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Multiphase Oil Air - Initialization CFX

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Old   September 9, 2021, 08:42
Exclamation Multiphase Oil Air - Initialization CFX
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Hello all,

I have a domain where I want to simulate oil-air mixture in CFX

I have a wall (rotor) which is rotating at high speed. There are inlets for oil defined with mass flow rate.

I want to simulate the effect of oil-air mixture on the rotor - how much the oil-air mixture can cool the rotor surface.

I have in my model, only inlets defined for oil. I know there is air present, but no inlet for incoming air.

My questions is;

1) Do I patch the domain with Volume Fraction of air = 1 and Volume Fraction of oil = 0 ?

2) Should I use for both Air and Oil the continous phase ? Or should I use for Oil as Dispersed Phase ?

Regards,

RJ
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Old   September 9, 2021, 10:00
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Is it an oil jet, or oil mist?

You can always initialize each domain, and there is a setting for the volume fraction. Just set it to 1 and 0 respectively.
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Old   September 9, 2021, 10:40
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Henrique Stel
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Where is the air coming from in the real geometry so that your domain of interest will eventually work with an oil-air mixture? Do you have any information about the expected morphology of this mixture in the real case?
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Old   September 9, 2021, 11:17
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Quote:
Originally Posted by Opaque View Post
Is it an oil jet, or oil mist?

You can always initialize each domain, and there is a setting for the volume fraction. Just set it to 1 and 0 respectively.
So basically, oil flowing through oil pipes. As soon as it enters the domain, it mixes with air and forms a mist.

The oil-mist spreads over the rotating surface and probably cools it.

So should I use air as continous phase and the oil as dispersed phase ?

Regards.
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Old   September 9, 2021, 19:17
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Yes, the air is the continuous phase and the oil is the dispersed phase. Have you considered what physical model you are going to use to model this? From what you have described a Eularian inhomogeneous model sounds likely, but you would need to describe it in more detail for us to be sure.
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Old   September 11, 2021, 07:19
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Quote:
Originally Posted by ghorrocks View Post
Yes, the air is the continuous phase and the oil is the dispersed phase. Have you considered what physical model you are going to use to model this? From what you have described a Eularian inhomogeneous model sounds likely, but you would need to describe it in more detail for us to be sure.
Sorry for my late reply.

I have tried both homogenous and non-homogenous model.
With the homogenous model, the simulation runs however I am not sure if it is the right way.

When I choose the non-homogenous option, the simulation crashes?

Any experience with these two options? any advice would be valuable?
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Old   September 11, 2021, 19:27
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You choose the models to use based on the physics you want to capture, not what appears to run.

If this is a fine oil mist then inhomogeneous is the model to use. Homogeneous is not appropriate.

Please upload your Output file from the inhomogeneous run and we can have a look at it. Also please post an image of what you are trying to model, and the results you expect to get.
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cfx, heat transfer, multiphase, oil, volume fraction

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