turbine

Abstract

A turbine (1) comprising : - a stationary support (3), such as a nacelle; - a stationary ring (5) supported by the stationary support; a turbine rotor (7) comprising a rotary ring (6); - rotor blades (8) extending outward from the rotary ring ( 6 ). The rotary ring and the stationary ring have outer surfaces jointly defining an annular aerofoil (19). The inner circumferential surface aerofoil defines a pressure surface (22) and forms a funnel, reducing the wake of the turbine.

Description

[0001] 41207-Zo / ml

[0002] TURBINE

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to the field of turbines such as wind turbines. The disclosure particularly relates to direct drive turbines, i. e., turbines without a gear transmission between the turbine rotor and the rotor of the generator.

[0005] BACKGROUND WO 2008 / 127114 Al discloses a turbine rotor for a wind or hydropower plant comprising a toroid ring carrying a number of rotor blades. The toroid ring has a hollow and closed profile. The use of such a toroid ring optimizes distribution of bending loads on the rotor blades to the central bearing.

[0006] US 11, 035, 344 discloses a wind turbine with a rotary ring encasing a generator rotor, while a complementary stationary ring comprises the generator stator, so as to provide a direct drive system. In this prior art turbine, wind flowing through the inside of the ring does not contribute to power generation.

[0007] A wind turbine is driven by wind impacting the rotor blades, which in turn exert torque on the rotor of a generator. At the leeward side of the wind turbine, wind passing the blades forms a wake, a zone of turbulence. A wind turbine located in the wake of an upstream wind turbine, will be exposed to a turbulent wind flow containing less energy and therefore substantially reducing the conversion efficiency. Wind turbines must therefore be placed at a sufficient distance from the wake of an upstream turbine. This limits the maximum number of turbines that can be placed on a given surface.It is an object of the invention to provide a turbine with improved efficiency to convert kinetic energy of a flow, such as a wind flow, into electrical energy. It is a further object to provide a turbine that can be placed closer to other turbines.

[0008] The object of the invention is achieved with a turbine comprising:

[0009] - a stationary support, such as a nacelle;

[0010] - a stationary ring supported by the stationary support;

[0011] - a turbine rotor comprising a rotary ring;

[0012] - rotor blades extending outward from the rotary ring; wherein the rotary ring and the stationary ring have outer surfaces jointly defining an annular aerofoil.

[0013] The annular aerofoil redirects oncoming wind to the swept area of the rotor blades. As a result, the wind flow across the swept area is substantially increased and intensified, so more power is generated.

[0014] Similarly, starting from a desired rated output, a turbine rotor can be used with a swept area that is less than would be needed with prior art turbines for generating the same rated output. The swept area depends on the length of the rotor blades, so a smaller swept area requires less material costs, and less costs for manufacturing, transport and construction of the turbine.

[0015] The inner surface of the annular aerofoil of the rotary and stationary rings defines a funnel. While part of the oncoming wind is diverted to the swept area, another part is diverted to flow through the funnel and along the nacelle.

[0016] Downstream of the funnel, the wind that has passed through the swept area rejoins the wind that has passed through the funnel, creating a mixing front. It has been found that this considerably shortens the wake of the turbine compared to a similar turbine without the funnel. Due to the shorter wakes,the turbines can be placed closer together and more turbines can be placed on a given area so as to increase total power output of the area.

[0017] An aerofoil, or airfoil, is a streamlined body generating an aerodynamic force with more lift than drag when the streamlined body deflects an oncoming flow. In this respect, lift is the component of the aerodynamic force perpendicular to the main direction of the oncoming flow at a distance upstream of the turbine (the so-called freestream), while drag is the component of the aerodynamic force parallel to the main direction of the oncoming flow at a distance upstream of the turbine.

[0018] An aerofoil has a leading edge and a trailing edge. The leading edge is the point that has maximum curvature (minimum radius). The trailing edge is the point most remote from the leading edge. An aerofoil has two opposite surfaces extending between the leading edge and the trailing edge: the suction surface and the pressure surface. Optionally, the annular aerofoil of the present disclosure has an outer circumferential surface defining the suction surface of the aerofoil, and an inner circumferential surface defining the pressure surface of the aerofoil. The annular pressure surface of the aerofoil defines a funnel.

[0019] Turbines typically have an upstream or windward side and a downstream or leeward side. If the turbine is an upwind turbine, the windward side is the side of the rotor, i. e., the side orientated against the wind during operation of the turbine. With a downwind turbine, the windward side is the side facing the stationary support, e. g., the nacelle and the tower. The windward side is typically yawed towards the main flow direction of the oncoming wind.

[0020] A prior art wind turbine with an annular aerofoil is disclosed in EP 3 546 741 Al. This so-called output reinforcement device is built of three segments mounted betweenthe rotor blades which extend through the aerofoil. This complicates blade pitching. EP 2 578 875 Al discloses a wind turbine with a shroud with an arcuate aerofoil section. The shroud is downstream of the rotor.

[0021] In a specific embodiment of the turbine of the present disclosure, the aerofoil has a leading edge at the windward side or upstream side of the turbine rotor and a trailing edge at the leeward side or downstream side of the turbine rotor.

[0022] In an exemplary embodiment, the rotary ring provides the leading edge of the aerofoil while the stationary ring provides the trailing edge of the aerofoil.

[0023] An aerofoil is also characterized by its chord line, which is a straight line connecting the leading and trailing edges, and a camber line, or mean line, through points midway between the suction and pressure surfaces.

[0024] The thickness of an aerofoil is the maximum distance between the suction surface and the pressure surface in a direction perpendicular to the chord line.

[0025] The angle of attack is the angle between the main wind direction of the oncoming wind and the chord line. The aerofoil may for example have an angle of attack a > 0, for example an angle of attack in the range of 0 < a < 15 degrees, such that the diameter of the aerofoil at the leading edge is larger than the diameter at the trailing edge.

[0026] Optionally, the aerofoil is cambered, i. e. having a curved camber line. The annular aerofoil may for example have a positive camber, i. e., the suction surface or outer surface being more convex than the pressure surface or inner surface.

[0027] The aerofoil may for example have a thickness to chord line ratio t / c > 0, 25, in particular a t / c of about 0, 3, which combines a large radial width relative to an axial length and an efficient aerodynamic behaviour. The aerofoil may in particular have a DU97-W-300 aerofoil profile, in particular a DU97-W-300 flatback profile.The annular aerofoil may have a radial cross section which is substantially constant over the full circumference of the aerofoil, except for the mounts for the rotor blades and spokes.

[0028] The turbine comprises a stationary support. In a specific embodiment, the turbine is a wind turbine, wherein the stationary support comprises a nacelle supporting the stationary ring, the nacelle being supported by a tower such as a concrete or steel tube tower or lattice tower. The stationary support and the stationary ring are stationary in the sense that they do not rotate with the rotor during operation. Of course, they may however be movable relative to the turbine foundation, e. g., during yawing.

[0029] In a specific embodiment, the turbine rotor comprises a hub, concentrically arranged within the rotary and stationary rings. In a specific embodiment, the hub can be rotatably supported by a central bearing in the stationary central support or nacelle. Alternatively, the aerofoil itself can be configured as a hub including a bearing, such as a magnetic bearing.

[0030] The turbine rotor may comprise one or more rotor spokes between the hub and the rotary ring, e. g., connecting to the pressure surface at a position between the leading edge and the stationary ring. These rotor spokes may extend substantially radial relative to the rotation axis of the turbine rotor. The rotor spokes support the annular aerofoil, e. g., stabilizing width of the generator air gap.

[0031] Optionally, one or more of the rotor spokes can be tubular channels, e. g., aligned with an associated one of the rotor blades. This way, the tubular rotor spokes can be used as a passage, e. g., for parts of a pitch drive.

[0032] In a specific embodiment, the rotor spokes can be streamlined for aerodynamic optimization of the flow through the funnel, e. g., having a cross section tapering down in wind flow direction.To streamline the hub, it can for example have a conical outer wall or nose cone provided with spoke mounts for the rotor spokes. In a specific embodiment, the nose cone and optionally a windward part of the nacelle may extend through the funnel. This results in a more compact design and allows further aerodynamic optimization.

[0033] The turbine may be provided with a pitch control, including a pitch drive, for adjusting the pitch of the rotor blades, e. g. dependent on wind flow velocity or rotor velocity. In a specific embodiment, to further reduce turbulence the rotor blades do not protrude beyond the trailing edge of the annular aerofoil in any pitch position. Optionally, the rotor blades do also not protrude beyond the leading edge of the annular aerofoil in any pitch position.

[0034] The stationary ring is supported by the stationary support, in particular the nacelle. The stationary ring can for example be supported by stator spokes extending between the stationary support and the stationary ring, e. g., connecting to the pressure surface at a position between the rotary ring and the trailing edge. These stator spokes may extend substantially radial relative to the rotation axis of the turbine rotor.

[0035] Optionally, one or more of the stator spokes can be tubular channels, which can be used as a passage for cables and circuitry for transferring electricity to equipment in the nacelle or the tower, such as a transformer or inverter.

[0036] In a specific embodiment, the stator spokes can be streamlined for aerodynamic optimization of the flow through the funnel, e. g., having a cross section tapering down in wind flow direction.

[0037] In a specific embodiment, the annular aerofoil encases a generator for generating power upon rotation of the turbine rotor. In particular, the rotary ring may comprise a generator rotor and the stationary ring may comprise a generator stator spaced from the generator rotor by an air gap, the generatorstator being aligned with the generator rotor to facilitate power generation upon rotation by the rotary ring. Arranging the generator in the annular aerofoil provides a generator with a large radius and consequently a large velocity of the generator rotor relative to the generator stator. No gear transmission is required so a low maintenance direct drive turbine is obtained.

[0038] In a specific embodiment, the generator rotor may comprise magnets and the generator stator may comprise coils, e. g., on a ring yoke. In a particular embodiment, the generator is an axial generator with the generator rotor and the generator stator as parallel rings of the same diameter, or the generator can be a radial generator with a cylindrical air gap and with the generator rotor and the generator stator being essentially coplanar and concentrical.

[0039] Optionally, the air gap between the generator stator and the generator rotor is part of an air gap extending between a pressure surface of the aerofoil and a suction surface of the aerofoil. This generates an airflow through the gap which cools the generator parts. As the wind force increases, both the heat generated and the airflow generated will increase accordingly.

[0040] All above-mentioned embodiments can be combined at will as far as technically feasible.

[0041] The turbine can for example be a wind turbine. However, the turbine of the present disclosure is also suitable for use as a turbine designed to be driven by a flow of any other fluid than wind, for example water. In that respect, the term "aerofoil" as used in the present disclosure, includes "hydrofoil".

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing a number of embodiments by way of example.

[0044] Fig. 1 shows a turbine as provided herein;Figs. 2-5 show the turbine in different perspective partial views;

[0045] Fig. 6 is a partial perspective cross section of the turbine of Figs. 1-5;

[0046] Fig. 7 is a partial cross section view, partly broken away of the turbine of Figs. 1-6;

[0047] Fig. 8 is a partial perspective cross section, partly broken away of the turbine;

[0048] Fig. 9 is a schematic cross section of the aerofoil. Fig. 10 shows a graph of wind distribution through a rotor of a wind turbine according to the invention.

[0049] DETAILED DESCRIPTION

[0050] Figure 1 show an exemplary embodiment of a wind turbine 1. Other embodiments may relate to different types of turbines, such as a hydropower turbine.

[0051] The wind turbine 1 comprises a tower 2, a nacelle 3 on top of the tower 2, a ring generator 4, shown in more detail in Figure 2. The ring generator 4 comprises a stationary ring 5 supported by the nacelle 3, and a rotary ring 6 forming part of a turbine rotor 7 of the wind turbine 1. The turbine rotor 7 further comprises rotor blades 8 extending radially from the rotary ring 6, a hub 9, centrally within the rotary ring 6, and rotor spokes 10 extending radially from the hub 9 to support the rotary ring 6. The rotor spokes 10 are aligned with the rotor blades 8 and are tubular (see Figure 6) to form a passage 11 for a driving axle 12 of a pitch drive.

[0052] As shown in Figure 6, the hub 9 is mounted to the nacelle 3 by means of a bearing 13 allowing rotation of the turbine rotor 7 relative to the nacelle 3.

[0053] The wind turbine 1 has a windward side W designed to face the oncoming wind, and a leeward side L opposite to the windward side (see for example Figure 4 ). During operation, theturbine rotor 7 is located on the windward side W while the tower 2 and the nacelle 3 are on the leeward side L. A yaw bearing 14 (Figures 4 and 5) between the nacelle 3 and the tower 2 enables yawing of the wind turbine 1 to direct the windward side of the turbine rotor 7 against the main wind flow direction during operation of the wind turbine 1.

[0054] The stationary ring 5 and the rotary ring 6 are coaxially aligned having the same diameter where they join each other, and having mutually interfacing surfaces 15A, 15B shown in more detail in Figure 8. The interfaces 15A, 15B are spaced by a gap 16 to allow free rotation of the rotary ring 6 relative to the stationary ring 5 with minimal friction, e. g., without bearing elements.

[0055] In an alternative embodiment, the assembly of the stationary and rotary rings 5, 6 may be provided with a bearing, such as a magnetic bearing, or ball bearings, e. g., fully or partly replacing the bearing of the hub 9, e. g., without the hub 9.

[0056] As shown in radial cross section in Figure 9, the rotary ring 6 and the stationary ring 5 have outer surfaces which are substantially flush with each other where they meet. This way, the outer surfaces of the rotary ring 6 and the outer surface of the stationary ring 5 jointly define an annular aerofoil 19 with a leading edge 20, a trailing edge 21, a pressure surface 22 and a suction surface 23. The leading edge 20 is the edge with the curvature of the smallest radius. The trailing edge 21 is the edge opposite to the leading edge 20. The suction surface 23 is the outer circumferential surface of the annular aerofoil 19, and the pressure surface 22 is the inner circumferential surface of the aerofoil 19. The annular pressure surface 22 of the aerofoil 19 defines a funnel 24.

[0057] The leading edge 20 is the annular windward tip edge of the rotary ring 6, while the trailing edge 21 is the annular leeward tip edge of the stationary ring 5. The aerofoil 19 has achord line c extending between the leading edge 20 and the trailing edge 21. The chord line c is upwardly tilted by an angle of attack a, i. e., with the diameter of the aerofoil 19 being larger at the leading edge 20 than at the trailing edge 21. The aerofoil 19 has a thickness t, defined as the maximum distance between the suction surface 23 and the pressure surface 22 in a direction perpendicular to the chord line c. The aerofoil 19 also has a curved camber line d, defined as the line through points midway between the suction surface 23 and the pressure surface 22.

[0058] In the shown embodiment, the aerofoil 19 is shaped as a DU97-W-300 flatback profile, having a thickness to chord line ratio t / c of about 0, 3. Other aerofoil profiles can also be used.

[0059] The aerofoil 19 houses a generator 25, shown in more detail in Figure 8 without the aerofoil 19. The generator 25 has a generator rotor 26 incorporated in the rotary ring 6 and a generator stator 27 incorporated in the stationary ring 5. The generator rotor 26 comprises a magnet ring yoke 28 carrying a circumferential array of magnets 29 of alternating polarity. The generator stator 27 comprises a circumferential array of magnet coils 30 carried on a coil ring yoke 31. The magnets 29 of the generator rotor 26 and coils 30 of the generator stator 27 are spaced by the gap 16. In the shown exemplary embodiment, the generator 25 is a radial generator, the generator rotor 26, generator stator 27 and the gap 16 being substantially concentric. The generator rotor 26 encircles the gap 16 and the generator stator 27. In other embodiments, this may be the other way around. In further alternative embodiments the generator can be an axial generator with the generator stator and rotor being of even diameter and coaxially aligned in a parallel arrangement, axially spaced by the gap. Other configurations, e. g., with a conical gap, can also be used.Wind flow along the aerofoil 19 generates a pressure difference between the pressure surface 22 and the suction surface 23 of the aerofoil 19. This induces an airflow (arrows A in Figure 8) through the gap 16 from the pressure surface 22 to the suction surface 23. The air flow A contributes substantially to the cooling of the generator coils 30. As the wind speed increases, the cooling air flow A increases with the increase in heat generated.

[0060] Stator spokes 33 mount the stationary ring 5 to the nacelle 3. The stator spokes 33 are tubular, so as to form passages for cables and further circuitry for transporting generated power from the generator 25 to equipment in the nacelle 3 or in the tower or further downstream. Like the rotor spokes 10, the stator spokes 33 can be streamlined, having a cross section tapering down in wind flow direction.

[0061] It is noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", and the like relate to the embodiments as oriented in the drawings, unless otherwise specified. Further, elements that are at least substantially identical or that perform an at least substantially identical function are denoted by the same numeral, where helpful individualised with alphabetic suffixes.

[0062] Figure 10 shows a graph of the horizontal wind speed distribution in and laterally of the rotor (the continuous line "0 rotor" ) and at various distances downstream from the rotor midplane: at a downstream distance of 0, 25*rotor diameter (dashed line "0, 25 rotor" ), at a downstream distance of 0, 5*rotor diameter (dotted line "0, 5 rotor" ), at a downstream distance of 0, 75*rotor diameter (second dashed line "0, 75 rotor" ), and at a downstream distance equal to the rotor diameter (dash-dotted line "1 rotor" ). The vertical dashed lines represent the outer diameter of the generator ring, while thecentral vertical dash-dotted line represents the center of the rotor. As expected, the wind speed distribution centrally within the rotor (the continuous line) varies considerably: low in the center and near the ring, and higher in between. The dashed 0, 25 rotor line is already substantially flatter and the dash-dotted 1 rotor line the graph is flattened further. This demonstrates a very quick energy recovery of the wind in the wake just downstream the turbine resulting in a much shorter and less turbulent wake. The wake of a wind turbine according to the invention is considerably shorter than with prior art systems.

[0063] The wind velocities shown in the graph were determined with wind tunnel tests using a scale model of a wind turbine according to the invention, having a rotor with a diameter of 0, 45 m, a generator ring with a diameter of 0, 15 m and a DU97-W-300 flatback aerofoil profile with a trailing edge at the leeward side, so the pressure side is at the inner side of the generator ring. The results were confirmed using Ansys Fluent simulation software modelling the same wind turbine configuration having a rotor diameter of 7, 5 m and a ring diameter of 2, 5 m.

[0064] The disclosure is not restricted to the above described embodiment which can be varied in a number of ways within the scope of the claims.

Claims

CLAIMS1. A turbine (1) comprising:- a stationary support (3), such as a nacelle;- a stationary ring (5) supported by the stationary support;- a turbine rotor (7) comprising a rotary ring (6); - rotor blades (8) extending outward from the rotary ring ( 6 );wherein the rotary ring and the stationary ring have outer surfaces jointly defining an aerofoil (19).

2. Turbine according to claim 1, wherein the aerofoil (19) has a leading edge (20) at an upstream or windward side of the turbine rotor and a trailing edge (21) at a downstream or leeward side, or nacelle side, of the turbine rotor (7).

3. Turbine according to claim 2, wherein the rotary ring ( 6) provides the leading edge (20) and the stationary ring (5) provides the trailing edge (21).

4. Turbine according to any preceding claim, wherein the radial cross section of the aerofoil (19) is constant over the full circumference of the aerofoil.

5. Turbine according to any preceding claim, wherein the aerofoil has an angle of attack a > 0 and / or wherein the aerofoil is cambered, e. g., has a positive camber.

6. Turbine according to claim 5, wherein the aerofoil (19) has a thickness to chord line ratio t / c > 0, 25, in particular t / c about 0, 3,and / orwherein the aerofoil has a DU97-W-300 profile, in particular a DU97-W-300 flatback profile.

7. Turbine according to any preceding claim, wherein the aerofoil (19) has an inner circumferential surface defining a pressure surface (22 ) of the aerofoil and forming a funnel (24 ).

8. Turbine according to any one of the preceding claims, wherein the turbine rotor (7 ) comprises a hub (9) concentrically arranged within the rotary ring (6) and stationary ring (5), e. g., rotatably supported by a main bearing (13) in the stationary support (3).

9. Turbine according to claim 8, comprising rotor spokes (10) mounting the rotary ring (6) to the hub (9).

10. Turbine according to claim 9, wherein the rotor spokes (10) are tubular and aligned with respective rotor blades (8), e. g., to form a passage for a pitch drive.

11. Turbine according to claim 9 or 10, wherein the rotor spokes (10) have a cross section tapering down in wind flow direction.

12. Turbine according to any one of the preceding claims, wherein the stationary support (3) comprises stator spokes supporting the stationary ring (5), e. g., tubular stator spokes, e. g., having a cross section tapering down in wind flow direction.

13. Turbine according to any one of the preceding claims, comprising a generator (25) for generating power upon rotation of the turbine rotor;wherein the generator comprises a generator rotor (26) in the rotary ring ( 6), and a generator stator (27) in the stationary ring (5), the generator stator and generator rotor being spaced by an air gap (32 ).

14. Turbine according to claim 13, wherein the air gap (32 ) is part of an air gap (16) extending between a pressure surface of the aerofoil and a suction surface of the aerofoil (19).

15. Turbine according to any one of the proceeding claims, wherein the turbine is a wind turbine, e. g., wherein the stationary support comprises a nacelle supported by a tower.

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