NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Dear Rocio,

The standalone AeroDyn driver input file can be set up to run multiple cases for different wind speeds (WndSpeed), rotor speeds (RotSpd), and pitch angles (Pitch) via the “Combined-Case Analysis” options. You can include the rotor aerodynamic power and torque in the AeroDyn output file by including “RtAeroCp” and “RtAeroCt” in the output list (OutList) in the AeroDyn primary input file. Simply run multiple cases and take the time- (or, preferably, azimuth-) averaged torque to find the RtAeroCp and RtAeroCt as a function of WndSpeed, RotSpd, and Pitch (or RtTSR).

Best regards,

Dear Jason,

Thank you for your answer.
Doing as you say, I would have to define a row for each simulation, fully specifying all of the wind speed, rotor speed and pitch values. And I get I would be obtaining an output file corresponding to each of these rows (containing the time-series information for each chosen output sensor), which given the number of simulations I would have to run to cover the value ranges I want, would be tough to post-process. I wonder if there is a way to run a parametric analysis, giving in the input file the direct ranges (e.g Pitch from -5 to 5 deg with a delta increment value of 1 deg → -5.0, 5.0,1.0 ) and obtain a single output file where I could find the tables with Cp/Ct values for each pair of wind speed and rotor speed, 1 table per pitch (Just the same as the output file that was obtained with WT_perf and that you posted on the 6th of March of 2012). If there is not, I will have to do as you propose.

Thank you again in advance.
Best regards,

Rocío

Dear Rocio,

No, the standalone AeroDyn driver is not set up to run a parametric analysis that generates one output file for multiple cases. I would think a simple script could be written to do this, but I don’t have one I can send you. The key is that the output from standalone AeroDyn for each case is a time series–and what you want is the mean of this time series (or preferably the azimuth average), resulting in one value of RtAeroCp and RtAeroCt for each case. If you have MATLAB, the MCrunch post-processor could be used to calculate these mean values, or you could write your own script to do that.

Best regards,

Dear Jason,

Ok, I understand that, thank you very much for your help.

Best regards,
Rocío

Hello again,
I’ve been working on NREL-5MW wind turbine and there is something bugging me. This turbine is rated at wind speed = 11.4m/s and TSR = 7 (as stated here: nrel.gov/docs/fy09osti/38060.pdf) for 5MW of power. Examining the document and assuming this is an offshore wind turbine, considering the air density as 1.225 kg/m^3, Cp at design conditions is 0.44. When I observe in Mr. Jonkman and Mr. Chaaban’s results, higher Cp is achieved at even lower wind speeds. I am also getting higher values using RANS-ALM methodology. Now I might be wrong but AeroDyn and FAST are used to obtain results in that document. I am not sure what I’m missing in the consistency here. I am also having a hard time finding reliable experimental or numerical results on this turbine in journals or papers.
Some data I have found:
iopscience.iop.org/article/10.10 … 082003/pdf
brage.bibsys.no/xmlui/bitstream … sAllowed=y (this paper also refers to this forum)
Other sources you might come across would be extremely valuable, as well as your ideas on the matter I’ve mentioned.
Best regards,
Hüseyin

Dear Hüseyin,

I’m not sure I understand your concern, but I would expect a maximum aerodynamic Cp of the NREL 5-MW wind turbine to be around 0.48 in region 2 using blade-element/momentum (BEM) theory. Of course, some power is lost in the mechanical-to-electrical conversion (generator efficiency), so, the effective electrical Cp would be less.

Best regards,

Dear Jason,

I computed the thrust coefficient vs wind speed with the stand alone Aerodyn V15.
The results are shown below.
Does the results seem coherent?

Thank you.

Best regards,
Etienne JARGOT
CTvsWIND.PNG

Dear Etienne,

Yes, your results look like what I would expect for the NREL 5-MW turbine.

Best regards,

Dear Jason,

In the post I am citing bellow, Rannam Chaaban asked you about the values to set for parameters in SIMPLE VARIABLE-SPEED TORQUE CONTROL.

As you answered in your reply, I would also expect to give VS_Rgn2K a value of 0.0255764 and VS_SlPc a value of 10.

Nevertheless, I do not understand why should VS_RtGnSp be the 99% of rated HSS speed.

As far as I understand, that point (wGen = 1162 rpm) in the torque curve corresponds to a higher torque value (43528.84 Nm). This was recently discussed in the following post: [url]http://forums.nrel.gov/t/nrel-5mw-torque-vs-genspeed-curve-points/2143/3].

Therefore, I would expect VS_RtGnSp to be the rated generator speed: 1173.7 rpm, which would correspond to the rated torque of 43093.55 Nm.

Here I put a summary of the values that I would expect:

---------------------- SIMPLE VARIABLE-SPEED TORQUE CONTROL --------------------
1173.7 VS_RtGnSp
43093.55 VS_RtTq
0.0255764 VS_Rgn2K
10 VS_SlPc

Are these values OK?

Thank you in advance,

Best regards,

Jon Martínez Rico

Dear Jon,

The simple variable-speed controller in the ServoDyn module of FAST v8 or OpenFAST cannot fully represent the characteristics of the baseline NREL 5-MW turque speed curve. This is because the simple variable-speed controller does not include Regions 1 and 1.5 and because Region 3 is considered using constant torque, rather than the constant power used in the NREL 5-MW baseline controller. I had recommend setting VS_RtGnSp equal to 99% of the actual rated speed of 1173.7 to ensure that the synchronous speed for Region 2.5 (i.e., 0.99*1173.7/(1+0.1) = 1056.33 rpm) was identical in both models. Also setting the rated speed right at the transition speeds between Regions 2.5 and 3 tends to cause problems in the blade-pitch controller.

Best regards,

Dear Jason,

Thank you very much for your anserwer.

Best regards,

Jon Martínez Rico

Dear Jason,

I have some doubts about thrust of NREL 5MW given in this article [Definition-of-a-5-MW-reference-wind-turbine-for-offshore-system-development](Figure 9-1. Steady-state responses as a function of wind speed).

I used ORIGIN to obtain the data of RotThrust vs wind speed, and then it was easy to get the CT(coefficient of thrust, the black line) with the formula(air density=1.225, Ad=3.1415*63^2)

At the same time, I used FAST to calculate Ct in different average wind speed ranged from 3-25 m/s(the red line).

The strange things is that those 2 line has huge difference. Why has this happened? Is it normal Ct is as high as 2.5?

Best regards,
Chenxu.Zhao
CT vs wind speed.png
RotThrust vs wind speed.png
formula-Ct.png

Dear Chenxu.Zhao,

The FAST (ElastoDyn) output RotThrust is the reaction force transmitted from the rotor to the shaft, so, not only includes the applied aerodynamic forces, but also the forces resulting from rotor weight (and in transient analysis, rotor inertia); see related forum posts on this topic. So, normally, RotThrust is shifted upward relative to the aerodynamic applied Thrust. If you are using AeroDyn v15, you can output the aerodynamic applied rotor thrust via AeroDyn output RtAeroFxh.

Best regards,

Dear Jason,

Thank you so much for your answer, sir! That had really solved most of my confusions.

But there is still one little problem. The red line was exactly caculated by using your method of getting ‘RtAeroFxh’ from FAST. And still when wind velocity equals 3m/s, the CT is somewhat higher than 1 as 1.1 . If this is the right way to do it, then what’s the reason for this abnormal phenomenum? From the textbooks I have read, they told me that CT was not allowed to be more than 1.

Best regards,
Chenxu.Zhao

Dear Chenxu,

Actually, the aerodynamic thrust is able to exceed 1, but in this situation, flow will recirculate around the rotor and momentum theory no longer applies. At high thrust, AeroDyn uses Glauert’s empirical correction with Buhl’s modification in place of momentum theory.

Best regards,

Dear Jason,

Thanks again! It turns out I need to do more researches about the theories used by FAST. Your guidence is really useful to me.

Best regards,
Chenxu.Zhao

Hi, everyone

I have some problems with the output parameters, “B1N1DynP”, “B1N1Fx” and “B1N1Fy”. Based on the “OutListParameters.excel” in the archive of FAST V8, I know the “B1N1Fx” and “B1N1Fy” refer to the normal and tangential forces to plane per unit length for Node 1 of Blade 1, and “B1N1DynP” means the dynamic pressure for Node 1 of Blade 1. If I want to employ these output parameters in my finite element model as the wind loading, How could I utilize these parameters? I have some ideas based on the attached figure, but I do not know whether it is right.

If I employ the parameters “B1N1Fx” and “B1N1Fy”, I prefer to adopt two methods:

  1. assuming only the forces per unit length at the nodes are accurate, the centering normal force at Node 3 could be calculated by B1N3Fx*(L2+L3)/2
  2. assuming the forces along the blade could be linearly interpolated, the concentrated force at Node 3 should be computed by ((B1N2Fx+B1N3Fx)/2+B1N3Fx)/2L2/2+((B1N3Fx+B1N4Fx)/2+B1N3Fx)/2L3/2

If I adopt the parameter “B1N1DynP”, How should I do?
Any hints would be much appreciated.

Best regards,
Jian

Dear Jian,

Are you referring to AeroDyn outputs? These are the aerodynamic applied loads per unit length along the blade.

I’m not sure I really understand your question, but if your FE model accepts applied forces per unit length, but the nodes are not co-located with the AeroDyn nodes, then, yes, you could interpolate the AeroDyn outputs before using them in your FE model.

Best regards,

Dear Jason,

Thank you for your timely response.
Yes, I refer to the AeroDyn outputs. I just edited my questions for clarity. I wonder if I want to impose the concentrated force on the blade, whether the method I mentioned is right? I am still confused about how to employ the parameter “B1N1DynP”, could you give me more clues. Thank you.

Best regards,
Jian

Dear Jian,

I think methods (1) and (2) will give very comparable results, especially as the element lengths decrease. We use a slightly different method in the internal Line2-to-Point mesh-to-mesh mapping in the FAST modularization framework (that also ensures that the overall moments balance between the two meshes), but again, I would guess the results would be very comparable as the element lengths decrease. You can read about the mesh-to-mesh mapping inherent within FAST in the attached paper.

Sprauge_Jonkman_Jonkman_FASTModularFrameworkForWindTurbineSimulation-NewAlgorithmsAndNumericalExamples_AIAA_2015.pdf (498 KB)
The dynamic pressure is defined such that:
B1N1Fx = B1N1CxB1N1DynPBlChord

Best regards,