Hi all

I am using CFX 10.0 in order to simulate air bubble behavior rising in a vertical pipe filled with stagnant water. I have chosen the follow sets: simulation type: transient, free-surface model, buoyant flow, gravity vector: (0;0;-9.81), reference density: rho.air, Surface tension: 0.0718 N/m. I started from a spherical bubble which is located in pipe bottom. However, bubble does not rise. what is wrong?

Thanks for your help

Post your command file

Joe, thanks a lot for your reply. This is my ccl file, If you need any file please give me your e-mail and I send to you.

# State file created: 2006/08/28 11:44:23 # CFX-10.0 build 2005.10.26-23.10

FLOW: COORD FRAME:Coord 1

Axis 3 Point = 0 [m], 0 [m], 1 [m]

Coord Frame Type = Cartesian

Option = Axis Points

Origin Point = 0 [m], 0 [m], 0 [m]

Plane 13 Point = 1 [m], 0 [m], 0 [m]

Reference Coord Frame = Coord 0 END DOMAIN:conducto

Coord Frame = Coord 1

Domain Type = Fluid

Fluids List = Air Ideal Gas,Water

Location = Assembly

BOUNDARYared

Boundary Type = WALL

Coord Frame = Coord 1

Location = F16.17,F18.17,F19.17,F20.17,F21.17,F22.17

FLUID:Air Ideal Gas

BOUNDARY CONDITIONS:

WALL INFLUENCE ON FLOW:

Option = Free Slip

END

END

END

FLUID:Water

BOUNDARY CONDITIONS:

WALL INFLUENCE ON FLOW:

Option = No Slip

WALL VELOCITY:

Option = Cartesian Components

Wall U = 0 [m s^-1]

Wall V = 0 [m s^-1]

Wall W = 0 [mm s^-1]

END

END

END

END

WALL CONTACT MODEL:

Option = Use Volume Fraction

END

END

DOMAIN MODELS:

BUOYANCY MODEL:

Buoyancy Reference Density = 1.164 [kg m^-3]

Gravity X Component = 0 [m s^-2]

Gravity Y Component = 0 [m s^-2]

Gravity Z Component = -9.81 [m s^-2]

Option = Buoyant

BUOYANCY REFERENCE LOCATION:

Cartesian Coordinates = 0 [m], 0 [m], 0.03 [m]

Option = Cartesian Coordinates

END

END

DOMAIN MOTION:

Option = Stationary

END

MESH DEFORMATION:

Option = None

END

REFERENCE PRESSURE:

Reference Pressure = 1 [atm]

END

END

FLUID:Air Ideal Gas

FLUID MODELS:

FLUID BUOYANCY MODEL:

Option = Density Difference

END

MORPHOLOGY:

Minimum Volume Fraction = 10e-12

Option = Continuous Fluid

END

END

END

FLUID:Water

FLUID MODELS:

FLUID BUOYANCY MODEL:

Option = Density Difference

END

MORPHOLOGY:

Minimum Volume Fraction = 10e-12

Option = Continuous Fluid

END

END

END

FLUID MODELS:

COMBUSTION MODEL:

Option = None

END

HEAT TRANSFER MODEL:

Fluid Temperature = 30 [C]

Homogeneous Model = False

Option = Isothermal

END

THERMAL RADIATION MODEL:

Option = None

END

TURBULENCE MODEL:

Homogeneous Model = False

Option = Laminar

END

END

FLUID PAIR:Air Ideal Gas | Water

Surface Tension Coefficient = 0.0718 [N m^-1]

INTERPHASE TRANSFER MODEL:

Maximum Length Scale for Area Density = 0.1 [mm]

Option = Free Surface

END

MASS TRANSFER:

Option = None

END

MOMENTUM TRANSFER:

DRAG FORCE:

Drag Coefficient = 0.44

Option = Drag Coefficient

END

END

SURFACE TENSION MODEL:

Curvature Under Relaxation Factor = 0.25

Option = None

Volume Fraction Smoothing Type = Volume-Weighted

END

END

INITIALISATION:

Coord Frame = Coord 1

Option = Automatic

FLUID:Air Ideal Gas

INITIAL CONDITIONS:

Velocity Type = Cartesian

CARTESIAN VELOCITY COMPONENTS:

Option = Automatic with Value

U = 0 [m s^-1]

V = 0 [m s^-1]

W = 0 [mm s^-1]

END

VOLUME FRACTION:

Option = Automatic with Value

Volume Fraction = FVG

END

END

END

FLUID:Water

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

VOLUME FRACTION:

Option = Automatic with Value

Volume Fraction = FVL

END

END

END

INITIAL CONDITIONS:

STATIC PRESSURE:

Option = Automatic with Value

Relative Pressure = PI

END

END

END

MULTIPHASE MODELS:

Homogeneous Model = False

FREE SURFACE MODEL:

Interface Compression Level = 1

Option = Standard

END

END END OUTPUT CONTROL:

RESULTS:

File Compression Level = Default

Option = Standard

END

TRANSIENT RESULTS:Transient Results 1

File Compression Level = Default

Include Mesh = No

Option = Selected Variables

Output Variables List = Absolute Pressure,Air Ideal Gas.Smoothed Volume Fraction,Air Ideal Gas.Velocity u,Air Ideal Gas.Velocity v,Air Ideal Gas.Velocity w,Air Ideal Gas.Volume Fraction,Total Pressure,Water.Smoothed Volume Fraction,Water.Velocity,Water.Volume Fraction

Time Interval = 0.1 [s]

END END SIMULATION TYPE:

Option = Transient

INITIAL TIME:

Option = Automatic with Value

Time = 0 [s]

END

TIME DURATION:

Option = Total Time

Total Time = 5 [s]

END

TIME STEPS:

Option = Timesteps

Timesteps = 0.1 [s]

END END SOLUTION UNITS:

Angle Units = [rad]

Length Units = [m]

Mass Units = [kg]

Solid Angle Units = [sr]

Temperature Units = [K]

Time Units = [s] END SOLVER CONTROL:

ADVECTION SCHEME:

Option = High Resolution

END

CONVERGENCE CONTROL:

Maximum Number of Coefficient Loops = 10

Timescale Control = Coefficient Loops

END

CONVERGENCE CRITERIA:

Residual Target = 1.E-4

Residual Type = RMS

END

TRANSIENT SCHEME:

Option = Second Order Backward Euler

END END END

LIBRARY: CEL:

EXPRESSIONS:

FVG = 1-FVL

FVL = step(esferoide)

PI = g*997[kg m^-3]*(0.03[m]-z)

esferoide = x^2/(0.4*1[mm^1])^2+y^2/(0.4*1[mm^1])^2+(z-4[mm^1])^2/(3*1[mm^1])^2-1

END END MATERIAL:Air Ideal Gas

Material Description = Air Ideal Gas (constant Cp)

Material Group = Air Data, Calorically Perfect Ideal Gases

Option = Pure Substance

Thermodynamic State = Gas

PROPERTIES:

Option = General Material

ABSORPTION COEFFICIENT:

Absorption Coefficient = 0.01 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Molar Mass = 28.96 [kg kmol^-1]

Option = Ideal Gas

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1 [atm]

Reference Specific Enthalpy = 0. [J/kg]

Reference Specific Entropy = 0. [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 2.61E-2 [W m^-1 K^-1]

END

END END MATERIAL:Air at 25 C

Material Description = Air at 25 C and 1 atm (dry)

Material Group = Air Data, Constant Property Gases

Option = Pure Substance

Thermodynamic State = Gas

PROPERTIES:

Option = General Material

Thermal Expansivity = 0.003356 [K^-1]

ABSORPTION COEFFICIENT:

Absorption Coefficient = 0.01 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Density = 1.185 [kg m^-3]

Molar Mass = 28.96 [kg kmol^-1]

Option = Value

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1 [atm]

Reference Specific Enthalpy = 0. [J/kg]

Reference Specific Entropy = 0. [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 2.61E-02 [W m^-1 K^-1]

END

END END MATERIAL:Water Ideal Gas

Material Description = Water Vapour Ideal Gas (100 C and 1 atm)

Material Group = Calorically Perfect Ideal Gases, Water Data

Option = Pure Substance

Thermodynamic State = Gas

PROPERTIES:

Option = General Material

ABSORPTION COEFFICIENT:

Absorption Coefficient = 1.0 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 9.4E-06 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Molar Mass = 18.02 [kg kmol^-1]

Option = Ideal Gas

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1.014 [bar]

Reference Specific Enthalpy = 0.0 [J/kg]

Reference Specific Entropy = 0.0 [J/kg/K]

Reference Temperature = 100 [C]

Specific Heat Capacity = 2080.1 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 193E-04 [W m^-1 K^-1]

END

END END MATERIAL:Water

Material Description = Water (liquid)

Material Group = Water Data, Constant Property Liquids

Option = Pure Substance

Thermodynamic State = Liquid

PROPERTIES:

Option = General Material

Thermal Expansivity = 2.57E-04 [K^-1]

ABSORPTION COEFFICIENT:

Absorption Coefficient = 1.0 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 8.899E-4 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Density = 997.0 [kg m^-3]

Molar Mass = 18.02 [kg kmol^-1]

Option = Value

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1 [atm]

Reference Specific Enthalpy = 0.0 [J/kg]

Reference Specific Entropy = 0.0 [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 4181.7 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 0.6069 [W m^-1 K^-1]

END

END END MATERIAL:Aluminium

Material Group = CHT Solids, Particle Solids

Option = Pure Substance

Thermodynamic State = Solid

PROPERTIES:

Option = General Material

EQUATION OF STATE:

Density = 2702 [kg m^-3]

Molar Mass = 26.98 [kg kmol^-1]

Option = Value

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Specific Enthalpy = 0 [J/kg]

Reference Specific Entropy = 0 [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 9.03E+02 [J kg^-1 K^-1]

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 237 [W m^-1 K^-1]

END

END END MATERIAL:Steel

Material Group = CHT Solids, Particle Solids

Option = Pure Substance

Thermodynamic State = Solid

PROPERTIES:

Option = General Material

EQUATION OF STATE:

Density = 7854 [kg m^-3]

Molar Mass = 55.85 [kg kmol^-1]

Option = Value

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Specific Enthalpy = 0 [J/kg]

Reference Specific Entropy = 0 [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 4.34E+02 [J kg^-1 K^-1]

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 60.5 [W m^-1 K^-1]

END

END END MATERIAL:Copper

Material Group = CHT Solids, Particle Solids

Option = Pure Substance

Thermodynamic State = Solid

PROPERTIES:

Option = General Material

EQUATION OF STATE:

Density = 8933 [kg m^-3]

Molar Mass = 63.55 [kg kmol^-1]

Option = Value

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Specific Enthalpy = 0 [J/kg]

Reference Specific Entropy = 0 [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 3.85E+02 [J kg^-1 K^-1]

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 401.0 [W m^-1 K^-1]

END

END END MATERIAL GROUP:Air Data

Group Description = Ideal gas and constant property air. Constant properties are for dry air at STP (0 C, 1 atm) and 25 C, 1 atm. END MATERIAL GROUP:Water Data

Group Description = Liquid and vapour water materials with constant properties. Can be combined with NASA SP-273 materials for combustion modelling. END MATERIAL GROUP:Gas Phase Combustion

Group Description = Materials which can be use for gas phase combustion. Properties are specified using the NASA SP-273 format. END MATERIAL GROUP:Constant Property Gases

Group Description = Gaseous substances with constant properties. Properties are calculated at STP (0C and 1 atm). Can be combined with NASA SP-273 materials for combustion modelling. END MATERIAL GROUP:Calorically Perfect Ideal Gases

Group Description = Ideal gases with constant specific heat capacity. Specific heat is evaluated at STP. END MATERIAL GROUP:Constant Property Liquids

Group Description = Liquid substances with constant properties. END MATERIAL GROUP:CHT Solids

Group Description = Pure solid substances that can be used for conjugate heat transfer. END MATERIAL GROUP:Particle Solids

Group Description = Pure solid substances that can be used for particle tracking END MATERIAL GROUP:Soot

Group Description = Solid substances that can be used when performing soot modelling END MATERIAL GROUP:User

Group Description = Materials that are defined by the user END MATERIAL GROUP:Interphase Mass Transfer

Group Description = Materials with reference properties suitable for performing either Eulerian or Lagrangian multiphase mass transfer problems.Examples include cavitation, evaporation or condensation. END MATERIAL GROUPry Redlich Kwong

Group Description = Materials with properties specified using the built in Redlich Kwong Equation of State. Suitable for dry real gas modelling. END MATERIAL GROUP:Wet Redlich Kwong

Group Description = Materials with properties specified using the built in Redlich Kwong Equation of State. Suitable for wet real gas modelling. END MATERIAL GROUPry Redlich Kwong RGP

Group Description = Materials with properties specified in TASCflow RGP files using the Redlich Kwong Equation of State. Suitable for dry real gas modelling. END MATERIAL GROUP:Wet Redlich Kwong RGP

Group Description = Materials with properties specified in TASCflow RGP files using the Redlich Kwong Equation of State. Suitable for wet real gas modelling. END MATERIAL GROUPry Steam

Group Description = Materials with properties specified in TASCflow RGP files using the Vukalovich virial equation of state. Suitable for dry steam modelling. END MATERIAL GROUP:Wet Steam

Group Description = Materials with properties specified in TASCflow RGP files using the Vukalovich virial equation of state. Suitable for wet steam modelling. END MATERIAL GROUP:Redlich Kwong Dry Steam

Group Description = Water materials which use the Redlich Kwong equation of state. Suitable for dry steam modelling. END MATERIAL GROUP:Redlich Kwong Wet Steam

Group Description = Water materials which use the Redlich Kwong equation of state. Suitable for condensing steam modelling. END MATERIAL GROUP:Redlich Kwong Dry Refrigerants

Group Description = Common refrigerants which use the Redlich Kwong equation of state. Suitable for dry real gas models. END MATERIAL GROUP:Redlich Kwong Wet Refrigerants

Group Description = Common refrigerants which use the Redlich Kwong equation of state. Suitable for condensing real gas models. END MATERIAL GROUP:Redlich Kwong Dry Hydrocarbons

Group Description = Common hydrocarbons which use the Redlich Kwong equation of state. Suitable for dry real gas models. END MATERIAL GROUP:Redlich Kwong Wet Hydrocarbons

Group Description = Common hydrocarbons which use the Redlich Kwong equation of state. Suitable for condensing real gas models. END END

COMMAND FILE: Version = 10.0 END

Why is BUOYANCY REFERENCE LOCATION: located at that particular position?

The air isnt feeling the gravity body force ...

Since ptotal=p+pref+rho.ref*(z-zref)*g, I choose zref on top of chanel in order to add hidrostatyc contribution due water. This is true if rho.ref=rho.water, but it isnt, right? rho.ref=rho.air.It`s my mistake. Where can I set zref?