uphold gas/VF of air Monitoring point

Zigec · October 21, 2016, 10:40

Hey,

I'm doing a two phase flow (water-air) in a mixing vessel. Everything runs fine, but I have a problem with an important monitoring point.

I need the data for Volume fraction of air or the Volume of air in the water. I have the VF data for the rotating domain and for the whole vessel, but i have no idea how to monitor this for the whole region under the surface of water (under the black line), because as you can see the geometry of this surface is so that i can't do a subdomain, which will fit to this criterion.

Had any one the same problem and knows how to deal with this?

"About the simulation:"
It's a transient simulation of a mixing vessel for the dispersion of air in water. The stirrer has a speed of 1000rpm and the air inlet is 12l/min.
Euler-Euler with ishii-zuber drag model.

ghorrocks · October 22, 2016, 04:53

In CFD-Post you can define the liquid region (ie under your black line) as a volume defined by an isosurface. Then you can get the volume fraction of air inside that volume.

Zigec · October 22, 2016, 05:23

I did the isosurface in cfx-post but it makes not only the surface from water on the top (black line) of the vessel, but also on all the other borders between air and water (where the bubbles are) so I don't truly understand how would you realize that idea of yours?

And the next thing is, I don't write every time step, I only do every 2000th of it. Because I only need a few parameters from monitoring and the output file would be to large. Also in cfx-post I can only get variables for the written time steps, or? If yes, than I get only 6 data in 1s simulation.

ghorrocks · October 23, 2016, 05:31

You have to make a volume from the isosurface. The isosurface is just a surface so you cannot do volume integrals on it.

Have a look in the output options to write either a reduced set of output variables for a large number of time steps, or even to do some basic post processing as the solver progresses.

Zigec · October 23, 2016, 05:33

I will try. Thank you for now

October 21, 2016, 10:40	uphold gas/VF of air Monitoring point	#1
Zigec New Member Ziga Join Date: Feb 2016 Location: Maribor, Slovenia Posts: 27 Rep Power: 10	Hey, I'm doing a two phase flow (water-air) in a mixing vessel. Everything runs fine, but I have a problem with an important monitoring point. I need the data for Volume fraction of air or the Volume of air in the water. I have the VF data for the rotating domain and for the whole vessel, but i have no idea how to monitor this for the whole region under the surface of water (under the black line), because as you can see the geometry of this surface is so that i can't do a subdomain, which will fit to this criterion. Had any one the same problem and knows how to deal with this? "About the simulation:" It's a transient simulation of a mixing vessel for the dispersion of air in water. The stirrer has a speed of 1000rpm and the air inlet is 12l/min. Euler-Euler with ishii-zuber drag model.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Monitoring a point in dynamic mesh	Modisa	FLUENT	1	December 19, 2008 03:04
monitoring fluctuations at a point	ED	FLUENT	2	February 24, 2007 04:05
monitoring fluctuations at a point	ED	Main CFD Forum	0	February 23, 2007 11:58
How can I create a rotating monitoring point?	Andy Cong	FLUENT	0	September 10, 2006 20:09
CFX4.3 -build analysis form	Chie Min	CFX	5	July 12, 2001 23:19

October 22, 2016, 04:53		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	In CFD-Post you can define the liquid region (ie under your black line) as a volume defined by an isosurface. Then you can get the volume fraction of air inside that volume.

October 22, 2016, 05:23		#3
Zigec New Member Ziga Join Date: Feb 2016 Location: Maribor, Slovenia Posts: 27 Rep Power: 10	I did the isosurface in cfx-post but it makes not only the surface from water on the top (black line) of the vessel, but also on all the other borders between air and water (where the bubbles are) so I don't truly understand how would you realize that idea of yours? And the next thing is, I don't write every time step, I only do every 2000th of it. Because I only need a few parameters from monitoring and the output file would be to large. Also in cfx-post I can only get variables for the written time steps, or? If yes, than I get only 6 data in 1s simulation.

October 23, 2016, 05:31		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You have to make a volume from the isosurface. The isosurface is just a surface so you cannot do volume integrals on it. Have a look in the output options to write either a reduced set of output variables for a large number of time steps, or even to do some basic post processing as the solver progresses.

October 23, 2016, 05:33		#5
Zigec New Member Ziga Join Date: Feb 2016 Location: Maribor, Slovenia Posts: 27 Rep Power: 10	I will try. Thank you for now