Light detection and ranging measurements of wake dynamics. Part II: two‐dimensional scanning

Abstract

A nacelle-mounted lidar system pointing downstream has been used to measure wind turbine wake dynamics. The new measurement and data analysis techniques allow estimation of quasi-instantaneous wind fi elds in planes perpendicular to the rotor axis. A newly developed wake tracking procedure delivers the instantaneous transversal wake position which is quantitatively compared with the prediction of the Dynamic Wake Meandering model. The results, shown for two 10-min time series, suggest that the conjecture of the wake behaving as a passive tracer is a fair approximation; this corroborates and expands the results of one-dimensional measurements already presented in the fi rst part of this paper. Consequently, it is now possible to separate the deterministic and turbulent parts of the wake wind fi eld, thus enabling capturing the wake in the meandering frame of reference. The results correspond, qualitatively and to some extent quantitatively, to the expectations from CFD simulations which are compared in the paper. LIDAR measurements of wake dynamics J.-J. Trujillo et al. 62with high resolution. In this regard, the light detection and ranging (lidar) technology presents great advantages due to its speed, robustness and fl exibility in measuring wind fi elds. For instance, infl ow measurements from the nacelle of a wind turbine have been successfully tested. 3,4 In that case the fast measurement at a fi xed point in front of the turbine assisted an advanced wind turbine control system. This paper describes the application of lidar to wind fi eld measurements in the wake of a 95 kW wind turbine. As in the previous example, the lidar system is installed at the nacelle but pointing downstream and implementing more complex scanning. The measurements were performed at a downstream distance of four diameters, which is considered to cover the far-wake regime. This investigation is conceived as a proof of concept of this type of measurement. New analysis techniques are developed to provide data useful for steady and dynamic wake model verifi cation. Part I of this paper 5 exposes the fi rst measurement campaign of this type along with the working principles of the instrument. Furthermore, the installation procedure on the wind turbine nacelle at the Risø test fi eld in Roskilde is also explained. Part II of the paper deals mainly with the analysis of the so-called two-dimensional wake measurements. These enable estimation of the wake wind fi eld in cross-sections perpendicular (here also named transversal) to the mean rotor axis and eventually large-scale dynamics of the wake. Here we explain fi rstly, the two-dimensional wake measurements in detail and the methods developed to capture wake dynamics; secondly, models for dynamic and deterministic wake are exposed and fi nally compared with two individual measurements.

Measurement procedures for characterization of wind turbine wakes with scanning Doppler wind LiDARs

“…Therefore, in order to investigate over larger measurement volumes, the use of remote sensing techniques is growing rapidly, in particular Doppler wind Light Detection and Ranging (LiDAR). Wind turbine wake measurements can be performed with groundbased LiDARs, as for Iungo et al (2013) and for the present work, or through nacelle-mounted LiDARs in order to keep the instrument always aligned with the mean wind direction for varying wind conditions (Bingöl et al, 2010;Trujillo et al, 2011).…”

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

“…The selected shape includes a wake position marker among other parameters with or without physical meaning. We find two examples of this, namely the approach by Trujillo et al (2011), whose objective is to L a t e r a l V e rt ic a l Lateral Vertical L a t e r a l V e rt ic a l Lateral Vertical L a t e r a l V e rt ic a l Lateral Vertical Figure 2. Example of bivariate function (Eq.…”

“…A full-field alternative tech-nique is the application of remote sensing techniques. Together with other researchers the first author of this paper proposed a wake-tracking technique in Trujillo et al (2011) which is based on two-dimensional lidar measurements from the wind turbine nacelle. In that research the technique is applied in the far wake at four diameters (4 D) downstream of a medium-scale wind turbine.…”

A Methodology for the Reconstruction of 2D Horizontal Wind Fields of Wind Turbine Wakes Based on Dual-Doppler Lidar Measurements

“…The high potential of lidars [5,6] has been demonstrated for different wind energy applications in general [7][8][9], and for measuring wakes in particular [10,11]. Coherent Doppler lidars [12,13] measure the Doppler shift of frequency between the emitted and backscattered laser light, which is converted to a radial velocity estimate.…”