Comparing model results from OpenFAST v3.5.3 and v4.1.2

Emma.Remien · January 21, 2026, 4:41pm

Good morning,

I have recently been trying to model isolated wave loads on the IEA 15MW turbine. I have created the same model in both OpenFAST v3.5.3 and v4.1.2, however I am getting different responses in each. I understand that there are some differences between the versions, and there were changes in regard to HydroDyn/SeaState specifically. I set up the simulations to match input files as closely as possible, but I am hoping that someone could help me explain the differences between the outputs I am getting. I am interested in looking at blade root moments.

For context,

No wind (Inflow off, ServoDyn off)
Idling, blades feathered
Hs = 6 m, depth = 40.8 m

As you can see in the figures below, I am getting some very large and sudden moments in the v4 model and instances of what look like unstable behavior, while the v3 model is much more stable. The v4 results also show a relatively consistent edgewise moment magnitude larger than that of v3. The wave elevation over time is exactly the same. It is not only this simulation where I see a response like this, but there are multiple that behave in a similar manner.

I can provide any input files or figures as need. Thank you in advance!

-Emma

Jason.Jonkman · January 21, 2026, 11:41pm

Dear @Emma.Remien,

I’m not sure I understand what is happening in the different solutions to comment, e.g., why the rotor starts spinning faster in v4.1.2. To isolate what is causing the differences, I suggest isolating different features of the simulation, e.g., do you get the results you expect if you disable all DOFs in ElastoDyn except the platform DOFs? Which feature, when enabled, results in a divergence of the results between the two solutions?

Best regards,

Emma.Remien · January 23, 2026, 3:51pm

Dear @Jason.Jonkman ,

Thank you for your quick response.

The results look more similar if I disable all DOFs in ElastoDyn except platform DOFs (as seen below), however I am still seeing sharp peaks in the moment response in v4.1.2 that are not seen in v3.

I would ideally like to use v4.1.2 for my simulations, however the v3 runs seem to be a lot more stable (but I do not want to blindly use v3 without understanding these differences). I am wondering if there are any parameters you suggest changing other than disabling DOFs? Or do you know of any major differences between the two versions that would cause such different results, even with all of the parameters set to be the same? I know the WaveStMod parameter is introduced in v4, but I turned that off so I could have consistency for comparison.

Best,

Emma

Jason.Jonkman · January 23, 2026, 4:51pm

Dear @Emma.Remien,

Can you provide more information on your model set-up and results? Are you using ElastoDyn or BeamDyn to model the blade structural dynamics? Are the results numerically converged; i.e., does reducing the time step (DT) or adding a correction step (NumCrctn > 0) change the solution? How does the floater motion and tower-base loads compare between the two versions of OpenFAST?

Best regards,

Emma.Remien · February 2, 2026, 7:01pm

Dear @Jason.Jonkman ,

Yes. I am using ElastoDyn to model the blade structural dynamics. I have attached an image of some of my set-up parameters. I am currently using a relatively small DT value of 0.0025, but would need to run a few more models to see if the results are converged. I have also increased NumCrctn up to 2 and it does not seem to change the solution significantly. I will run a few more simulations to check though.

This is a fixed monopile structure, so there is no floater motion. However, here are the results for the tower base shear in the fore-aft and side-to-side directions. In this simulation, the turbine is in a parked state to isolate the differences in blade loads.

Thank you,

Emma

Jason.Jonkman · February 2, 2026, 7:51pm

Dear @Emma.Remien,

My understanding is that the rotor is parked in this simulation. With InflowWind disabled but AeroDyn enabled, presumably you are aiming for still-air aerodynamic drag loads on the blades and tower. Does disabling AeroDyn cause the two solutions to converge? What features of AeroDyn have you enabled, both in OpenFAST v3.5.3 and v4.1.2?

Best regards,

Emma.Remien · February 3, 2026, 5:55pm

Dear @Jason.Jonkman ,

Yes, the rotor was parked in that simulation and yes, the intent for keeping AeroDyn enabled was to account for any still-air drag loads from blade rotation. However, I am not sure how necessary that is for my current purposes.

Disabling AeroDyn does seem to cause convergence, or at least the results have almost identical behavior, with v3.5.3 having slightly higher loads. This also seems to remove the instabilities I was previously seeing in the rotor idling condition.

Here is the same model with AeroDyn disabled and NumCrctn = 0. I have simulated both with the rotor parked (top figure) and idling (bottom figure).

rotor = parked :

rotor = idling :

Here are my AeroDyn files for each version which include the variables that are enables/disabled.

v4.1.2 AeroDyn Input File

------- AERODYN v15.03.* INPUT FILE ------------------------------------------------
IEA MW - Offshore Reference Turbine
====== General Options ============================================================================
False Echo - Echo the input to “.AD.ech”? (flag)
Default DTAero - Time interval for aerodynamic calculations {or “default”} (s)
0 Wake_Mod - Wake/induction model (switch) {0=none, 1=BEMT, 3=OLAF} [Wake_Mod cannot be 2 or 3 when linearizing]
1 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}
1 TwrShadow - Calculate tower influence on wind based on downstream tower shadow (switch) {0=none, 1=Powles model, 2=Eames model}
True TwrAero - Calculate tower aerodynamic loads? (flag)
False CavitCheck - Perform cavitation check? (flag) [UA_Mod must be 0 when CavitCheck=true]
False Buoyancy - Include buoyancy effects? (flag)
False NacelleDrag - Include Nacelle Drag effects? (flag)
False CompAA - Flag to compute AeroAcoustics calculation [used only when Wake_Mod = 1 or 2]
AeroAcousticsInput.dat AA_InputFile - AeroAcoustics input file [used only when CompAA=true]
====== Environmental Conditions ===================================================================
“default” AirDens - Air density (kg/m^3)
“default” KinVisc - Kinematic air viscosity (m^2/s)
“default” SpdSound - Speed of sound (m/s)
“default” Patm - Atmospheric pressure ¶ [used only when CavitCheck=True]
“default” Pvap - Vapour pressure of fluid ¶ [used only when CavitCheck=True]
====== Blade-Element/Momentum Theory Options ====================================================== [used only when WakeMod=1]
1 BEM_Mod - BEM model {1=legacy NoSweepPitchTwist, 2=polar} (switch) [used for all Wake_Mod to determine output coordinate system]
— Skew correction
1 Skew_Mod - Skew model {0=No skew model, -1=Remove non-normal component for linearization, 1=skew model active}
False SkewMomCorr - Turn the skew momentum correction on or off [used only when Skew_Mod=1]
1 SkewRedistr_Mod - Type of skewed-wake correction model (switch) {0=no redistribution, 1=Glauert/Pitt/Peters, default=1} [used only when Skew_Mod=1]
default SkewRedistrFactor - Constant used in Pitt/Peters skewed wake model {or “default” is 15/32*pi} (-) [used only when Skew_Mod=1 and SkewRedistr_Mod=1]
— BEM algorithm
True TipLoss - Use the Prandtl tip-loss model? (flag) [unused when Wake_Mod=0 or 3]
True HubLoss - Use the Prandtl hub-loss model? (flag) [unused when Wake_Mod=0 or 3]
True TanInd - Include tangential induction in BEMT calculations? (flag) [unused when Wake_Mod=0 or 3]
True AIDrag - Include the drag term in the axial-induction calculation? (flag) [unused when Wake_Mod=0 or 3]
True TIDrag - Include the drag term in the tangential-induction calculation? (flag) [unused when Wake_Mod=0,3 or TanInd=FALSE]
Default IndToler - Convergence tolerance for BEMT nonlinear solve residual equation {or “default”} (-) [unused when Wake_Mod=0 or 3]
500 MaxIter - Maximum number of iteration steps (-) [unused when Wake_Mod=0]
— Shear correction
False SectAvg - Use sector averaging (flag)
1 SectAvgWeighting - Weighting function for sector average {1=Uniform, default=1} within a sector centered on the blade (switch) [used only when SectAvg=True]
default SectAvgNPoints - Number of points per sectors (-) {default=5} [used only when SectAvg=True]
default SectAvgPsiBwd - Backward azimuth relative to blade where the sector starts (<=0) {default=-60} (deg) [used only when SectAvg=True]
default SectAvgPsiFwd - Forward azimuth relative to blade where the sector ends (>=0) {default=60} (deg) [used only when SectAvg=True]
— Dynamic wake/inflow
2 DBEMT_Mod - Type of dynamic BEMT (DBEMT) model {0=No Dynamic Wake, -1=Frozen Wake for linearization, 1:constant tau1, 2=time-dependent tau1, 3=constant tau1 with continuous formulation} (-)
29.03 tau1_const - Time constant for DBEMT (s) [used only when Wake_Mod=2 and DBEMT_Mod=1]
====== OLAF – cOnvecting LAgrangian Filaments (Free Vortex Wake) Theory Options ================== [used only when Wake_Mod=3]
../IEA-15-240-RWT-OLAF/IEA-15-240-RWT_OLAF.dat OLAFInputFileName - Input file for OLAF [used only when Wake_Mod=3]
====== Unsteady Airfoil Aerodynamics Options ====================================================
True AoA34 - Sample the angle of attack (AoA) at the 3/4 chord or the AC point {default=True} [always used]
3 UA_Mod - Unsteady Aero Model Switch (switch) {0=Quasi-steady (no UA), 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}
True FLookup - Flag to indicate whether a lookup for fprime 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 UA_Mod>0]
3 IntegrationMethod - Switch to indicate which integration method UA uses (1=RK4, 2=AB4, 3=ABM4, 4=BDF2)
0.1 UAStartRad - Starting radius for dynamic stall (fraction of rotor radius [0.0,1.0]) [used only when UA_Mod>0; if line is missing UAStartRad=0]
1 UAEndRad - Ending radius for dynamic stall (fraction of rotor radius [0.0,1.0]) [used only when UA_Mod>0; 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 (-)
50 NumAFfiles - Number of airfoil files used (-)
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_00.dat” AFNames - Airfoil file names (NumAFfiles lines) (quoted strings)
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_01.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_02.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_03.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_04.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_05.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_06.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_07.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_08.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_09.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_10.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_11.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_12.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_13.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_14.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_15.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_16.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_17.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_18.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_19.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_20.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_21.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_22.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_23.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_24.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_25.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_26.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_27.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_28.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_29.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_30.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_31.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_32.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_33.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_34.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_35.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_36.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_37.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_38.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_39.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_40.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_41.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_42.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_43.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_44.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_45.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_46.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_47.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_48.dat”
“IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_49.dat”
====== Rotor/Blade Properties =====================================================================
True UseBlCm - Include aerodynamic pitching moment in calculations? (flag)
“IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_blade.dat” ADBlFile(1) - Name of file containing distributed aerodynamic properties for Blade #1 (-)
“IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_blade.dat” ADBlFile(2) - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
“IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_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]
0.0 VolHub - Hub volume (m^3)
0.0 HubCenBx - Hub center of buoyancy x direction offset (m)
====== Nacelle Properties ========================================================================== [used only when Buoyancy=True or NacelleDrag=True]
0 VolNac - Nacelle volume (m^3)
0.0, 0.0, 0.0 NacCenB - Position of nacelle center of buoyancy from yaw bearing in nacelle coordinates (m)
0, 0, 0 NacArea - Projected area of the nacelle in X, Y, Z in the nacelle coordinate system (m^2)
0, 0, 0 NacCd - Drag coefficient for the nacelle areas defined above (-)
0, 0, 0 NacDragAC - Position of aerodynamic center of nacelle drag 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, or TwrAero=True]
10 NumTwrNds - Number of tower nodes used in the analysis (-) [used only when TwrPotent/=0, TwrShadow/=0, or TwrAero=True]
TwrElev TwrDiam TwrCd TwrTI TwrCb
(m) (m) (-) (-) (-)
15 10 5.00E-01 1.00E-01 0
28 10 5.00E-01 1.00E-01 0
41 9.93E+00 5.00E-01 1.00E-01 0
67 8.83E+00 5.00E-01 1.00E-01 0
80 8.15E+00 5.00E-01 1.00E-01 0
93 7.39E+00 5.00E-01 1.00E-01 0
106 6.91E+00 5.00E-01 1.00E-01 0
119 6.75E+00 5.00E-01 1.00E-01 0
132 6.57E+00 5.00E-01 1.00E-01 0
1.44E+02 6.50E+00 5.00E-01 1.00E-01 0
====== Outputs ====================================================================================
False SumPrint - Generate a summary file listing input options and interpolated properties to “.AD.sum”? (flag)
0 NBlOuts - Number of blade node outputs [0 - 9] (-)
0 BlOutNd - Blade nodes whose values will be output (-)
0 NTwOuts - Number of tower node outputs [0 - 9] (-)
0 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, (-)
“RtFldFxh”
“RtFldFyh”
“RtFldFzh”
“RtFldMxh”
“RtFldMyh”
“RtFldMzh”
“RtVAvgxh”
“RtFldCp”
“RtFldCt”
“RtArea”
“RtSpeed”
RtAeroFxh
RtAeroFyh
RtAeroFzh
RtAeroMxh
RtAeroMyh
RtAeroMzh
“RtTSR”
END
====== Outputs for all blade stations (same ending as above for B1N1… =========================== [optional section]
1 BldNd_BladesOut - Number of blades to output all node information at. Up to number of blades on turbine. (-)
“All” 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, (-)
Vrel
Alpha
Vindx
Vindy
Cn
Ct
Fn
Ft
Fx
Fy
TnInd
AxInd
END (the word “END” must appear in the first 3 columns of this last OutList line in the optional nodal output section)

v3.5.3 AeroDyn Input File

------- AERODYN v15.03.* INPUT FILE ------------------------------------------------
IEA 15 MW Offshore Reference Turbine
====== General Options ============================================================================
False Echo - Echo the input to “.AD.ech”? (flag)
default DTAero - Time interval for aerodynamic calculations {or “default”} (s)
0 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]
1 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}
1 TwrShadow - Calculate tower influence on wind based on downstream tower shadow (switch) {0=none, 1=Powles model, 2=Eames model}
True 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 [only used when WakeMod=1 or 2]
AeroAcousticsInput.dat AA_InputFile - AeroAcoustics input file [used only when CompAA=true]
====== Environmental Conditions ===================================================================
“default” AirDens - Air density (kg/m^3)
“default” KinVisc - Kinematic air viscosity (m^2/s)
“default” SpdSound - Speed of sound (m/s)
“default” Patm - Atmospheric pressure ¶ [used only when CavitCheck=True]
“default” Pvap - Vapour pressure of fluid ¶ [used only when CavitCheck=True]
====== Blade-Element/Momentum Theory Options ====================================================== [used only when WakeMod=1]
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]
True TipLoss - Use the Prandtl tip-loss model? (flag) [unused when WakeMod=0 or 3]
True 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]
True AIDrag - Include the drag term in the axial-induction calculation? (flag) [unused when WakeMod=0 or 3]
True 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]
500 MaxIter - Maximum number of iteration steps (-) [unused when WakeMod=0]
====== Dynamic Blade-Element/Momentum Theory Options ====================================================== [used only when WakeMod=1]
2 DBEMT_Mod - Type of dynamic BEMT (DBEMT) model {1=constant tau1, 2=time-dependent tau1} (-) [used only when WakeMod=2]
29.03 tau1_const - Time constant for DBEMT (s) [used only when WakeMod=2 and DBEMT_Mod=1]
====== OLAF – cOnvecting LAgrangian Filaments (Free Vortex Wake) Theory Options ================== [used only when WakeMod=3]
../IEA-15-240-RWT-OLAF/IEA-15-240-RWT_OLAF.dat 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) {1=Baseline model (Original), 2=Gonzalez"s variant (changes in Cn,Cc,Cm), 3=Minnema/Pierce variant (changes in Cc and Cm)} [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]
0.1 UAStartRad - Starting radius for dynamic stall (fraction of rotor radius) [used only when AFAeroMod=2]
1.0 UAEndRad - Ending radius for dynamic stall (fraction of rotor radius) [used only when AFAeroMod=2]
====== 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 (-)
50 NumAFfiles - Number of airfoil files used (-)
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_00.dat” AFNames - Airfoil file names (NumAFfiles lines) (quoted strings)
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_01.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_02.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_03.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_04.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_05.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_06.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_07.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_08.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_09.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_10.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_11.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_12.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_13.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_14.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_15.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_16.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_17.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_18.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_19.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_20.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_21.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_22.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_23.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_24.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_25.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_26.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_27.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_28.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_29.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_30.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_31.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_32.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_33.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_34.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_35.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_36.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_37.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_38.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_39.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_40.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_41.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_42.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_43.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_44.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_45.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_46.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_47.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_48.dat”
“../IEA-15-240-RWT/Airfoils/IEA-15-240-RWT_AeroDyn15_Polar_49.dat”
====== Rotor/Blade Properties =====================================================================
True UseBlCm - Include aerodynamic pitching moment in calculations? (flag)
“../IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_blade.dat” ADBlFile(1) - Name of file containing distributed aerodynamic properties for Blade #1 (-)
“../IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_blade.dat” ADBlFile(2) - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
“../IEA-15-240-RWT/IEA-15-240-RWT_AeroDyn15_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]
0.0 VolHub - Hub volume (m^3)
0.0 HubCenBx - Hub center of buoyancy x direction offset (m)
====== Nacelle Properties ========================================================================== [used only when Buoyancy=True]
0.0 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, or TwrAero=True]
10 NumTwrNds - Number of tower nodes used in the analysis (-) [used only when TwrPotent/=0, TwrShadow/=0, or TwrAero=True]
TwrElev TwrDiam TwrCd TwrTI TwrCb !TwrTI used only with TwrShadow=2, TwrCb used only with Buoyancy=True
(m) (m) (-) (-) (-)
15 10.000 0.5 0.1 0.0
28.001 10.000 0.5 0.1 0.0
41.000 9.926 0.5 0.1 0.0
67.000 8.833 0.5 0.1 0.0
80.000 8.151 0.5 0.1 0.0
93.000 7.390 0.5 0.1 0.0
106.000 6.909 0.5 0.1 0.0
119.000 6.748 0.5 0.1 0.0
132.001 6.572 0.5 0.1 0.0
144.386 6.500 0.5 0.1 0.0
====== Outputs ====================================================================================
False SumPrint - Generate a summary file listing input options and interpolated properties to “.AD.sum”? (flag)
0 NBlOuts - Number of blade node outputs [0 - 9] (-)
0 BlOutNd - Blade nodes whose values will be output (-)
0 NTwOuts - Number of tower node outputs [0 - 9] (-)
0 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, (-)
“RtFldFxh”
“RtFldFyh”
“RtFldFzh”
“RtFldMxh”
“RtFldMyh”
“RtFldMzh”
“RtVAvgxh”
“RtFldCp”
“RtFldCt”
“RtArea”
“RtSpeed”
“RtAeroFxh”
“RtAeroFyh”
“RtAeroFzh”
“RtAeroMxh”
“RtAeroMyh”
“RtAeroMzh”
“RtTSR”
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]
0 BldNd_BladesOut - Number of blades to output all node information at. Up to number of blades on turbine. (-)
“All” 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, (-)
END (the word “END” must appear in the first 3 columns of this last OutList line in the optional nodal output section)

Thank you,

Emma

Jason.Jonkman · February 3, 2026, 6:10pm

Dear @Emma.Remien,

I’m glad the issue has been isolated to AeroDyn.

Looking briefly at your two input files, I see that you’ve disabled BEM in both versions; however, you have disabled unsteady airfoil aerodynamics (UA) in v3.5.3, but not in v4.1.2. To disable UA, you should set AFAeroMod = 1 in v3.5.3, but in v4.1.2, you should set UAMod = 0 (you’ve set it to 3). Does changing that in v4.1.2 resolve the differences?

Best regards,

Emma.Remien · February 4, 2026, 5:44pm

Dear @Jason.Jonkman ,

I see, I did not catch that difference. I set UAMod = 0 and the results seem to converge pretty nicely. There are still some small differences, but it could be coming from another small difference that I missed in the input files. The v4.1.2 model also looks a lot more stable which is great.

Do you have any idea why UA would make such a big difference in the v4.1.2 simulation results? Especially with a model that does not include wind? I think I am happy with these results, just trying to make sense of the differences.

Thank you!

Jason.Jonkman · February 4, 2026, 7:04pm

Dear @Emma.Remien,

That is great; I’m glad the original issue has been solved!

The UA models available in AeroDyn are tailored to work under normal operating conditions of a wind turbine and are likely not valid for conditions that are far from that. I can’t comment right on the exact source of the numerical issue you are experiencing for a parked rotor in still air, but certainly UA was not implemented for that condition, so, disabling it is best anyway.

Best regards,

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