Turbine Wake Deflection Measurement in a Wind Tunnel with a Lidar WindScanner

Abstract

Wind turbines are typically closely spaced in wind farms, and thus operate in the wake of upstream turbines and experience power losses. Currently, one of the techniques to reduce the wake interaction between turbines within a wind farm is to yaw the upstream turbine with regards to the incident wind direction. The objective is to deflect the wake, which can potentially increase the overall power output and the annual energy production of the wind farm. Experimental data can aid the process to thoroughly analyse the wake deflection under different inflow conditions, which is necessary to apply a yaw-based wind farm control model. The aim of the present research is to investigate the possibility and accuracy of the experimental setup to measure the wake characteristics with a high spatial and temporal resolution through the use of a short-range Lidar WindScanner, within the wind tunnel of ForWind-Oldenburg. This technique provides the opportunity to analyse the flow structures at different operational and inflow conditions in a relative fast manner without disturbing the flow. Experiments were conducted using a model wind turbine in a large cross-section wind tunnel. The short-range Lidar WindScanner is used as the primary instrument to map the wind turbine wake at different downstream locations. The flow structures of the wake were measured from 1 D up to 10 D downstream of the turbine rotor. A stable flow within the wind tunnel segment is measured, which is crucial for the analyses of the evolution of the wake. In addition, a high detailed spatial resolution of the wake profile is observed, showing the symmetric and asymmetric behaviour of the wake, for unyawed and yawed conditions, respectively. Furthermore, the calculation of the thrust coefficient from the velocity data show expected behaviour, giving further credibility to the measurement technique.

Analytical solution for the cumulative wake of wind turbines in wind farms

“…This is consistent with recent laboratory results reported by Hulsman et al. (2020). The next important term in the momentum equation is the Reynolds normal stress.…”

Wake steering of multirotor wind turbines

“…Details of cross‐stream components of wake velocity have been examined by Martínez‐Tossas et al, 11 in which a ‘curled‐wake’ model is formulated, and by Shapiro et al, 12 in which yawed turbines are viewed as lifting lines. In recent developments, several wind tunnel studies (for example, 13‐16 ), numerical simulations (for example, 17‐20 ), as well as field studies (for example, 21‐26 ) have examined wake steering for wind farms of single‐rotor wind turbines, in which improvements have been seen in terms of both power output and reliability.…”

Reduction and analysis of rotor blade misalignments on a model wind turbine

“…This way a collective pitching of all three rotor blades is achieved. Initially the rotor blade shafts of the MoWiTO 0.6 have been connected via screws to the rotor blade mount 5 O. However, both the exact positioning of the drill hole for the screws and the tightening of the screws led to blade misalignments mentioned above.…”

“…Experiments that take advantage of more than one model wind turbine, especially experiments which aim at simulating whole wind farms, create a demand for relatively small model wind turbines due to limited wind tunnel sizes. In Oldenburg, this need is met with a new version of the MoWiTO 0.6 that has a rotor diameter of 0.58 m [5] [6]. The rotor blades are based on an SD7003 airfoil profile [4].…”

“…The rotor blades are based on an SD7003 airfoil profile [4]. This model turbine type is well suited for multiple turbine experiments inside the Oldenburg wind tunnel, with a size of 3 x 3 x 30 m³ [5]. However, its small size comes at the cost of having a collective pitch control mechanism explained in [6], instead of an individual pitch control.…”