Fluids

Fluids

Simulation of a Water Spray

    • mrglobetrotter
      Subscriber

      Hello everybody


      I'm currently working on my Bachelor Thesis for my Mechanical Engineering degree.


      The task is to simulate a water spray which is going to be injected into air as ideal gas. Both fluids need to be set as continuous fluid, so it should not be a large breakup model simulation to investigate every single drop. The nozzle diameter is 0.75mm and the injection velocity is 150 m/s.


      I've already done my first setup but the result isn't quite comprehensibly. The water spray keeps cylindrical over a whole injection length of 200mm. I expect that the flow will spread after a time.


      My question now is if someone has experience in modelling this kind of sprays? Do I need to add some special models or some other sort of physics? If you have some questions, please ask me!


      Thanks for all replies in advance.


       

    • raul.raghav
      Subscriber

      How did you come with the geometry for your simulation? And what are the boundary conditions? 2D or 3D? Can you provide a better schematic of the geometry and how you setup the BC's?


      Which solver and what model are you using to solve this simulation?


      And if you want more information about setting up the simulation, Raef has some really good youtube tutorials on jet flow which would help you immensely:


      CFD ANSYS Tutorial - Air jet flow simulation through a nozzle revisited | FLUENT


      CFD Tutorial – Converging diverging (CD) nozzle supersonic flow | Fluent ANSYS

    • mrglobetrotter
      Subscriber

      Hi Rahul


      Thanks for your answer.


      I thought since the inlet is round, I'm going to do also a cylindrical opening. So I can create an ogrid (for the inlet) in an ogrid (for the opening). I meshed everything with hexa and did a refinement on the passage area between liquid and gas fluid. The mesh quality is really good and my supervisor is quite happy with it. So, everything is 3D, see pictures:




      My boundary conditions: 
      FLOW: Flow Analysis 1



      • ANALYSIS TYPE:
        Option = Steady State
        EXTERNAL SOLVER COUPLING:
        Option = None


       



      • DOMAIN: Default Domain
        Coord Frame = Coord 0
        Domain Type = Fluid
        Location = BODY

      • BOUNDARY: Inlet
        Boundary Type = INLET
        Location = INLET
        BOUNDARY CONDITIONS:

        FLOW REGIME:
        Option = Subsonic

        HEAT TRANSFER:
        Option = Fluid Dependent

        MASS AND MOMENTUM:
        Option = Cartesian Velocity Components
        U = 0 [m s^-1]
        V = 0 [m s^-1]
        W = 150 m/s

        TURBULENCE:
        Option = Low Intensity and Eddy Viscosity Ratio

        FLUID: Air
        BOUNDARY CONDITIONS:

        HEAT TRANSFER:
        Option = Static Temperature
        Static Temperature = 298 [K]

        VOLUME FRACTION:
        Option = Value
        Volume Fraction = 0

        FLUID: Water
        BOUNDARY CONDITIONS:

        HEAT TRANSFER:
        Option = Static Temperature
        Static Temperature = 298 [K]

        VOLUME FRACTION:
        Option = Value
        Volume Fraction = 1



      • BOUNDARY: Opening
        Boundary Type = OPENING
        Location = SIDE,BACK

        BOUNDARY CONDITIONS:
        FLOW DIRECTION:
        Option = Normal to Boundary Condition

        FLOW REGIME:
        Option = Subsonic

        HEAT TRANSFER:
        Option = Fluid Dependent

        MASS AND MOMENTUM:
        Option = Opening Pressure and Direction
        Relative Pressure = 1 [atm]

        TURBULENCE:
        Option = Low Intensity and Eddy Viscosity Ratio

        FLUID: Air
        BOUNDARY CONDITIONS:

        HEAT TRANSFER:
        Option = Static Temperature
        Static Temperature = 298 [K]

        VOLUME FRACTION:
        Option = Zero Gradient

        FLUID: Water
        BOUNDARY CONDITIONS:

        HEAT TRANSFER:
        Option = Static Temperature
        Static Temperature = 298 [K]

        VOLUME FRACTION:
        Option = Zero Gradient



      • BOUNDARY: Wall
        Boundary Type = WALL
        Location = WALL

        BOUNDARY CONDITIONS:
        HEAT TRANSFER:
        Option = Adiabatic

        MASS AND MOMENTUM:
        Option = Free Slip Wall
        FLUID PAIR: Air | Water

        BOUNDARY CONDITIONS:
        WALL ADHESION:
        Option = None



      • DOMAIN MODELS:
        BUOYANCY MODEL:
        Option = Non Buoyant

        DOMAIN MOTION:
        Option = Stationary

        MESH DEFORMATION:
        Option = None

        REFERENCE PRESSURE:
        Reference Pressure = 0 [atm]

        FLUID DEFINITION: Air
        Material = Air Ideal Gas

        MORPHOLOGY:
        Option = Continuous Fluid

        FLUID DEFINITION: Water
        Material = Water
        Option = Material Library

        MORPHOLOGY:
        Option = Continuous Fluid

        FLUID MODELS:
        COMBUSTION MODEL:
        Option = None

        FLUID: Air
        HEAT TRANSFER MODEL:
        Include Viscous Work Term = True
        Option = Total Energy

        FLUID: Water
        HEAT TRANSFER MODEL:
        Include Viscous Dissipation Term = On
        Option = Thermal Energy

        HEAT TRANSFER MODEL:
        Homogeneous Model = Off
        Option = Fluid Dependent

        TURBULENCE MODEL:
        Option = SST

        TURBULENT WALL FUNCTIONS:
        Option = Automatic

        FLUID PAIR: Air | Water
        Surface Tension Coefficient = 0.072 [N m^-1]

        INTERPHASE HEAT TRANSFER:
        Heat Transfer Coefficient = 10 [W m^-2 K^-1]
        Option = Heat Transfer Coefficient

        INTERPHASE TRANSFER MODEL:
        Option = Free Surface

        MASS TRANSFER:
        Option = None

        SURFACE TENSION MODEL:
        Option = Continuum Surface Force
        Primary Fluid = Water

        MULTIPHASE MODELS:
        Homogeneous Model = On

        FREE SURFACE MODEL:
        Option = Standard

        INITIALISATION:
        Option = Automatic

        FLUID: Air


             INITIAL CONDITIONS:
             SET!


      Does this help? Please feel free to ask for more!


       


      Thank you very much for the youtube tutorials! They seem quite useful! My only question is, how adaptable is it for CFX? Can I use it as a CFX user?


       


       

    • sahil
      Subscriber

      Hi mrglobetrotter,


       


      I have seen your question and project. I am working on same kind of project. can you please help me by sharing your work ( Maybe you have completed because your question is from 2018), this would be a great help to me. Thank you in advance 


      Sahil

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