Custom Fluids (Hydraulic Oil)

n3rdmusic · July 5, 2012, 11:43

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

ghorrocks · July 5, 2012, 18:27

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?

n3rdmusic · July 5, 2012, 22:03

Quote:

Originally Posted by ghorrocks

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

ghorrocks · July 6, 2012, 02:04

Yes, by bulk properties I mean simply a fluid with a density, viscosity and vapour pressure representative of the true water-glycol mixture.

July 5, 2012, 11:43	Custom Fluids (Hydraulic Oil)	#1
n3rdmusic New Member John Smith Join Date: Jul 2012 Posts: 2 Rep Power: 0	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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July 5, 2012, 18:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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?

July 6, 2012, 02:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Yes, by bulk properties I mean simply a fluid with a density, viscosity and vapour pressure representative of the true water-glycol mixture.