Solidworks Flow simulation Boundary condition question [image included]

diego11 · July 22, 2012, 18:03

Hey everyone,

I need some help with the boundary conditions of this problem. The water tank you see here has some jets on the inside corners (highlighted yellow) and along some of the walls. each one of the jet should shoot water into the tank at 4.6 m/s. I think I got that one...

But, I need a volume flow rate on these floor drains that should be releasing 40% of the volume as an outlet. There will be other drains that release 60% of the volume.

When I try to do this, it requests a pressure outlet, though.

can you guys help me set up the boundary conditions on this?

Also, the top lid of the tank is required for the solidworks flow simulation but it will actually be open to air and shouldn't ever overflow. is there a boundary condition I should be putting on this?

Thanks so much everybody!

edit: also, what goals should i be putting on this problem? trying to find the velocity of water in the tank at several points, but i think vectors/contours will tell me that after anyway

Boris_M · August 6, 2012, 03:52

Hi Diego,
the problem you are trying to solve is hard to solve with SW Flow Simulation. It is a free surface flow you are trying to solve. For some of these tasks you can simplify the model just like you did with the lid on top fixing a fluid surface. But with the requested boundary conditions you have it doesn't work as SWFS needs to have either at least two pressure openings or at least one pressure and one flow rate openings. With two flow rate openings you have not defined a pressure and therefore it cannot be solved. The initial condition settings with pressure do not define where the pressure lies, with a pressure boundary condition a specific pressure is defined at a certain location and the pressure distribution can be calculated.

Where do you get your velocity from or the outlet volume flow?
If you have another opening that takes 60% of the volume flow rate then why not define a pressure boundary condition there and a volume flow rate condition to the 40% opeing. then you have at least one pressure opeing and since the mass balance has the be fulfilled it will be by pushing in a certain mass through the pipes and sucking out a certain mass through the one opening and the rest goes through the other opening.

I hope this helps,
Boris

diego11 · August 7, 2012, 16:44

Boris,

Thank you so much for reaching out. On this problem, I did just that:

I put an ideal lid on the top. I placed a pressure outlet on the center drains that are on the floor and on another outlet I placed a 60% mass flow boundary condition.

those inlet jets remained as a velocity inlet.

In the surface goals, i placed a mass flow goal on the center drain and in fact did see 40% of the flow leaving that drain.

I'm not sure if the pressure gradients solved by SWFS were correct. Thanks again for your help. Is this approach similar to the one you described?

p.s. - If anyone has any advice on this one, I'm happy to hear it and run a new simulation.

Boris_M · August 8, 2012, 03:26

Hi Diego,
that's exactly what I meant. You could also run a simulation where you define the mass flow rate on the 40% opening and the pressure opening on the 60% so you can see a difference on the simulation results that may occure due to forcing a suction boundary condition on the one outlet but not on the other.

It is hard to say if the pressure field is good as the software is not really capable of doing such free flow/free surface flows. So this is just an aproximation.

Boris

July 22, 2012, 18:03	Solidworks Flow simulation Boundary condition question [image included]	#1
diego11 New Member Diego Join Date: Jul 2012 Posts: 3 Rep Power: 14	Hey everyone, I need some help with the boundary conditions of this problem. The water tank you see here has some jets on the inside corners (highlighted yellow) and along some of the walls. each one of the jet should shoot water into the tank at 4.6 m/s. I think I got that one... But, I need a volume flow rate on these floor drains that should be releasing 40% of the volume as an outlet. There will be other drains that release 60% of the volume. When I try to do this, it requests a pressure outlet, though. can you guys help me set up the boundary conditions on this? Also, the top lid of the tank is required for the solidworks flow simulation but it will actually be open to air and shouldn't ever overflow. is there a boundary condition I should be putting on this? Thanks so much everybody! edit: also, what goals should i be putting on this problem? trying to find the velocity of water in the tank at several points, but i think vectors/contours will tell me that after anyway

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August 6, 2012, 03:52		#2
Boris_M Disabled Join Date: Jul 2009 Posts: 616 Rep Power: 24	Hi Diego, the problem you are trying to solve is hard to solve with SW Flow Simulation. It is a free surface flow you are trying to solve. For some of these tasks you can simplify the model just like you did with the lid on top fixing a fluid surface. But with the requested boundary conditions you have it doesn't work as SWFS needs to have either at least two pressure openings or at least one pressure and one flow rate openings. With two flow rate openings you have not defined a pressure and therefore it cannot be solved. The initial condition settings with pressure do not define where the pressure lies, with a pressure boundary condition a specific pressure is defined at a certain location and the pressure distribution can be calculated. Where do you get your velocity from or the outlet volume flow? If you have another opening that takes 60% of the volume flow rate then why not define a pressure boundary condition there and a volume flow rate condition to the 40% opeing. then you have at least one pressure opeing and since the mass balance has the be fulfilled it will be by pushing in a certain mass through the pipes and sucking out a certain mass through the one opening and the rest goes through the other opening. I hope this helps, Boris

August 7, 2012, 16:44		#3
diego11 New Member Diego Join Date: Jul 2012 Posts: 3 Rep Power: 14	Boris, Thank you so much for reaching out. On this problem, I did just that: I put an ideal lid on the top. I placed a pressure outlet on the center drains that are on the floor and on another outlet I placed a 60% mass flow boundary condition. those inlet jets remained as a velocity inlet. In the surface goals, i placed a mass flow goal on the center drain and in fact did see 40% of the flow leaving that drain. I'm not sure if the pressure gradients solved by SWFS were correct. Thanks again for your help. Is this approach similar to the one you described? p.s. - If anyone has any advice on this one, I'm happy to hear it and run a new simulation.

August 8, 2012, 03:26		#4
Boris_M Disabled Join Date: Jul 2009 Posts: 616 Rep Power: 24	Hi Diego, that's exactly what I meant. You could also run a simulation where you define the mass flow rate on the 40% opening and the pressure opening on the 60% so you can see a difference on the simulation results that may occure due to forcing a suction boundary condition on the one outlet but not on the other. It is hard to say if the pressure field is good as the software is not really capable of doing such free flow/free surface flows. So this is just an aproximation. Boris