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Old   July 5, 2012, 11:43
Default Custom Fluids (Hydraulic Oil)
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John Smith
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Hi CFD fans/experts,

Firstly I really appreciate any help at all as I've been through many ANSYS CFD customer portal tutorials, forum posts etc. but am still struggling to find a solution

I am attempting to model cavitation of hydraulic fluids through a pipe orifice restriction. I am trying to simulate water-glycol (40% water content) in the CFD-pre material designer. I only know its viscosity, density, operating temperature (and %diol polymers in fluid, not sure if relevant?).

I am wondering if to model the fluid as a fixed composite mixture or pure substance.

If doing it as a pure substance do I do a multiphase with water vapour (in the assumption that it has a higher vapour pressure and hence will cavitate out before the glycol itself).

In doing it as a fixed composite, do I set the child materials as water and glycol (don't know what type though)? however I only know the combined viscosity and density; and what is the mass fraction in this case?
Are mixture properties okay to not utilise if unknown? or should I attempt (as fluid properties obtained from an experimental report) to find them online?


Thanks in advance, any assistance would be much appreciated!
Regards,
Sam
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Old   July 5, 2012, 18:27
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Glenn Horrocks
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The CFX tutorials has an example on how to set up cavitation models.

I would start this model using the simple bulk material properties, as per the example. I would more complex than that if you have a clear reason to do so - do you have a good reason why bulk properties would not be adequate?
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Old   July 5, 2012, 22:03
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John Smith
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Quote:
Originally Posted by ghorrocks View Post
The CFX tutorials has an example on how to set up cavitation models.

I would start this model using the simple bulk material properties, as per the example. I would more complex than that if you have a clear reason to do so - do you have a good reason why bulk properties would not be adequate?
Thank for the quick response!

Assuming by bulk material properties you mean a pure substance model (for the water-glycol), and create multiphase fluid with this liquid and vapor (as seen in hydrofoil cavitation tutorial?) ?

In doing this do I just use the water vapor provided, even though I'm using a water-glycol fluid?

Thanks again mate!

Sam
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Old   July 6, 2012, 02:04
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Yes, by bulk properties I mean simply a fluid with a density, viscosity and vapour pressure representative of the true water-glycol mixture.
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