
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Old   December 18, 2019, 15:49
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In principle, you are not mixing anything, correct? it is just a fake/dummy setup to trick the software into independent physics in two different passages

Have you tried to setup the case with standard materials? i.e. materials provided by the software.

I personally do not like the multi component approach to set up this type of problems, but others in the forum have been successful in the past; therefore, it is a process that works.
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Old   December 18, 2019, 17:40
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Originally Posted by Opaque View Post
In principle, you are not mixing anything, correct? it is just a fake/dummy setup to trick the software into independent physics in two different passages

Have you tried to setup the case with standard materials? i.e. materials provided by the software.

I personally do not like the multi component approach to set up this type of problems, but others in the forum have been successful in the past; therefore, it is a process that works.
Yes, this trick was only to choose different material components for each fluid domain. So, as I mentioned before it work even as mixture of air and oil defined by user, but only when I put numerical value for mass fractions. When I switch to expression inside()@Domain_name it's going to crash.. So, my modeling with this approach has finished at that step - problem with expression Have you got idea if they should be defined in other way?
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