The flow in the blade root region of horizontal axis wind turbines is highly three-dimensional. Furthermore, it is influenced by the presence of strong trailing vortices. In this work we study the complex root flow by means of experiments and numerical simulations. The simulations are shown to be reliable at predicting the main flow features of the rotor blades. Additionally, new insight into the physical mechanisms governing the blade root aerodynamics is given.
We have developed flow models from different complexities. Unfortunately, high quality and reliable wind observations affected by obstacles are rare and so we have few means to evaluate our models. We have therefore performed a campaign in which we measured the effect of a fence on the atmosphere using laser-based instruments. The effect can still be noticed as far as 11 fence heights. A wake theory seems to predict the obstacle effect when we are looking at distances beyond 6 fence heights.
Year-to-year variability of wind speeds limits the certainty of wind-plant preconstruction energy estimates ("resource assessments"). Using 62-year records from 60 stations across Canada we show that resource highs and lows persist for decades, which makes estimates 2–3 times less certain than if annual levels were uncorrelated. Comparing chronological data records with randomly permuted versions of the same data reveals this in an unambiguous and easy-to-understand way.
The wake flow downstream of yaw misaligned wind turbines is studied in numeric simulations of different atmospheric turbulence and shear conditions. We find that the average trajectory of the wake as well as the variation about this average is influenced by the thermal stability of the atmosphere. The results suggest that an intentional intervention in the yaw control of individual turbines to increase overall wind farm performance might be not successful during unstable thermal conditions.
This innovative calibration method for a spinner anemometer allows a cheaper and faster installation of a spinner anemometer system, removing the need for the additional yaw position sensor. The method leverages the non-linearity of the spinner anemometer model to determine the calibration constant related to flow angle measurements. The method was applied to a database of 29 calibration campaigns and shown to be sufficiently robust.
Wind turbines are controlled through the electrical torque on the generator and the pitch of the blades. The tuning of the controller determines the dynamics of the system, which can then be good (smooth yet responsive) or bad (ineffective or unstable). A methodical investigation was conducted to determine the minimal model of the wind turbine structure and aerodynamics that can be used to tune the controller gains for large, multi-MW offshore wind turbines.
This paper presents a method to assess the stability of a wind turbine. The proposed approach uses the recorded time history of the system response and fits to it a periodic reduced-order model that can handle stochastic disturbances. Stability is computed by using Floquet theory on the reduced-order model. Since the method only uses response data, it is applicable to any simulation model as well as to experimental test data. The method is compared to the well-known operational modal analysis.
In order to reduce the cost of wind energy, it is necessary to reduce the loads that wind turbines withstand over their lifetime. The combination of blade rotation with newly designed blade shape changing actuators is demonstrated experimentally. While load reduction is achieved, the additional flexibility implies that careful control design is needed to avoid instability.
We use turbine nacelle-based measurements and measurements from an upwind tower to calculate wind turbine power curves and predict the production of energy. We explore how different atmospheric parameters impact these power curves and energy production estimates. Results show statistically significant differences between power curves and production estimates calculated with turbulence and stability filters, and we suggest implementing an additional step in analyzing power performance data.
This paper contributes to the scientific knowledge of flow behaviour over complex topography by extending the physical modelling work of the flow over the Bolund Hill escarpment, a test case for the validation of numerical models in complex terrain for wind resource assessment. The influence of inflow conditions on the flow over the topography has been examined in detail using a large-scale topographic model at high resolution at the unique WindEEE dome wind research facility.
Fluid–structure interaction analysis of a membrane blade concept has been performed for a non-rotating blade under steady inflow conditions. The membrane blade consists of a rigid mast at the leading edge, ribs along the blade, tensioned edge cables at the trailing edge, and membranes forming the upper and lower surface of the blade. The studied membrane blade shows a higher lift curve slope and higher lift-to-drag ratio compared with its rigid-blade counterpart.
The modal dynamics of wind turbines are the fingerprints of their responses under the stochastic excitation from the wind field. Commercial wind turbines have typically three-bladed rotors, and their modal dynamics are well understood. Two-bladed turbines are still commercially less successful, and this work also shows that their modal dynamics are significantly more complex than that of turbines with three or more blades.
The paper discusses different concepts for reducing loads on wind turbines using movable blade tips. Passive and semi-passive tip solutions move freely in response to air load fluctuations, while in the active case an actuator drives the tip motion in response to load measurements. The various solutions are compared with a standard blade and with each other in terms of their ability to reduce both fatigue and extreme loads.
Given a wind farm with known dimensions and number of wind turbines, we try to find the optimum positioning of wind turbines that maximises wind-farm energy production. We propose an optimisation approach that is based on a hybrid combination of large-eddy simulation (LES) and the Jensen model; in this approach optimisation is mainly performed using the Jensen model, and LES is used at a few points only during optimisation for online tuning of the Jensen model.
Wind turbines rarely operate in isolation but rather in close proximity within wind farms. Currently analysis methods are designed for analyzing turbines in isolation, or within a waked region. Actuator cylinder theory is extended to handle multiple vertical axis wind turbines in close proximity. We find good agreement in power predictions as compared to available higher-fidelity simulation data. The corresponding code may be useful for conceptual design and has been fully open-sourced.