# Multiphase flow - incorrect velocity on inlet

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New Member

Michal Tomáek
Join Date: Sep 2015
Location: Czech republic
Posts: 5
Rep Power: 10 ]Hi everybody,
I am new in CFX and I am working on multiphase flow in diffuser behind the centrifugal compressor. The domain is consisted from ideal air and water vapour. It is called mixture. In the upper part of diffuser is injected water from three particle injection region for cooling mixture which flowing inside.
I define boundary condition for inlet as the mass flow and outlet by pressure.
I have problem with value of substance of velocities on inlet which are very small. I tried to solve this problem only for ideal air and the inlet velocities are valid with another results from numeca. So it is correct. I try to set up this results as initial values, but it is solved as well as without initial values.
The problem is solved as homogenous substance, where the particle of water are vaporized to mixture (ideal gas, water vapour)

Do you know, where is the problem with solve the inlet velocity?
Sorry for my english skills I hope that it is clear from my text.
I enclose the out. file below:

LIBRARY:
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
EQUATION OF STATE:
Molar Mass = 28.96 [kg kmol^-1]
Option = Ideal Gas
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 1 [atm]
Reference Specific Enthalpy = 0. [J/kg]
Reference Specific Entropy = 0. [J/kg/K]
Reference Temperature = 25 [C]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 2.61E-2 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 0.01 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0.0 [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1.0 [m m^-1]
END
END
END
MATERIAL: Gas Mixture
Material Group = Air Data,Gas Phase Combustion
Materials List = Air Ideal Gas,H2O
Option = Variable Composition Mixture
Thermodynamic State = Gas
END
MATERIAL: H2O
Material Description = Water Vapour
Material Group = Gas Phase Combustion, Interphase Mass Transfer, Water \
Data
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Molar Mass = 18.02 [kg kmol^-1]
Option = Ideal Gas
END
SPECIFIC HEAT CAPACITY:
Option = NASA Format
LOWER INTERVAL COEFFICIENTS:
NASA a1 = 0.03386842E+02 []
NASA a2 = 0.03474982E-01 [K^-1]
NASA a3 = -0.06354696E-04 [K^-2]
NASA a4 = 0.06968581E-07 [K^-3]
NASA a5 = -0.02506588E-10 [K^-4]
NASA a6 = -0.03020811E+06 [K]
NASA a7 = 0.02590233E+02 []
END
TEMPERATURE LIMITS:
Lower Temperature = 300 [K]
Midpoint Temperature = 1000 [K]
Upper Temperature = 5000 [K]
END
UPPER INTERVAL COEFFICIENTS:
NASA a1 = 0.02672146E+02 []
NASA a2 = 0.03056293E-01 [K^-1]
NASA a3 = -0.08730260E-05 [K^-2]
NASA a4 = 0.01200996E-08 [K^-3]
NASA a5 = -0.06391618E-13 [K^-4]
NASA a6 = -0.02989921E+06 [K]
NASA a7 = 0.06862817E+02 []
END
END
REFERENCE STATE:
Option = NASA Format
Reference Pressure = 1 [atm]
Reference Temperature = 25 [C]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 9.4E-06 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 193E-04 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 1.0 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0.0 [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1.0 [m m^-1]
END
END
END
MATERIAL: H2Ol
Material Description = Water Liquid (H2O)
Material Group = Interphase Mass Transfer, Liquid Phase Combustion, \
Water Data
Option = Pure Substance
Thermodynamic State = Liquid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 958.37 [kg/m^3]
Molar Mass = 18.02 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 4215.6 [J/kg/K]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 3.169 [kPa]
Reference Specific Enthalpy = -15860961.15 [J/kg]
Reference Specific Entropy = 2824.82 [J/kg/K]
Reference Temperature = 298.15 [K]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 0.00028182 [Pa s]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 0.67908 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 1 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0 [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1 [m m^-1]
END
END
END
MATERIAL: H2Ovl
Binary Material1 = H2O
Binary Material2 = H2Ol
Material Description = Water Mixture
Material Group = Liquid Phase Combustion,Gas Phase Combustion
Option = Homogeneous Binary Mixture
SATURATION PROPERTIES:
Option = General
PRESSURE:
Antoine Enthalpic Coefficient B = 1687.54 [K]*ln(10)
Antoine Pressure Scale = 1 [bar]
Antoine Reference State Constant A = 5.11564*ln(10)
Antoine Temperature Offset C = (230.23-273.15) [K]
Option = Antoine Equation
END
TEMPERATURE:
Option = Automatic
END
END
END
END
FLOW: Flow Analysis 1
SOLUTION UNITS:
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
EXTERNAL SOLVER COUPLING:
Option = None
END
END
DOMAIN: Default Domain
Coord Frame = Coord 0
Domain Type = Fluid
Location = fl_stator
BOUNDARY: Default Domain Default
Boundary Type = WALL
BOUNDARY CONDITIONS:
HEAT TRANSFER:
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
FLUID: H2Ol
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: Domain Interface 1 Side 1
Boundary Type = INTERFACE
Location = per_b
BOUNDARY CONDITIONS:
COMPONENT: H2O
Option = Conservative Interface Flux
END
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: Domain Interface 1 Side 2
Boundary Type = INTERFACE
Location = per_a
BOUNDARY CONDITIONS:
COMPONENT: H2O
Option = Conservative Interface Flux
END
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: Inlet
Boundary Type = INLET
Location = in
BOUNDARY CONDITIONS:
COMPONENT: H2O
Mass Fraction = 0.0
Option = Mass Fraction
END
FLOW DIRECTION:
Option = Cylindrical Components
Unit Vector Axial Component = 0
Unit Vector Theta Component = 166
Unit Vector r Component = 120
AXIS DEFINITION:
Option = Coordinate Axis
Rotation Axis = Coord 0.3
END
END
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 357 [K]
END
MASS AND MOMENTUM:
Mass Flow Rate = 0.260456 [kg s^-1]
Option = Mass Flow Rate
END
TURBULENCE:
Option = Medium Intensity and Eddy Viscosity Ratio
END
END
FLUID: H2Ol
BOUNDARY CONDITIONS:
END
END
END
BOUNDARY: Out
Boundary Type = OUTLET
Location = out
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Average Static Pressure
Pressure Profile Blend = 0.05
Relative Pressure = 660000 [Pa]
END
PRESSURE AVERAGING:
Option = Average Over Whole Outlet
END
END
END
BOUNDARY: hub_stat_wall
Boundary Type = WALL
Location = w_hub
BOUNDARY CONDITIONS:
HEAT TRANSFER:
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
FLUID: H2Ol
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: in_castice
Boundary Type = INLET
Location = in_castice
BOUNDARY CONDITIONS:
COMPONENT: H2O
Mass Fraction = 0.0
Option = Mass Fraction
END
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 300 [K]
END
MASS AND MOMENTUM:
Normal Speed = 0 [m s^-1]
Option = Normal Speed
END
TURBULENCE:
Option = Medium Intensity and Eddy Viscosity Ratio
END
END
FLUID: H2Ol
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 300 [K]
END
MASS AND MOMENTUM:
Option = Cylindrical Velocity Components
Velocity Axial Component = -60 [m s^-1]
Velocity Theta Component = -60 [m s^-1]
Velocity r Component = 60 [m s^-1]
AXIS DEFINITION:
Option = Coordinate Axis
Rotation Axis = Coord 0.2
END
END
PARTICLE DIAMETER DISTRIBUTION:
Diameter = 4e-6 [m]
Option = Specified Diameter
END
PARTICLE MASS FLOW RATE:
Mass Flow Rate = 8.6e-5 [kg s^-1]
END
PARTICLE POSITION:
Option = Uniform Injection
NUMBER OF POSITIONS:
Number = 500
Option = Direct Specification
END
END
END
END
END
BOUNDARY: rot_wall
Boundary Type = WALL
Location = w_hub_rot
BOUNDARY CONDITIONS:
HEAT TRANSFER:
END
MASS AND MOMENTUM:
Option = No Slip Wall
WALL VELOCITY:
Angular Velocity = 22360 [rev min^-1]
Option = Rotating Wall
AXIS DEFINITION:
Option = Coordinate Axis
Rotation Axis = Coord 0.3
END
END
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
FLUID: H2Ol
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: shroud_stac_wall
Boundary Type = WALL
Location = w_shroud
BOUNDARY CONDITIONS:
HEAT TRANSFER:
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
FLUID: H2Ol
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
DOMAIN MODELS:
BUOYANCY MODEL:
Buoyancy Reference Density = 1.2 [kg m^-3]
Gravity X Component = 0 [m s^-2]
Gravity Y Component = -9.81 [m s^-2]
Gravity Z Component = 0 [m s^-2]
Option = Buoyant
BUOYANCY REFERENCE LOCATION:
Option = Automatic
END
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 0 [atm]
END
END
FLUID DEFINITION: Gas Mixture
Material = Gas Mixture
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID DEFINITION: H2Ol
Material = H2Ol
Option = Material Library
MORPHOLOGY:
Option = Dispersed Particle Transport Fluid
PARTICLE DIAMETER DISTRIBUTION:
Diameter = 3e-06 [m]
Option = Specified Diameter
END
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
FLUID: Gas Mixture
COMPONENT: Air Ideal Gas
Option = Constraint
END
COMPONENT: H2O
Option = Transport Equation
END
FLUID BUOYANCY MODEL:
Option = Density Difference
END
HEAT TRANSFER MODEL:
Option = Total Energy
END
WALL CONDENSATION MODEL:
Option = None
END
END
FLUID: H2Ol
EROSION MODEL:
Option = None
END
FLUID BUOYANCY MODEL:
Option = Density Difference
END
HEAT TRANSFER MODEL:
Option = Particle Temperature
END
PARTICLE ROUGH WALL MODEL:
Option = None
END
END
HEAT TRANSFER MODEL:
Option = Fluid Dependent
END
Option = None
END
TURBULENCE MODEL:
Option = SST
BUOYANCY TURBULENCE:
Option = None
END
END
TURBULENT WALL FUNCTIONS:
High Speed Model = Off
Option = Automatic
END
END
FLUID PAIR: Gas Mixture | H2Ol
Particle Coupling = Fully Coupled
COMPONENT PAIR: H2O | H2Ol
Option = Liquid Evaporation Model
LATENT HEAT:
Option = From Material Properties
END
END
INTERPHASE HEAT TRANSFER:
Option = Ranz Marshall
END
MOMENTUM TRANSFER:
DRAG FORCE:
Option = Schiller Naumann
END
Option = None
END
TURBULENT DISPERSION FORCE:
Option = None
END
VIRTUAL MASS FORCE:
Option = None
END
END
END
PARTICLE INJECTION REGION: Particle Injection Region 1
Coord Frame = Coord 0
FLUID: H2Ol
INJECTION CONDITIONS:
INJECTION METHOD:
Option = Cone
CONE DEFINITION:
Injection Centre = -0.02 [m], 0.4 [m], 0.28 [m]
Option = Point Cone
INJECTION DIRECTION:
Injection Direction X Component = 0
Injection Direction Y Component = -1
Injection Direction Z Component = 0
Option = Cartesian Components
END
END
INJECTION VELOCITY:
Cone Angle = 30 [deg]
Injection Velocity Magnitude = 30 [m s^-1]
Option = Velocity Magnitude
END
NUMBER OF POSITIONS:
Number = 500
Option = Direct Specification
END
END
PARTICLE DIAMETER DISTRIBUTION:
Diameter = 4e-06 [m]
Option = Specified Diameter
END
PARTICLE MASS FLOW RATE:
Mass Flow Rate = 0.000086 [kg s^-1]
END
TEMPERATURE:
Option = Value
Temperature = 300 [K]
END
END
END
END
Attached Images difusor.png (39.5 KB, 16 views)

Last edited by Mike_Tom; September 27, 2016 at 17:35.   September 27, 2016, 14:32 #2 New Member   Michal Tomáek Join Date: Sep 2015 Location: Czech republic Posts: 5 Rep Power: 10 PARTICLE INJECTION REGION: Particle Injection Region 3 Coord Frame = Coord 0 FLUID: H2Ol INJECTION CONDITIONS: INJECTION METHOD: Option = Cone CONE DEFINITION: Injection Centre = 0 [m], 0.4 [m], 0.28 [m] Option = Point Cone INJECTION DIRECTION: Injection Direction X Component = 0 Injection Direction Y Component = -1 Injection Direction Z Component = 0 Option = Cartesian Components END END INJECTION VELOCITY: Cone Angle = 30 [deg] Injection Velocity Magnitude = 30 [m s^-1] Option = Velocity Magnitude END NUMBER OF POSITIONS: Number = 500 Option = Direct Specification END END PARTICLE DIAMETER DISTRIBUTION: Diameter = 4e-06 [m] Option = Specified Diameter END PARTICLE MASS FLOW RATE: Mass Flow Rate = 0.000086 [kg s^-1] END TEMPERATURE: Option = Value Temperature = 300 [K] END END END END END DOMAIN INTERFACE: Domain Interface 1 Boundary List1 = Domain Interface 1 Side 1 Boundary List2 = Domain Interface 1 Side 2 Interface Type = Fluid Fluid INTERFACE MODELS: Option = Rotational Periodicity AXIS DEFINITION: Option = Coordinate Axis Rotation Axis = Coord 0.3 END END MESH CONNECTION: Option = Automatic END END INITIALISATION: Option = Automatic INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic END COMPONENT: H2O Option = Automatic END STATIC PRESSURE: Option = Automatic END TEMPERATURE: Option = Automatic END TURBULENCE INITIAL CONDITIONS: Option = Medium Intensity and Eddy Viscosity Ratio END END END OUTPUT CONTROL: RESULTS: File Compression Level = Default Option = Standard END END SOLVER CONTROL: Turbulence Numerics = High Resolution ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Maximum Number of Iterations = 100 Minimum Number of Iterations = 1 Physical Timescale = 0.002 [s] Timescale Control = Physical Timescale END CONVERGENCE CRITERIA: Residual Target = 1.E-4 Residual Type = RMS   September 28, 2016, 02:03 #3 Senior Member   Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 14 If I understood you well: You set an inlet mass flow and you estimated the inlet velocities for air ideal gas Now you run your simulation and you get very much smaller inlet velocities for the same inlet mass flow ?!? Could it be that you might be using something like liquid water on your inlet, so that for the same mass flow you would get much lower velocities due to the higher density?   September 28, 2016, 03:41 #4 New Member   Michal Tomáek Join Date: Sep 2015 Location: Czech republic Posts: 5 Rep Power: 10 Hi monkey1, thanks for reply Yes, you understood well. I set as inlet mass flow with speeds components of direction and as outlet total pressure. Those variables I got. Now, I find out that the main problem is the setting on the beginning. I took only diffuser without injection of water and without multiphase flow. If I set up the fluid as air at 25°C degree. I got the results with good values but this choise is bad because the air at 25°C has constant density so it is incorrect for compressible flow. But the components of velocities are almost same as compare results with numeca. If I set up ideal gas. It would be correct becouse ideal gas is compressible and has a variable density. But the results of components velocities are bad. I looked at the result of density on inlet and outlet and there is very big value of density (around 3,9 kg/m3). So I think that the main problem is in result of density. Do you know what can cause this huge increase of density ? Thank you.   September 28, 2016, 03:55 #5 Senior Member   Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 14 The high density occurs with "air ideal gas"? Or with your substances? In the first case what pressure and temperature do you have? At 4 bar pressure, air would have somth. around 4 kg/m^3. If you used your own substances you will have to check wether you are injecting water or a mixture air + water particles leading to this high density!   September 28, 2016, 05:40 #6 New Member   Michal Tomáek Join Date: Sep 2015 Location: Czech republic Posts: 5 Rep Power: 10 The high density is for pure substance "air ideal gas". My setting is: Inlet : mass flow= 0.2392kg/s Total temperature =357K Outlet: Average static pressure = 3,06 bar. The results : density (out) =2.99734 kg/m3 density (in) = 2.97kg/m3 Total energy in entire diffuser is constant that is correct with theory. Mass flow is as same as on inlet and on outlet. It is correct too. The static pressure on outlet is higher than on inlet. Inlet(302026Pa) Outlet (306399Pa). I would expect that density would be more different on inlet and on outlet , but it can be my mistake. Can you tell me what happen if I change boundary condition? I mean I set up Inlet as total pressure if I know pressure ratio (between outlet and inlet) and Outlet as Mass flow becouse the mass flow must have same value on inlet as on outlet. I want to know it because it can cause the difference the results between results from numeca and CFX. I found out that numeca was set on this boundary condition. (inlet = total pressure, outlet= mass flow)   September 29, 2016, 01:27 #7 Senior Member   Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 14 The change in density is directly proportional to the change in pressure. Your pressures at in and outlet differ by a little more than 1%. The difference in density is also around 1%. Therefore, from a thermodynamical point of view everything is ok. What happens when you change the boundaries? Got no idea, just try it out!  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