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Old   October 18, 2012, 08:52
Default what should i do
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recently, i have been using CFX to simulate spray and atomization. But the results are not good.
I have tried to solve the problem, but it do not work.
What should i do ,i am a little down
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Old   October 18, 2012, 09:17
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Quote:
Originally Posted by sjtusyc View Post
recently, i have been using CFX to simulate spray and atomization. But the results are not good.
I have tried to solve the problem, but it do not work.
What should i do ,i am a little down
that's a really tough issue. It's a multiphase flow with cavitation.

biggest problem is to describe size and dispersion of drops (just after nozzle), as you can't measure it.

are you sure, you've regarded all these issues?

If so, which kind of mesh and setup do you use?
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Old   October 18, 2012, 17:21
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Yes, this is a tough flow to model. Even tougher to answer with such a vague question.

Have you looked at the FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   October 22, 2012, 07:46
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I use lagrangian and Eluer method to simulate spray and atomization.
Preussre-swirl atomizer spray into the static ambient environment.
pressure difference ,cone angle ,mass flow is supplied.
LISA model for the primary brekup and TAB for the second breakup model.
But the result is not good.
The second breakup seems does not take place, the particle diameter does not change along the spray direction.
In fluent ,it use dynamic law as the drag law. In CFX,that law is not available.
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Old   October 22, 2012, 07:56
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Quote:
Originally Posted by ghorrocks View Post
Yes, this is a tough flow to model. Even tougher to answer with such a vague question.

Have you looked at the FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
I use lagrangian and Eluer method to simulate spray and atomization.
Preussre-swirl atomizer spray into the static ambient environment.
pressure difference ,cone angle ,mass flow is supplied.
LISA model for the primary brekup and TAB for the second breakup model.
But the result is not good.
The second breakup seems does not take place, the particle diameter does not change along the spray direction.
In fluent ,it use dynamic law as the drag law. In CFX,that law is not available.
Attached Images
File Type: jpg particle diameter.jpg (36.6 KB, 36 views)
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Old   October 22, 2012, 07:57
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CCL file


ANALYSIS TYPE:
Option = Steady State
EXTERNAL SOLVER COUPLING:
Option = None
END
END
DOMAIN: Default Domain
Coord Frame = Coord 0
Domain Type = Fluid
Location = SOLID
BOUNDARY: Default Domain Default
Boundary Type = WALL
Location = OUTLET,WALL
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
FLUID: water
BOUNDARY CONDITIONS:
PARTICLE WALL INTERACTION:
Option = Equation Dependent
END
VELOCITY:
Option = Restitution Coefficient
Parallel Coefficient of Restitution = 1.0
Perpendicular Coefficient of Restitution = 1.0
END
END
END
END
BOUNDARY: outlet
Boundary Type = OPENING
Location = INLET
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Entrainment
Relative Pressure = 0 [kPa]
END
TURBULENCE:
Option = Low Intensity and Eddy Viscosity Ratio
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: air
Material = Air at 25 C
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID DEFINITION: water
Material = Water
Option = Material Library
MORPHOLOGY:
Option = Dispersed Particle Transport Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
FLUID: water
EROSION MODEL:
Option = None
END
PARTICLE ROUGH WALL MODEL:
Option = None
END
END
HEAT TRANSFER MODEL:
Fluid Temperature = 25 [C]
Option = Isothermal
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = RNG k epsilon
END
TURBULENT WALL FUNCTIONS:
Option = Scalable
END
END
FLUID PAIR: air | water
Particle Coupling = Fully Coupled
Surface Tension Coefficient = 0.072 [N m^-1]
MOMENTUM TRANSFER:
DRAG FORCE:
Option = Particle Transport Drag Coefficient
DRAG COEFFICIENT:
Drag Coefficient = 0.424
Option = Value
END
END
PRESSURE GRADIENT FORCE:
Option = None
END
TURBULENT DISPERSION FORCE:
Option = None
END
VIRTUAL MASS FORCE:
Option = None
END
END
PARTICLE BREAKUP:
Option = TAB Model
Use Liu Dynamic Drag Modification = On
END
END
PARTICLE INJECTION REGION: Particle Injection Region 1
Coord Frame = Coord 0
FLUID: water
INJECTION CONDITIONS:
INJECTION METHOD:
Option = Cone with Primary Breakup
NOZZLE DEFINITION:
Injection Centre = 0.0[m],0.0[m],0.0[m]
Option = Full Nozzle
Radius of Injection Plane = 1.82 [mm]
INJECTION DIRECTION:
Injection Direction X Component = 0
Injection Direction Y Component = 0
Injection Direction Z Component = 1
Option = Cartesian Components
END
END
NUMBER OF POSITIONS:
Number = 5000
Option = Direct Specification
END
PARTICLE PRIMARY BREAKUP:
Density Probe Normal Distance = 40 [mm]
Injection Pressure Difference = 0.8 [MPa]
Option = LISA Model
CONE ANGLE:
Cone Angle = 40 [degree]
Option = Cone Angle
END
END
END
PARTICLE MASS FLOW RATE:
Mass Flow Rate = 0.0096 [kg s^-1]
END
END
END
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic with Value
U = 0 [m s^-1]
V = 0 [m s^-1]
W = 0 [m s^-1]
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 0 [Pa]
END
TURBULENCE INITIAL CONDITIONS:
Option = Low Intensity and Eddy Viscosity Ratio
END
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
END
SOLVER CONTROL:
Turbulence Numerics = First Order
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Local Timescale Factor = 5.0
Maximum Number of Iterations = 200
Minimum Number of Iterations = 1
Timescale Control = Local Timescale Factor
END
CONVERGENCE CRITERIA:
Residual Target = 1.E-4
Residual Type = RMS
END
DYNAMIC MODEL CONTROL:
Global Dynamic Model Control = On
END
PARTICLE CONTROL:
PARTICLE INTEGRATION:
First Iteration for Particle Calculation = 10
Iteration Frequency = 10
Option = Forward Euler
Particle Source Change Target = 0.01
END
PARTICLE UNDER RELAXATION FACTORS:
Velocity Under Relaxation Factor = 0.50
END
END
END
END
COMMAND FILE:
Version = 14.0
END
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Old   October 29, 2012, 09:09
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Quote:
Originally Posted by sjtusyc View Post
recently, i have been using CFX to simulate spray and atomization. But the results are not good.
I have tried to solve the problem, but it do not work.
What should i do ,i am a little down
Can anyone help?
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Old   October 29, 2012, 17:19
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Glenn Horrocks
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To get something like a multiphase spray model accurate you should expect to require to do extensive verification, validation, comparison to experimental results, and checking of all the important physics one bit at a time before combining it to a single model which is hopefully accurate.

It is unlikely you will somebody to indentify a problem and then everything works.
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Old   October 30, 2012, 10:56
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Thanks for you reply, i will try.
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