## Fluids

#### free surface vortex

• AhmedCfx
Subscriber

Dear All,

I need to simulate a water tank with a suction pipe. How can I make the level of water fixed at some level and the suction pipe make a vortex for a prolonged period? I've tried to make negative pressure at the outlet of the pipe, but the water level in the tank reduced. Please, any help with this problem?

Best regards

• peteroznewman
Subscriber

How about having an inlet pipe to the tank that has a mass flow rate of X kg/s and set a mass flow rat of X kg/s at the outlet? Then the level would remain steady.

• AhmedCfx
Subscriber
There is no BC in the outlet except the pressure , how can I add mass flow rate at the outlet?
• peteroznewman
Subscriber

So use a pressure outlet BC, and guess a value for X.  After you converge on the solution, you can report on the mass flow rate at the outlet, then change the inlet mass flow rate to match that value and rerun the simulation.

• AhmedCfx
Subscriber

Dear Peter

I did it, It works as normal flowrate inlet and outlet but the main goal of my project is to form a vortex just like the image below.

• AhmedCfx
Subscriber

What about negative pressure outlet? do you think it's work? and how can I calculate it?

• peteroznewman
Subscriber

Why change the water BCs if you have a stable flow from inlet to outlet without a change in level?

You should focus on the mesh to ensure it is fine enough to develop large eddy structures.

Is this a VOF model with air and water?  What are the BCs for the air?

How are you initializing the model?  Do you patch in the Air region?

• Rob
Ansys Employee

You can use a velocity boundary, just set the vector to be "out" or (you'll need to check this) use a negative value.

Balancing the flow will be more difficult without disturbing the free surface, but an open channel bc may be the solution.  As Peter comments you are going to need a very fine mesh so may struggle with the Student version as you're limited to 512k cells.