Simulation of a Water Spray

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.

 

Comments

  • raul.raghavraul.raghav Bethlehem, PAMember
    edited May 2018

    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

  • edited May 2018

    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?

     

     

  • sahilsahil Member
    edited July 10

    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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