Boundary conditions on free water surface

Per · October 15, 2012, 03:00

Hi everybody

I am modeling water flow around an object in a flume tank. (Basically a circulating water tank open to the air at the test section). I am using simpleFoam.

I am not quite sure how to model the free surface. So far zero gradient for pressure and slip condition for velocity have been used (U_normal=0 and zero gradient parallel to the surface). The turbulence parameters have also been given slip boundary conditions. Does anyone have an idea of what is correct in this situation?

Any help is appreciated

Per

michielm · October 15, 2012, 06:25

I am far from an expert on turbulence modelling, but I guess you would need to switch to the interFoam solver if you wish to capture the free surface (and its motion) correctly.

Per · October 15, 2012, 06:33

Thanks for the reply.

The velocity (of the uniform water current field) is so small that there will be no significant water elevation (as observed from physical experiments done of the exact same case I am modeling). Therefor I am only interested in boundary conditions that give the correct (or near enough) velocity profile and pressure near and at the free surface. I do not want to introduce unphysical constraints on the flow due to incorrect water surface modeling.

Per

liu · October 15, 2012, 11:19

No good solution.

Free slip (or rigid lid) kills vertical fluctuation of turbulence. It also distorts the distribution of other flow variables.

Quote:

Originally Posted by Per

Hi everybody

I am modeling water flow around an object in a flume tank. (Basically a circulating water tank open to the air at the test section). I am using simpleFoam.

I am not quite sure how to model the free surface. So far zero gradient for pressure and slip condition for velocity have been used (U_normal=0 and zero gradient parallel to the surface). The turbulence parameters have also been given slip boundary conditions. Does anyone have an idea of what is correct in this situation?

Any help is appreciated

Per

Per · October 16, 2012, 03:31

Well, ok. That's not good. Do you have any suggestion for how I can model the water surface? That is the correct velocities and pressure. I need to use a turbulence model. My Reynolds number is in the order of magnitude 3e5.

Per

October 15, 2012, 03:00	Boundary conditions on free water surface	#1
Per New Member Per Christian Endresen Join Date: Feb 2012 Location: Trondheim, Norway Posts: 13 Rep Power: 14	Hi everybody I am modeling water flow around an object in a flume tank. (Basically a circulating water tank open to the air at the test section). I am using simpleFoam. I am not quite sure how to model the free surface. So far zero gradient for pressure and slip condition for velocity have been used (U_normal=0 and zero gradient parallel to the surface). The turbulence parameters have also been given slip boundary conditions. Does anyone have an idea of what is correct in this situation? Any help is appreciated Per

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October 15, 2012, 06:25		#2
michielm Member Michiel Join Date: Oct 2010 Location: Delft, Netherlands Posts: 97 Rep Power: 15	I am far from an expert on turbulence modelling, but I guess you would need to switch to the interFoam solver if you wish to capture the free surface (and its motion) correctly.

October 15, 2012, 06:33		#3
Per New Member Per Christian Endresen Join Date: Feb 2012 Location: Trondheim, Norway Posts: 13 Rep Power: 14	Thanks for the reply. The velocity (of the uniform water current field) is so small that there will be no significant water elevation (as observed from physical experiments done of the exact same case I am modeling). Therefor I am only interested in boundary conditions that give the correct (or near enough) velocity profile and pressure near and at the free surface. I do not want to introduce unphysical constraints on the flow due to incorrect water surface modeling. Per

October 16, 2012, 03:31		#5
Per New Member Per Christian Endresen Join Date: Feb 2012 Location: Trondheim, Norway Posts: 13 Rep Power: 14	Well, ok. That's not good. Do you have any suggestion for how I can model the water surface? That is the correct velocities and pressure. I need to use a turbulence model. My Reynolds number is in the order of magnitude 3e5. Per