This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2012 021 620.3, filed on Nov. 6, 2012 in Germany, the disclosure of which is incorporated herein by reference in its entirety.
The present disclosure relates to a wave energy converter having at least one rotor which is configured to convert a wave motion into a rotational motion of the at least one rotor, and to a method for converting wave energy in which such a wave energy converter is used.
A series of different devices are known for converting energy from movements of water in bodies of water into usable energy. An overview of this is given, for example, by G. Boyle, “Renewable Energy”, 2nd edition, Oxford University Press, Oxford 2004. Such devices are also referred to as “wave energy converters”.
In wave energy converters, the energy can be extracted from the respective water motion in different ways. For example, buoys which float on the surface of the water and whose upward and downward movements drive a linear generator are known. A planar resistance element, which is tilted to and from by the motion of the water, can also be mounted at the bottom of the body of water. The kinetic energy is, for example, converted into electrical energy in a generator.
Within the scope of the present disclosure, in particular wave energy converters are of interest which are arranged with their moving parts under the surface of the water and which utilize a wave orbital motion which is present there.
The wave orbital motion can be converted into a rotational motion by means of rotors. For this purpose, rotors with coupling bodies, for example hydrodynamic lift profiles, can be used. Such a system is disclosed in US 2010/0150716 A1.
As in all hydrodynamic lift profiles with a finite length, eddying which is induced by the pressure differences between the pressure side and the suction side also occur here at the ends of the lift profiles, said eddying also being known as vortex trails. These can considerably limit the efficiency.
From aircraft construction, it is known to use elliptical lift profiles which reduce the formation of vortex trails to a certain extent. Alternatively, closed profile systems can also be used in which the ends of the lift profiles are curved and correspondingly joined together (referred to as looped wings). Such profiles are, however, costly to fabricate. What are referred to as winglets at the ends of the lift profiles can be used as the smallest expansion level, but said winglets have to be adapted to the respective prevailing flow conditions. In avionics, winglets are therefore always adapted to the profile of the journey (short distance/long distance).
In wave energy converters, in particular in those with rotating lift profiles, there continues to be a need for corresponding improvements.
According to the disclosure, a wave energy converter having at least one rotor which is configured to convert a wave motion into a rotational motion of the at least one rotor, and a method for converting wave energy in which such a wave energy converter is used, are proposed. Advantageous refinements are a subject matter of the following description.
The present disclosure is based on the recognition that in wave energy converters, in particular in those with rotating lift profiles, vortex trails do not necessarily have to be avoided but instead can even be used in a way which is beneficial to operation. As a result, it is possible to increase the efficiency.
In a wave energy converter which is proposed according to the disclosure and which has at least one rotor which is configured to convert a wave motion into a rotational motion of the at least one rotor, at least two elongate lift profiles are connected by in each case one end to a rotor base and are each connected in pairs to one another via vortex trail-guiding devices in the region of their free ends (or at their free ends) which are not connected to the rotor base.
Two lift profiles are advantageously arranged offset through 180° on the rotor of a wave energy converter according to the disclosure. In this context, the orientation of the two lift profiles is preferably such that in one lift profile the suction side is oriented radially toward the inside and in the other lift profile it is oriented radially toward the outside. In the two lift profiles, the lift is therefore basically oriented in one direction. The suction side, and therefore the direction of the lift, occur as a result of the shape of the lift profiles and the incoming flow onto the body of water, as explained below.
As a result, the respective rotation of the vortex trails of the lift profiles has an opposing orientation, as illustrated in detail with reference to
The arrangement corresponds here, when transferred to a linear motion, essentially to a concatenation of an infinite number of lift profiles, of which the pressure side and the suction side are each alternately oriented upward. A rotor which is embodied according to the disclosure therefore advantageously has an even number of lift profiles which each have suction sides which alternate with one another.
The vortex trail-guiding devices provided according to the disclosure between the free ends of the lift profiles therefore ensure here that the vortex trails are carried out of the rotor path of the blades through flow effects and/or motions of the rotor. They therefore prevent said positive canceling-out effect from being reduced or eliminated. Such “carrying out” also explicitly means here deflection toward the center of the rotor, as conventionally also occurs with wave energy converters which are not influenced by the flow.
Vortex trail-guiding devices which connect the lift profiles of a corresponding wave energy converter in each case in pairs at the devices' free ends are advantageously embodied as largely semicircular guiding elements. These run, in particular, along the aforementioned circular path which the lift profiles describe during their rotation and on which the vortex trails are also intended to circulate. They connect the respectively rear free corner of a lift profile to the corresponding front free corner of the following lift profile. The terms “at the front” and “at the rear” relate to the direction of rotation. The vortex trail-guiding devices are advantageously embodied in a flexible way in order to permit adjustment of the angles of attack of the lift profiles.
The vortex trail-guiding devices can be embodied here, for example, in a solid fashion (that is to say in the form of rod-shaped elements which are curved in accordance with the circular path). In this case they can have, for example, a round cross section. In this case, the vortices of the vortex trails advantageously run concentrically around the vortex trail-guiding devices, with the result that the vortex trails remain on the annular cross section. In another embodiment, tubular elements can also be used, for example, said tubular elements likewise being curved in accordance with the circular path and being interrupted by the lift profiles. The vortices of the vortex trails are guided here into the tubular vortex trail-guiding device, that is to say they run here in the vortex trail-guiding devices, instead of around said vortex trail-guiding devices as before. The diameter of a corresponding tubular vortex trail-guiding device should be advantageously selected to be sufficiently large here that the resistance of the flow through the tube does not become too large. Diameters of, for example, approximately 0.5 m have proven favorable here. A tubular vortex trail-guiding device can also be provided with a favorable cross-sectional geometry which facilitates initiation of the vortex trails. The respectively used material advantageously has a smooth surface or a defined degree of roughness in order to minimize friction losses. In both specified embodiments, the cross-sectional shape is advantageously constant over the length of the element.
Even in cases in which lateral flows, lateral rotation of a wave energy converter and/or other effects occur, the vortex trail-guiding devices therefore ensure that the vortex trails run along these guiding elements.
With respect to features and advantages of the method which is also proposed according to the disclosure for converting wave energy, reference is made to the explanations above and to those below. The method according to the disclosure is particularly efficient by virtue of the use of the vortex trail-guiding device.
The disclosure and preferred refinements are explained further below with reference to the appended drawings.
Identical or identically acting elements have identical reference symbols in the figures. The explanations will not be repeated.
As a result of the incoming flow, which occurs here relative to the lift profile 10 in an incoming flow direction 11, different rates occur above and below the lift profile 10, with the result that lift (directed upward here and denoted by a force vector F) occurs. Said lift “pulls” on what is referred to as a suction side (here the upper side) of the lift profile 10. The opposite side (here the underside) is also referred to as the pressure side of the lift profile 10.
The lift profile 10 has a finite length, with the result that the eddying already mentioned occurs at its ends. The ends of the lift profile 10 continue here parallel to the incoming flow direction in virtual projection lines (represented by dashes). Owing to the different flow rates above and below the lift profile, vortex trails are formed, illustrated here schematically in the form of vortices 12. The latter are provided only partially with reference symbols.
The motion of the medium brings about here in each case a rotation of the medium in a direction from below to above the lift profile 10, that is to say from the pressure side to the suction side of the lift profile 10, downstream thereof (viewed from the direction of the incoming flow). The vortex trails therefore represent rotating rollers which extend rearward from the ends of the lift profile 10. The latter are illustrated in idealized form in
Owing to the wave motion, wave orbital motions in the form of orbital paths 23, which are provided only partially with reference symbols, occur under the surface of the body of water. Directly under this surface of the body of water, these orbital paths 23 each have radii r which correspond to the amplitude of the wave 20. The radii reduce as the distance from the surface of the body of water increases. In deep water the orbital paths 23 are circular, and in shallow water they are increasingly elliptical.
The local motion of the water is illustrated in
The lift profiles 3 are arranged at an angle of 180° with respect to one another in relation to the axis of the rotor 2, 3, 4. The lift profiles 3 are preferably connected to the lever arms 4 in the vicinity of their pressure point in order to reduce rotational moments on the lift profiles 3 during operation, and therefore to reduce the requirements made of the securing means and/or the adjustment devices.
The radial distance between a suspension point of a lift profile 3 and the rotor axis is 1 m to 50 m, preferably 2 m to 40 m and particularly preferably 6 m to 30 m. The chord length of the lift profiles 3 is, for example, 1 m to 8 m. The maximum extent of length can be, for example, 6 m or more.
The wave energy converter 1 has an integrated generator. In this context, the rotor base 2 is rotatably mounted in a generator housing 7. The rotor base 2 forms the rotor of the generator, and the generator housing 7 forms the stator of said generator. The necessary electrical devices such as coils and lines are not illustrated. In this way, a rotational motion of the rotor base 2 which is induced by the wave orbital motion can be converted with the lift profiles 3 mounted thereon via the lever arms 4 directly into electrical energy. However, the disclosure can be used not only in such wave energy converters with an integrated generator but is also suitable for systems in which the rotational motion is applied to a generator, for example via a transmission.
Even though
The rotor arms 4 also do not necessarily have to be embodied in the way illustrated. For example, the lift profiles 3 can also be connected to the rotor base 2 via a disk-shaped element. For the disclosure it is essential that a wave energy converter 1 has elongate lift profiles 3 which are connected by one end to a rotor base 2 and by their respective other end project freely into the body of water. As is explained below with reference to
In
The rotor 2, 3, 4 is arranged below the surface of the water of an agitated body of water, for example an ocean. In this context, for example deep water conditions are assumed to be present in which the orbital paths 23 of the water molecules run largely in a circular shape. A rotational axis of the rotor (perpendicular to the plane of the paper) is assumed to be oriented largely horizontally and largely perpendicularly with respect to the direction 21 of propagation of the waves 20 of the agitated body of water.
By means of the adjustment devices 5 (denoted only on the right-hand lift profile), an angle of attack or pitch angle α of the two lift profiles 3 can be set with respect to a tangent to the rotor which runs respectively perpendicularly upward or downward (shown only on the left-hand lift profile). The angles of attack a of the two lift profiles are preferably oriented opposite one another and have, for example, values of −20° to +20°. However, in particular when the wave energy converter 1 is started, it is also possible to provide larger angles of attack. For example, the angles of attack a can be adjusted independently of one another. The adjustment devices 5 may be, for example, electromotive adjustment devices, preferably with stepping motors, and/or can be hydraulic and/or pneumatic components.
The two adjustment devices 5 can, as mentioned, be assigned position sensors 6 for determining the current angles of attack a. A further sensor system (not illustrated) can determine the rotational angle of the rotor base 2 with respect to the housing 7. However, the disclosure is also suitable for systems without adjustment devices 5 for adjusting the angles of attack a or pitch angles and/or corresponding sensor systems.
The orbital flow flows against the wave energy converter 1 with an incoming flow speed . The incoming flow here is the orbital flow of sea waves (see
In the case illustrated, the rotation of the orbital flow is oriented in the counter-clockwise direction, and the associated wave therefore propagates from right to left. In the case of so-called monochromatic waves, the incoming flow direction changes here with the angular speed Ω=2πf=const., wherein f is the frequency of the monochromatic wave. In multichromatic waves, Ω is subject to a change over time, Ω=f(t), since the frequency f is a function of the time, f=f(t). There is provision that the rotor 2, 3, 4 rotates in synchronism with the orbital flow of the wave motion with an angular speed co, wherein the term synchronicity is to be understood as chronological average.
As a result of the effect of the flow with the incoming flow speed on the lift profiles 3, in each case lift is generated (specified in each case by the force vector F) and as a result a first torque acting on the rotor 2, 3, 4 is generated. In order to set the synchronicity, a preferably variable second torque in the form of a resistance, that is to say a braking torque, or an acceleration torque, can be applied to the rotor 2, 3, 4. Means for generating the second torque can be arranged between the rotor base 2 and the generator housing 7.
A phase angle Δ whose value can be influenced by a suitable setting of the first and/or second torque is present between the rotor orientation, which is illustrated by a lower dashed line and runs through the rotor axis and the center of the two adjustment devices 5, and the direction of the orbital flow, which is illustrated by an upper dashed line and runs through one of the speed arrows . In this context, a phase angle from −45° to 45°, preferably from −25° to 25° and particularly preferably from −15° to 15° for generating the first torque appears particularly advantageous since here the orbital flow and the incoming flow are oriented largely perpendicularly with respect to one another owing to the intrinsic rotation, which brings about maximization of the rotor torque.
The illustration of the lift profiles 3 in
As a result of rotation of the rotor 2, 3, 4, vortex trails also form here at the ends of the lift profiles 3 and are illustrated again in the form of vortices 12, in a highly schematic fashion. The vortices 12 denote the vortices which form at the free ends of the lift profiles 3 which are not mounted on the lever arms 4.
Owing to the rotational motion to, the suction side of the lift profile 3 on the left in
In reality, corresponding vortex trails do not run in the plane of the paper around the center point of the rotor 2, 3, 4 but converge, for example, with respect to the axis of the rotor and/or run out of the plane of the paper. This is where the present disclosure comes in.
In this context, by means of suitable vortex trail-guiding devices between the lift profiles 3 it is ensured that the vortex trails of the respective one lift profile are deflected onto the respective following lift profile (in the direction of rotation).
Such a wave energy converter is shown in
Even though flat structures are shown as vortex trail-guiding devices 8 in
Number | Date | Country | Kind |
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10 2012 021 620.3 | Nov 2012 | DE | national |