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

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 fiuctuations 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 lifi coefficient at midspan of this modern turbine would vary by ¡2% 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.

Proof of concept for turbulence measurements with the RPAS SUMO during the BLLAST campaign

“…The rapid development of remotely piloted aircraft systems (RPASs) during the last decade has provided new airborne sensor platforms for ABL research (Elston et al, 2015), with several of them having proven their capability for turbulence investigations (e.g., Thomas et al, 2012;Reineman et al, 2013;Martin et al, 2011;van den Kroonenberg et al, 2012;Braam et al, 2016;Wildmann et al, 2014Wildmann et al, , 2015. The continuous miniaturization of electronic components and sensors, both for measurement of meteorological parameters and the required attitude control of the aircraft's autopilot, now also provides the required capability for a micro-RPAS, with a take-off weight below 1 kg (Mansour et al, 2011;Reuder et al, 2012).…”

A fast response miniature probe for wet steam flow field measurements

“…The design and operation of the new fast-response probe for steam measurements are based on the developments made over the past two decades at the Laboratory for Energy Conversion at ETH Zurich [13][14][15][16][17]. In particular, the new FRAP-HTH probe is an improved version of the FRAP-HT probe developed by Lenherr et al as presented in [16].…”

Experimental Characterization of Propeller-Induced Flow (PIF) below a Multi-Rotor UAV

“…The commercial availability of corresponding airframes with sufficient payload capacities and the accessibility of freely programmable open-source autopilot solutions make UAVs now also well-suited as sensor platforms for atmospheric turbulence measurements. Turbulence measurements on fixed-wing systems, with typical cruising speeds of 15 m s −1 to 25 m s −1 , usually rely on multi-hole probes [22][23][24][25][26][27][28] and require complex correction and compensation algorithms for the attitude and, in particular, the relatively high horizontal speed of the aircraft [29][30][31][32]. With typical flight times ranging from 30 min to several hours, those systems can measure turbulence along the flight path over larger areas.…”