Two phase simulation - velocity of water above air-water interface isn't zero

Zeljko · February 27, 2018, 10:12

Hi,

I have a multiphase simulation of mixing vessel (water has been mixed and air is above water while vessel is closed on the top). When I check the results and velocity contours of water (water.Velocity) on some vertical plane, I get non-zero velocity of water above the water level. What is the reason for that? Besides, volume fraction of water is as expected (0 above water level and 1 below water level).

Thank you.

ghorrocks · February 27, 2018, 14:58

I assume you are doing a homogenous free surface simulation. In these simulations there is a single velocity field which is shared for both water and air. So the post processor will show water.Velocity everywhere, even locations where the water volume fraction is zero. This holds for inhomogenous free surface simulations as well, the velocity field of all phases covers the entire domain, even where the volume fraction is zero.

Zeljko · February 27, 2018, 15:30

Hi ghorrocks,

Thanks for your reply. Does it mean that I can't see air velocity field although in case of inhomogenous simulation? Shouldn't each fluid have it's own velocity field in that case?

ghorrocks · February 27, 2018, 15:37

Regardless of whether the simulation is inhomogeneous or homogeneous, the post processor will show velocity fields for all phases, eg air.Velocity, water.Velocity. In a homogeneous simulation the air.Velocity and water.Velocity fields will be the same.

Zeljko · February 27, 2018, 15:45

Ok, so I am able to observe the difference in velocity fields for air and water in case of inhomogenous.

February 27, 2018, 10:12	Two phase simulation - velocity of water above air-water interface isn't zero	#1
Zeljko New Member Join Date: May 2011 Posts: 8 Rep Power: 14	Hi, I have a multiphase simulation of mixing vessel (water has been mixed and air is above water while vessel is closed on the top). When I check the results and velocity contours of water (water.Velocity) on some vertical plane, I get non-zero velocity of water above the water level. What is the reason for that? Besides, volume fraction of water is as expected (0 above water level and 1 below water level). Thank you.

February 27, 2018, 14:58		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I assume you are doing a homogenous free surface simulation. In these simulations there is a single velocity field which is shared for both water and air. So the post processor will show water.Velocity everywhere, even locations where the water volume fraction is zero. This holds for inhomogenous free surface simulations as well, the velocity field of all phases covers the entire domain, even where the volume fraction is zero. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 27, 2018, 15:37		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Regardless of whether the simulation is inhomogeneous or homogeneous, the post processor will show velocity fields for all phases, eg air.Velocity, water.Velocity. In a homogeneous simulation the air.Velocity and water.Velocity fields will be the same. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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February 27, 2018, 15:30		#3
Zeljko New Member Join Date: May 2011 Posts: 8 Rep Power: 14	Hi ghorrocks, Thanks for your reply. Does it mean that I can't see air velocity field although in case of inhomogenous simulation? Shouldn't each fluid have it's own velocity field in that case?

February 27, 2018, 15:45		#5
Zeljko New Member Join Date: May 2011 Posts: 8 Rep Power: 14	Ok, so I am able to observe the difference in velocity fields for air and water in case of inhomogenous.