Hi everyone
I conducted a dynamic analysis of a 5MW fixed-bottom wind turbine. I applied the Blade Element Momentum Theory to calculate the aerodynamic forces of the wind turbine, with the wind speed set as a steady-state wind profile that accounts for shear variations along the height.
I perform computations for each time step using the following algorithm（No correction models were considered in the calculations.During the simulation, the rotor speed was maintained constant, and servo control systemswere disabled）) :
All parameters in the formulas are sourced from the OpenFAST input files(NRELOffshrBsline5MW_AeroDyn_blade.dat).,“The wind speed V0 was calculated via [v₀ᵢ = HWindSpeed× [(RefHt + (r_hub + r_blade) × cos(Azimuth)) / RefHt]^PLExp， i=1,2,3] and validated against the output variable VUndx.” However, there are certain discrepancies between the calculated Pn (normal force) and Pt (tangential force) and the OpenFAST output variable ABaN00bFx``ABaN00bFy" ,particularly pronounced within the initial few seconds of the simulation."
I am deeply puzzled about where I made errors in my calculations.
I would appreciate any thoughts or insights.
Thank you and best regards,
------- AERODYN v15 for OpenFAST INPUT FILE -----------------------------------------------
NREL 5.0 MW offshore baseline aerodynamic input properties.
====== General Options ============================================================================
False Echo - Echo the input to “.AD.ech”? (flag)
“default” DTAero - Time interval for aerodynamic calculations {or “default”} (s)
1 WakeMod - Type of wake/induction model (switch) {0=none, 1=BEMT, 2=DBEMT, 3=OLAF} [WakeMod cannot be 2 or 3 when linearizing]
1 AFAeroMod - Type of blade airfoil aerodynamics model (switch) {1=steady model, 2=Beddoes-Leishman unsteady model} [AFAeroMod must be 1 when linearizing]
0 TwrPotent - Type tower influence on wind based on potential flow around the tower (switch) {0=none, 1=baseline potential flow, 2=potential flow with Bak correction}
0 TwrShadow - Calculate tower influence on wind based on downstream tower shadow? (switch) {0=none, 1=Powles model, 2=Eames model}
False TwrAero - Calculate tower aerodynamic loads? (flag)
False FrozenWake - Assume frozen wake during linearization? (flag) [used only when WakeMod=1 and when linearizing]
False CavitCheck - Perform cavitation check? (flag) [AFAeroMod must be 1 when CavitCheck=true]
False Buoyancy - Include buoyancy effects? (flag)
False CompAA - Flag to compute AeroAcoustics calculation [used only when WakeMod = 1 or 2]
“unused” AA_InputFile - AeroAcoustics input file [used only when CompAA=true]
====== Environmental Conditions ===================================================================
“default” AirDens - Air density (kg/m^3)
“default” KinVisc - Kinematic viscosity of working fluid (m^2/s)
“default” SpdSound - Speed of sound in working fluid (m/s)
“default” Patm - Atmospheric pressure ¶ [used only when CavitCheck=True]
“default” Pvap - Vapour pressure of working fluid ¶ [used only when CavitCheck=True]
====== Blade-Element/Momentum Theory Options ====================================================== [unused when WakeMod=0 or 3]
1 SkewMod - Type of skewed-wake correction model (switch) {1=uncoupled, 2=Pitt/Peters, 3=coupled} [unused when WakeMod=0 or 3]
“default” SkewModFactor - Constant used in Pitt/Peters skewed wake model {or “default” is 15/32*pi} (-) [used only when SkewMod=2; unused when WakeMod=0 or 3]
False TipLoss - Use the Prandtl tip-loss model? (flag) [unused when WakeMod=0 or 3]
False HubLoss - Use the Prandtl hub-loss model? (flag) [unused when WakeMod=0 or 3]
TRUE TanInd - Include tangential induction in BEMT calculations? (flag) [unused when WakeMod=0 or 3]
False AIDrag - Include the drag term in the axial-induction calculation? (flag) [unused when WakeMod=0 or 3]
False TIDrag - Include the drag term in the tangential-induction calculation? (flag) [unused when WakeMod=0,3 or TanInd=FALSE]
“Default” IndToler - Convergence tolerance for BEMT nonlinear solve residual equation {or “default”} (-) [unused when WakeMod=0 or 3]
100 MaxIter - Maximum number of iteration steps (-) [unused when WakeMod=0]
====== Dynamic Blade-Element/Momentum Theory Options ============================================== [used only when WakeMod=2]
1 DBEMT_Mod - Type of dynamic BEMT (DBEMT) model {1=constant tau1, 2=time-dependent tau1, 3=constant tau1 with continuous formulation} (-) [used only when WakeMod=2]
4 tau1_const - Time constant for DBEMT (s) [used only when WakeMod=2 and DBEMT_Mod=1 or 3]
====== OLAF – cOnvecting LAgrangian Filaments (Free Vortex Wake) Theory Options ================== [used only when WakeMod=3]
“unused” OLAFInputFileName - Input file for OLAF [used only when WakeMod=3]
====== Beddoes-Leishman Unsteady Airfoil Aerodynamics Options ===================================== [used only when AFAeroMod=2]
3 UAMod - Unsteady Aero Model Switch (switch) {2=B-L Gonzalez, 3=B-L Minnema/Pierce, 4=B-L HGM 4-states, 5=B-L HGM+vortex 5 states, 6=Oye, 7=Boeing-Vertol} [used only when AFAeroMod=2]
True FLookup - Flag to indicate whether a lookup for f’ will be calculated (TRUE) or whether best-fit exponential equations will be used (FALSE); if FALSE S1-S4 must be provided in airfoil input files (flag) [used only when AFAeroMod=2]
0 UAStartRad - Starting radius for dynamic stall (fraction of rotor radius [0.0,1.0]) [used only when AFAeroMod=2; if line is missing UAStartRad=0]
1 UAEndRad - Ending radius for dynamic stall (fraction of rotor radius [0.0,1.0]) [used only when AFAeroMod=2; if line is missing UAEndRad=1]
====== Airfoil Information =========================================================================
1 AFTabMod - Interpolation method for multiple airfoil tables {1=1D interpolation on AoA (first table only); 2=2D interpolation on AoA and Re; 3=2D interpolation on AoA and UserProp} (-)
1 InCol_Alfa - The column in the airfoil tables that contains the angle of attack (-)
2 InCol_Cl - The column in the airfoil tables that contains the lift coefficient (-)
3 InCol_Cd - The column in the airfoil tables that contains the drag coefficient (-)
4 InCol_Cm - The column in the airfoil tables that contains the pitching-moment coefficient; use zero if there is no Cm column (-)
0 InCol_Cpmin - The column in the airfoil tables that contains the Cpmin coefficient; use zero if there is no Cpmin column (-)
8 NumAFfiles - Number of airfoil files used (-)
“../5MW_Baseline/Airfoils/Cylinder1.dat” AFNames - Airfoil file names (NumAFfiles lines) (quoted strings)
“../5MW_Baseline/Airfoils/Cylinder2.dat”
“../5MW_Baseline/Airfoils/DU40_A17.dat”
“../5MW_Baseline/Airfoils/DU35_A17.dat”
“../5MW_Baseline/Airfoils/DU30_A17.dat”
“../5MW_Baseline/Airfoils/DU25_A17.dat”
“../5MW_Baseline/Airfoils/DU21_A17.dat”
“../5MW_Baseline/Airfoils/NACA64_A17.dat”
====== Rotor/Blade Properties =====================================================================
True UseBlCm - Include aerodynamic pitching moment in calculations? (flag)
“../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(1) - Name of file containing distributed aerodynamic properties for Blade #1 (-)
“../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(2) - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
“../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(3) - Name of file containing distributed aerodynamic properties for Blade #3 (-) [unused if NumBl < 3]
====== Hub Properties ============================================================================== [used only when Buoyancy=True]
0 VolHub - Hub volume (m^3)
0 HubCenBx - Hub center of buoyancy x direction offset (m)
====== Nacelle Properties ========================================================================== [used only when Buoyancy=True]
0 VolNac - Nacelle volume (m^3)
0, 0, 0 NacCenB - Position of nacelle center of buoyancy from yaw bearing in nacelle coordinates (m)
====== Tail Fin Aerodynamics =======================================================================
False TFinAero - Calculate tail fin aerodynamics model (flag)
“unused” TFinFile - Input file for tail fin aerodynamics [used only when TFinAero=True]
====== Tower Influence and Aerodynamics ============================================================ [used only when TwrPotent/=0, TwrShadow/=0, TwrAero=True, or Buoyancy=True]
12 NumTwrNds - Number of tower nodes used in the analysis (-) [used only when TwrPotent/=0, TwrShadow/=0, TwrAero=True, or Buoyancy=True]
TwrElev TwrDiam TwrCd TwrTI TwrCb ! TwrTI used only when TwrShadow=2; TwrCb used only when Buoyancy=True
(m) (m) (-) (-) (-)
0.0000000E+00 6.0000000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
8.5261000E+00 5.7870000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
1.7053000E+01 5.5740000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
2.5579000E+01 5.3610000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
3.4105000E+01 5.1480000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
4.2633000E+01 4.9350000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
5.1158000E+01 4.7220000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
5.9685000E+01 4.5090000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
6.8211000E+01 4.2960000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
7.6738000E+01 4.0830000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
8.5268000E+01 3.8700000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
8.7600000E+01 3.8700000E+00 1.0000000E+00 1.0000000E-01 0.0000000E+00
====== Outputs ====================================================================================
True SumPrint - Generate a summary file listing input options and interpolated properties to “.AD.sum”? (flag)
0 NBlOuts - Number of blade node outputs [0 - 9] (-)
1, 9, 19 BlOutNd - Blade nodes whose values will be output (-)
0 NTwOuts - Number of tower node outputs [0 - 9] (-)
1, 2, 6 TwOutNd - Tower nodes whose values will be output (-)
OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
“RtArea”
“B1N3Clrnc, B2N3Clrnc, B3N3Clrnc”
“RtAeroFxh”
“RtAeroFyh”
“RtAeroFzh”
“RtAeroMxh”
“RtAeroMyh”
“RtAeroMzh”
“RtAeroFxi”
“RtAeroFyi”
“RtAeroFzi”
“RtAeroMxi”
“RtAeroMyi”
“RtAeroMzi”
END of input file (the word “END” must appear in the first 3 columns of this last OutList line)
====== Outputs for all blade stations (same ending as above for B1N1… =========================== [optional section]
3 BldNd_BladesOut - Number of blades to output all node information at. Up to number of blades on turbine. (-)
50 BldNd_BlOutNd - Future feature will allow selecting a portion of the nodes to output. Not implemented yet. (-)
OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
“Fx”
“Fy”
“VUndy”
“VUndx”
“VUndz”
“TnInd”
“AxInd”
“Alpha”
“Theta”
“Phi”
“Cl”
“Cd”
“Cx”
“Cy”
END (the word “END” must appear in the first 3 columns of this last OutList line in the optional nodal output section)