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Multiphase flow  incorrect velocity on inlet 

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September 27, 2016, 14:31 
Multiphase flow  incorrect velocity on inlet

#1 
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Michal Tomášek
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]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 = 1.831E05 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E2 [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 = 0.03474982E01 [K^1] NASA a3 = 0.06354696E04 [K^2] NASA a4 = 0.06968581E07 [K^3] NASA a5 = 0.02506588E10 [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 = 0.03056293E01 [K^1] NASA a3 = 0.08730260E05 [K^2] NASA a4 = 0.01200996E08 [K^3] NASA a5 = 0.06391618E13 [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 = 9.4E06 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 193E04 [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 = (230.23273.15) [K] Option = Antoine Equation END TEMPERATURE: Option = Automatic END END END END FLOW: Flow Analysis 1 SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END ANALYSIS TYPE: Option = Steady State 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 Location = w_blade BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic 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: Option = Adiabatic 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 = 4e6 [m] Option = Specified Diameter END PARTICLE MASS FLOW RATE: Mass Flow Rate = 8.6e5 [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: Option = Adiabatic 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: Option = Adiabatic 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 = 3e06 [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 THERMAL RADIATION MODEL: 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 PRESSURE GRADIENT FORCE: 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 = 4e06 [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 Last edited by Mike_Tom; September 27, 2016 at 17:35. 

September 27, 2016, 14:32 

#2 
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Michal Tomášek
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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 = 4e06 [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.E4 Residual Type = RMS 

September 28, 2016, 02:03 

#3 
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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 
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Michal Tomášek
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Location: Czech republic
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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 
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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 
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Michal Tomášek
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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 
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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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