Error When Modifying the Sweep Parameters of the 15MW Wind Turbine Blades

[vacupenda]

Description

I carefully compared the content of https://github.com/IEAWindSystems/IEA-15-240-RWT/blob/master/OpenFAST/IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_blade.dat and https://github.com/IEAWindSystems/IEA-15-240-RWT/blob/master/OpenFAST/IEA-15-240-RWT/IEA-15-240-RWT_BeamDyn.dat, and found that 'BlSpn' and 'BlTwist' in 'AeroDyn15_blade.dat' correspond to 'kp_zr' and 'initial_twist' in 'BeamDyn.dat', respectively. In my understanding, 'kp_xr' and 'kp_yr' should correspond to 'BlCrvAC' and 'BlSwpAC', respectively. However, there is a significant difference between these parameters. Therefore, when I want to study pre-bent and swept blades, I am wondering which parts I should modify.
I modified the parameter kp_yr in the file IEA-15-240-RWT_BeamDyn.dat to study the impact of sweep magnitude on the wind turbine. However, when I changed the tip sweep to 6 meters, an error occurred. I would like to know whether the problem lies in the modification or if a 6-meter sweep displacement is not allowed. The error messages are as follows:

Running ROSCO-v2.9.0
A wind turbine controller framework for public use in the scientific field
Developed in collaboration: National Renewable Energy Laboratory
Delft University of Technology, The Netherlands

Generator speed: 7.6 RPM, Pitch angle: 1.0 deg, Power: 0.0 kW, Est. wind Speed: 11.1 m/s

FAST_Solution:FAST_AdvanceStates:SrvD_UpdateStates:DLL_controller_call:BladedInterface option was
designed for an explicit-loose coupling scheme. Using last calculated values from DLL on all
subsequent calls until time is advanced. Warning will not be displayed again.

Warning: SkewedWakeCorrection encountered a large value of chi (-146.16 deg), so the yaw
correction will be limited. This warning will not be repeated though the condition may persist.
See the AD15 chi output channels, and consider turning off the Pitt/Peters skew model (set
SkewMod=1) if this condition persists.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:RotCalcOutput:BEMT_CalcOut
put(node 47, blade 1):UA_CalcOutput:UA_BlendSteady:Temporarily turning off UA due to high angle
of attack or low relative velocity. This warning will not be repeated though the condition may
persist.
FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:RotCalcOutput:BEMT_CalcOut
put(node 47, blade 1):UA_CalcOutput:Mach number exceeds 0.3. Theory is invalid. This warning will
not be repeated though the condition may persist.

The BEM solution is being turned off due to low TSR. (TSR = 1.1806). This warning will not be
repeated though the condition may persist. (See GeomPhi output channel.)

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:RotCalcOutput:BEMT_CalcOut
put(node 46, blade 1):UA_CalcOutput:Mach number exceeds 1.0. Equations cannot be evaluated.

OpenFAST encountered an error at simulation time 4.00000E-03 of 600 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.

[ptrbortolotti]

Hi @vacupenda,
the two 3D axis are different. AeroDyn takes as input the 3D line connecting the aerodynamic centers. BeamDyn takes as input an arbitrary axis, which is however not the line going through the aerodynamic centers, rather the axis that pins each airfoil along span according to this field

IEA-15-240-RWT/WT_Ontology/IEA-15-240-RWT.yaml

Line 24 in 6b3fd8a

pitch_axis:

When we generate the two files in WEIS, we take the 3D coordinates of the reference axis

IEA-15-240-RWT/WT_Ontology/IEA-15-240-RWT.yaml

Line 27 in 6b3fd8a

reference_axis: &id001

and we then find the coordinates of the aerodynamic center using this function https://github.com/WISDEM/WEIS/blob/0da256fe7b02de10cf0726830b3f1da26c087c8f/weis/aeroelasticse/openmdao_openfast.py#L2710
I hope this helps!
Best regards,

[vacupenda]

Thank you very much for your detailed explanation on how to calculate BlCrvAC and BlSwpAC. I understand that these values are derived from the following function:

def get_ac_axis(self, inputs):   
  
    # Get the absolute offset between pitch axis (rotation center) and aerodynamic center
    ch_offset = inputs['chord'] * (inputs['ac'] - inputs['le_location'])
    # Rotate it by the twist using the AD15 coordinate system
    x , y = util.rotate(0., 0., 0., ch_offset, -np.deg2rad(inputs['theta']))
    # Apply offset to determine the AC axis
    BlCrvAC = inputs['ref_axis_blade'][:,0] + x
    BlSwpAC = inputs['ref_axis_blade'][:,1] + y
    
    return BlCrvAC, BlSwpAC

I have a couple of questions regarding two variables in this function that I would greatly appreciate your guidance on:

1. The first parameter, ac, represents the aerodynamic center of the airfoil. Could you kindly advise where I might find this data? I am unsure of its source or how to determine it for my calculations.
2. The second parameter, le_location, appears to define the leading-edge position relative to a reference axis. Is this parameter defined in the following file: IEA-15-240-RWT.yaml#L24?

My understanding of this function is that x andyare related to the chord, ac, le_location, and theta at different spanwise positions. If I only introduce pre-bend or sweep to the blade, these parameters (chord, ac, le_location, theta) will not change. Instead, only the ref_axis_blade parameter will be modified. Therefore, I can use the existing AeroDyn15_blade.dat file to determine the x and y values in the function. When I adjust the parameters in ref_axis_blade, I can then calculate the corresponding BlCrvAC and BlSwpAC.

You previously mentioned that the files 'AeroDyn15_blade.dat' and 'BeamDyn.dat' are generated using WEIS. Could you kindly provide guidance on the steps required to generate these files? Specifically, what programs or tools do I need to install and run to accomplish this?My computer is running on Windows. Does that mean it doesn't support installation?

Thank you very much for your time and assistance. I truly appreciate your support and look forward to your response.

Best regards,

[ptrbortolotti]

Hi,
The aerodynamic center line can be built from the yaml file by combining the spanwise positions of the airfoils (

IEA-15-240-RWT/WT_Ontology/IEA-15-240-RWT.yaml

Line 17 in 6b3fd8a

labels: [circular, circular, SNL-FFA-W3-500, FFA-W3-360, FFA-W3-330blend, FFA-W3-301, FFA-W3-270blend, FFA-W3-241, FFA-W3-211, FFA-W3-211]

) and each aerodynamic center per airfoil (https://github.com/IEAWindSystems/IEA-15-240-RWT/blob/6b3fd8ac92935f7f6fe1810a909afc2430f6896f/WT_Ontology/IEA-15-240-RWT.yaml)
You are correct about #2
The installation instructions for WEIS are available here https://github.com/WISDEM/WEIS. You should be able to install it on Windows (readme is slightly outdated, thanks for reminding us to update it)
Note that WEIS does not yet support BeamDyn. To generate those files, you need the tool SONATA, which comes with an example for the IEA15, see here https://github.com/ptrbortolotti/SONATA/tree/develop/examples/1_IEA15MW
A long term goal is to bring WEIS and SONATA together
And lastly yes, to introduce sweep, you can simply add a y component to the ref_axis field and regenerate the openFAST model with WEIS (for AD15) and SONATA (for BeamDyn)

[vacupenda]

When performing calculations using the newly generated files IEA-15-240-RWT_AeroDyn15_blade.dat and IEA-15-240-RWT_BeamDyn.dat, the error message shown in the figure appears. Could you please tell me what the issue is and how it can be resolved?

[gbarter]

It looks like your simulation is going unstable, likely from too high of a time step. I would suggest lowering your time step. You may need to iterate with trial-and-error to find a value that is consistently stable.