 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

mrglobetrotter posted this 17 May 2018

Hi Rahul

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:

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

BOUNDARY CONDITIONS:
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? Close 