Learning Forum

[mrglobetrotter]

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]

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]

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]

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