I’m studying the aerodynamic blade tower interaction (BTI) of the upwind config. of the Phase VI HAWT. However I have a question about the experimental data and I’m hoping someone can help. Attached is a picture of the aero power developed by the rotor in Seq. S, 5 m/s. The rotor is rotating at ~72 RPM, which gives a rotational period of 0.8 sec.
In the attached picture, from the NREL experimental data, notice the well defined power loss at the the rotor period (0.8 s, 1.6 s, 2.4 s) as one of the blades passes in front of the tower. However, as there are two blades, shouldn’t there be power loss at the 1/2 period as well (here 0.4 s, 1.2 s, 2.0 s, etc)? As this data is based on a strain gage on the LS shaft it seems like the power drop of the second blade should be there. Can anyone clarify this for me?
I agree that there should probably be a 2P impact on rotor power, but there is not much we can do without knowing exactly what file and channel you are looking at. I am also curious where you got the data, as it is not publicly available and we distribute subsets only on request.
I’m looking at channel 822,“ROTPOW”,"Aerodynamic power from rotor " from the file S1000000.ENG from sequence S.
I should note that I do not have all of the data. I’m currently assembling a test matrix and have contacted Dr. Scott Schreck to acquire the data I’m requesting. This is a reproduced plot from one of my project colleagues who acquired the data through proper channels and published it in:
The only thing I can think of to explain it is that because the blades are different, one stalls more than the other. One blade has pressure taps and tufts and that might affect stall behavior. Although Sequence S did not have 5-hole probes, other tests did. S1000000 didn’t have a yaw error and the turbine had no shaft tilt. The wind tunnel should not have any wind shear, so the only thing I can think of that would periodically affect the rotor power for a balanced, upwind rotor would be tower influence and it would normally cause a 2P. The rotor power is computed from the LSS torque, so rotor inertia has an effect. I think the blades have the same mass and CM, but I am not positive. If the rotor were not balanced, I would expect to see a very sinusoidal 1P, but this is only roughly sinusoidal.
It might be interesting to do an azimuth average of the signal. Some of our postprocessors can generate azimuth averages. That would tell you where the blades are when the power dips.
I wonder about the shape of the curve, I would expect to see a dip in power that applies over a small range in azimuth and is fairly constant elsewhere.
I talked to Lee Jay Fingersh about this at lunch today. He was one of the test engineers who set up the instrumentation and ran the tests. He says there is a 1P in the LSS torque (used to compute the rotor power) because of shaft bending. It causes the strain gages to not measure pure torque. He says the rotor was not perfectly balanced, either. If you want to see if there is a 1P in actual power, look at the generator power, which should be very smooth. There is a 2P due to bow wake from the tower, but it is slight because the overhang is fairly large and the tower diameter is pretty small.
Sorry about the delayed response. Thanks for all the help. I’m now looking into doing some verification studies regarding this and was wondering if sequence S had ever been run in FAST and, if so, where the results of that simulation were published. Or, in the interest of running it myself, were ‘ready-made’ input files for the Phase VI sequence in FAST ever released?
My first task when I first started at NREL in 2001 was to validate the old FAST_AD software against the UAE NASA Ames wind tunnel data. I did this using the wind tunnel data and the results from partipants in the “Blind Comparison” excercise. You can find these old results in my MSC Thesis-turned NREL report available here: nrel.gov/docs/fy04osti/34755.pdf. Please note that my results where using the old FAST_AD software, without all of the improvements made to FAST over the past 10+ years.
After my project concluded, Marshall Buhl adopted my original FAST_AD model of the UAE turbine and calibrated it a bit to better match the NASA Ames wind tunnel data. I don’t recall that this project ever concluded with a publication, but the resulting model is included in the FAST archive as CertTest cases #9 and #10. Perhaps Marshall can comment more.
Actually, I got redirected and never completed the tuning of the airfoil data to improve the comparison to the test data; no publication resulted from the work. The partially tuned airfoil tables I was modifying are definitely included in the FAST CertTest\UAE_VI\AeroData folder. They give better agreement to the test data for rotor power than the original data, but the comparison is not very good at some wind speeds: