# Centrifugal fan-reverse flow in outlet lesds to a mass in flow field

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Join Date: Feb 2017
Posts: 3
Rep Power: 7 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!
Attached Images 1.jpg (44.7 KB, 30 views) 2.jpg (80.2 KB, 30 views) 3.jpg (57.4 KB, 23 views) 4.jpg (73.4 KB, 26 views)   March 29, 2017, 06:33 here my CEL #2 New Member   Join Date: Feb 2017 Posts: 3 Rep Power: 7 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   March 29, 2017, 10:49 #3 New Member   Join Date: Sep 2015 Posts: 17 Rep Power: 9 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.   March 29, 2017, 11:00 #4
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Join Date: Feb 2017
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Rep Power: 7 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)
Attached Images 22.jpg (77.9 KB, 26 views)  Tags centrifugal fan impeller, reverse flow, unsymmetric flow field Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post edu_aero FLUENT 29 February 3, 2020 09:38 Nitin FLUENT 9 June 17, 2017 11:30 clgs.1903 FLUENT 6 November 30, 2016 00:15 Zev Xavier FLUENT 3 May 9, 2016 07:42 idiroft CFX 5 June 10, 2014 08:34

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