[xiexing]

Hi, i am try to simulate a centrifugal fan, and try to estimate the effiency (just only impeller, so i add a former extention and a latter one, just can see in the images).
inlet is massflow（rated flow）,outlet is static pressure, the number of fans is 17.
question is ：along the solving process，in the early iterations,the result seems just OK，and the RMS decrease. but with the iteratons increase,the solver manager show that a reverse flow in the outlet,and always exsisting,and the RMS tendency becomes unstable,the flow field of result is unsymmetric.
i have tried to change the outlet to opening, and change to a high quality mesh and so on，but the problem always existing.
i really want to know is this phenomenon is just normal exsisting or just the numerical problem(somewhere i am wrong).
thanks a lot!

[xiexing]

LIBRARY:
CEL:
EXPRESSIONS:
NJ = torque_z()@R2 Blade+torque_z()@R2 Hub+torque_z()@R2 Shroud
desty = 4.003[g/mol]*Absolute Pressure /(R*Temperature )
dp = massFlowAve(Total Pressure in Stn Frame )@S2 \
Outlet-massFlowAve(Total Pressure in Stn Frame )@s1inlet
END
END
MATERIAL: he
Material Group = User
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Molar Mass = 4.003 [kg kmol^-1]
Option = Ideal Gas
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 5189.4 [J kg^-1 K^-1]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 7 [MPa]
Reference Specific Enthalpy = 2744337.8 [J kg^-1]
Reference Specific Entropy = 22105.7 [J kg^-1 K^-1]
Reference Temperature = 250 [C]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 0.00003 [Pa s]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 0.2333 [W m^-1 K^-1]
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: R2
Coord Frame = Coord 0
Domain Type = Fluid
Location = Entire Passage
BOUNDARY: R2 Blade
Boundary Type = WALL
Frame Type = Rotating
Location = Entire BLADE
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: R2 Hub
Boundary Type = WALL
Frame Type = Rotating
Location = Entire HUB
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: R2 Shroud
Boundary Type = WALL
Frame Type = Rotating
Location = Entire SHROUD
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: r2 to s2 Side 1
Boundary Type = INTERFACE
Location = Entire OUTFLOW
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: s1 to r2 Side 1 1
Boundary Type = INTERFACE
Location = Entire INFLOW
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
END
DOMAIN MOTION:
Alternate Rotation Model = true
Angular Velocity = 4000 [rev min^-1]
Option = Rotating
AXIS DEFINITION:
Option = Coordinate Axis
Rotation Axis = Coord 0.3
END
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: He Ideal Gas
Material = he
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Include Viscous Work Term = True
Option = Total Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = k epsilon
END
TURBULENT WALL FUNCTIONS:
High Speed Model = Off
Option = Scalable
END
END
END
DOMAIN: S2
Coord Frame = Coord 0
Domain Type = Fluid
Location = HFLUID
BOUNDARY: S2 Outlet
Boundary Type = OPENING
Location = HOUTLET
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 530 [K]
END
MASS AND MOMENTUM:
Option = Entrainment
Relative Pressure = 7.2 [MPa]
PRESSURE OPTION:
Option = Static Pressure
END
END
TURBULENCE:
Option = Zero Gradient
END
END
END
BOUNDARY: r2 to s2 Side 2
Boundary Type = INTERFACE
Location = HINLET
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: s2updown
Boundary Type = WALL
Location = HDOWNFACE,HUPFACE
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = Free Slip Wall
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: He Ideal Gas
Material = he
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Include Viscous Work Term = True
Option = Total Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = k epsilon
END
TURBULENT WALL FUNCTIONS:
High Speed Model = Off
Option = Scalable
END
END
END
DOMAIN: s1
Coord Frame = Coord 0
Domain Type = Fluid
Location = FFLUID
BOUNDARY: s1 to r2 Side 2 1
Boundary Type = INTERFACE
Location = FOUTLET
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: s1cemian
Boundary Type = WALL
Location = FCEMAIN
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = Free Slip Wall
END
END
END
BOUNDARY: s1inlet
Boundary Type = INLET
Location = FINLET
BOUNDARY CONDITIONS:
FLOW DIRECTION:
Option = Normal to Boundary Condition
END
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 250 [C]
END
MASS AND MOMENTUM:
Mass Flow Rate = 96 [kg s^-1]
Mass Flow Rate Area = As Specified
Option = Mass Flow Rate
END
TURBULENCE:
Option = Zero Gradient
END
END
END
BOUNDARY: s1solid
Boundary Type = WALL
Location = FSOLID
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
WALL VELOCITY:
Angular Velocity = 4000 [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
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: He Ideal Gas
Material = he
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Include Viscous Work Term = True
Option = Total Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = k epsilon
END
TURBULENT WALL FUNCTIONS:
High Speed Model = Off
Option = Scalable
END
END
END
DOMAIN INTERFACE: r2 to s2
Boundary List1 = r2 to s2 Side 1
Boundary List2 = r2 to s2 Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = Frozen Rotor
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
MOMENTUM INTERFACE MODEL:
Option = None
END
END
PITCH CHANGE:
Option = Specified Pitch Angles
Pitch Angle Side1 = 360 [degree]
Pitch Angle Side2 = 360 [degree]
END
END
MESH CONNECTION:
Option = GGI
END
END
DOMAIN INTERFACE: s1 to r2
Boundary List1 = s1 to r2 Side 1 1
Boundary List2 = s1 to r2 Side 2 1
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = Frozen Rotor
END
MASS AND MOMENTUM:
Option = Conservative Interface Flux
MOMENTUM INTERFACE MODEL:
Option = None
END
END
PITCH CHANGE:
Option = Specified Pitch Angles
Pitch Angle Side1 = 360 [degree]
Pitch Angle Side2 = 360 [degree]
END
END
MESH CONNECTION:
Option = GGI
END
END
OUTPUT CONTROL:
BACKUP RESULTS: Backup Results 1
Extra Output Variables List = Absolute Pressure
File Compression Level = Default
Option = Standard
Output Equation Residuals = All
OUTPUT FREQUENCY:
Iteration Interval = 100
Option = Iteration Interval
END
END
MONITOR OBJECTS:
MONITOR BALANCES:
Option = Full
END
MONITOR FORCES:
Option = Full
END
MONITOR PARTICLES:
Option = Full
END
MONITOR POINT: niuju
Coord Frame = Coord 0
Expression Value = NJ
Option = Expression
END
MONITOR POINT: ych
Coord Frame = Coord 0
Expression Value = dp
Option = Expression
END
MONITOR RESIDUALS:
Option = Full
END
MONITOR TOTALS:
Option = Full
END
END
RESULTS:
File Compression Level = Default
Option = Standard
END
END
SOLVER CONTROL:
Turbulence Numerics = High Resolution
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Length Scale Option = Conservative
Maximum Number of Iterations = 1000000
Minimum Number of Iterations = 1
Timescale Control = Auto Timescale
Timescale Factor = 1
END
CONVERGENCE CRITERIA:
Residual Target = 0.00001
Residual Type = RMS
END
DYNAMIC MODEL CONTROL:
Global Dynamic Model Control = On
END
END
END
COMMAND FILE:
Version = 16.0
Results Version = 16.0
END
SIMULATION CONTROL:
EXECUTION CONTROL:
EXECUTABLE SELECTION:
Double Precision = Yes
END
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.2
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: dellpc
Remote Host Name = DELL-PC
Installation Root = D:\ANSYS16.0\ANSYS Inc\v%v\CFX
Host Architecture String = winnt-amd64
END
END
PARTITIONER STEP CONTROL:
Multidomain Option = Automatic
Runtime Priority = Standard
EXECUTABLE SELECTION:
Use Large Problem Partitioner = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.2
END
PARTITION SMOOTHING:
Maximum Partition Smoothing Sweeps = 100
Option = Smooth
END
PARTITIONING TYPE:
MeTiS Type = k-way
Option = MeTiS
Partition Size Rule = Automatic
Partition Weight Factors = 0.10000, 0.10000, 0.10000, 0.10000, \
0.10000, 0.10000, 0.10000, 0.10000, 0.10000, 0.10000
END
END
RUN DEFINITION:
Solver Input File = E:\2017-3-27\wu-yplu-try\66\66_002.res
Run Mode = Full
Solver Results File = E:\2017-3-27\wu-yplu-try\66\66_003.res
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.2
END
PARALLEL ENVIRONMENT:
Number of Processes = 10
Start Method = Platform MPI Local Parallel
Parallel Host List = dellpc*10
END
END
END
END

[guillaume74]

Instead of using those BC, I would use total pressure at the inlet and mass flow rate at the outlet. It is usually recommended when you have rotating domains.

[xiexing]

very appreciate for your advice,but i don't know the total pressure in the inlet.(but i've tried static pressure as inlet,and massflow as outlet,also remains the problem), i attached the RMS for you(i thank the later iterations is somewhere wrong)