the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Blade surface pressure and drag measurement of a blade section on a 4.3 MW turbine with trailing edge flaps
Abstract. In this paper we present the measurements of local aerodynamic sectional characteristics on a full-scale rotor blade with a novel add-on instrumentation comprising a wake rake, a pressure belt, and a five hole Pitot tube. The general objective of the research work is to provide information on the differences between airfoil performance in wind tunnel flow and on a full-scale rotor. Although pressure belt measurements have been performed in earlier studies, this is the first campaign to use a wake rake at the full-scale level. We present the wake rake development and testing in the wind tunnel and on a rotating test rig which finally led up to installation on the 4.3 MW turbine. A more specific objective with the campaign has been to characterize the aerodynamic performance of a trailing edge active flap system installed on one of the blades. The short measurement campaign of two days comprised measurements of the flaps actuated at constant time intervals of 60 s between fully retracted and activated with a control set point of 75 % of full deflection. The lift and drag characteristics are compared with a similar flap actuation in a wind tunnel experiment. Both the relative change in lift and drag coefficients as a function of flap actuation correlate well with wind tunnel measurements, but the absolute drag levels measured on the rotor are higher than the wind tunnel data. During the measurement campaign, it was also demonstrated that it is possible to clearly measure the increased drag from adding a roughness tape at the leading edge of the airfoil. This illustrates the potential use of the measurement system to capture the effect of variations of the local aerodynamic performance at full-scale even for elements at boundary layer scale, e.g. the impact of roughness or the positioning of add-ons such as vortex generators.
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RC1: 'Comment on wes-2025-75', Anonymous Referee #1, 28 May 2025
This is a very interesting paper with a unique measurement on a full scale wt.
I have only three small comments/recommendations:1) In Fig. 6b the green tape is hardly visible. It would be nice if a close-up photo could be included.
2) If any turbulence data from the met mats are available they should be mention in chapter 3.
3) The existence of the VGs should be mentioned already in section 2.3.2
Citation: https://doi.org/10.5194/wes-2025-75-RC1 -
RC2: 'Comment on wes-2025-75', Anonymous Referee #2, 15 Jun 2025
General comments:
A very nice article about the evolution of an innovative measurement technique that contributes to closing the gap between the wind tunnel results used in design and unknown sectional performance in the field. From this viewpoint the article provides new and valuable insight and is worthy of publication. The storyline is clear and well conveyed.It is recommended to follow up on the below suggestions for improvement:
-p4/5 section 2.2.1
Can the authors comment on the applicability of Jones' method in a rotor setting? In particular concerning static pressure assumptions made by this method and the static pressure variations that might be present due to rotor blockage.-p5 section 2.2.1
Some illustration of the mentioned results from the parameter variations are recommended. In addition to that, has the influence of the downstream position of the wake rake on the result also been verified?-p12 section 2.3.6 and section 4
The block and moving averaging procedure is explained to act as a low pass filter. In the end the results are presented by means of sectional polar plots like fig.10, which appear quite steady without hysteresis. In how far does the post-processing procedure filter out the dynamics present in the field? What is the non-dimensional frequency k at this section based on 1P? Would it be interesting to also show a polar plot like figure 10 without the pre-processing procedure (based on raw data),or would that result in a rather large cloud op points?-p13 section 2.3.7 Uncertainty
Pressure measurements on wind turbines are often complicated by drift due to e.g. temperature changes and the difficulty of a providing a stable reference pressure. Although there is a referral to a previous paper from 2022 about this measurement system, could the authors comment on these challenges in relation to their system?-p16 section 4
A discrepancy in the drag coefficient between field and wind tunnel is noted. Is the same offset present between RTR and wind tunnel?-It is mentioned that the turbine has been instrumented to measure loads and power. It would be helpful if the influence of the added external sectional instrumentation on the loads and power can be quantified. Also, have the effects of flaps and zz-tape on power and loads also been measured or were these effects too small?
Citation: https://doi.org/10.5194/wes-2025-75-RC2
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