Hi All!

In my previous work I have done some Rotating domain steady state solutions.But for wind turbines i have no ideas of setting up Boundary conditions.In some references i got velocity inlet,constant pressure outlet and no slip walls.

But i needs the rpm,How should i specify it? Does it need a time bounded(transient) run?

Thanks in advance for your clues.

Pankaj.

I am realy stuck with the problem of how to define RPM.

Can anybody help me out?

Hi,

Read the manual about rotating frames of reference. You can probably use a frozen rotor/stator approach so you don't need to model the full transient effects. This will be heaps quicker than a full transient simulation.

Glenn Horrocks

Hi

It is a flow driven problem, the rpm will be defined by software itself. My question comes to the torque load from the generator, how to define this? Is it a correct way to do it: -to assume a group of different torque value to get a performace curve (Torque-RPM) and then -to match the generator?

Or there are other way to do it?

Thanks

Ahlo

Hi,

Read the Best practices guide for turbo machinery in the documentation. I think there is one on cavitation which discusses generating pummp curves too, that may be useful.

Glenn Horrocks

I have the same problem analyzing a Savonius Rotor (VAWT)

I'm not sure if i'am in the right way...

I have been using CFdesign and it has an option called "flow-driven motion". You only need to specify the inertia of the rotor (fluid zone with the rotor) and a resistive torque that opposes to the rotation. Once you analyze the model (transient analysis) you can obtain the RPM (this will depend on the Torque that you choose, if it is too big the rotor will not move)

In this case you can obtain the power by multiplying the specified Torque with the RPMs that the rotor reaches.

As Ahlo said (I'm analyzing like him) you can vary the resistive torque and obtain the optimum performance. Then you need to choose a generator that match the optimum torque. Of course the analysis is made at a specific wind speed, so it will be the optimum at the specified wind speed.

Any suggestion? is there a way of obtaining the RPMs with a steady analysis.

[davidohyer]

I'm currently using CFDesign, but we are thinking about moving to ansys. How would you set up a flow driven turbine in Ansys CFX as stated?

"I have been using CFdesign and it has an option called "flow-driven motion". You only need to specify the inertia of the rotor (fluid zone with the rotor) and a resistive torque that opposes to the rotation. Once you analyze the model (transient analysis) you can obtain the RPM (this will depend on the Torque that you choose, if it is too big the rotor will not move)"

If I can't set up a turbine blade model like this, then there is no way I can move to ansys for CFD as I do a lot of turbine analysis. Any suggestions? I'd really like to see how this is done so I can upgrade to ansys.

[ghorrocks]

This cannot currently be done in CFX. Well, at least it can't be done easily. It is a very commonly requested feature but so far it has not appeared. Try contacting your CFX support person and pushing them for it - eventually CFX will add the feature.

[sivarama1]

Setting up CFX Solver run ...

|| CFX Command Language for Run |
LIBRARY:
CEL:
EXPRESSIONS:
dt = 0.04 [s]
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
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
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
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
END
FLOW:
SOLUTION UNITS:
Angle Units = [rad]
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
SIMULATION TYPE:
Option = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 300.0*dt
END
TIME STEPS:
Option = Timesteps
Timesteps = dt
END
END
DOMAIN: rotordisc
Coord Frame = Coord 0
Domain Type = Fluid
Fluids List = Air Ideal Gas
Location = turbine Assembly,turbine Assembly 2
BOUNDARY: discback Side 1
Boundary Type = INTERFACE
Location = DISKOUTLET,DISKOUTLET 2
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: frontdisc Side 2
Boundary Type = INTERFACE
Location = DISKINLET,DISKINLET 2
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: outerdisc Side 1
Boundary Type = INTERFACE
Location = SHROUD 2,SHROUD
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: per1 Side 1
Boundary Type = INTERFACE
Location = PER1
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: per1 Side 2
Boundary Type = INTERFACE
Location = PER2 2
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: per2 Side 1
Boundary Type = INTERFACE
Location = PER1 2
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: per2 Side 2
Boundary Type = INTERFACE
Location = PER2
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: rotordisc Default
Boundary Type = WALL
Frame Type = Rotating
Location = BLADE,BLADE 2,HUB,HUB 2
BOUNDARY CONDITIONS:
WALL INFLUENCE ON FLOW:
Option = No Slip
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
END
DOMAIN MOTION:
Alternate Rotation Model = On
Angular Velocity = 71.9 [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 MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Fluid Temperature = 283.15 [K]
Option = Isothermal
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = SST
END
TURBULENT WALL FUNCTIONS:
Option = Automatic
END
END
INITIALISATION:
Coord Frame = Coord 0
Frame Type = Rotating
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cylindrical
CYLINDRICAL VELOCITY COMPONENTS:
Option = Automatic with Value
Velocity Axial Component = 7 [m s^-1]
Velocity Theta Component = 0 [m s^-1]
Velocity r Component = 0 [m s^-1]
END
K:
Fractional Intensity = 0.05
Option = Automatic with Value
k = 0.1875 [m^2 s^-2]
END
OMEGA:
Option = Automatic
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 101325 [Pa]
END
END
END
END
DOMAIN: tunnel
Coord Frame = Coord 0
Domain Type = Fluid
Fluids List = Air Ideal Gas
Location = tunnel Assembly
BOUNDARY: discback Side 2
Boundary Type = INTERFACE
Location = F519.452,F521.452
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: frontdisc Side 1
Boundary Type = INTERFACE
Location = F518.452,F516.452
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: inlet
Boundary Type = INLET
Location = inlet
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Normal Speed = 7 [m s^-1]
Option = Normal Speed
END
TURBULENCE:
Option = High Intensity and Eddy Viscosity Ratio
END
END
END
BOUNDARY: outerdisc Side 2
Boundary Type = INTERFACE
Location = F517.452,F515.452
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Conservative Interface Flux
END
TURBULENCE:
Option = Conservative Interface Flux
END
END
END
BOUNDARY: outlet
Boundary Type = OUTLET
Location = outlet
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Average Static Pressure
Relative Pressure = 0 [Pa]
END
PRESSURE AVERAGING:
Option = Average Over Whole Outlet
END
END
END
BOUNDARY: tunnel Default
Boundary Type = WALL
Location = \
F522.452,F524.452,F525.452,F526.452,F527.452,F528. 452,F529.452,F530.4\
52,F531.452,F532.452,F541.452,F551.452
BOUNDARY CONDITIONS:
WALL INFLUENCE ON FLOW:
Option = No Slip
END
END
END
BOUNDARY: wall
Boundary Type = WALL
Location = wall
BOUNDARY CONDITIONS:
WALL INFLUENCE ON FLOW:
Option = No Slip
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 MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Fluid Temperature = 283.15 [K]
Option = Isothermal
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = SST
END
TURBULENT WALL FUNCTIONS:
Option = Automatic
END
END
INITIALISATION:
Coord Frame = Coord 0
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic
END
K:
Option = Automatic
END
OMEGA:
Option = Automatic
END
STATIC PRESSURE:
Option = Automatic
END
END
END
END
DOMAIN INTERFACE: discback
Boundary List1 = discback Side 1
Boundary List2 = discback Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = Transient Rotor Stator
END
PITCH CHANGE:
Option = None
END
END
MESH CONNECTION:
Option = GGI
END
END
DOMAIN INTERFACE: frontdisc
Boundary List1 = frontdisc Side 1
Boundary List2 = frontdisc Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = Transient Rotor Stator
END
PITCH CHANGE:
Option = None
END
END
MESH CONNECTION:
Option = GGI
END
END
DOMAIN INTERFACE: outerdisc
Boundary List1 = outerdisc Side 1
Boundary List2 = outerdisc Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = Transient Rotor Stator
END
PITCH CHANGE:
Option = None
END
END
MESH CONNECTION:
Option = GGI
END
END
DOMAIN INTERFACE: per1
Boundary List1 = per1 Side 1
Boundary List2 = per1 Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = None
END
PITCH CHANGE:
Option = None
END
END
MESH CONNECTION:
Option = Automatic
END
END
DOMAIN INTERFACE: per2
Boundary List1 = per2 Side 1
Boundary List2 = per2 Side 2
Interface Type = Fluid Fluid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = None
END
PITCH CHANGE:
Option = None
END
END
MESH CONNECTION:
Option = GGI
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Option = Standard
Output Boundary Flows = All
OUTPUT FREQUENCY:
Option = Timestep Interval
Timestep Interval = 101
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 10
Minimum Number of Coefficient Loops = 3
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Conservation Target = 0.01
Residual Target = 1.E-4
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 11.0
Results Version = 11.0
END
EXECUTION CONTROL:
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
EXECUTABLE SELECTION:
Double Precision = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: sivaram
Installation Root = C:\Program Files\Ansys Inc\v%v\CFX
Host Architecture String = amd_opteron.sse2_winnt5.1
END
END
PARTITIONER STEP CONTROL:
Multidomain Option = Independent Partitioning
Runtime Priority = Standard
EXECUTABLE SELECTION:
Use Large Problem Partitioner = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARTITIONING TYPE:
MeTiS Type = k-way
Option = MeTiS
Partition Size Rule = Automatic
END
END
RUN DEFINITION:
Definition File = D:/tutorial/CFX/wind_3d_new.def
Interpolate Initial Values = Off
Run Mode = Full
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
EXECUTABLE SELECTION:
Double Precision = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 1
Start Method = Serial
END
END
END

Ignoring Fractional Intensity for K IC.

| |
| Solver |
| |

| |
| ANSYS CFX Solver 11.0 |
| |
| Version 2007.01.15-19.20 Mon Jan 15 19:24:21 GMTST 2007 |
| |
| Executable Attributes |
| |
| single-int32-32bit-novc6-optimised-supfort-noprof-nospag-lcomp |
| |
| Copyright 1996-2007 ANSYS Europe Ltd. |


| Job Information |

Run mode: serial run

Host computer: SIVARAM
Job started: Tue Jun 23 11:04:09 2009

| Memory Allocated for Run (Actual usage may be less) |


Data Type Kwords Words/Node Words/Elem Kbytes Bytes/Node

Real 109379.1 425.67 268.98 427262.1 1702.66
Integer 31344.0 121.98 77.08 122437.5 487.92
Character 2932.5 11.41 7.21 2863.8 11.41
Logical 65.0 0.25 0.16 253.9 1.01
Double 1208.0 4.70 2.97 9437.5 37.61


| Mesh Statistics |


Domain Name : rotordisc

Total Number of Nodes = 201532

Total Number of Elements = 186990
Total Number of Hexahedrons = 186990

Total Number of Faces = 28664

Minimum Orthogonality Angle [degrees] = 9.2 !
Maximum Aspect Ratio = 150.4 ok
Maximum Mesh Expansion Factor = 1071.9 !

Domain Name : tunnel

Total Number of Nodes = 55428

Total Number of Elements = 219652
Total Number of Tetrahedrons = 173432
Total Number of Prisms = 46051
Total Number of Pyramids = 169

Total Number of Faces = 10224

Minimum Orthogonality Angle [degrees] = 28.2 ok
Maximum Aspect Ratio = 23.6 OK
Maximum Mesh Expansion Factor = 46.0 !

Global Statistics :

Global Number of Nodes = 256960

Global Number of Elements = 406642
Total Number of Tetrahedrons = 173432
Total Number of Prisms = 46051
Total Number of Hexahedrons = 186990
Total Number of Pyramids = 169

Global Number of Faces = 38888

Minimum Orthogonality Angle [degrees] = 9.2 !
Maximum Aspect Ratio = 150.4 ok
Maximum Mesh Expansion Factor = 1071.9 !

Domain Interface Name : per1

Non-overlap area fraction on side 1 = 0.00E+00
Non-overlap area fraction on side 2 = 0.00E+00

Domain Interface Name : per2

Non-overlap area fraction on side 1 = 0.00E+00
Non-overlap area fraction on side 2 = 0.00E+00

| |
| FATAL ERROR : |
| |
| Initial values are required for all variables in TRANSIENT runs. |
| In this simulation, no initial value was set for |
| |
| Variable : Pressure |
| Domain : tunnel |
| |
| The value can be set using the Initial Values panel in CFX Pre. |
| |
| To bypass this message and use default solver initial values, |
| set the expert parameter "transient initialisation override = t" |
| |




| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver has terminated without writing a results |
| file. Command on host sivaram exited with return code 0. |


End of solution stage.


| The following user files have been saved in the directory |
| D:\tutorial\CFX\wind_3d_new_006: |
| |
| mon |

[ghorrocks]

And your question is ......?

I trust you are not going to ask "Why did this run stop?". The answer to that is bleedingly obvious and the error message tells you exactly what you need to do. And while you are at it, check your mesh - an expansion factor of 1079 is pretty bad.