Drone-Based Experimental Investigation of Three-Dimensional Flow Structure of a Multi-Megawatt Wind Turbine in Complex Terrain

Abstract

The aerodynamic characteristics of wakes in complex terrain have a profound impact on the energy yield of wind farms and on the fatigue loads on wind turbines in the wind farm. In order to detail the spatial variations of the wind speed, wind direction, and turbulent kinetic energy (TKE) in the near-wake, comprehensive drone-based measurements at a multi-megawatt (MW) wind turbine that is located in complex terrain have been conducted. A short-time Fourier transform (STFT)-based analysis method is used to derive time-localized TKE along the drone's trajectory. In upstream and in the near-wake, the vertical profiles of wind speed, wind direction, and TKE are detailed. There is an increase in the TKE from upstream to downstream of the wind turbine, and whereas, the characteristic microscale length scales increase with increasing height above the ground upstream of the turbine, in the near-wake the microscale lengths are of constant, smaller magnitude. The first-ever measurements of the pressure field across a multi-MW wind turbines rotor plane and of the tip vortices in the near-wake are also reported. It is shown that the pitch between subsequent tip vortices, which are shed from the wind turbines blades, increases in the near-wake as the wake evolves. These details of the near-wake can have an important effect on the subsequent evolution of the wake and must be incorporated into the three-dimensional (3D) field wake models that are currently under intensive development.

Aerodynamics of wind turbine wakes in flat and complex terrains

“…Indeed the scale of the Reynolds number is relevant in physical process such as turbulent mixing, the entrainment of kinetic energy, the evolution and breakdown of tip vortices, etc, all of which are features of wakes in wind farms. The present work extends the authors prior work [15,16] with detailed measurements of the wake up to six diameters in flat and complex terrains. Thus the primary objective of this work is to detail and distinguish the vortex structure and mixing properties of wakes in flat and complex terrains.…”

“…The drones are detailed elsewhere [15,16] but some salient characteristics are summarised in Table 2. The seven-sensor fast response aerodynamic probe that is used for wind measurements is described in detail by Mansour et al [17].…”

Exploring the potential of the RPA system SUMO for multipurpose boundary-layer missions during the BLLAST campaign

“…Both systems are particularly suited for flying kilometre-scale-level legs and performing high-frequency measurements of wind components, temperature and humidity fluctuations and therefore for the determination of heat, momentum and moisture fluxes (e.g. van den Kroonenberg et al, 2012;Wildmann et al, 2013). The MASC system, participating in a prototype version, suffered from technical problems and no data sets could be supplied to the BLLAST data archive (http://bllast.sedoo.fr/ database/).…”

“…In this context, the hand-starting capability of the SUMO system has proven to be a huge benefit compared to the larger airframes that require starting aid in the form of a catapult or at least a bungee cord, the latter being negatively affected both by very low and very high temperatures. A modified SUMO aeroplane has been equipped with a specifically designed 7-hole flow probe that has been developed by ETH in Zürich, Switzerland (Kocer et al, 2011;Subramanian et al, 2015) for the purpose of turbulence measurements in the wake of wind turbines. The integration of a 5-hole probe (5HP) on the SUMO systems of GFI Båserud et al, 2014) is also partly motivated by that purpose, but will of course also be beneficial for ABL research in general.…”

Adaptive modeling and sampling methodologies for Internet of Things applications

“…The benefit of the latter is illustrated in Figure 2: instead of purely spacefilling, the generated experimental design increases focus on a non-linear region. This is specifically useful for devices which are used to actively acquire data, such as for instance dronebased measuring [38], [39], or devices such as robot vacuum cleaners. Rather than performing simulations, a drone collects real-time measurements.…”