Constant Water level at top of waterway


I'm researching different designs for water passages that aid fish to swim in upstream direction(whenever the current is too strong or there is a man made obstacle constructed). For this design I've modelled a simple 3d sample and generated a mesh around it. I've set the boundary conditions in Fluent and made a first calculation of the simulation. One of the desired boundary conditions is that the water level upstream level stays constant, that means that the volume of water at the top stays the same while there is water flowing out of this section. I used the patch option in the Initialize menu, but I've only managed to start with this volume at t=0. From then, all the water from the volume flows out until it is empty. I was therefore wondering whether it's possible to set the boundary conditions so that the water height (volume at the top) stays constant throughout the whole simulation? I've tried adding an inlet that matches the outflow into the water passage but it's given me an error several times.

Here is a picture of the conditions just when the simulation starts (there is a pressure outlet at the bottom box:

I would appreciate any help! Thanks in advance

Tristan Cheaz

Best Answer


  • Thanks for the help! I'm not familiar with Open Channel Flow boundary conditions. I'd assume at the top "reservoir" I would have to add the height and depth in the Multiphase interface for the BC. Would this then be an inlet/outlet boundary condition?

  • RobRob UKForum Coordinator

    It is, it's designed for channel flows where we know a water level and speed at one end and a hold up at the other.

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