GB2175351A

GB2175351A - Aerodynamic/hydrodynamic control devices

Info

Publication number: GB2175351A
Application number: GB08607344A
Authority: GB
Inventors: Derek Alan Taylor; David John Sharpe
Original assignee: Open University
Current assignee: Open University
Priority date: 1985-03-26
Filing date: 1986-03-25
Publication date: 1986-11-26
Also published as: GB8507875D0; GB8607344D0; GB2175351B

Abstract

A control device for a blade (10), such as a wind turbine blade, has an aerofoil cross-section body (16) pivotably mounted above the blade and movable through at least 90 DEG to exert a braking effect on the motion of the blade. A second braking body (18) may be provided below the blade. The braking bodies (16,18) may be actively operated or be passive. In an alternative, the braking body is positioned at the tip of the blade. <IMAGE>

Description

SPECIFICATION Aerodynamic/Hydrodynamic control devices This invention relates generally to devices which are used to provide aerodynamic or hydrodynamic control. The devices of the present invention are particularly appropriate to provide aerodynamic control to regulate the power and/or the speed of wind turbines, aircraft propellers, fans, helicopter rotors, etc.

The devices of the present invention are also appropriate for providing hydrodynamic control to regulate the power and/or the speed of water turbines, ship propellers, pumps, etc.

Although the control devices of the present invention have wide application to situations where blades are subject to the action of fluids, they are particularly well suited to the aerodynamic control of wind turbines. The device of the present invention is usable on vertical axis or crossflow wind turbines, as well as on horizontal axis or axial flow wind turbines, or wind turbines of the Wagner type.

It is an object of the present invention to provide a control device for a blade which reduces the structural loads on the blade and which, as a consequence, enables the blade to be made of lighter materials.

It is a further object of the present invention to provide a control device which can be used in an active or in a passsive mode.

It is a further object of the present invention to provide a control device for a blade which will stop, or at least substantially reduce, the possibility of overspeeding of the blade.

It is yet a further object of the present invention to provide a control device which does not affect the structural integrity of the blade, in contrast to control systems which employ pitchable tips for the blades.

In accordance with the present invention, there is provided a control device for a blade which is subject to the effect of fluid flowing past the blade, the device comprising a body adapted to be positioned on the blade so as to extend above and/or below the blade at a narrow zone lengthwise of the blade, the body being pivotable about an axis extending substantially perpendicular to the root-to-tip span and to the width of the blade between a first position in which the body presents minimum braking effect when subject to the fluid flow and one or more second positions in which the body exerts a braking effect.

Preferably, the body, when viewing the blade in plan, has a cross-sectional shape which is an aerofoil profile, either symmetrical or asymmetrical. It is preferable if the body behaves a "slender body" device in aerodynamic terms.

Although the braking body can be positioned anywhere along the length of the blade from the root to the tip, it may be desirable if the braking body is positioned inboard, away from the tip of the blade.

In order that the invention may be more fully understood, a number of embodiments of control device in accordance with the invention will now be briefly described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows the use of a "double" control device on a blade; Figure 2a is a plan view of part of a blade showing an alternative embodiment of control device; Figure 2b shows the control device of Fig.

2a in front elevation; Figures 3a and 3b show the provision of a modified form of control device at the tip of a blade; and Figure 4 is a schematic view of a wind turbine comprising a tower with blades having control devices in accordance with the present invention at the blade tips.

Referring first to Fig. 1, this shows a main blade 10 arranged for rotation in the direction of the arrow 12. The tip of the blade is indicated at 14. A control device in the form of a body 16 is mounted on the upper surface of the blade 10, and an equivalent body 18 is mounted below the blade. Each of the bodies 16 and 18 is mounted to be pivotable about a pivot axis 20, for example by providing a pivot pin through the body and into the main blade. This pivot pin can project out of one or both faces of the blade 10 at an angle of substantially 90" to the plane of the blade.

The general plane of the bodies 16 and 18 is oriented such that they are perpendicular to the plane of the main blade 10. In normal operation, as shown in solid outline in Fig. 1, the bodies 16 and 18 are aligned with the tangent to the direction of rotation of the blade 10, i.e. they extend generally across the width of the blade 10.

When the bodies 16 and 18 are to be used as braking means, or spoilers, they rotate (passively) or are rotated (actively) about the pivot axis 20 so that the plane of the bodies is no longer aligned with the tangent to the direction of rotation of the blade 10. The greatest braking effect is achieved when the plane of the bodies 16 and 18 is in alignment with the span of the blade 10, as indicated by broken lines in Fig. 1. The deployment position shown in broken lines in Fig. 1 is one possible deployment position. Alternatively, the bodies 16 and 18 could be rotated so that the bodies are turned through 1800 from the broken line position illustrated, i.e. with the tail of the bodies pointing inboard away from the blade tip 14.

The bodies 16 and 18 can be arranged to rotate passively, under the influence of centri fugal and/or aerodynamic and/or hydrodynamic forces, or they can be rotated actively by hydraulic, electrical, pneumatic or mechanical means. The devices could also be oper ated actively and remotely by transmitting control signals to receiver units mounted in the control devices themselves.

The span of the bodies 16 and 18, i.e. their length from head to tip, is very short compared with the span of the main blade 10, i.e.

its length from tip 14 to root (not shown).

Although, normally, the braking bodies 16 and 18 will not extend beyond the contour of the blade 10, they can alternatively be lengthened to extend fore and/or aft of the blade, if necessary.

Figs. 2a and 2b show an alternative embodiment, where there is provided just one rotatable body 16 above the blade 10, having a span or length equal to the width of the associated blade 10. The blade 10 is here secured to a central tower or hub (not shown) by cables 22. As will be seen from Figs. 2a and 2b, the body 16 here spans the width of the main blade 10 and its pivot axis lies very close to the leading edge of the blade 10. As in the case of the embodiment shown in Fig.

1, the braking body 16 can pivot to either side of the undeployed, normal position which is shown in solid outline in Fig. 2a.

Figs. 3a and 3b show a further embodiment of control device. In this embodiment the braking device takes the form of a "slender delta" streamlined body 24 located at the tip of the blade 10. A pivot pin 20 supports the brake body 24 at the tip of the blade and the brake body is shaped with a recess 25 which thus permits the brake body to rotate through at least 90" relative to the blade, as shown in Fig. 3b.

The planewise shape of the braking body is not restricted, but it is preferable for this shape to be a slender delta, or triangle, analogous to a paper dart model aeroplane. Alternatively, one can use a "swept arrow" shape, or a rectangular, elliptical or circular shape.

The plane cross-sectional shape of the spoiler is also not restricted, although the preferred shape is that of an aerofoil profile, as shown in Fig. 1, either symmetrical or asymmetrical. Alternatively, one could use a flat, cambered or kinked plate.

In aerodynamic terms it is desirable if the or each spoiler behaves as a "slender body" device. This helps to avoid problems due to stalling.

Fig. 4 shows the use of a control device of this type of a wind turbine which comprises a tower 30 and two blades 32 held by cables 34. Spoiler bodies 36 are positioned at the tip of each of the blades 32 of this vertical axis wind turbine.

The spoiler bodies can be positioned at any location along the length of the blades from root to tip although in certain embodiments it is desirable for the body or bodies to be inboard from the tip.

Among the advantages of the present invention are that this control device provides a much simpler, cheaper and lighter weight solution to the problems of aerodynamic control than many of the means currently employed.

The control device does not affect the structural integrity of the blade, whereas control systems which use pitchable tips do adversely affect the structural integrity. in the case of an active control device, the mechanism required to operate it can be simple and cheap. If it is actuated mechanically, then one need only provide a mechanical cable or rod linkage through or along the blade, which does not add greatly to the weight of the blade. The same applies if the control device is actuated hydraulically, pneumatically or electrically. The control device of the present invention also does not adversely affect the type of blade/hub attachment, whereas full span pitchable blades require a special attachment to allow the blade to rotate about its longitudinal axis.

Claims

1. A control device for a blade which is subject to the effect of fluid flowing past the blade, the device comprising a body adapted to be positioned on the blade so as to extend above and/or below the blade at a narrow zone lengthwise of the blade, the body being pivotable about an axis extending substantially perpendicular to the root-to-tip span and to the width of the blade between a first position in which the body presents minimum braking effect when subject to the fluid flow and one or more second positions in which the body exerts a braking effect.

2. A control device according to claim 1, in which the body, when viewing the blade in plan, has a cross-sectional shape which is an aerofoil profile.

3. A control device according to claim 2, in which the aerofoil profile is symmetrical.

4. A control device according to any preceding claim, which has two braking bodies, one below the blade and one above the blade, and both pivotable about a common axis.

5. A control device according to any preceding claim, in which the or each said body is pivotable through at least 90".

6. A control device according to any preceding claim, in which the leading edge to trailing edge length of the body is substantially equal to the width of the blade.

7. A control device according to any preceding claim, in which the body or bodies is/are positioned inboard from the tip of the blade.

8. A control device according to any preceding claim, in which the body is located at the tip of the blade and has a streamlined shape in cross-section viewed along the length of the blade.

9. A control device for a blade, substantially as hereinbefore described with reference to Fig. 1, Figs. 2a and 2b, or Figs. 3a and 3b, of the accompanying drawings.