Demonstration and uncertainty analysis of synchronised scanning lidar measurements of 2-D velocity fields in a boundary-layer wind tunnel

Abstract

Abstract. This paper combines the research methodologies of scaled wind turbine model experiments in wind tunnels with short-range WindScanner lidar measurement technology. The wind tunnel at the Politecnico di Milano was equipped with three wind turbine models and two short-range WindScanner lidars to demonstrate the benefits of synchronised scanning lidars in such experimental surroundings for the first time. The duallidar system can provide fully synchronised trajectory scans with sampling timescales ranging from seconds to minutes. First, staring mode measurements were compared to hot-wire probe measurements commonly used in wind tunnels. This yielded goodness of fit coefficients of 0.969 and 0.902 for the 1 Hz averaged u and v components of the wind speed, respectively, validating the 2-D measurement capability of the lidar scanners. Subsequently, the measurement of wake profiles on a line as well as wake area scans were executed to illustrate the applicability of lidar scanning to the measurement of small-scale wind flow effects. An extensive uncertainty analysis was executed to assess the accuracy of the method. The downsides of lidar with respect to the hotwire probes are the larger measurement probe volume, which compromises the ability to measure turbulence, and the possible loss of a small part of the measurements due to hard target beam reflection. In contrast, the benefits are the high flexibility in conducting both point measurements and area scanning and the fact that remote sensing techniques do not disturb the flow during measuring. The research campaign revealed a high potential for using short-range synchronised scanning lidars to measure the flow around wind turbines in a wind tunnel and increased the knowledge about the corresponding uncertainties.

Wake behavior and control: comparison of LES simulations and wind tunnel measurements

“…The IB method is employed to avoid the use of surface-conforming meshes to represent the shape of such bodies (Mittal and Iaccarino, 2005). The present IB approach, based on a discrete forcing method, uses a direct imposition of the boundary conditions (Uhlmann, 2005), thus preserving the sharpness of the body shape. Boundary conditions and wall models can be directly imposed on the IB surfaces with this approach, yielding good solution quality for high-Reynolds viscous flows (Bandringa, 2010).…”

“…Two different flow conditions are considered in the present study. In the first case, the flow velocity is obtained from a lidar-scanned low-turbulence (< 2 %) inflow condition (van Dooren et al, 2017). Measurements also accounts for a slight nonuniformity of the flow within the wind tunnel (Wang et al, 2017a).…”

Temporal Up-Sampling of Planar Long-Range Doppler LiDAR Wind Speed Measurements Using Space-Time Conversion

“…LiDARs are configured as continuous-wave (CW) devices for short distances (<200 m) [13] or as pulsed systems for longer distances (<6000 m) [14]. Though LiDAR is commonly used for free-field measurements, Van Dooren et al [15] took LiDAR measurements in a wind tunnel under controlled conditions in order to investigate wake behaviour using a synchronised dual-short-range LiDAR setup. Van Dooren et al [15] captured two-dimensional (2D) flow situations of a model wind farm with three turbines in the range of 20 s per horizontal scan.…”

“…Though LiDAR is commonly used for free-field measurements, Van Dooren et al [15] took LiDAR measurements in a wind tunnel under controlled conditions in order to investigate wake behaviour using a synchronised dual-short-range LiDAR setup. Van Dooren et al [15] captured two-dimensional (2D) flow situations of a model wind farm with three turbines in the range of 20 s per horizontal scan. Bartl et al [16] investigated how selected yaw misalignments affected wake properties by varying the inflow turbulence and shear in a wind tunnel.…”

Wind speed deviations in complex terrain

“…A state-of-the-art measurement approach is the combination of several scanning LIDARs to measure a 3D wind field. Such systems were successfully used to detect and analyse wind phenomena in several experiments, from wind tunnel (van Dooren et al, 2017) to full scale experiments (Pauscher et al, 2016;Vasiljević et al, 2017). However, scanning…”