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Cavitation in N-Hexane

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Old   January 9, 2015, 14:41
Default Cavitation in N-Hexane
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Curtis F.
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I am trying to run a simulation of hydrodynamically induced cavitation in hexane. I am using C6H14l and C6H14 imported from the IPMT Library. Using the same geometry, mesh, physics, and boundary conditions I am able to converge with very good solutions that match experimental results neck-in-neck when using Water at 25C and Water Vapor at 25C.

When I change my working materials to hexane I start to run into trouble.
First I initialize the problem by just using liquid. My solution converges to RMS values less than 1e-5 and imbalances are less than 1%. Then I run a simulation using hexane liquid and vapor with the cavitation model turned off. Again, I run until RMS is less than 1e-5 and imbalances are less than 1% (this usually takes a long time even when ran in parallel).

The problem is two fold. A) I have small amounts of hexane vapor in my solution even when the cavitation model is turned off and B) when I turn on cavitation, initialized from simulation with it turned off, I am not able to converge and my imbalances go crazy. Why is this?

I have tried setting the density off the vapor to make for incompressible flow but this has had no affect on the issue.

I've attached my ccl file to look at as well.

Hopefully someone can catch the silly mistake I am making. This is my first time posting and have been using the forum for some time now for learning how to use CFX. You guys have been a great resource. Any help with this would be very much appreciated!
-Pugnax
Attached Files
File Type: txt Hex_30psi_90F_LVC.txt (13.6 KB, 10 views)

Last edited by Pugnax; January 12, 2015 at 15:16.
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Old   January 18, 2015, 05:41
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Glenn Horrocks
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Quote:
A) I have small amounts of hexane vapor in my solution even when the cavitation model is turned off
If it is a small amount then why worry about it? CFD is not exact, especially with cavitation models.

Quote:
B) when I turn on cavitation, initialized from simulation with it turned off, I am not able to converge and my imbalances go crazy. Why is this?
Cavitation models are always hard to converge. You are probably not making a silly mistake, these things are hard. If all the standard tricks do not work (http://www.cfd-online.com/Wiki/Ansys...do_about_it.3F) then you probably need to run this as a transient simulation.
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