Full-field assessment of wind turbine near-wake deviation in relation to yaw misalignment

Abstract

Abstract.Presently there is a lack of data revealing the behaviour of the path followed by the near wake of full scale wind turbines and its dependence on yaw misalignment. Here we present an experimental analysis of the horizontal wake deviation of a 5 MW offshore wind turbine between 0.6 and 1.4 diameters downstream. The wake field has been scanned with a short-range lidar and the wake path has been reconstructed by means of two-dimensional Gaussian tracking. We analysed the measurements for rotor yaw misalignments arising in normal operation and during partial load, representing high thrust coefficient conditions. We classified distinctive wake paths with reference to yaw misalignment, based on the nacelle wind vane, in steps of 3 • in a range of ±10.5 • . All paths observed in the nacelle frame of reference showed a consistent convergence towards 0.9 rotor diameters downstream, suggesting a kind of wake deviation shift. This contrasts with published results from wind tunnels which in general report a convergence towards the rotor. The discrepancy is evidenced in particular in a comparison which we performed against published paths obtained by means of tip vortex tracking.

Three-dimensional structure of wind turbine wakes as measured by scanning lidar

“…This result becomes more evident when the laser beam is more perpendicular to the wake. This result is due to the aspect ratio of the lidar "pixels" and thus would affect other wake characterization approaches relying on instruments not co-located with the turbine -such as in Banta et al (2015) and Aitken et al (2014a) -but would not affect nacelle-mounted wake measurements, such as in Bingöl et al (2010) and Aitken and Lundquist (2014), as nacelle-mounted wake measurements are usually aligned with the wake unless the wake is intentionally yawed Trujillo et al, 2016).…”

Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different turbulent inflow conditions

“…Even though the wake behind full-scale wind turbines was recently measured (Kocer et al, 2011;Kumer et al, 2015;Trujillo et al, 2016), the unsteady inflow conditions in fullscale experiments make it very difficult to use those data to verify wake prediction models. Therefore, wind tunnel experiments on model turbines under controlled boundary conditions are an appropriate method for verifying simulation tools.…”

Brief communication: On the influence of vertical wind shear on the combined power output of two model wind turbines in yaw

“…One promising concept is the wake deflection by intentional yaw misalignment of single wind turbines. The principle of deflecting the velocity deficit behind a wind turbine was observed in field measurements by Trujillo et al (2016), in wind tunnel experiments (e.g., Medici and Alfredsson, 2006;Krogstad and Adaramola, 2012) and in numerical simulations (e.g., Jiménez et al, 2010;Gebraad et al, 2014;Vollmer et al, 2016). Further, Gebraad et al (2014) and Fleming et al (2016) applied the concept to wind farm control strategies using large-eddy simulation (LES) methods, showing a potential power increase in wind farm applications.…”