3 Replies Latest reply on Nov 18, 2016 11:11 AM by Amit Katz

    Defining boundary conditions at the surface of water.

    Anugrah Singh

      I am trying to simulate steering in an open top beaker. I am having trouble defining my water surface at the top. Right now I have placed a lid and applied open to atmosphere boundary condition but the solver gives an error warning saying "a vortex crosses the pressure boundary".

       

      I am using a rotation region around my impeller and I have defined the bottom lid and the inner surface of beaker as stationary real wall. Please advise how to correctly define the boundary condition at the top.

        • Re: Defining boundary conditions at the surface of water.
          Amit Katz

          I am guessing that what you are trying to accomplish is to simulate the water-air boundary within your domain. If this is the case, it will not work. Flow Sim does not have the capability to simulate a fluid-fluid interface. Only rigid fluid-solid interfaces.

          What you have right now is an environmental boundary condition, which merely applies the condition of the default fluid as defined in your project settings (I'm guessing in your case it's water at standard room temperature and 1 atmosphere.) The reason you are getting the error message is that the motion inside your computational domain is creating a vortex across your boundary, which means you have both inlet and outlet conditions there. The software is simply informing you of this. From the online help documentation:

           

          • The Environment Pressure condition is interpreted by Flow Simulation as a total pressure for inlet flows and as a static pressure for outlet flows. If in the course of calculation a vortex crosses an opening with the Environment pressure condition specified, this pressure is considered as the total pressure for the part of opening through which the flow enters the model and as the static pressure for the part of opening through which the flow leaves the model.  Additionally, you can specify fluid temperature (and concentrations for multiple fluids), turbulence parameters and boundary layer parameters. These settings define the fluid entering the model through the opening.

          • Re: Defining boundary conditions at the surface of water.
            Amit Katz

            You can mix similar phase fluids (liquid-liquid or gas-gas) as long as the density differences aren't too great. But I think you may be asking more of this program than it can do with your sim.