A WIND ROTOR MEMBER

Abstract: A wind rotor member (10) comprises a central hub portion (14, 15) by which it may be mounted for rotary movement around a substantially horizontal axis, and a number of rotor blades (16) which are secured to said hub portion (14, 15) in stationary positions relatively thereto and which extend in generally radial outward directions from the hub portion. In order to enable operation within a very wide range of wind speeds, each rotor blade has a larger blade angle (vC) at its outer end than at its inner end (vA).

Description: A wind rotor member The present invention relates to a wind rotor member, i.e. a rotor member intended to be driven by the wind. More particularly, the invention relates to a wind rotor member of the kind comprising a central hub portion by which the rotor member may be mounted for rotary move¬ ment around a substantially horizontal axis, and a number of rotor blades which are secured to said hub portion in fixed positions relatively thereto and extend in generally radial outward directions from the hub portion. Such rotor members are utilized primarily as driving means for electric wind power plants. However, they may be utilized also as driving means for other wind power operated arrangements. A serious drawback of prior art wind power plants is that it is possible to obtain electrical power from them only when the magnitude of the wind speed at the location of the plant falls within a comparatively restricted range. This is due to the fact that the wind speed has to exceed a comparatively high lower limit value to facilitate any operation at all of known wind power plants, while at wind speeds exceeding a comparatively low upper limit value, it has been necessary to take the plants out of operation to prevent them from becoming damaged as a consequence of excessive high mechanical strain. In order to make it possible to take the plants out of operation at impermissible high wind speeds, the plants have usually been driven by wind rotor members having moveable blades, i.e. blades which may be turned relatively to the hub portion around their longitudinal axes while the plants are in operation. The invention has for its purpose to provide an improved wind rotor member of the kind initially specified, which may operate within a substantially increased range of variation of the existing wind speed while simultaneously offering a considerably improved safety of operation as compared to prior art wind rotor members. In accordance with the invention, for said purpose, there is proposed a wind rotor member of- said kind which is characterized primarily in that each rotor blade has a larger blade angle at its outer end than at its inner end. In this context, the term blade angle is intended to be understood as the angle which a rotor blade, at any location along its length, forms with its rotary plane, i.e. with a plane perpendicular to the rotary axis of the rotor member. The arrangement of the rotor blades suggested according to the invention results in that the torque applied on the rotor member by the wind at low wind speeds will become considerably higher than at rotor members hitherto known, where the blades have been constructed in the same manner as in the case of air planepropellers, i.e. with a larger blade angle at their inner ends than at their outer ends. As a consequence, the rotor member according to the invention may start operating at substantially lower wind speeds than has previously been possible. The proposed shape of the rotor blades, i.e. with blade angle increasing in a direction from their inner ends towards their outer ends, additionally results in that, during operation, a conical vortex will be gene¬ rated in the air in front of the rotor member. Said vortex causes the incoming air flow to become deflected towards the radially outer portions of the rotor blades while forming a negative pressure zone, or vacuum zone, at the radially inner portion of the rotor member. The diameter of the conical vortex will increase with in¬ creasing wind speed and increasing rotary speed of the rotor member. Hereby, the rotor member will become self- regulating at high wind speeds, i.e. it will automatically adjust its rotary speed so as to bring the incoming air flow to exert only a restricted driving action on the rotor member. Accordingly, the rotor member according to the invention may be permitted to operate at unlimitedly high wind speeds. Preferably, the blade angle of each rotor blade may increase gradually from the inner end of the rotor blade towards the outer end thereof. The blade angle at the inner end of each rotor blade may suitably amount to about 0° - about 10°, while the blade angle at the outer end of each rotor blade may amount to about 20 - about 50°, preferably about 30° - about 45°. In order to promote the above vortex formation and the self-regulating function of the rotor member caused thereby, the hub portion of the rotor member may preferably have a generally conical front section. The length of each rotor blade may suitably be of the same order of magnitude as the diameter of the hub portion at the widest section thereof. Preferably, the length of each rotor blade may amount to about 0,5 - about 3 times said diameter. The above-mentioned generally conical front section of the hub portion should preferably have a considerable axial length,- suitably of the same order of magnitude as the radius or diameter, respectively, of the widest section of the hub portion. Below the invention will be described in further detail, reference being had to the accompanying diagram¬ matic drawings, in which:- Figure 1 shows a perspective view of an electric wind power turbine provided with a driving means consist¬ ing of a wind rotor member according to an embodiment of the invention, selected by way of example; Figures 2A, 2B and 2C show three different enlarged sections through a rotor blade of said rotor member; Figure 3 shows a part-sectional side elevation view of an electric wind power turbine of slightly modi¬ fied construction; Figures 4A, 4B and 4C show three different enlarged sections, similar to Figures 2A, 2B and 2C, respectively, " through a rotor blade of the wind rotor member of the turbine of Figure 3; Figure 5 shows a partial sectional view, illu¬ strating a preferred type of connection between a rotor blade and a central hub portion of the rotor member. The wind power turbine shown in Figure 1 comprises a wind rotor member, generally designated 10. This rotor member serves as a driving means for an electric power generator (not shown) which is mounted within a cylind- rical housing 11. Said housing 11 also encloses bearing means (not shown in Figure 1) by which rotor member 10 is supported for rotation around a substantially hori¬ zontal axis, as well as gear and transmission means (not shown) for providing a suitable driving connection bet- ween rotor member 10 and the generator. At the end thereof remote from rotor member 10, housing 11 is provided with a wind actuated steering vane 12 which is rigidly connected to said housing by means of a rod 13. Reference numeral 17 designates an upper portion of a mast provided with means 18 for supporting housing 11 freely rotatable around a substantially vertical axis. The provision of steering vane 12 and rotatable supporting means 18 results in that housing 11 will continously assume a position causing rotor member 10 to be turned against the wind. Rotor member 10 comprises a central hub portion, consisting of a generally conical front section 14 and a generally cylindrical rear section 15 from which a number of rotor blades 16 extend in equally spaced generally radial directions. In the case illustrated in Figure 1, the rotor member is provided with three blades. However, any other number of rotor blades may be selected, although said number should preferably be three or a multiple of three, e.g. six. Rotor blades 16 are secured to rear hub section 15 in stationary positions relatively thereto. However, the connection between the rotor blades and said hub sec¬ tion may advantageously be such as to make it possible, when securing said blades to the hub, to set their angular positions appropriately to match local circumstances at the location of each installation. One suitable type of such connection has been shown in Figure 5. A characteristic feature of the rotor blades has been illustrated in Figures 2A, 2B and 2C. These figures show sections through a rotor blade taken along dash- dotted lines A, B and C, respectively, in Figure 1. As may be seen from said sectional views, the blade angle of rotor blades 16 increases gradually from the inner end of each blade towards its outer end. Said angle has been illustrated as an angle v., v„ and v c , respectively, bet- ween the rotary plane R of blades 16 extending perpendicu¬ larly to the horizontal rotary axis of rotor member 10, and the chord of the blade section in question. As can be seen from Figures 2A, 2B and 2C, angle v. at section A near the inner end of blade 16 is only about 2°, while angle v D Is at section B near the middle of blade 16 is sub- stantially wider, about 20 , and angle v_ at section C near the outer end of blade 16 is still wider, about 40 . As a consequence of the illustrated shape and arrangement of rotor blades 16, during operation of the device, a conical vortex will be formed in the air in front of rotor member 10. This vortex formation will be enhanced by the generally conical front hub section 14, the axial length of which is of the same order as the widest diameter of the hub portion which, in its turn, is of about the same order as the length of rotor blades 16. As a result of said vortex formation, the incoming air will become deflected in a radial outward direction towards outer peripheral portions of the annular surface swept by rotor blades 16 during rotation of rotor member 10. The magnitude of this deflection of the incoming air and the diameter of the vacuum zone simultaneously caused will depend on the existing wind speed and the rotary speed of rotary member 10. At high wind speeds, the rotor member will become self-regulating, thereby constantly maintaining its rotary speed below the permitted maximum speed, even when wind speeds of extremely high magnitude occur. The modified construction shown in Figures 3, 4A, 4B and 4C differs from the arrangement shown in Figures 1, 2A, 2B and 2C only in minor respects. In Figure 3, front hub section 14 is shorter than in Figure 1 and the number of rotor blades is only two instead of three. Additionally, housing 11 has been shown as having a diame¬ ter substantially equal to the maximum diameter of the hub portion of rotor member 10. Moreover, the left end of housing 11 has been shown in section to partially uncover a central horizontal shaft 19 which is rigidly connected to rear hub section 15 and rotatably mounted in two annu¬ lar supporting plates 20 by means of bearings 21. A chamber 22 defined between plates 20 within housing 11 has been illustrated as filled with lubricating oil for bearings 21. The sectional views shown in Figures 4B and 4C are substantially equal to the corresponding views shown in Figures 2B and 2C. However, Figure 4A differs from Figure 2A in that the blade angle A is about 10° instead of 2° and in that blade 16 is thinner than in Figure 2A. The connection between a rotor blade 16 and hub section 15 shown in Figure 5 serves to make it possible, when securing the blades of a rotor member to the hub portion thereof, to set the blade angle appropriately for said rotor member. The illustrated connection comprises a mounting base 23, rigidly secured to rear hub section 15, a split upper clamping ring 24, and clamping bolts 25. At its inner end, blade 16 is provided with a head 26 having chamfered end surfaces adapted to be clamped bet¬ ween correspondingly chamfered surfaces of ring 24 and base 23 to enable blade 16 to be firmly locked in suitably adjusted position. A wind power turbine generally similar to the tur- bine shown in Figure 1 and having anoverall rotor diameter of about 400 centimetres and a maximum hub diameter of about 100 centimetres has been tested continuously during a four months period. During this period, the wind speed has varied from 0 to about 30 metres per second. The rotor has been found to start rotating at wind speeds of about 2-3 metres per second and the maximum speed has been esti¬ mated to about 1500 rpm. The invention is not restricted to the embodiments above described and shown in the drawings. Instead, many other embodiments will be feasible within the scope of the i ventio .

Claims: Claims 1. A wind rotor member comprising a central hub por¬ tion by which the rotor member may be mounted for rotary movement around a substantially horizontal axis, and a number of rotor blades which are secured to said hub portion in fixed positions relatively thereto and extend in generally radial outward directions from the hub por¬ tion, characterized in that each rotor blade (16) has a larger blade angle (v) at its outer end than at its inner end. 2. A wind rotor member according to claim 1, characterized in that the blade angle (v) of each rotor blade (16) increases gradually from the inner end of the rotor blade towards the outer end thereof. 3. A wind rotor member according to claim 1 or 2, characterized in that the blade angle (v A ) at the inner end of each rotor blade (16) amounts to about 0° - about 10°, while the blade angle (v_) at the outer end of each rotor blade (16) amounts to about 20° - about 50°, preferably about 30° - about 45°. 4. A wind rotor member according to any of claims 1-3, characterized in that the hub portion (14, 15) has a generally conical front section (14) . 5. A wind rotor member according to any of the prece¬ ding claims, characterized in that the length of each rotor blade (16) is of the same order of magnitude as the diameter of the hub portion (14, 15) at the widest section (15) thereof. 6. A wind rotor member according to claim 5, characterized in that the length of each rotor blade (16) amounts to about 0,5 - about 3 times said diameter. 7. A wind rotor member according to claim 4, characterized in that the generally conical front section (14) of the hub portion (14, 15) has a considerable axial length. 8. A wind rotor member according to claim 7, characterized in that said axial length is of the same order of magnitude as the radius or diameter, respectively, of the widest section (15) of the hub portion (14, 15)

Inventors: OERTENHEIM BJOERN AOKE, OERTENHEIM, BJOERN, AOKE
Applicants: STUBINEN UTVECKLINGS AB, STUBINEN UTVECKLING AB
Application year: 1985
Main classification: F03D1
IPC codes: F03D1