Simulation of a Water Spray

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  • Last Post 17 May 2018
mrglobetrotter posted this 17 May 2018

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.

 

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raul.raghav posted this 17 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

Rahul

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mrglobetrotter posted this 17 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?

 

 

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