First identification and quantification of detached-tip vortices behind a wind energy converter using fixed-wing unmanned aircraft system

Mauz, Moritz; Rautenberg, Alexander; Platis, Andreas; Cormier, Marion; Bange, Jens

doi:https://doi.org/10.5194/wes-4-451-2019

Articles | Volume 4, issue 3

https://doi.org/10.5194/wes-4-451-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wes-4-451-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 4, issue 3

Research article

|

29 Aug 2019

Research article |

| 29 Aug 2019

First identification and quantification of detached-tip vortices behind a wind energy converter using fixed-wing unmanned aircraft system

Moritz Mauz, Alexander Rautenberg, Andreas Platis, Marion Cormier, and Jens Bange

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Final revised paper (published on 29 Aug 2019)
Preprint (discussion started on 01 Mar 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

SC1: 'recent publication by the authors considering airspeed variations for wind and turbulence measurements with MASC-3', Alexander Rautenberg, 19 Mar 2019
- AC1: 'calibration error on vortex strenght results', Moritz Mauz, 20 Mar 2019
RC1: 'Review', Anonymous Referee #1, 25 Mar 2019
- AC3: 'AC on RC#1', Moritz Mauz, 24 Apr 2019
RC2: 'Review', Anonymous Referee #2, 07 Apr 2019
- AC2: 'AC on RC#2', Moritz Mauz, 24 Apr 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Moritz Mauz on behalf of the Authors (21 May 2019) Manuscript

ED: Referee Nomination & Report Request started (27 May 2019) by Sandrine Aubrun

RR by Anonymous Referee #1 (08 Jun 2019)

Suggestions for revision or reasons for rejection

General comments
The manuscript by Mauz et al. describes in-situ measurements of wind turbine tip vortices with a UAS. From these measurements, circulation of the vortices is calculated using the Burnham-Hallock wake vortex model.
These measurements are unique and I do not know of any other study in which a UAS operated in such close proximity to an operating wind turbine and even in its wake.
The authors can convincingly show that wake vortices can be measured with the UAS.
There are still some issues in the revised manuscript that I think need to be taken care of.

Specific comments:
p.1,ll.11f: "Also proposition..." Something is wrong with the grammar here.\\
p.1,l.13: What is "overall turbulence"?
p.1,l.18: recommendation: "... the capacity of a single turbine"\\
p.2,l.2: "Not least, because of improvements ..." - please revise.\\
p.2,l.12: There are also short-range continuous-wave lidars which have significantly higher spatial resolution for short focal distances and have been applied for WEC wake measurements. These measurements can still not resolve the tip vortices, but should be mentioned for completeness. See e.g.:
Menke, R., Vasiljevic, N., Hansen, K. S., Hahmann, A. N., and Mann, J.: Does the wind turbine wake follow the topography? A multi-lidar study in complex terrain, Wind Energ. Sci., 3, 681-691, 2018.
Herges, T. G., Maniaci, D. C., Naughton, B. T., Mikkelsen, T. K., & Sjöholm, M. (2017). High resolution wind turbine wake measurements with a scanning lidar: Paper. In Wake Conference 2017 (Vol. 854). Journal of Physics: Conference Series
p.3,l.5: I think the link to Pixhawk should be given as a proper reference.
p.5,Fig.3: Please label or mark the WEC more clearly in the picture.
p.5,l.6: You state that only a single flight leg is presented, but then say the presente data was captured within 15 minutes. I do not think the one flight leg took that long, so pleases be more precise in the description of the data. The TKE seems very low, even for a quasi-marine boundary layer. Can you please add information about the time of day and any kind of information about the synoptic cor mesoscale situation. You say that TKE was caclculated from a ten second measurement which would be way too short for a point measurement. I assume you calculated it along a flight leg, but you have to let the reader know, including the length of the leg.
p.12,l.9: "blade-tip vortices are theoretically measurable." - I recommend to eliminate this sentence. It is trivial and does not add any
p.14,l.12: Figure 15 is mentioned before Figure 14.
p.14,l.14f: Changing the name of the new coordinate system is not enough. There is still an explanation of the new coordinate system required and this should probably go to section 3, because it is a method and not a result. In line 22 it is still called vortex coordinate system by the way.
p.15,Fig.13: Please explain the x-axis in the caption.
p.15,l.19f: I think this is a critical finding, because it looks like during the pass through tip vortex 1, the measured sideslip angle is outside the calibration range. In the conclusion and the data availability section it is said that data outside the calibration range cannot be used. In Figure 13, winds speeds in that range that range where sideslip is out of range is definitely shown.
p.19,l.17: I still think that from an experiment with a single sample it cannot be stated as a fact that a model is valid.
p.20,l.21: What is a (small) error? Please be more ojective.
p.28,l.28: I disagree that a calibration range of a 5-hole probe can "simply" be expanded to larger angles. The characteristics of the probe geometry have to allow this.
p.20,l.30: I do not understand why path accuracy and RTK GPS is relevant for this study. It is not mentioned as an issue.

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RR by Anonymous Referee #2 (28 Jun 2019)

ED: Reconsider after major revisions (30 Jun 2019) by Sandrine Aubrun

AR by Moritz Mauz on behalf of the Authors (08 Jul 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (16 Jul 2019) by Sandrine Aubrun

AR by Moritz Mauz on behalf of the Authors (24 Jul 2019) Author's response Manuscript

ED: Publish as is (26 Jul 2019) by Sandrine Aubrun

ED: Publish as is (31 Jul 2019) by Gerard J.W. van Bussel (Chief editor)

AR by Moritz Mauz on behalf of the Authors (01 Aug 2019)

Short summary

UAS systems provide in situ measurements of turbulence and wind conditions. In the presented paper, the tip vortex generated by wind energy converters (WECs) is measured by a fixed-wing UAS and compared to an analytical model as well as a literature value. The results show good agreement. The presented method is a basis for future measurement campaigns to compare UAS measurements with numerical simulations of WEC wakes.