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October 18, 2012, 08:52 
what should i do

#1 
Member
leo
Join Date: Jun 2012
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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 

October 18, 2012, 09:17 

#2  
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Christoph
Join Date: May 2011
Location: Germany
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Quote:
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? 

October 18, 2012, 17:21 

#3 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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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.cfdonline.com/Wiki/Ansys..._inaccurate.3F 

October 22, 2012, 07:46 

#4 
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leo
Join Date: Jun 2012
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I use lagrangian and Eluer method to simulate spray and atomization.
Preussreswirl 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. 

October 22, 2012, 07:56 

#5  
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leo
Join Date: Jun 2012
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Quote:
Preussreswirl 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. 

October 22, 2012, 07:57 

#6 
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leo
Join Date: Jun 2012
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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.E4 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 

October 29, 2012, 09:09 

#7 
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leo
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October 29, 2012, 17:19 

#8 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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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. 

October 30, 2012, 10:56 

#9 
Member
leo
Join Date: Jun 2012
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Rep Power: 5 
Thanks for you reply, i will try.


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