Power coefficient/Aerodynamic torque

Dear Dr. Jonkman,
Thanks again for your prompt response. I used FAST 8 and Aerodyn v15.03!
Best regards,
Sina

Dear Jason,

I have performed simulation of WP1.5MW using FAST for the conditions specified below. I observe that Cp is greater than 1 as shown in figures. But it should be below Betz limit. Right? Could you please help me how to interpret this.

Uniform wind speed: 6 m/s.
Pitch controller: No pitch controller. (4 deg constant pitch angle).
Tower and blades are rigid.
Only GenDof is kept on for the gear box.
“WakeMod =0” is chosen.
Simple VScontrol .
Power.JPG Cp.JPG

From output:
Torque at steady state: 385.4 kN-m (plot not attached)
Rotor speed at steady state:14.8 RPM (plot not attached)

Also, Cp is calculated as the ratio of output power of rotor to the (0.5* air density * Disk Area * wind vel^3). Correct?

Regards,
Kumara

Dear Kumara,

Are you plotting AeroDyn output RtAeroCp?

With WakeMod = 0 in AeroDyn v15, the induced velocity calculation is disabled (meaning the induction is zero and the angle of attack will be determined geometrically), so, you are not using BEM and the Betz limit can be violated. The WakeMod = 0 option should only be used when simulating parked/idling conditions (when not producing power).

I suspect you’ll get a result that makes more sense for an operational wind turbine when enabling BEM by setting WakeMod = 1.

Best regards,

Yes Jason. I am plotting AeroDyn output RtAeroCp.
Yes, Induced velocity calculation is disabled in my simulation. I did not think about the fact that Betz limit is valid only when BEMT is used.
Thanks for pointing that. Now I understand that exceeding Betz limit is sensible, but how is it possible to generate more power than that is available in the wind? Kindly advice me incase i’m missing something fundamental here. Thanks.

Regards,
Kumara

Dear Kumara,

Without induction, energy is not preserved in this simulation, so, energy-related quantities are not accurate. I would set WakeMod = 1.

Best regards,

Dear Jason,

Many thanks for your quick response. I’ll do that.

Regards,
Kumara

Dear all,

Issue: Difference in the aerodynamic power of rotor between Standalone AeroDyn calculation and OpenFAST calculation.

I have calculated Rotor aerodynamic power for WindPact 1.5MW turbine at (pitch=2.2 deg, rotor speed=24RPM, wind speed=12 m/s Uniform) using

  1. Standalone version of AeroDyn15.04 and 2) OpenFAST-V2.40 but i see the difference in aerodynamic power of the rotor.

  2. RtAeroPwr = 1954.472 kW

  3. ‘RtAeroPwr’= 2003.206 kW

In the OpenFAST simulation case some of the settings are GenDOF = 0, CompAero=2, shafttilt=0,precone=0.

I have made sure that the settings are same for both. What could be the reason for this discrepancy?
Also, does the Elastodyn play role in the calculation of the rotor aerodynamic power (“RtAeroPwr’”) in OpenFast?

Regards,
Kumara

Dear Kumara,

If all structural DOFs are disabled in ElastoDyn and if the geometry and wind are set up identically between the OpenFAST and standalone AeroDyn driver simulations, then I would expect the standalone AeroDyn driver to give the same aerodynamic power as OpenFAST. If the power predictions are different, I would expect that structural DOFs are enabled in ElastoDyn or some geometry or wind differs. Enabling structural DOFs in OpenFAST–e.g., blade deflection–can impact the aerodynamic power calculated by AeroDyn.

Best regards,

Dear Jason,

I have made sure that all the parameters are the same between both AeroDyn (stand alone version) and AeroDyn in OpenFAST. But still I see significant difference between the Aerodynamic Power calculated using standalone Aerodyn vs OpenFAST.

Wind speed (m/s) Pitch (deg) Rotor speed (RPM) RtTSR RtArea (m^2) RtAeroPwr (W) RtAeroCp
12 5 15 4.5815 3848.4510 1420687.0 0.3488
12 5 15 4.5815 3848.4510 1417626.0 0.3480

Also, the AeroDyn input file of OpenFAST (V2.40) require some extra inputs like “AA_InputFile”, “DBEMT_Mod”,“tau1_const”, which are not present in the standalone AeroDyn input file. This may be because of the version difference. But I made sure that, the options I chose are agnostic to these differences, unless modifications are made to the way calculations are performed even with the same settings between the two (like “AFAeroMod”=1).

Currently I am using stand alone version of “AeroDyn_v15.04.02”. If there is latest version, please let me know where to download it from.

I have attached relevant files. If it is not a big ask, could you please go through the attachment and and let me know if I am making any mistakes? Thanks.

Regards,
Kumara
Test_AeroDYN.zip (60.4 KB)

Dear Kumara,

I did a quick comparison between your OpenFAST model and standalone AeroDyn model and don’t see any obvious differences that would lead to different power.

I’m guessing the problem is that you are using two different versions of AeroDyn between the cases. You mention that you are using OpenFAST v2.4 and standalone AeroDyn v15.04. While we don’t provide precompiled Windows executable of the standalone modules (like AeroDyn) with each OpenFAST release, the source code needed to compile the standalone AeroDyn driver is included in the OpenFAST v2.4 repository. The AeroDyn driver input file has not changed between AeroDyn v15.04 and OpenFAST v2.4. So, all you should have to do is compile the standalone AeroDyn driver for OpenFAST v2.4, use your AeroDyn driver file together with the AeroDyn input file(s) from your OpenFAST v2.4 model, and rerun the driver-level simulation.

Best regards,

Dear Sina Sir,
I am also facing the same error while running the file Run_OpenLoop.m
Error using Run_OpenLoop (line 30)
Error reported by S-function ‘FAST_SFunc’ in ‘OpenLoop/FAST Nonlinear Wind Turbine/S-Function’:
FAST_InitializeAll:FAST_Init:FAST_ReadPrimaryFile:OpenFInpFile:The input file, “…\CertTest\Test01.fst”, was not found.

Please guide how to solve this.
Thanks and regards,
Shivaji

Dear Shivaji,

This error means that the input file “Test01.fst” does not exist, i.e., the filename is wrong or the path to it is incorrect.

As I told Sina, "In the transition from FAST v8 to OpenFAST, what used to be the CertTest of FAST v8 has been changed to the regression tests (r-test) of OpenFAST: github.com/OpenFAST/r-test. The primary input file names have also been changed.

Best regards,

Dear Jason,

I wanted to look at the change of the power coefficient Cp of a waked wind turbine. Thus, in FAST.Farm, I considered 2 wind turbines, one 4*D upstream the second one (D is the rotor diameter), and I plot the Tip-Speed Ratio (RtTSR), the rotor speed (RtSpeed), the averaged-disk wind speed (RtVAvgxh), the power coefficient (RtAeroCp), and the output power of the turbines.
I am surprised to have a Cp of the waked wind turbine increasing higher than the Cp_max =0.48, even though I made sure that the controllers are on (pitch & torque), and WakeMod=1. I checked also TSR and RtSpeed, and they seem to be the ones I expected (referring to the plots in the 5MW NREL Definition)
I was expecting a decrease of Cp for the second turbine as the TSR increases (going from Region 2 to Region 1/2). Do you have any idea where this issue may come from?

Kindest regards

Younes

Dear Younes,

Are you running a FAST.Farm simulation using OpenFAST models of the NREL 5-MW baseline wind turbine or something else? What inflow conditions are you simulating in FAST.Farm (presumably steady, uniform inflow based on the smooth curves in your plots)? What structural DOFs and aerodynamic settings are enabled in your OpenFAST models?

I would generally expect the NREL 5-MW baseline wind turbine to have a Cpmax of 0.482 at a TSR of 7.55, but that was computed a while ago and different aerodynamic settings in AeroDyn v15 or enabling/disabling structural DOFs may have some effect on that. The peak of the Cp-TSR surface is also fairly flat for small changes in TSR, so, I could see that small variations in TSR will may have a small effect on Cp. However, a Cp of 0.54 sounds a bit higher than I would expect.

Best regards,

Dear Jason,

Thank you for the reply.

Yes, I am using the NREL 5MW baseline. Otherwise, where can I download its files again?

Yes, steady of 10m/s.

For the structural DOFs, only the Generator is enabled as can be seen here:

[code]------- ELASTODYN v1.03.* INPUT FILE -------------------------------------------
NREL 5.0 MW Baseline Wind Turbine for Use in Offshore Analysis. Properties from Dutch Offshore Wind Energy Converter (DOWEC) 6MW Pre-Design (10046_009.pdf) and REpower 5M 5MW (5m_uk.pdf)
---------------------- SIMULATION CONTROL --------------------------------------
False Echo - Echo input data to “.ech” (flag)
3 Method - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-)
“DEFAULT” DT - Integration time step (s)
---------------------- ENVIRONMENTAL CONDITION ---------------------------------
9.80665 Gravity - Gravitational acceleration (m/s^2)
---------------------- DEGREES OF FREEDOM --------------------------------------
False !JASON:True FlapDOF1 - First flapwise blade mode DOF (flag)
False !JASON:True FlapDOF2 - Second flapwise blade mode DOF (flag)
False !JASON:True EdgeDOF - First edgewise blade mode DOF (flag)
False TeetDOF - Rotor-teeter DOF (flag) [unused for 3 blades]
False !JASON:True DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
True GenDOF - Generator DOF (flag)
False !JASON:True YawDOF - Yaw DOF (flag)
False !JASON:True TwFADOF1 - First fore-aft tower bending-mode DOF (flag)
False !JASON:True TwFADOF2 - Second fore-aft tower bending-mode DOF (flag)
False !JASON:True TwSSDOF1 - First side-to-side tower bending-mode DOF (flag)
False !JASON:True TwSSDOF2 - Second side-to-side tower bending-mode DOF (flag)
False PtfmSgDOF - Platform horizontal surge translation DOF (flag)
False PtfmSwDOF - Platform horizontal sway translation DOF (flag)
False PtfmHvDOF - Platform vertical heave translation DOF (flag)
False PtfmRDOF - Platform roll tilt rotation DOF (flag)
False PtfmPDOF - Platform pitch tilt rotation DOF (flag)
False PtfmYDOF - Platform yaw rotation DOF (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
0 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
0 IPDefl - Initial in-plane blade-tip deflection (meters)
0 BlPitch(1) - Blade 1 initial pitch (degrees)
0 BlPitch(2) - Blade 2 initial pitch (degrees)
0 BlPitch(3) - Blade 3 initial pitch (degrees) [unused for 2 blades]
0 TeetDefl - Initial or fixed teeter angle (degrees) [unused for 3 blades]
0 Azimuth - Initial azimuth angle for blade 1 (degrees)
11.0 !JASON: 12.1 RotSpeed - Initial or fixed rotor speed (rpm)
0 NacYaw - Initial or fixed nacelle-yaw angle (degrees)
0 TTDspFA - Initial fore-aft tower-top displacement (meters)
0 TTDspSS - Initial side-to-side tower-top displacement (meters)
0 PtfmSurge - Initial or fixed horizontal surge translational displacement of platform (meters)
0 PtfmSway - Initial or fixed horizontal sway translational displacement of platform (meters)
0 PtfmHeave - Initial or fixed vertical heave translational displacement of platform (meters)
0 PtfmRoll - Initial or fixed roll tilt rotational displacement of platform (degrees)
0 PtfmPitch - Initial or fixed pitch tilt rotational displacement of platform (degrees)
0 PtfmYaw - Initial or fixed yaw rotational displacement of platform (degrees)
---------------------- TURBINE CONFIGURATION -----------------------------------
3 NumBl - Number of blades (-)
63 TipRad - The distance from the rotor apex to the blade tip (meters)
1.5 HubRad - The distance from the rotor apex to the blade root (meters)
-2.5 PreCone(1) - Blade 1 cone angle (degrees)
-2.5 PreCone(2) - Blade 2 cone angle (degrees)
-2.5 PreCone(3) - Blade 3 cone angle (degrees) [unused for 2 blades]
0 HubCM - Distance from rotor apex to hub mass [positive downwind] (meters)
0 UndSling - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
0 Delta3 - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
0 AzimB1Up - Azimuth value to use for I/O when blade 1 points up (degrees)
-5.0191 OverHang - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters)
1.912 ShftGagL - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
-5 ShftTilt - Rotor shaft tilt angle (degrees)
1.9 NacCMxn - Downwind distance from the tower-top to the nacelle CM (meters)
0 NacCMyn - Lateral distance from the tower-top to the nacelle CM (meters)
1.75 NacCMzn - Vertical distance from the tower-top to the nacelle CM (meters)
-3.09528 NcIMUxn - Downwind distance from the tower-top to the nacelle IMU (meters)
0 NcIMUyn - Lateral distance from the tower-top to the nacelle IMU (meters)
2.23336 NcIMUzn - Vertical distance from the tower-top to the nacelle IMU (meters)
1.96256 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
87.6 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
0 TowerBsHt - Height of tower base above ground level [onshore] or MSL [offshore] (meters)
0 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)
---------------------- MASS AND INERTIA ----------------------------------------
0 TipMass(1) - Tip-brake mass, blade 1 (kg)
0 TipMass(2) - Tip-brake mass, blade 2 (kg)
0 TipMass(3) - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
56780 HubMass - Hub mass (kg)
115926 HubIner - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
534.116 GenIner - Generator inertia about HSS (kg m^2)
240000 NacMass - Nacelle mass (kg)
2.60789E+06 NacYIner - Nacelle inertia about yaw axis (kg m^2)
0 YawBrMass - Yaw bearing mass (kg)
0 PtfmMass - Platform mass (kg)
0 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
0 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
0 PtfmYIner - Platform inertia for yaw rotation about the platform CM (kg m^2)
---------------------- BLADE ---------------------------------------------------
17 BldNodes - Number of blade nodes (per blade) used for analysis (-)
“NRELOffshrBsline5MW_Blade.dat” BldFile(1) - Name of file containing properties for blade 1 (quoted string)
“NRELOffshrBsline5MW_Blade.dat” BldFile(2) - Name of file containing properties for blade 2 (quoted string)
“NRELOffshrBsline5MW_Blade.dat” BldFile(3) - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- ROTOR-TEETER --------------------------------------------
0 TeetMod - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades]
0 TeetDmpP - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetDmp - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
0 TeetCDmp - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
0 TeetSStP - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetHStP - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetSSSp - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
0 TeetHSSp - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- DRIVETRAIN ----------------------------------------------
100 GBoxEff - Gearbox efficiency (%)
97 GBRatio - Gearbox ratio (-)
8.67637E+08 DTTorSpr - Drivetrain torsional spring (N-m/rad)
6.215E+06 DTTorDmp - Drivetrain torsional damper (N-m/(rad/s))
---------------------- FURLING -------------------------------------------------
False Furling - Read in additional model properties for furling turbine (flag) [must currently be FALSE)
“unused” FurlFile - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- TOWER ---------------------------------------------------
20 TwrNodes - Number of tower nodes used for analysis (-)
“NRELOffshrBsline5MW_Onshore_ElastoDyn_Tower.dat” TwrFile - Name of file containing tower properties (quoted string)
---------------------- OUTPUT --------------------------------------------------
True SumPrint - Print summary data to “.sum” (flag)
1 OutFile - Switch to determine where output will be placed: {1: in module output file only; 2: in glue code output file only; 3: both} (currently unused)
True TabDelim - Use tab delimiters in text tabular output file? (flag) (currently unused)
“ES10.3E2” OutFmt - Format used for text tabular output (except time). Resulting field should be 10 characters. (quoted string) (currently unused)
0 TStart - Time to begin tabular output (s) (currently unused)
1 DecFact - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
0 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
10, 19, 28 TwrGagNd - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
3 NBlGages - Number of blade nodes that have strain gages for output [0 to 9] (-)
5, 9, 13 BldGagNd - List of blade nodes that have strain gages [1 to BldNodes] (-) [unused if NBlGages=0]
OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
“OoPDefl1” - Blade 1 out-of-plane and in-plane deflections and tip twist
“IPDefl1” - Blade 1 out-of-plane and in-plane deflections and tip twist
“TwstDefl1” - Blade 1 out-of-plane and in-plane deflections and tip twist
“BldPitch1” - Blade 1 pitch angle
“HSShftTq”
“HSShftPwr”
“YawPzn”
“Azimuth” - Blade 1 azimuth angle
“RotSpeed” - Low-speed shaft and high-speed shaft speeds
“GenSpeed” - Low-speed shaft and high-speed shaft speeds
“TTDspFA” - Tower fore-aft and side-to-side displacements and top twist
“TTDspSS” - Tower fore-aft and side-to-side displacements and top twist
“TTDspTwst” - Tower fore-aft and side-to-side displacements and top twist
“Spn2MLxb1” - Blade 1 local edgewise and flapwise bending moments at span station 2 (approx. 50% span)
“Spn2MLyb1” - Blade 1 local edgewise and flapwise bending moments at span station 2 (approx. 50% span)
“RootFxb1” - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
“RootFyb1” - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
“RootFzb1” - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
“RootMxb1” - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
“RootMyb1” - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
“RootMzb1” - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
“RotTorq” - Rotor torque and low-speed shaft 0- and 90-bending moments at the main bearing
“LSSGagMya” - Rotor torque and low-speed shaft 0- and 90-bending moments at the main bearing
“LSSGagMza” - Rotor torque and low-speed shaft 0- and 90-bending moments at the main bearing
“YawBrFxp” - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
“YawBrFyp” - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
“YawBrFzp” - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
“YawBrMxp” - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
“YawBrMyp” - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
“YawBrMzp” - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
“TwrBsFxt” - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
“TwrBsFyt” - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
“TwrBsFzt” - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
“TwrBsMxt” - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
“TwrBsMyt” - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
“TwrBsMzt” - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

[/code]

Here is my AeroDyn file as well:

[code]------- AERODYN v15 for OpenFAST INPUT FILE -----------------------------------------------
NREL 5.0 MW offshore baseline aerodynamic input properties, with OC3 Monopile tower
====== 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? (flag)
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 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 ===================================================================
1.225 AirDens - Air density (kg/m^3)
1.464E-05 KinVisc - Kinematic air viscosity (m^2/s)
335 SpdSound - Speed of sound (m/s)
103500 Patm - Atmospheric pressure ¶ [used only when CavitCheck=True]
1700 Pvap - Vapour pressure of fluid ¶ [used only when CavitCheck=True]
0.5 FluidDepth - Water depth above mid-hub height (m) [used only when CavitCheck=True]
====== Blade-Element/Momentum Theory Options ====================================================== [unused when WakeMod=0 or 3]
2 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]
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]
2 DBEMT_Mod - Type of dynamic BEMT (DBEMT) model {1=constant tau1, 2=time-dependent tau1} (-) [used only when WakeMod=2]
4 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]
“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) {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]
====== 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 (-)
“Airfoils/Cylinder1.dat” AFNames - Airfoil file names (NumAFfiles lines) (quoted strings)
“Airfoils/Cylinder2.dat”
“Airfoils/DU40_A17.dat”
“Airfoils/DU35_A17.dat”
“Airfoils/DU30_A17.dat”
“Airfoils/DU25_A17.dat”
“Airfoils/DU21_A17.dat”
“Airfoils/NACA64_A17.dat”
====== Rotor/Blade Properties =====================================================================
True UseBlCm - Include aerodynamic pitching moment in calculations? (flag)
“NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(1) - Name of file containing distributed aerodynamic properties for Blade #1 (-)
“NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(2) - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
“NRELOffshrBsline5MW_AeroDyn_blade.dat” ADBlFile(3) - Name of file containing distributed aerodynamic properties for Blade #3 (-) [unused if NumBl < 3]
====== Tower Influence and Aerodynamics ============================================================= [used only when TwrPotent/=0, TwrShadow=True, or TwrAero=True]
12 NumTwrNds - Number of tower nodes used in the analysis (-) [used only when TwrPotent/=0, TwrShadow/=0, or TwrAero=True]
TwrElev TwrDiam TwrCd TwrTI (used only with TwrShadow=2)
(m) (m) (-) (-)
0.0000000E+00 6.0000000E+00 1.0000000E+00 1.0000000E-01
8.5261000E+00 5.7870000E+00 1.0000000E+00 1.0000000E-01
1.7053000E+01 5.5740000E+00 1.0000000E+00 1.0000000E-01
2.5579000E+01 5.3610000E+00 1.0000000E+00 1.0000000E-01
3.4105000E+01 5.1480000E+00 1.0000000E+00 1.0000000E-01
4.2633000E+01 4.9350000E+00 1.0000000E+00 1.0000000E-01
5.1158000E+01 4.7220000E+00 1.0000000E+00 1.0000000E-01
5.9685000E+01 4.5090000E+00 1.0000000E+00 1.0000000E-01
6.8211000E+01 4.2960000E+00 1.0000000E+00 1.0000000E-01
7.6738000E+01 4.0830000E+00 1.0000000E+00 1.0000000E-01
8.5268000E+01 3.8700000E+00 1.0000000E+00 1.0000000E-01
8.7600000E+01 3.8700000E+00 1.0000000E+00 1.0000000E-01
====== 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] (-)
2, 9, 16, 4, 5, 7, 11, 13, 14 BlOutNd - Blade nodes whose values will be output (-)
0 NTwOuts - Number of tower node outputs [0 - 9] (-)
1, 2, 3, 4, 5 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, (-)
“RtAeroFxh”
“RtAeroCt”
“RtAeroCp”
“RtSpeed”
“RtVAvgxh”
“RtTSR”
END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

[/code]

I agree with your statements and I was expecting the same. Do you think the issue comes from one of the files?

Sorry for the inconvenience

Kindest regards

Younes

Dear Younes,

OK, thanks for clarifying. You can find a complete OpenFAST model of the NREL 5-MW baseline wind turbine from the OpenFAST r-test (github.com/OpenFAST/r-test), but I suspect you are using the correct data anyway.

Another thought I have is that the inflow to the second wind turbine is not uniform, but includes a (likely Gaussian-shaped) wake deficit from the upwind turbine. Perhaps the value of the rotor disk-averaged wind speed (RtVAvgxh), which is also used to compute the rotor aerodynamic power coefficient (RtAeroCp), is not computing the disk-averaged wind speed accurately enough for this inflow condition. RtVAvgxh is computed simply by summing the relative velocity at each aerodynamic analysis node along each blade and dividing by the total number of nodes. In reality, the more outboard nodes should have a higher weighting in this summation than the inboard nodes because they sweep a larger area, but this weighting is not included in the spatial averaging. You could look at the inflow to the second turbine from the FAST.Farm outputs and manually compute a more accurate representation of the disk-averaged wind speed and associated rotor aerodynamic power coefficient. I suspect if you do that, you’ll get a TSR and Cp that is more consistent with the upstream turbine.

Best regards,

Dear Jason,

Thank you so much for the reply and guidance. For the maximum power coefficient, I found using the AeroDyn module that it is Cp=0.4862, for a TSR_opt=7.55 and Pitch_opt=0°, as we discussed it in the “NREL 5-MW reference turbine - CP, CQ, CT Coefficients” topic [url]Question #1 for turbulence fields (points outside of field)], which is very close to the 0.482 found a while ago. I think the difference comes from the blade nodes considered while computing Cp, and the different aerodynamic settings in AeroDyn v15, and/or enabling/disabling structural DOFs may have some effect, as you highlighted.

Regarding your suggestion for the computation of RtVAvgxh, I compute it now by double integrating the local wind speeds, in the following nodes, on the swept area divided by (R^2)*pi.

eq.PNG

The nodes: OutRadii = 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 51 57 60 63 dr=1 (m)

The results on the waked wind turbine are:
RtVAvgxh= 6.8052 m/s
TSR_waked= 8.1119
Cp_waked= 0.4829

Which are what I expected when looking at the 5MW characteristics, and also not in the second region anymore, but in region 1/2 (Cp < Cp_max):

Thank you so much again

Kindest regards

Younes

I’m glad that worked!

Hi Jason,
A basic question as I haven’t had much experience with openFAST.
I am working with r-tests. But I am struggling to get around the naming convention of r-tests. ReadMe file doesn’t have much information. Also, I didn’t get much info from the “naming scheme from testNN”. E.g what does “5MW_ITIBarge_DLL_WTurb_WavesIrr” mean?
I need to run the simulation for a 5MW, three-bladed,variable-speed offshore(fixed monopile) turbine. Which test should I refer to?
Warm regards

Dear @Ahmed.Hassan,

The r-test named 5MW_ITIBarge_DLL_WTurb_WavesIrr is a simulation of the NREL 5-MW baseline wind turbine atop the floating offshore ITI Energy barge with the controller DISCON DLL excited by wind turbulence and irregular waves.

A description of most of the OpenFAST r-tests is provided in Table 6 of the old FAST v8 ReadMe: https://openfast.readthedocs.io/en/main/_downloads/5f2ddf006568adc9b88d8118dc3f1732/FAST8_README.pdf (although in this table, the tests were numbered from Test01-Test26). The previous CertTest cases from FAST v8 were migrated into what is now the r-test in OpenFAST.

A model of the NREL 5-MW baseline wind turbine atop the fixed offshore OC3-monopile with fixed foundation is provided in the following OpenFAST r-test: r-test/glue-codes/openfast/5MW_OC3Mnpl_DLL_WTurb_WavesIrr at main · OpenFAST/r-test · GitHub.

Best regards,

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