Fluids

Fluids

Outlet Boundary Conditions for VOF

    • shal3391
      Subscriber

      Hi,

      I am trying to model a liquid injection into a air flow.

      My domain is a 3D cylinder with a nozzle at the top, a cross section is attached.

      I have a fluid velocity inlet at the nozzle of 4.3m/s and an air velocity inlet at the top of the cylinder of 36m/s.

      I have currently selected an 'outflow' at the bottom, however the air velocity is increasing exponentially at this outflow. Shown in the figures attached.

      What outlet boundary conditions should I use?

      And do you have any recommendations regarding turbulence models, relaxation factors or solving schemes. Because I am also struggling choosing these parameters.


      Many Thanks,


    • Rob
      Ansys Employee
      Use a pressure outlet. Outflow is an old boundary dating back to before compressible flow and GUIs. nRe models and settings have a read through the documentation and come back with some suggestions and reasons for using a model or setting. n
    • shal3391
      Subscriber
      Thanks Rob,nnAt the moment I am using the standard k-epsilon turbulence model because the majority of my fluid flow is far from any walls. However I am unsure if I need the turbulence dampening provided by the k-omega model. Would a k-epsilon realisable model or a k-omega SST model be an adequate compromise ?nMy goal is to induce fluid breakup in a jet stream, so I want there to be adequate turbulence fro this to happen. At the moment I am using the default values for all relaxation factors, would increasing the turbulent kinetic energy factor (default is 0. provide more accurate turbulence representation ? My understanding is to reduce the relaxation factors if the residuals are increasing, my residuals (attached) aren't necessarily increasing but don't look to be particularly stable.nI am currently using a SIMPLEC solving scheme (based on trial and error) but have read that a coupled scheme is generally better for VOF models. I am using a 'Compressive' volume fraction solver. I have also read that I should tick Pseudo Transient, but am unsure as to what it does.nI am using a variable time step to cap the Global Courant Number at 0.5.nThanks Again
    • Keyur Kanade
      Ansys Employee
      Please check nPlease check nAnd nArrayRegards,nKeyurnGuidelines for Posting on Ansys Learning ForumnHow to access ANSYS help linksnn
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