multiphaseInterFoam, velocity appears from nowhere

Leo43 · September 10, 2013, 05:22

Hello,

I have only few experience on OpenFoam and I have a problem that I can not solve...

I have a cylinder filled with 2 different fluids with different density, the fluid with the lower density is on the upper part.
2phases.jpg
checkMesh.log.txt
(the mesh is quite inaccurate, but even if I do it more precisely, this problem still appears).

The cylinder is closed (every boundary condition = wall )
Every initial condition (internal/boundary conditions, p_rgh, U, alphas) are set up to uniform0 or ZeroGradient, and there is no initial velocity.
p_rgh.txt
U.txt
So, I was expecting that the system remains stable in the time, I mean always egal to the initial configuration.

But, after lauching the simulation, a velocity appears inside the cylinder from nowhere, for example here, after 200s computation, we have a max velocity of 0.03 m/s around the interface of the 2 fluids.
velocity.jpg

I don't know where is my mistake... Can someone helps me to solve this ?

Thank you !

Phicau · September 10, 2013, 05:45

Hi Leopold,

these are the infamous "parasitic currents" (a.k.a. "spurious velocities") that appear due to the kind of VOF function used in OpenFOAM.

There are lots of information about them in the forum, you should take some time to learn about them, but in short, no one has been able to make them disappear (yet).

Best,

Pablo

Leo43 · September 10, 2013, 06:22

Ok !
Thank you very much Pablo, as you had suggested, I will look for information about this problem, as I can now put a name on it !

Leo

September 10, 2013, 05:22	[Solved] multiphaseInterFoam, velocity appears from nowhere	#1
Leo43 New Member a Join Date: Aug 2012 Posts: 2 Rep Power: 0	Hello, I have only few experience on OpenFoam and I have a problem that I can not solve... I have a cylinder filled with 2 different fluids with different density, the fluid with the lower density is on the upper part. 2phases.jpg checkMesh.log.txt (the mesh is quite inaccurate, but even if I do it more precisely, this problem still appears). The cylinder is closed (every boundary condition = wall ) Every initial condition (internal/boundary conditions, p_rgh, U, alphas) are set up to uniform0 or ZeroGradient, and there is no initial velocity. p_rgh.txt U.txt So, I was expecting that the system remains stable in the time, I mean always egal to the initial configuration. But, after lauching the simulation, a velocity appears inside the cylinder from nowhere, for example here, after 200s computation, we have a max velocity of 0.03 m/s around the interface of the 2 fluids. velocity.jpg I don't know where is my mistake... Can someone helps me to solve this ? Thank you ! Last edited by Leo43; September 10, 2013 at 06:23. Reason: [Solved]

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September 10, 2013, 05:45		#2
Phicau Senior Member Pablo Higuera Join Date: Jan 2011 Location: Auckland Posts: 627 Rep Power: 19	Hi Leopold, these are the infamous "parasitic currents" (a.k.a. "spurious velocities") that appear due to the kind of VOF function used in OpenFOAM. There are lots of information about them in the forum, you should take some time to learn about them, but in short, no one has been able to make them disappear (yet). Best, Pablo

September 10, 2013, 06:22		#3
Leo43 New Member a Join Date: Aug 2012 Posts: 2 Rep Power: 0	Ok ! Thank you very much Pablo, as you had suggested, I will look for information about this problem, as I can now put a name on it ! Leo