AERODYNAMIC BRAKE ON A WIND ROTOR FOR A WINDMILL

Abstract: The invention relates to an aerodynamic brake on a wind rotor for a windmill, which brake comprises the turnable outermost end of the wings of the wind rotor. This turnable part consists of a radially outermost first section in the full width of the wing and a hereto connected second section which extends radially inwards from the first section and only constitutes a part of the width of the wing. The turnable part is hingedly connected to the wing. Preferably the second part constitutes the trailing part of the wing as seen in the direction of rotation. The dividing line between the wing and the turnable part extends approximately parallel to the longitudinal direction of the wing, and the axis of the hinge means extends obliquely backwards and radially inwards on the wing.

Description: AERODYNAMIC BRAKE ON A WIND ROTOR FOR A WINDMILL. The invention relates to a wind rotor for a windmill, which wind rotor has wings with an aerodynamic brake which may be activated either at the transgression of a predetermined rotational speed of the wind rotor or to regulate said speed, which brake consists of a turnable part of said wings and which turnable part preferably is the radially outmost part of the wings. A windmill is a machine which extracts energy from the wind by means of the force acting upon the wind rotor of the windmill, which machine transforms the energy of the wind to an electric, mechanical or other useful form of energy. The type of windmill, for which the invention most advantageously can be put to use, is a windmill with a horizontal or approximately horizontal axis and with a wind rotor consisting of an arbitrary number of wings rotating in an approximately vertical plane perpendicular to the direction of the wind. It is demanded for the authorization of a windmill that it is provided with two braking systems which each on its own is able to prevent the rotor of the windmill to attain an excessive number of revolutions. One of the two braking systems may conveniently be an aerodynamic braking system, which is activated at an excessive speed and which through the braking effect of the forces of the air limits the number of revolutions of the rotor to a value which secures against damages. The excessive speed may for instance occur if the mechanical axial brake of the windmill fails during a stop of the windmill. The aerodynamic brake may also, beside this primary emergency function, be employed to function together with the mechanical brake during the normal function of the windmill. However this demands that the brake is maneuvered from the control system of the windmill. Various types of aerodynamic brakes on wind rotors for windmills are known, and the following may be mentioned heres a) Pitch control Here the whole wing may be turned around the longitudinal axis and used for the effect control of the windmill. Pitch control is a solution of another kind than the one covered by the comprehensive term of the invention. b) Braking parachute A braking parachute is placed in a collapsed state in a space in the wing tip, i. e. the radially outermost part of the wing. The parachute may be made to unfold and brake the wing. The use of a braking parachute implies two problems; first that it is time consuming to fold up and again deposit the parachute in the space after it has been in use, and secon that it is problematic strengthwise to use braking parachutes in connection with long wings because the braking will be ver sudden. c) Air brakes Air brakes consist of plates which are inserted in the wing, and which plates may be turned into or shifted into the ai stream. This type of brake is similar to the brakes used i gliders. Experience with such brakes on windmills shows tha they are not sufficiently effective unless they are very lon in proportion to the length of the wing and therefor disproportionately expensive. d) Leading edge flap On the radially outer part of the wing, app. 15% of the lengt of the wing, the leading part, which may consist of 15-20% o the width of the wing, is hingedly connected to th trailing fixed part of the wing in such a way that it may b pivoted to a position almost perpendicular to the wing. It is a problem to construct the hinge parts of a leading edge flap in such a way that it will assume the correct position with great accuracy when it is folded up, which is necessary as just a small inaccuracy in its position in relation to the fixed part of the wing behind it may produce considerable changes in the aerodynamic characteristics of the wing profile. e) Swing tip The radially outer part of the wing, the tip, which part typically constitutes the outer 15% of the total length of the wing, may be turned on an axle which is placed in the longitudinal direction of the wing approximately at the middle of the wing. When the swing tip is activated it is turned to a position approximately perpendicular to the the rotational plane of the wing. The suspension of this axle presents a number of problems, and at the passage between the fixed part of the wing and the swing tip the axle is exposed to considerable bending strains. This makes a heavy dimensioning of the axle necessary which involves a corresponding increase of the thickness of the wing. It is therefore the object of the invention to indicate an embodiment of an aerodynamic brake which is without the above mentioned disadvantages of the known art. The basis of the invention is a wind rotor with a swing tip. This object will be achieved by a wind rotor of the above mentioned description, which wind rotor is characteristic according to the invention in that the turnable part consists of a first and a second section of which the first section consists of the radially outermost part of the full width of the wing, that the second section extends radially inwards from the first section and consists of a part of the wing in its full width, and that the turnable part is connected to the wing by means of hinges between the second section and the wing. Compared to the known swing tip the advantage is that the axle, around which the swing tip turns, is avoided. The construction principle according to the invention using hinges built into the structure of the wing may better than an axle withstand the aerodynamic forces and the centrifugal forces, and the wing therefore does not need to be as thick, whic confers a higher efficiency to the wing. For the same reaso the brake may be made longer than a swing tip and therefore achieve a better braking effect. The second section of the turnable part will preferabl constitute the trailing edge part of the wing, seen in th direction of rotation, cfr. claim 2, as this produces the bes aerodynamical shape of the wing. An advantageous embodiment of the turnable part is obtaine when the dividing line between the second section and the win according to claim 3 extends substantially in the longitudina direction of the wing, the axis of the hinge constructio extends in the plane of the wing, and the radially innermos part of the hinge construction preferably is placed at greater distance from the leading edge of the wing than th radially outmost part. The aerodynamic brake according to the invention belongs t the type of brakes in which a part of the wing is pivoted int a position perpendicular to the normal working position an thereby offer aerodynamic resistance to the rotation of th wing around the axle of the windmill. Compared to the known aerodynamic brake constructions th principle according to the invention will result in construction which makes the brake more efficient, safer stronger and less expensive. The wind rotor according to the invention will be further explained in the following with reference to the drawings, in whichϊ fig. 1 shows an embodiment of a turnable part on the radially outermost end of a wing according to the invention in which the wing is assumed to rotate clockwise seen from the front, i. e. in the direction of the wind, fig. 2a and 2b show two alternative directions of pivoting of the part shown in fig. 1, and fig. 3a and 3b is a section along the line III-III in fig. 1, in which the turnable part is placed respectively in a withdrawn and in an extended position. The radially outermost end of a wing 1 for a wind rotor of a windmill is shown in fig. 1. The wing is regarded in the direction of the wind and is assumed to rotate in the direction shown by the arrow 2, i. e. clockwise. When the wind rotor is functioning the wing will be acted upon by external forces, the forces of the air acting on the wing and the centrifugal force which is indicated by the arrow 3. At the end of the wing a wing tip 4 is placed which constitutes an aerodynamic brake for the wing 1. This wing tip 4 comprises a first section 5 and a second section 6 of which the first section 5 constitutes the radially outmost end of the wing 1 in its full width, as the contour of the section 5 forms a natural part of the contour of the wing. The second section 6 extends radially inwards from the first section 5 and is integrally connected hereto. The second section constitutes a part of the width of the wing. The second section 6 is shown in the drawings as constitutin the trailing part of the wing 1 and/or the tip of the wing with reference to the direction of rotation 2, but it i within the scope of the invention that the second section ma constitute the leading part of the width of the wing 1. The dividing line between the second section 6 and the wing extends in a Z-shape and may be divided into a radiall outermost first part 8, a radially innermost third part 10 an an intermediate second part 9. The intermediate second part of the dividing line extends essentially parallel to th leading edge 11 of the wing 1. The wing 1 may have one or more beams 12 which constitute part of the structure of the wing. The beam or the beams ar suggested by dot-and-dash lines in fig. 1. The wing tip 4 is pivotally connected to the wing 1 by hinge 13, 14 which provide a pivot line 15. The pivot line 15 may b placed close to the surface of the wing 1 or inside the win 1, for instance in the middle of the wing. The pivot line 15 extends in the plane of the wing 1 an preferably in such a way that the radially innermost hinge 1 is at a greater distance from the leading edge 11 of the win 1 than the radially outermost hinge 13, so that the pivot lin 15 extends obliquely to the rear and radially inwards from th leading edge 11. The radially outermost first part 8 and the radially innermos third part 10 of the dividing line extends in plane perpendicular to the pivot line 15. Two optional possibilities of the direction of the pivoting o the brake are shown in fig. 2. In the embodiment a the leadin edge of the brake is turned against the direction of the wind, which is shown by the arrow 16, and in the embodiment b th leading edge of the brake is turned away from the direction o the wind. The direction of the movement of the wing during th rotation around the axis is indicated by the arrow 17. Th choice of direction of the turning is quite immaterial t the invention. Slits between the wing 1 and the wing tip 4 will necessaril occur at the dividing lines 8, 9 and 10, which slits ma produce undesired air flow along the wing. The brake may bear against abutments, which are indicate schematically by the references 18 and 19 in fig. 2, in orde to limit the air flow through the slits between the wing an the wing tip 4, as the abutments function as labyrinth seals. Fig. 3 shows the section through the wing and the brake whic in fig. 1 is indicated by the line III-III. This figure concerns the embodiment in which the brake is turned in the direction a in fig. 2. Fig. 3 shows a possible embodiment o the mechanical elements which are active in the maneuvering of the brake. As mentioned in the introduction there are two possibilities of maneuvering the brake. One is that the brake solely has an emergency function, i. e. that it is activate in case the rotor has achieved an excessive speed, the other one is that the brake in addition to the said function also takes part in the normal functioning procedure. In the first mentioned case the brake is to be activated at excessive speeds and as this implies an increased centrifugal force, it is sufficient to provide the brake with a trip which is activated by the increased centrifugal force. This may in a simple way be achieved by known means, and a possible place for the trip is indicated at 20. It is appropriate if the brake remains active, as the malfunction, which has caused the excess speed, may be such that it has to be corrected manually. The brake therefore also has to be put back into th operational position manually. To limit the impact forces, which result from a sudden turning of the brake, and also t admit time for the activation of the brakes of the other wing before the rate of rotation falls, it is required that th turning of the brake takes place in a damped way. For thi reason a hydraulic, pneumatic or mechanical damper may b provided. The damper is indicated by 21 and is connected t the brake at the bearing 22 in the element 23 which is mounte on the brake and fixed in relation to the pivot line 15. Th other end of the damper is connected to the fixed part of th wing by a bearing 24. When the brake is activated it takes u the position which is shown in fig. 3b. The turning movement of the brake is achieved partly by th moment of the aerodynamic forces around the pivot line, partl by the centrifugal force in case sufficient weights are buil in, and partly by built-in moment producers. The torque of th aerodynamic forces will depend on the angle of incidence o the air flow in relation to the profiles of the wing in th current operational situation in which the brake is to b actuated. A situation which may appear at all wind speeds. I the wind speed is low, the angle of incidence will be small as the direction of the relative air speed will be dominate by the tangential speed of the rotation. If the wind speed i great, the angle of incidence correspondingly will be great It is therefore not possible to predict how great the momen of the aerodynamic forces will be and it is therefore require to actively influence the turning of the brake by built-i moment producers. The turning movement may be produced actively in several way of which three wil be explained: a) A compression spring may be built into the damper 21. b) A torsion spring (not shown) may be mounted at a arbitrary point along the pivot line 15. c) Weights, such as metal blocks which are indicat schematically in fig. 3a by the reference 25, may be bui in, which weights are acted, upon by the centrifugal for and because of the oblique angle of the pivot line wi contribute to the turning of the brake. In case it is desired to use the aerodynamic brake also as ordinary operational brake, possibly in connection with t mechanical brake of the windmill, the system may be arrange accordingly by the use of a hydraulic, pneumatic electr mechanical or other system to act upon the trip for releas controlled by the control system of the windmill and to tu back the brake to the normal operational position in the sa way, controlled by the control system of the windmill.

Claims: C L A I M S 1. Wind rotor for a windmill which wind rotor has wings wit an aerodynamic brake which may be activated either at th transgression of a predetermined fixed rotational speed of th windrotor or to regulate the said speed, which brake consist of a turnable part of the said wings, and which turnable par preferably is the radially outermost part of the wing c h a r a c t e r i s e d in that the turnable part comprise a first and a second section- of which the first sectio consists of the radially outermost part of the wing in it full width, that the second section extends radially inward from the first section and consists of a part of the width o the wing, and that the turnable part is connected to the win by means of hinges between the second section and the wing. 2. Wind rotor according to claim 1, c h a r a c t e r i s e in that the second section preferably is inserted as th trailing part of the wing as seen in the direction o rotation. 3. Wind rotor according to claim 2, c h a r a c t e r i s e in that the dividing line between the second section and th wing extends substantially in the longitudinal direction o the wing, that the axis of the hinge means extends in th plane of the wing, and that the radially innermost part of th hinge means preferably is placed at a greater distance fro the leading edge of the wing than the radially outermost part

Inventors: PETERSEN HELGE, PETERSEN, HELGE
Applicants: PETERSEN HELGE, PETERSEN, HELGE
Application year: 1989
Main classification: F03D1
IPC codes: F03D7