Blade pitch

About: Blade pitch is a research topic. Over the lifetime, 5321 publications have been published within this topic receiving 63134 citations.

Model based power optimisation of wind farms

Abstract: We present a framework for maximising the power output of a wind farm considering wake effects. A parameter representing the total power coefficient of a wind farm is introduced, which quantifies the wind speed deficit due to wake. For any given wake model, this parameter is a function of the blade pitch angle and the tip speed ratio of the individual turbines, and is independent of the wind speed. Thus, the variables associated with each turbine can be optimised offline, given the wind farm layout, in order to determine reference set points that maximise power production. An MPC controller is designed for individual turbines to track the optimal reference set points. The performance is illustrated with the turbine simulator FAST and the wind farm simulator Aeolus SimWindFarm.

Propeller and horizontal-shaft windmill

Abstract: A propeller, wherein the tip parts of the propeller blades (3) of a horizontal-shaft windmill are tilted in the front direction of the propeller blades (3) to form inclination parts (3c). The inclination angle of the tilted parts (3c) is set within the range of 25 to 50° relative to the longitudinal direction of the propeller blades (3).

Optimal dynamic induction control of a pair of inline wind turbines

Abstract: We study dynamic induction control for mitigating the wake losses of a pair of inline wind turbines. In order to explore control strategies that account for unsteady interactions with the flow, we employ optimal control and adjoint-based optimization in combination with large-eddy simulations. The turbines are represented with an actuator line model. We consider a simple uniform inflow case with two NREL 5 MW turbines spaced 5 diameters apart and find that optimal control leads to 25% gains compared to standard Maximum-Power-Point Tracking (MPPT). It is further found that only the control dynamics of the first turbine are changed, improving wake mixing, while the second turbine controller remains close to the MPPT control. We further synthesize the optimal generator torque and blade pitch controls of the first turbine into a signal that can be periodically used as an open-loop controller, with a Strouhal number of 0.38, while realizing the same gains as the original optimal control signal. Further analysis of the improved wake mixing resulting from the open-loop signal reveals periodic shedding of a three-vortex ring system, which interacts and merges downstream of the first turbine, increasing entrainment of high-speed momentum into the wake. The sensitivity of the open-loop signal to inlet turbulence levels and turbine spacing is also investigated. At low to medium turbulence levels, the control remains effective, while at higher levels, the coherence of the vortex rings degrades too fast for them to remain effective.

Compliant Blades for Wind Turbines

Abstract: Recent advances in analysis capabilities for wind turbine blade aerodynamics and structural dynamics enables a through understanding of the connection between the aerodynamic excitation and structural response of blades. By designing the blades using fibre reinforced composite materials, coupling between bending and torsion for example, can be built-in. In the present work the objective was to investigate the capability of a 50kW constant speed wind turbine to automatically shed power in gusts by feathering the blades, i.e. twisting them towards the relative wind vector thus reducing the angle of attack, whilst bending away from the wind. This numerical study demonstrated that it is difficult to achieve constant power output with complaint blades for a fixed speed wind turbine because a large amount of twist is required. When a gust arrives at a blade the relative wind vector is rotated forwards, thus increasing the angle of attack, and hence the lift coefficient. In order to reduce the power, the blade feather angle must be larger than this gust induced increased angle of attack. This will typically be several degrees, and mean that induced blade pitch angles need to be at least 15 degrees or so in order to be effective. However, the bending of blades in gusts helps. As the blade bends away from the wind it presents a lower projected area to the wind. As well, a blade which is bent away from the wind has a velocity component along the blade, which reduces the effective angle of attack and the magnitude of the relative velocity normal to the blade. Although the design of soft or complaint blades is rather more complex than rigid blades, it is being seriously considered by wind turbine manufactures, and so is certainly worthy of study. It has the advantage of reducing the aerodynamic loads at their source, and consequently this reduces the loads which need to be carried by the power train and the tower. Wind turbine designers have experienced some difficulty developing active controllers to pitch blades fast enough to control the power generation and so in windy gusty conditions such as in hilly New Zealand terrain, one would expect the power output of fixed speed pitch controlled wind turbines to vary rather more than desired. Complaint blades may offer a more effective means of power control. This paper details the investigation and results obtained in this aeroelastic study of complaint blades made from fibre reinforced composite materials.

Propeller sound field modification systems and methods

Abstract: A propeller system for an aircraft includes an assembly for modifying a sound field of the propeller system. The propeller system includes a rotor supported for rotation about a rotor axis. The rotor has a central hub and a plurality of blades each extending outwardly from the hub to a tip. The rotor and blades are operable to propel an aircraft to travel in a direction. The rotor blades define a rotor plane perpendicular to the rotor axis. The blade tips define a circumferential rotational path as the blades are rotated by the rotor. The propeller system includes an acoustic resonator or multiple resonators having openings disposed within a distance to the propeller blade tip that is small compared to the wavelength of the propeller's fundamental blade tone and proximate to the rotor plane. The resonators are excited by tip flow of the blade as it passes the opening. The acoustic resonators are configured and positioned so as to direct acoustic energy to modify the sound field of the propeller system at blade pass or higher harmonic frequency tones in a desired direction relative to the aircraft.