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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

# Seven-Sensor Fast-Response Probe for Full-Scale Wind Turbine Flowfield Measurements

[+] Author and Article Information
M. Mansour, G. Kocer, C. Lenherr, N. Chokani, R. S. Abhari

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion, ETH Zürich, Zurich 8092, Switzerland

J. Eng. Gas Turbines Power 133(8), 081601 (Apr 05, 2011) (8 pages) doi:10.1115/1.4002781 History: Received May 18, 2010; Revised May 20, 2010; Published April 05, 2011; Online April 05, 2011

## Abstract

The unsteady wind profile in the atmospheric boundary layer upstream of a modern wind turbine is measured. The measurements are accomplished using a novel measurement approach that is comprised of an autonomous uninhabited aerial vehicle (UAV) that is equipped with a seven-sensor fast-response aerodynamic probe (F7S-UAV). The autonomous UAV enables high spatial resolution ($∼6.3%$ of rotor diameter) measurements, which hitherto have not been accomplished around full-scale wind turbines. The F7S-UAV probe developed at ETH Zurich is the key-enabling technology for the measurements. The time-averaged wind profile from the F7S-UAV probe is found to be in very good agreement to an independently measured profile using the UAV. This time-averaged profile, which is measured in moderately complex terrain, differs by as much as 30% from the wind profile that is extrapolated from a logarithmic height formula; therefore, the limited utility of extrapolated profiles, which are commonly used in site assessments, is made evident. The time-varying wind profiles show that at a given height, the velocity fluctuations can be as much as 44% of the time-averaged velocity, therefore indicating that there are substantial loads that may impact the fatigue life of the wind turbine’s components. Furthermore, the shear in the velocity profile also subjects the fixed pitch blade to varying incidences and loading. Analysis of the associated velocity triangles indicates that the sectional lift coefficient at midspan of this modern turbine would vary by 12% in the measured time-averaged wind profile. These variations must be accounted in the structural design of the blades. Thus, the measurements of the unsteady wind profile accomplished with this novel measurement system demonstrate that it is a cost effective complement to the suite of available site assessment measurement tools.

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## Figures

Figure 1

Autonomous time-resolved wind measurement aircraft based on the model airframe Funjet

Figure 2

(a) Pressure sensitivity versus applied temperature and (b) zero pressure offset versus temperature

Figure 3

(a) Flow angles convention and (b) pressure taps numbering and sectoring scheme

Figure 4

Aerocalibration coefficients: (a) yaw flow angle, (b) pitch flow angle, (c) total pressure, and (d) dynamic pressure

Figure 5

Amplitude response of stagnation pressure sensor 7. The measured response is from grid generated turbulence.

Figure 6

Flight pattern during time-resolved wind measurements performed upstream of a Vestas V80 wind turbine

Figure 7

The 10 min-averaged uncorrected wind speed measured by the wind turbine nacelle’s anemometer. Blue- and red-dashed areas represent the 7S-FRAP and UAV circle-flight wind profile measurement time.

Figure 8

Profiles of wind speed from 7S-FRAP and UAV circle-flight measurements. The nacelle anemometer averaged data are indicated with black markers. All wind velocity are nondimensionalized with the wind velocity measured at 200 m.

Figure 9

Profile of wind speed measured with 7S-FRAP with its maximum and minimum wind speed based on the standard deviation of time-resolved wind speed. The black line shows the logarithmic wind profile based on the reference wind velocity measured at 85 m.

Figure 10

Velocity triangles for a span position r/R=0.5 at (a) H=83 m and (b) H=118 m

## Errata

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