Fluids

Fluids

VOF WITH INLETS

    • ovm0002
      Subscriber

      Hello,

      Please, I am running a simulation with three phases and inlets, air, water and PCM. Water comes in at a high temperature to melt the PCM, air gets compressed because of this. I run it to about 4.5secs and I shut off the inlets and allow the water melt the PCM. I noticed that when I shutoff the inlet, air volume increases(which is understandable) while pressure and temperature decreases. I also noticed that water volume decreases(density increases) which is weird and wrong because my system is incompressible(boussinesq), plus the density of the pcm increases (volume decreases) which is also meant to be constant because of bousinesq approximation. I don't know how to solve this problem, can someone please suggest to me how to fix this?

       

      Thank you

    • Rob
      Ansys Employee

      If everything is incompressible the air volume can't change. What are the densities of the three phases, and how good is the convergence? 

    • ovm0002
      Subscriber

      The density of the air is ideal gas, the density of water and PCM are bousinessq. For the convergence, continuity and velocity are 10^-4 while energy and vf-pcm and vf-water are 10^-9. I am also using the PISO solver.

    • Rob
      Ansys Employee

      Inwhich case the air volume should be constant as the other two phases can't change. When you stop the flow do you also switch the inlet to be a wall? 

    • ovm0002
      Subscriber

      The volume of the pcm changing from time zero is very strange to me. The air increase after shutdown is understandable. Yes, When I stop the flow, I switch the inlet to be a wall.

    • Rob
      Ansys Employee

      Please can you post some images. Phase contours with & without node values on and separately the mesh. 

    • ovm0002
      Subscriber

      okay, find attached below. I am only allowed to upload one image and I can't upload the mesh because the size is too big.

    • ovm0002
      Subscriber

      okay, find attached below

    • Rob
      Ansys Employee

      An image of the mesh shouldn't be any larger than the contour plot. I'm not permitted to download files in any case. Please zoom in towards the free surface with the mesh image: I need to see the resolution. 

    • ovm0002
      Subscriber

      Find atached below. Thank you so much for your assistance.

    • Rob
      Ansys Employee

      What inlet condition is set? You've got enough resolution by the looks of it, so everything ought to behave. 

    • ovm0002
      Subscriber

      Velocity at the inlet is 0.2m/s and water coming in at the inlet is at 365K. Pressure at the inlet is atmospheric.

       

      Thank you so much.

    • Rob
      Ansys Employee

      With no outlets? The air ought to compress, and the PCM then melt. I assume you can't fill the head space in the brief period that water flows in?  

    • ovm0002
      Subscriber

      Yes not outlets. I agree the air is ought to compres but as the PCM melts, the PCM fraction decreases (volume decreases) which is meant to be constant because of bousinesq approximation while it's melting. I shut off the inlet at 4 secs so as the allow the water in the system completely settle in and melt the PCM via conduction.

    • ovm0002
      Subscriber

      Does it depend on the VOF METHOD I use? Implicit or Explicit?

       

       

    • Rob
      Ansys Employee

       

      It can if you’re not resolving everything (including time) sufficiently. If you plot the phase mass with time (use a volume monitor) how does it look? You may need to monitor inlet mass too to confirm you've got the right amount entering the system. 

       

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