GB1588694A

GB1588694A - Bladed rotor control systems

Info

Publication number: GB1588694A
Application number: GB3539/78A
Authority: GB
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-04-29

Description

(54) IMPROVEMENTS IN OR RELATING TO BLADED ROTOR CONTROL SYSTEMS (71) We, BRITISH AEROSPACE, a State Corporation of Brooklands Road, Weybridge, Surrey KT13,. England, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to bladed rotor control systems and, more particularly, to means for ensuring that the rotor speed of a turbine is held within limits, whereby the mechanical safety of the rotor and associated turbine apparatus is ensured.

While in one form the invention will hereinafter be described as embodied in a winddriven turbine employed forsgenerating electrical power, it is to be understood that the principle may be applied to other forms of turbine, e.g. steam, water, gas or other fluid or to thrust-producing means utilising bladed rotors.

In accordance with the invention there is provided a fluid-driven (or fluid-impelling) bladed rotor having on at least one blade a trailing edge flap that can be deployed for braking or starting the rotor and means automatically operating the flap regardless of the rotor loading at a predetermined rotor speed and/or fluid stream velocity the flap being so mounted on the blade that when the flap is deployed a gap is opened between the trailing edge of the blade and the flap.

The automatic operating means may be arranged to deploy the flap to brake the rotor when a predetermined maximum rotor speed is exceeded.

A description of one embodiment of the invention as applied to a two-bladed winddriven turbine will now be given with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic pictorial view of the hub section of the turbine, and Figure 2 is a diagrammatic pictorial view of a brake flap and its mounting and operating connections.

Referring firstly to Figure 2 a brake flap 11, of which there is one on each blade 12, is hinged just below the top skin 18 (wind pressure side) of the blade aerofoil section and rotates through approximately 90" about the hinge axis 13 when fully deployed. Each of the hinges 14 is attached to a central spar 19 of the flap and both locates the brake flap 11 spanwise and reacts the centrifugal load. When deployed the leading edge 15 of the brake flap is aft of the trailing edge 16 as regards the airstream 17 surrounding the blade 12.

With this arrangement the brake flap 11, after release and initial slight rotation, is self-deploying as the air forces its way between the leading edge 15 of the brake flap 11 and the top skin of the blade. When fully deployed, the air load moments about the hinge axis 13 acting on the leading and trailing parts of the brake flap will tend to balance each other.

When fully deployed, the brake flap 11 has two effects: 1) It destroys 'lift' of the blade 12, thereby reducing the driving force producing the torque on the turbine. 2) It adds drag to slow down the turbine to a safe speed, but it will not bring the turbine to a standstill. The brake flap 11 is constructed with slightly more twist than the main blade 12 so that when the flap tip section is held aligned with the main blade tip section, the inner end has to be strained into the closed position, to conform to the local blade profile, by tension in operating rods 20 that extend spanwise of the blade and close the flap by pulling on bell crank levers 21 that are in turn connected to the flap by links 22. A spring pot 23 in the blade 12 near the inner end of the brake flap, acts through a plunger 24 to bias the leading edge open.

On initiation of flap release there are therefore three forces trying to push open the leading edge of the inner end of the brake flap, and to rupture and obstruction along the spanwise joint line. These are:1) Built in strain in the brake flap.

2) The small spring pot at the inner end of the brake flap.

3) Centrifugal loads on the operating rods 20, etc.

In operation, the brake flap 11 is held in the closed position, conforming to the blade section, by tension in the rods 20.

These rods 20 pass inboard inside the trailing portion of the blade section and may be partially counter-balanced against centrifugal loads by weights on the levers 21. The inner rod 20 from each blade 12 (Figure 1) is connected to a crank 25 on a cross shaft 26 in the hub section 40 of the rotor. Shaft 26 has a cam 27 fixed on it and the cam is prevented from turning by a locking roller 28 at the end of a roller rocker 29 which is pivoted between arms of two lever plates 30, one on each side of the cam. Lever plates 30 are free to rotate on shaft 26 but are prevented from doing so by a rod 31, pivotally connected to an arm 32 on a lever plate, which rod is held by being pivotally connected at its other end to a lower lever 33 fast on a shaft 34.

Shaft 34 passes toward a fixed tube 35 extending along the centre of the hollow turbine shaft 41, and this shaft carries a forked lever 36 at its end near the centre of rotation. Between the forks of lever 36 is a roller 37 attached to a sleeve 38 which rotates with the turbine about the fixed centre tube 35 and is therefore stationary relative to lever 36. Sleeve 38 is mounted for sliding movement axially along tube 35 but is prevented from sliding by a rod 39 which extends along the fixed tube 35 in the centre of the turbine shaft.

Rod 39 terminates in a connecting rod 42 pivotally connected to a bell crank lever 43 on a cross shaft 44 fixed to the stationary support structure for the turbine. The other arm of lever 43 is held either by a manuallyoperable lever, or, as in the arrangement shown, is pivotally connected to the rod 45 of an actuating jack 46. While the turbine is rotating normally the forces trying to deploy the brake flaps are prevented from effecting such deployment by the fact that the lever 43 is locked against movement.

From the foregoing it will be seen that once the restraining force of jack 46 is released (or the manually-operated lever is released) at any rotor speed down to a few r.p.m., or if any part of the linkage fails, the brake flaps will deploy and bring the turbine down to a safe speed.

The centrifugal force trying to open the brake flaps may, if desired, be increased by adding weight to rods 20. A further bias to open the brake flaps and to overcome friction may be necessary for very low rotational speeds when centrifugal forces may be too low. This can be a spring strut 47 which acts through a lever on cam 27, fast on shaft 26, to push rods 20 outboard.

To prevent excessive loads on the stops when the brake flaps fly open a damper 48 is coupled to an arm 49 on the shaft 26.

In addition to the above a back-up overspeed shut down mechanism is provided, all within the hub, which operates as fol lows.

Centrifugal trip weights 50 are held from flying outward by large springs 51 reacting against brackets 52 fixed to the hub. At a predetermined rotational speed of the turbine the centrifugal force on the weights 50 just equals the minimum load at which the springs 51 will deflect. Above this speed, the springs 51 compress allowing the weights 50 to fly outwards. This acts through rod 54 and arms 55 to turn a shaft 56 and this shaft carries a finger 57 which bears against a roller 58 on roller rocker 29 thereby shifting the roller 28 at the other end of the rocker 29 free of cam 27 so that shaft 26 is free to rotate, thereby allowing the brake flaps to deploy.

With this mechanical arrangement both brake flaps deploy together. As the trip weights 50 act together on a common shaft 56, it is not possible for one weight to trip without the other. Likewise as both brake flap mechanisms are interconnected, it is not possible for one brake flap to deploy without the other.

The sensitivity of this last arrangement for deploying the brake flaps cannot be too fine and 10% overspeed is probably the minimum tolerance on the spring/weight combination to avoid possible premature turbine shut down. The maximum shut down overspeed tolerance, having regard to spring weight and friction, could possible be 25%. Provision is made for adding or removing weights, as at 53, to trim the trip loads. A further way of effecting brake flap deployment, should the centrifugal control system fail to respond to excessive wind speed, is by having a paddle or vane 59 on a long arm 60 in the free wind stream to act on an extension 62 of shaft 56 after overcoming a spring strut 61 at a predetermined load.To keep this system and the centrifugal system from interfering with one another, it is necessary to have some form of lost-motion joint or one-way coupling, e.g.

between the two parts of the shaft 56.

From the foregoing it will be apparent that it is possible by appropriate modifica tion to employ such movable blade flaps to facilitate the starting of a wind turbine or -windmill from rest. Advantageously, that part of the flap furthest from the blade root may be used, whereby the maximum torque is exerted upon the blade, and the mechanism is arranged so that when the rotor has aquired a predetermined speed the flap is closed automatically to conform with the aerofoil blade shape.

WHAT WE CLAIM IS:- 1. A fluid-driven (or fluid-impelling) bladed rotor having on at least one blade

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Claims

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in the closed position, conforming to the blade section, by tension in the rods 20.

These rods 20 pass inboard inside the trailing portion of the blade section and may be partially counter-balanced against centrifugal loads by weights on the levers 21. The inner rod 20 from each blade 12 (Figure 1) is connected to a crank 25 on a cross shaft 26 in the hub section 40 of the rotor. Shaft 26 has a cam 27 fixed on it and the cam is prevented from turning by a locking roller 28 at the end of a roller rocker 29 which is pivoted between arms of two lever plates 30, one on each side of the cam. Lever plates 30 are free to rotate on shaft 26 but are prevented from doing so by a rod 31, pivotally connected to an arm 32 on a lever plate, which rod is held by being pivotally connected at its other end to a lower lever 33 fast on a shaft 34.

Shaft 34 passes toward a fixed tube 35 extending along the centre of the hollow turbine shaft 41, and this shaft carries a forked lever 36 at its end near the centre of rotation. Between the forks of lever 36 is a roller 37 attached to a sleeve 38 which rotates with the turbine about the fixed centre tube 35 and is therefore stationary relative to lever 36. Sleeve 38 is mounted for sliding movement axially along tube 35 but is prevented from sliding by a rod 39 which extends along the fixed tube 35 in the centre of the turbine shaft.

Rod 39 terminates in a connecting rod 42 pivotally connected to a bell crank lever 43 on a cross shaft 44 fixed to the stationary support structure for the turbine. The other arm of lever 43 is held either by a manuallyoperable lever, or, as in the arrangement shown, is pivotally connected to the rod 45 of an actuating jack 46. While the turbine is rotating normally the forces trying to deploy the brake flaps are prevented from effecting such deployment by the fact that the lever 43 is locked against movement.

From the foregoing it will be seen that once the restraining force of jack 46 is released (or the manually-operated lever is released) at any rotor speed down to a few r.p.m., or if any part of the linkage fails, the brake flaps will deploy and bring the turbine down to a safe speed.

The centrifugal force trying to open the brake flaps may, if desired, be increased by adding weight to rods 20. A further bias to open the brake flaps and to overcome friction may be necessary for very low rotational speeds when centrifugal forces may be too low. This can be a spring strut 47 which acts through a lever on cam 27, fast on shaft 26, to push rods 20 outboard.

To prevent excessive loads on the stops when the brake flaps fly open a damper 48 is coupled to an arm 49 on the shaft 26.

In addition to the above a back-up overspeed shut down mechanism is provided, all within the hub, which operates as fol lows.

Centrifugal trip weights 50 are held from flying outward by large springs 51 reacting against brackets 52 fixed to the hub. At a predetermined rotational speed of the turbine the centrifugal force on the weights 50 just equals the minimum load at which the springs 51 will deflect. Above this speed, the springs 51 compress allowing the weights 50 to fly outwards. This acts through rod

54 and arms 55 to turn a shaft 56 and this shaft carries a finger 57 which bears against a roller 58 on roller rocker 29 thereby shifting the roller 28 at the other end of the rocker 29 free of cam 27 so that shaft 26 is free to rotate, thereby allowing the brake flaps to deploy.

With this mechanical arrangement both brake flaps deploy together. As the trip weights 50 act together on a common shaft 56, it is not possible for one weight to trip without the other. Likewise as both brake flap mechanisms are interconnected, it is not possible for one brake flap to deploy without the other.

The sensitivity of this last arrangement for deploying the brake flaps cannot be too fine and 10% overspeed is probably the minimum tolerance on the spring/weight combination to avoid possible premature turbine shut down. The maximum shut down overspeed tolerance, having regard to spring weight and friction, could possible be 25%. Provision is made for adding or removing weights, as at 53, to trim the trip loads. A further way of effecting brake flap deployment, should the centrifugal control system fail to respond to excessive wind speed, is by having a paddle or vane 59 on a long arm 60 in the free wind stream to act on an extension 62 of shaft 56 after overcoming a spring strut 61 at a predetermined load.To keep this system and the centrifugal system from interfering with one another, it is necessary to have some form of lost-motion joint or one-way coupling, e.g.

between the two parts of the shaft 56.

From the foregoing it will be apparent that it is possible by appropriate modifica tion to employ such movable blade flaps to facilitate the starting of a wind turbine or -windmill from rest. Advantageously, that part of the flap furthest from the blade root may be used, whereby the maximum torque is exerted upon the blade, and the mechanism is arranged so that when the rotor has aquired a predetermined speed the flap is closed automatically to conform with the aerofoil blade shape.

WHAT WE CLAIM IS:- 1. A fluid-driven (or fluid-impelling) bladed rotor having on at least one blade

a trailing edge flap that can be deployed for braking or starting the rotor, and means automatically operating the flap, regardless of the rotor loading, at a predetermined rotor speed and/or fluid stream velocity, the flap being so mounted on the blade that when the flap is deployed a gap is opened between the trailing edge of the blade and the flap.
2. A rotor according to claim 1, wherein the automatic operating means is arranged to deploy the flap to brake the rotor when a perdetemined maximum rotor speed is exceeded.
3. A rotor according to claim 1 or claim 2, wherein the automatic operating means is arranged to close the flap, after it has been at least partially deployed for starting the rotor, when a predetermined rotor speed is reached.
4. A rotor according to claim 2, wherein the automatic operating means is actuated by centrifugal force.
5. A rotor according to claim 2 or claim 4, wherein the automatic operating means is actuated by fluid pressure.
6. A rotor according to any one of the preceding claims, wherein the flap is arranged to deploy under the influence of fluid pressure and/or centrifugal force and/ or spring pressure, a latch is provided to prevent the flap deploying under such influences, and centrifugal-force-responsive means are arranged to release the latch at a predetermined rotor speed or fluid stream velocity.
7. A rotor according to claim 6, wherein manually-operable means are additionally provided for releasing the latch.
8. A rotor according to claim 6 or claim 7, wherein the latch comprises a cam and roller mechanism.
9. A rotor according to claim 6 or claim 8, wherein the centrifugal force responsive means comprises a weight and spring combination.
10. A rotor according to any one of claims 6 to 9, wherein the fluid-pressureresponsive means comprises a paddle or vane in the fluid stream acting against a spring.
11. A rotor according to any one of the preceding claims, wherein the flap is urged to deploy by centrifugal force acting on flap-operating rods extending along the blade.
12. A rotor according to any one of the preceding claims, wherein the flap is urged to deploy by spring means on the blade.
13. A rotor according to any one of the preceding claims, wherein the flap has a greater amount of twist than the blade so that it has to be flexed and strained to keep it fully closed.
14. A rotor according to any one of the preceding claims, wherein, once the gap has been slightly opened, the flap is urged to deploy by fluid pressure acting on it.
15. A rotor according to any one of the preceding claims, wherein a damper is provided to prevent the flap from deploying too violently.
16. A multi-bladed rotor according to any one of the preceding claims, wherein each blade has a flap and the flaps are interconnected so that they are constrained to deploy together.
17. A wind-driven turbine rotor substantially as described with reference to the accompanying drawings.