Fluid reaction surfaces (i.e. – impellers) – With means moving working fluid deflecting working member...
Patent
1985-12-12
1987-09-08
Powell, Jr., Everette A.
Fluid reaction surfaces (i.e., impellers)
With means moving working fluid deflecting working member...
416 32, 416169R, 416236R, F03D 704
Patent
active
046920951
DESCRIPTION:
BRIEF SUMMARY
This invention relates to wind turbine blades and to wind turbines incorporating the same.
Wind turbine blades have been fashioned in many different configurations and wind turbines themselves operate according to different philosophies depending at least to some extent on the use to which the turbine is put. Wind turbines are commonly used to generate electricity, and can be connected directly or indirectly to a generator. It is often desired to generate current at a predetermined frequency, and direct connection then requires either that the turbine be operated at constant speed, or that a variable frequency output be converted in for example a static converter to a fixed frequency.
A variable speed fixed pitch turbine may be operated for optimum power capture at constant tip speed ratio, for example by altering the torque reaction on the turbine shaft with the shaft speed.
Overspeed conditions can be controlled by braking means acting on the turbine shaft. Variable pitch blades can be feathered in high wind conditions, and in any event the blades may be designed to stall in certain conditions so as to avoid overspeeding.
The use of centrifugally operated air brakes has also been proposed, such brakes being arranged for example at the blade tips and set to fly out against a resilient bias at a predetermined rotational speed.
The choice of airfoil section and blade configuration generally for wind turbines is based on different considerations than apply to airplane wings, propellers and helicopter rotor blades. A major consideration in the case of wind turbines is rigidity. Another major consideration is that the wind to which the turbine is subjected is itself subject to rapid and substantial fluctuation both as to speed and direction, which cannot often be accommodated by correspondingly rapid pitch changing and which can put substantial strain on the blades and on the transmission.
The present invention provides a solution to these problems.
The invention comprises a wind turbine blade having a first side which in ordinary operation is a high pressure side and a second side which in ordinary operation is a low pressure side, which sides can, in abnormal operation, become reversed, so that the said first side becomes the low pressure side and the said second side becomes the high pressure side, said blade having spoiler means automatically deployed on the low pressure side in abnormal operation.
Said spoiler means may be permanently deployed on said first side and may comprise a blade spar or part thereof. Such blade spar may have a greater depth than the depth from said first to said second side and extend from said second side to beyond said first side. Said spar may be about twice the depth of the blade from said first to said second side.
Said spar may comprise a rigid plate extending substantially perpendicularly to the chord of an airfoil section comprising said first and said second side. Said spar may otherwise comprise a box section, and may comprise a triangular box section having a base adjacent the said second side and an apex projecting from said first side.
Said first side of said blade may be substantially wholly or partly open between the leading and trailing edges of the blade.
Said blade may be essentially of a conventional airfoil section forward of said spoiler means and essentially comprise only the low pressure side of a conventional airfoil section aft of said spoiler means.
Said blade may have spoiler means on said second side deployable between an inactive position during normal operation and an active position during abnormal (high speed) operation so as to extend from said second side (while said second side remains the low pressure side) to retard the blade. Said spoiler means may comprise a plate member lying in its inactive position flush or substantially so with the surface of said second side and in its active position standing up from said second side substantially perpendicular thereto. Said spoiler means may be actuated by motor means disposed inboard of the blade, and
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Powell Jr. Everette A.
Sir Henry Lawson-Tancred, Sons & Co. Ltd.
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