Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model

Abstract

Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion.

Wind tunnel experiments on wind turbine wakes in yaw: Redefining the wake width

“…a pitch motion will deflect the wake upwards, see Rockel et al (2014). This vertical deflection will interact with the vertical transport shown in Figure 11.…”

Wake to wake interaction of floating wind turbine models in free pitch motion: An eddy viscosity and mixing length approach

“…Further details on the inflow characteristics can be found in Ref. [20], where measurements were performed to observe the differences in the wake of a fixed versus a pitching single wind turbine; these results were then compared to various wake models. Here, a second wind turbine was positioned in the wake of the upwind turbine at a distance of 7.5D.…”

“…The air density is given by r, the mean pressure by P and F xi is the thrust force by the turbine, which mainly acts in the streamwise direction [3,9,19,20]. The vertical transport of kinetic energy in the wake region is connected to the Reynolds shear stress by the mean kinetic energy equation, which is given by,…”

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

“…Over the past few years, several research groups have focused attention on wind tunnel experiments with the innovative idea of supporting research not only related to the validation of purely aerodynamic models, but also to support numerical activities on control and aero-servo-elasticity (Bottasso et al, 2014) as well as to understand the interaction of wind turbines with turbulent flow (Rockel et al, 2014). In fact, the full-scale testing of wind turbines in the atmospheric boundary layer imposes several constraints, such as the difficulty in obtaining accurate knowledge and repeatability of the environmental conditions and higher costs.…”