Mixing with free surface

ah_eshtiaghi · April 8, 2013, 23:37

Hi
I have a problem of a mixing tank with free surface which diverges after 15 iterations.
My problem is a simple cylindrical tank of 6m in diameter and 18m high. the tank has two inlets and two outlets at elevation of 1m that mixing two water streams and extract water from two different outlets. the water height in the tank is 5m and rest of the tank is air above the water. I used VOF model in cfx. above the tank, there is a hole that keeps the air pressure above the water atmospheric. I set the inlet and outlet mass flow rates in a way that the total mass balance is zero. I solved the problem as steady state and initially used an expression of WaterHt=if(y<6 [m],1,0) as initial value. My simulation runs for 15 iterations and then it diverges. i do not understand what I did wrong. I am new in the two phase simulation and spent a long time studying VOF modeling in CFX.
I would be grateful if someone can help me on solving this problem.
Regards

evcelica · April 12, 2013, 00:17

How are you defining you inlets and outlets? Does the surface really affect the flow, meaning can you just do single phase?

April 8, 2013, 23:37	Mixing with free surface	#1
ah_eshtiaghi New Member Amir Eshtiaghi Join Date: Apr 2009 Location: Massachusetts, USA Posts: 9 Rep Power: 17	Hi I have a problem of a mixing tank with free surface which diverges after 15 iterations. My problem is a simple cylindrical tank of 6m in diameter and 18m high. the tank has two inlets and two outlets at elevation of 1m that mixing two water streams and extract water from two different outlets. the water height in the tank is 5m and rest of the tank is air above the water. I used VOF model in cfx. above the tank, there is a hole that keeps the air pressure above the water atmospheric. I set the inlet and outlet mass flow rates in a way that the total mass balance is zero. I solved the problem as steady state and initially used an expression of WaterHt=if(y<6 [m],1,0) as initial value. My simulation runs for 15 iterations and then it diverges. i do not understand what I did wrong. I am new in the two phase simulation and spent a long time studying VOF modeling in CFX. I would be grateful if someone can help me on solving this problem. Regards

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Thermocapillary free surface flow	zakifoam	OpenFOAM Running, Solving & CFD	10	December 12, 2016 12:44
Free surface in mixing vessel	blubb1612	CFX	8	November 28, 2012 11:16
curve of vortex of free surface in mixing tank	bioman66	CFX	1	June 30, 2006 07:19
Equilibrium of a free surface under surface tensio	Ryan	Main CFD Forum	1	August 7, 2001 17:14
Modeling Free Surface Flows	Elliot Schwartz	Main CFD Forum	5	August 25, 1998 22:03

April 12, 2013, 00:17		#2
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,186 Rep Power: 23	How are you defining you inlets and outlets? Does the surface really affect the flow, meaning can you just do single phase?