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    Wind Turbines are often proving to be more economical than fossil fuel fired power stations both in capital costs and generation costs. With the use of HVDC power lines electricity can be efficiently distributed over thousand of kilometers.

    This new research could be a massive leap in making wind turbines more cost effective and usable in marginal areas.

    Using flexible blades: Abstract

    Wind energy is becoming a significant alternative solution for future energy production. Modern turbines now benefit from engineering expertise, and a large variety of different models exists, depending on the context and needs. However, classical wind turbines are designed to operate within a narrow zone centred around their optimal working point. This limitation prevents the use of sites with variable wind to harvest energy, involving significant energetic and economic losses. Here, we present a new type of bioinspired wind turbine using elastic blades, which passively deform through the air loading and centrifugal effects. This work is inspired from recent studies on insect flight and plant reconfiguration, which show the ability of elastic wings or leaves to adapt to the wind conditions and thereby to optimize performance. We show that in the context of energy production, the reconfiguration of the elastic blades significantly extends the range of operating regimes using only passive, non-consuming mechanisms. The versatility of the new turbine model leads to a large increase of the converted energy rate, up to 35%. The fluid/elasticity mechanisms involved for the reconfiguration capability of the new blades are analysed in detail, using experimental observations and modelling.

     

    (a) Three-bladed turbine model used in this work. (b) Sketch of a blade section in the rotating frame of reference, showing symbols and notation. During the operating regime, the blade is subjected to the aerodynamic force (decomposed into lift fL and drag fD), which tends to fold the blade through the action of the torque ma, and the centrifugal force fC, which conversely tends to align the blade with the rotation plane due to the torque mc exerted in the opposite direction. As a result, the blade bends, which modifies the angle of attack β between the apparent wind V and the blade and θ, the angle between the blade and the plane of rotation. (c) Bent elastic blades for three characteristic values of the speed ratio λ measured at the tip blade. The red profile shows the reference configuration (λ=0, θ0=28°). The two white profiles show the bent blades for (λ=0.25, θ=30.8°) and (λ=2.35, θ=25.3°). Credit: (c) Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science (2017). DOI: 10.1098/rspa.2016.0726

    Narrow band of oncoming wind speeds

    Current wind turbines are efficient at specific working points . This limitation is mainly due to the fact that for a given blade design (setting local angles of attack and aerodynamic coefficients along the blade), the turbine reaches its best performance over a narrow band of oncoming wind speeds and turbine loads [1,2].

    As a consequence, the energy conversion is poor when the turbine is working far from its operating regime. For current installation, this difficulty is generally overcome either by seeking sites with stable and constant head wind or by introducing active motorized controls of blade pitch angle [2] or active trailing edge flaps [3]. Nevertheless, a large amount of potential available wind energy is not converted by the turbines, leading to a significant energetic and economic losses. This lack of versatility limits the development of small or middle-sized turbine models and the expansion of short supply chains.

    This work introduces a solution to this technological limitation, using flexible blades inspired by the flapping flight of insects and reconfiguration of plants. Slender elastic structures, such as wings or leaves, adjust the torque exerted by the fluid pressure when bending through the action of the incoming wind, changing the balance between external mechanical loads [46]. Plants bend during wind conditions, which reduces drag and avoids damage [79]. Insects, on the other hand, use this ability to change the direction of the pressure forces to improve thrust production, without extra input energy [1012]. Along the same line of thought, flexible blades can be implemented on wind turbines.

    Blade flexibility is currently a centre of attention in the turbine community. The principal concern has been the structural instability of large size turbines operating at high tip speed ratios. The main goal of these works has been to include blade flexibility into models and simulations to give accurate predictions of the blade bending and flutter threshold [2,13,14]. On the other hand, blade flexibility has also been perceived as a way to improve the performance of the rotor. Several numerical studies have addressed chordwise bending of the blade through the action of the aerodynamic load and have shown that performance could be increased in specific cases [1521], but did not consider the blade pitch angle as a key parameter. This parameter is, however, crucial for flexible blades because the main property of flexibility is to allow the pitch angle to dynamically adapt to the wind forcing and extracted power. We propose an experimental and theoretical study covering a relevant range of the parameter space.

    We show that the most notable feature of the blade reconfiguration capability is to keep the mechanical system efficient away from the optimal operating point (in the case of wind conditions, which are below or above the nominal speed, for instance). This crucial feature can significantly extend the performance range of wind turbines beyond their specific working regime. Our experimental results show an increase in potential energy production up to 35%, which is obtained using passive, non-consuming mechanisms, from the reservoir of energy available at non-nominal wind conditions.

    More information:

    I highly recommend going to this link to see the extensive experimental data

    V. Cognet et al. Bioinspired turbine blades offer new perspectives for wind energy, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science (2017).LINK: DOI: 10.1098/rspa.2016.0726

     

     

    Mike Nunnerley's SMD Cell
    Tiny turbine power removes EV range anxiety
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