Boundary conditions for sump pump modeling

    • yachi
      Hello everyone. I would like to model a pump submerged in a tank with two phases (air and water) to study the fluid flow profile, particularly the vortex generated by the pump suction. But, I am not sure if my boundary conditions are correct as I couldn't get the desired streamline profile.
      The water will flow into the tank via the inlet and leave the tank via suction produced by a 116m^3/h pump.
      The current model and boundary conditions used are:
      Steady-state, multiphase flow (air and water; water level at 0.45m), open channel flow with gravity ON, SST k-omega
      A velocity flow inlet with negative velocity magnitude is prescribed at the outlet, and the remaining not labeled surfaces are set as wall BC.
      Below is the streamline profile I obtained...there is no streamline in the pump tube which doesn't make sense to me.
      Are my boundary conditions correct? And, I wonder why the pump tube wireframe went missing in the post-processing.
      I am not familiar with two-phase flow with an open channel. Your help is very much appreciated. Thank you.
    • Karthik R
      Hello A few questions to think about - is your final "steady state" solution dependent on the initial conditions of your problem? If so, you cannot model this problem using the steady state solver. You will need to solve this as a transient problem.
      Also, why don't you use pressure inlet (for your flow inlet) and pressure outlet (for the flow outlet)? Also, why do you have a pressure outlet condition on what you refer to as the "Free Surface"?

    • yachi
      Hi Karthik, thank you very much for your reply.
      I am planning to first obtain the steady state solution and use it as initialization for the transient solution. This is because I have trouble getting converged transient solution.
      I chose pressure outlet condition for the top surface of the air domain (free surface) to assign the atmospheric pressure condition...
      Thanks for the suggestion. I have tried using pressure inlet with velocity of 0.11m/s for the flow inlet and pressure outlet as flow outlet but there are reversed flow on both the pressure inlet and outlet boundary conditions, and the results did not converged. Also, there is no water being pump out of the tank (see figure below)?
      Do you know what are the other possible boundary conditions to pump the water out of the tank (via the top outlet) that is consistently filled with water at a particular level?
      Thank you.
    • Rob
      Ansys Employee

      Can you check the outlet pipe has a wall and wall shadow pair? Otherwise it'll just suck out air. The normal approach here is to move the outlet nearer to the bell mouth, and use an open channel boundary setting on the inlet. 

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