Wind tunnel experiments on wind turbine wakes in yaw: effects of inflow turbulence and shear (original) (raw)

Experimental Investigation of Wind Turbine Wakes in the Wind Tunnel

Energy Procedia, 2013

Detailed wake measurements of two model wind turbine setups in the wind tunnel were performed. Two similar model wind turbines with a rotor diameter of 0.9m were operated in the large closed--loop wind tunnel of the Department of Energy and Process Engineering at The Norwegian University of Science and Technology. A single turbine arrangement and a tandem setup, where a wind turbine was operated in the wake of an upstream turbine wind turbine, were tested. Measurements of the cross section in the near and far wake as well as measurements in axial direction are presented. The wake measurements mainly agree with wakes predicted by wake theory. However, a strong tower wake was observed. The influence of the tower is often not covered by wake theory and computational models. The tower wake deflected as it interacted with the rotating rotor wake. A strongly non--uniform velocity and turbulence distribution in the far wake was found. A relationship to the influence of the tower wake is expected.

Field investigation on the influence of yaw misalignment on the propagation of wind turbine wakes

Wind Energy, 2018

A comprehensive understanding of the wake development of wind turbines is essential for improving the power yield of wind farms and for reducing the structural loading of the turbines. Reducing the overall negative impact of wake flows on individual turbines in a farm is one goal of wind farm control. We aim to demonstrate the applicability of yaw control for deflecting wind turbine wakes in a full-scale field experiment. For this purpose, we conducted a measurement campaign at a multimegawatt onshore wind turbine including inflow and wake flow measurements using ground-and nacelle-based long-range light detection and ranging devices. Yaw misalignments of the turbine with respect to the inflow direction of up to 20 • were investigated. We were able to show that under neutral atmospheric conditions, these turbine misalignments cause lateral deflections of its wake. Larger yaw misalignments resulted in greater wake deflection. Because of the inherent struggle in capturing complex and highly dynamic ambient conditions in the field using a limited number of sensors, we particularly focused on providing a comprehensive and comprehensible description of the measurement setup, including the identification of potential uncertainties.

Wind Tunnel Investigation of the Near-wake Flow Dynamics of a Horizontal Axis Wind Turbine

Journal of Physics: Conference Series, 2014

Experiments conducted in a large wind tunnel setup investigate the 3D flow dynamics within the near-wake region of a horizontal axis wind turbine. Particle Image Velocimetry (PIV) measurements quantify the mean and turbulent components of the flow field. Measurements are performed in multiple adjacent horizontal planes in order to cover the area behind the rotor in a large radial interval, at several locations downstream of the rotor. The measurements were phase-locked in order to facilitate the reconstruction of the threedimensional flow field. The mean velocity and turbulence characteristics clearly correlate with the near-wake vortex dynamics and in particular with the helical structure of the flow, formed immediately behind the turbine rotor. Due to the tip and root vortices, the mean and turbulent characteristics of the flow are highly dependent on the azimuth angle in regions close to the rotor and close to the blade tip and root. Further from the rotor, the characteristics of the flow become phase independent. This can be attributed to the breakdown of the vortical structure of the flow, resulting from the turbulent diffusion. In general, the highest levels of turbulence are observed in shear layer around the tip of the blades, which decrease rapidly downstream. The shear zone grows in the radial direction as the wake moves axially, resulting in velocity recovery toward the centre of the rotor due to momentum transport.

Experimental study of yawed inflow around wind turbine rotor

2012

In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and to predict the performance of wind turbines as well.

Effects of Inflow Conditions on Wind Turbine Performance and near Wake Structure

Open Journal of Fluid Dynamics

Knowledge about the structure and development of wakes behind wind turbines is important for power optimization of wind power farms. The high turbulence levels in the wakes give rise to undesired unsteady loadings on the downstream turbines, which in the long run might cause fatigue damages. In the present study, the near wake behind a small-scale model wind turbine was investigated experimentally in a wind tunnel. The study consists of measurements with particle image velocimetry using two different inlet conditions: a freely developing boundary layer, causing an almost uniform inflow across the rotor disc, and an inflow with strong shear across the rotor disc, in order to model the atmospheric boundary layer. The results show a faster recovery of the wake in the case with shear inflow, caused by the higher turbulence levels and enhanced mixing of momentum. The increased inlet turbulence levels in this case also resulted in a faster breakdown of the tip vortices as well as different distributions of the streamwise and vertical components of the turbulence intensity in the wake. An analysis comparing vortex statistics for the two cases also showed the presence of strong tip vortices in the case with lower inlet turbulence, while the case with higher inlet turbulence developed a different distribution of vortices in the wake.

Comparative study on the wake deflection behind yawed wind turbine models

Journal of Physics: Conference Series, 2017

In this wind tunnel campaign, detailed wake measurements behind two different model wind turbines in yawed conditions were performed. The wake deflections were quantified by estimating the rotor-averaged available power within the wake. By using two different model wind turbines, the influence of the rotor design and turbine geometry on the wake deflection caused by a yaw misalignment of 30 • could be judged. It was found that the wake deflections three rotor diameters downstream were equal while at six rotor diameters downstream insignificant differences were observed. The results compare well with previous experimental and numerical studies.

Experimental analysis of the wake dynamics of a modelled wind turbine during yaw manoeuvres

Journal of Physics: Conference Series, 2018

This work focuses on the dynamic analysis of a modelled wind turbine wake during yaw manoeuvres. Indeed, in the context of wind farm control, misalignment of wind turbines is envisaged as a solution to reduce wind turbine wake interactions, by skewing the wake trajectory. To optimize the control strategies, the aerodynamic response of the wake to this type of yaw manoeuvres, as well as the global load response of the rotor disc of the downstream wind turbine, must be quantified. As a first approach, the identification of the overall system is performed through wind tunnel experiments, using a rotor model based on the actuator disc concept. A misalignment scenario of the upstream wind turbine model is imposed and the wind turbine wake deflection is dynamically captured and measured by the use of Particle Imaging Velocimetry.

Near-Wake Flow Dynamics of a Horizontal Axis Wind Turbine

2012

Experiments have been conducted in a large wind tunnel setup in order to study the flow structures within the near-wake region of a horizontal axis wind turbine. Particle Image Velocimetry (PIV) has been employed to quantify the mean and turbulent components of the flow field. The measurements have been performed in multiple adjacent horizontal planes in order to cover the area behind the rotor in a large radial interval, at several locations downstream Moreover, the PIV results have also been compared with the results obtained from the velocity measurements performed by previous investigators in small wind tunnel setups , in order to assess the scaling effects, and in particular the effect of local chord Reynolds number. The tip speed ratio is considered to be similar for all measurement to satisfy the kinematic similarity requirement. The comparison shows that the axial velocity profiles are highly dependent on Reynolds number. This is an important finding in terms of simulating scaled models of wind turbines and wind farms in wind tunnel settings. v Keywords: horizontal axis wind turbine, wake, wind tunnel experiments, Particle Image Velocimetry, large scale experimental setup, turbulent flow field, phase-locked measurement vi ACKNOLEDGEMENTS I wish to express my profound appreciation and sincere gratitude to my supervisor, Professor Horia M. Hangan, for his thoughtful insights, invaluable advices, stimulating suggestions, as well as his continuous encouragement, patience support and guidance throughout this research. I gratefully acknowledge my co-supervisor, Professor Kamran Siddiqui, for his support, expert help, thoughtful advices and useful guidelines throughout this research in particular in PIV measurements and data analysis. I would also like to thank the staff of the Boundary Layer Wind Tunnel Laboratory and the