Boundary condition flow distribution three pipes

Klavoir · April 5, 2024, 05:46

Hi,

I have 3 pipes with different diameters which come together in one pipe. I know the total flow coming out of the pipe at the outlet. I want to calculate the distribution of the total flow over the three pipes. Therefore at the outlet I want to define a mass flow outlet.
What should I define as boundary condition at each of the inlets of the three pipes? Since the flow in the three pipes will be different also the pressures at the inlets will be different and unknown, so I cannot use a pressure inlet where I should have to define a pressure. What should I do? Thanks if anyone can help.

Maddy1984 · April 5, 2024, 06:54

Hello,

well in your case I would test it with an "Outflow". The help function states: "Outflow boundary conditions in ANSYS FLUENT are used to model flow exits where the details of the flow velocity and pressure are not known prior to solving the flow problem"

Sure, it would change it to an "outlet" but I'm currently not sure if that should be a problem for the simulation if you don't have an inlet.

If it is a problem, maybe change your "mass flow outlet" to an "mass flow inlet" and change your value to a negative value. I know it works for an velocity inlet if you want reverse flow, but I'm not sure if it also works for an "mass flow inlet".

Regards

April 5, 2024, 05:46	Boundary condition flow distribution three pipes	#1
Klavoir New Member Join Date: Sep 2021 Posts: 22 Rep Power: 4	Hi, I have 3 pipes with different diameters which come together in one pipe. I know the total flow coming out of the pipe at the outlet. I want to calculate the distribution of the total flow over the three pipes. Therefore at the outlet I want to define a mass flow outlet. What should I define as boundary condition at each of the inlets of the three pipes? Since the flow in the three pipes will be different also the pressures at the inlets will be different and unknown, so I cannot use a pressure inlet where I should have to define a pressure. What should I do? Thanks if anyone can help.

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April 5, 2024, 06:54		#2
Maddy1984 New Member Andreas Join Date: Jul 2022 Location: Southern Germany Posts: 5 Rep Power: 3	Hello, well in your case I would test it with an "Outflow". The help function states: "Outflow boundary conditions in ANSYS FLUENT are used to model flow exits where the details of the flow velocity and pressure are not known prior to solving the flow problem" Sure, it would change it to an "outlet" but I'm currently not sure if that should be a problem for the simulation if you don't have an inlet. If it is a problem, maybe change your "mass flow outlet" to an "mass flow inlet" and change your value to a negative value. I know it works for an velocity inlet if you want reverse flow, but I'm not sure if it also works for an "mass flow inlet". Regards