# Help about BEM and NREL's Phase VI

First of all, thank you for the opportunity to be a member of this forum.

I’m currently doing an iteration in Excel about NREL’s Phase VI wind turbine for validation purposes.

I tried using 6 m/s as the free stream velocity and the radial sections selected (Fig 1) are attached on this post.

However, when I am about to compute the torque using the Trapezoidal approach (Fig 2) and use the value to compute the power, it did not match the rating of 19.8 kW. Any suggestions about these?

The other approach that I am looking, is analyze another study that employs NREL’s Phase VI wind turbine. Though it operates on a different speed, (e.g. 7 m/s) I am observing if the induction factors of a certain section (e.g. r/R = 0.3) matches with my excel computation, then this will validate things.

Dear Wesley,

I’m not sure I understand your question. I don’t see in your post what values of A_i and B_i you used and what the source of that data is.

Best regards,

Oh, my apologies sir. and thanks for replying )

sir, I’ll start with the BEM iteration, if I will use 6 m/s as free stream velocity, when the BEM iteration converges, the power computed is 19.8kW? Or the 6 m/s only indicates that this is the cut-in speed? I’ve seen several studies that used more than one velocities (e.g. 7 m/s, 15 m/s and so on…)

kind regards,
Wes

Dear Wes,

6 m/s is the cut-in wind speed of UAE Phase VI rotor (although some tests were run at lower wind speeds). Rated power will not be reached until higher wind speeds.

Best regards,

Sir, got a new question… I’ve read somewhere in this forum (re: NREL Phase VI), about the tip pitch angle (3 degrees) and section pitch angle, (around 4.815 degrees).

I’ve read from the book of Manwell et al., (2009) that the formula for twist angle is section PA - blade PA at the tip.

The twist angle at the tip from NREL Phase VI is -1.815 degrees and if I will use Manwell’s formula, it would be 1.815 degrees and not -1.815 degrees.

Any idea sir why it became this way?

Kind regards,
Wesley

Dear Wesley,

I’m not sure I really understand your question, but in FAST/AreoDyn, the local angle of the chordline from the rotor plane (theta), is the sum of the blade-pitch angle (theta_p) and the local blade-twist angle (theta_t), the latter of which includes both aerodynamic twist and elastic (live) twist. That is:

theta = theta_p + theta_t

Thus, solving for the local blade-twist angle:

theta_t = theta - theta_p

And using values at the tip:

-1.815 = 3 - 4.815

I hope that helps.

Best regards,

Kind regards,
Wesley

Sir, there’s a literature that it’s important to consider aerodynamic, gravitational and centrifugal loads. If the coning angle is zero, do I have to include centrifugal loads?

Dear Wesley,

I’m not really sure I understand your question, but centrifugal loads are important if you are determining the reaction loads in the blade or calculating blade deformation, regardless of whether the coning angle is zero or not.

Best regards,

By the way, are there any data concerning the tip deflection of NREL’s Phase VI similar to this,

Dear Wesley,

Are you asking about real physical data? The blade deflections were not measured in UAE Phase VI experiments.

Best regards,

Yes sir.
The real physical data will be used for my aeroelastic validation using NREL’s Phase VI.
Any suggestions sir?

Dear Wesley,

Sorry, but I’m not aware of a publicly available dataset that includes physical measurements of blade deflection when the turbine is operating.

We have validated the new capability of FAST v8 for advanced aero-elastically tailored blades, including blade deflection, but this was using experimental data that was proprietary through a collaboration with Siemens: nrel.gov/docs/fy16osti/65389.pdf.

Best regards,

Sir,

one question - are there any torsional stiffness/rigidity data concerning NREL Phase VI similar to this?

kind regards,
Wesley

Dear Wesley,

Appendix A from the UAE Phase VI report provides some estimates of the torsional stiffness (among other blade structural properties): nrel.gov/docs/fy02osti/29955.pdf.

However, I did a quick comparison between the blade structural data provided in that report with the data included in the old FAST v7 model of the UAE Phase VI rotor*, and there are certainly some differences. Marshall Buhl of NREL, now retired, developed this model many years ago, and while I don’t know the details, I do know he did a bit of manual tuning to ensure the model functioned appropriately.

I hope that helps.

Best regards,

*These are available in the models of Test09 and Test10 in the CertTest directory of the old FAST v7 archive, available here: nwtc.nrel.gov/system/files/FAST … 0a-bjj.exe).

Sir, thanks for the file that you provided. I checked it and observed that the data concerning structural properties covers the radius until 5m only.

I’m using the r= 5.029m.

any idea about this one sir? should I extrapolate for instance to get the data @ 5.029m?

Dear Wesley,

You could extrapolate, or perhaps use the data from r=5 at the tip.

Please keep in mind that these are “estimates” and their accuracy is not guaranteed. You may need to do “tuning” anway to get the desired response.

Also keep in mind that the UAE Phase VI rotor was very rigid for conventional blade standards. It may not matter how accurate the properties are because the aero-elastic effects of this rotor are mostly negligible.

Best regards,

Sir,

Good day!

Sir, if I’ll use NREL Phase VI for aerodynamic validation, could I use cn, ct as the parameters of comparison for my BEM code? I’ve seen a tabulated data about this (i.e. Jonkman, 2003), though I have some reservation upon reading that these data (cl, cd, wind speed, aoa, cn, ct) reflects the operational environment of the wind turbine. Should I use the experimental data concerning power, torque (as functions of wind speed) instead?

Kind regards,
Wesley

Dear Wesley,

I guess it all depends on what you intend to validate. All channels recording during the NREL Phase VI Unsteady Aerodynamics Experiment (UAE) will well tested/calibrated.

Best regards,

I see, thanks sir.

My data got closer to the computed power, however variation exists in cn, ct.
Sir, concerning the formula for cn, ct= are they in terms of inflow angle or angle of attack?
btw, sir, regarding structural modelling,any idea how’s proportional modelling approached?

Kind regards,
Wesley