WO2005024226A1

WO2005024226A1 - Vertical axis water current turbine

Info

Publication number: WO2005024226A1
Application number: PCT/IT2003/000538
Authority: WO
Inventors: Domenico Coiro; Elio Matacena; Alberto Moroso; Fabrizio Nicolosi
Original assignee: Ponte Di Archimede S.P.A.
Priority date: 2003-09-09
Filing date: 2003-09-09
Publication date: 2005-03-17
Also published as: AU2003266496A1; CN1839258A; TR200600993T2

Abstract

Improved vertical axis hydraulic turbine comprising a rotor (1) equipped with at least three vanes (2), each of which is pivotally connected on said rotor (1), characterized in that the arrangement is such that during the rotation of the rotor (1) each vane (2) is apt to pivot within a range of from 80° to 90° with respect to the radial direction of the rotor (1). Elevated powers and ease of starting are obtained with the present turbine.

Description

VERTICAL AXIS WATER CURRENT TURBINE Description The present invention refers to a vertical axis hydraulic turbine and, more precisely, to a vertical axis hydraulic turbine of the kind apt to exploit energy from marine or river streams, converting it into electric energy. Vertical axis hydraulic turbines, i.e. with the vanes extending in the longitudinal direction and orthogonally to the stream direction are already known. Such machines are a convenient energy extraction means, when compared to the exploitation of other renewable energy sources. Such a turbine provides that during a revolution of the axis the vanes offer their maximum drag when moving stream-wise, i.e. according to the flow direction, and offer their minimum drag when moving against the stream direction. This is made possible by virtue of a rotor-mounted mechanism blocking the vane in a preset fixed position during the stream-wise revolution fraction and, subsequently, lets it free to pivot '^•flag-like', thereby placing it in a position offering minimum drag in the remainder of the revolution. In order to implement such a kinematics, the rotor is of the movable-vane kind. A first kind of hydraulic turbine thus made with flow-wise pivotable vanes entails a drawback in that such a construction foresees complex leverages and yaw mechanisms, the latter constituting a weakness for the machine and moreover remarkably increasing its manufacturing and managing costs. Moreover, a second kind of hydraulic turbine with flow-wise pivotable vanes is described in IT 1302404 to the same applicant. Such a turbine, though improving the abovementioned drawbacks by eliminating the presence of complex leverages or mechanisms for the rotation of the vanes with respect to the turbine axis, exhibits however a moderate efficiency. This is due to the fact that the vanes of such a turbine are free to pivot about their hinge axis of angles even greater than 90° (with respect to the radial direction of the rotor) so that the torque is mainly generated by drag from the vanes. However, a drawback subsists in that the turbine is incapable of autonomously increasing its angular velocity, since after its starting the same operates within a range of angular velocities in which the output power tends to be negative. In these conditions, the turbine is incapable of accelerating up to the number of revolutions of maximum power without the intervention of an external motor. Hence, object of the present invention is to solve the abovementioned drawbacks by providing an improved movable-vane vertical axis hydraulic turbine, so that the same be capable of autonomously self-starting, further exhibiting an improved efficiency with respect to the hydraulic turbines of the state of the art. Another object of the present invention is to provide an improved movable-vane vertical axis hydraulic turbine that be even simpler to manufacture with respect to known-art turbines, and therefore of lower manufacturing cost. A further object of the present invention is to provide an improved movable-vane vertical axis hydraulic turbine requiring, once installed, a reduced maintenance. Hence, the present invention provides an improved hydraulic turbine according to claim 1. The turbine of the present invention will be better illustrated hereinafter by the detailed description of a preferred embodiment thereof, given by way of example and without limitative purposes, making reference to the annexed drawings, wherein: Figure 1 is a schematic view illustrating the rotor of the turbine according to the present invention; Figure 2 is a partial view illustrating in detail a portion of a rotor vane of the turbine of the present invention; Figure 3 is a schematic view of the turbine of the present invention when mounted on a support structure and immersed in a stream; Figure 4 is a schematic top plan view of the rotor, depicting the angles of attack of the rotor vanes of the turbine of the present invention; Figure 5 is an output power v angular velocity diagram of some known-art rotors and the rotor of the turbine according to the present invention; Figure 6 is an output power v angular velocity diagram of the rotor of the turbine of the present invention as a function of different stream speeds; and Figure 7 is a diagram of the output power v linear velocity of the stream impinging on the rotor of the turbine of the present invention. Several tests were conducted on various kinds of vertical axis hydraulic turbines having fixed vanes and vanes pivoting between determined angles. More precisely, a reference 3-vane turbine model was immersed in a stream with a speed of 8.5 m/s. Then, various tests were conducted with different vane configurations for the reference rotor, i.e. with vanes fixed and pivoting between angles ranging from 0° to 95°. Referring to Figure 5, there is illustrated the graph of the output power for each kind of turbine as a function of the kind of rotor-mounted vanes, according to the test. The first small-sized turbine model was built and tested in the tow tank of the Department of Naval Architecture at the University of Naples Federico II. The vanes of this first model were free to pivot about their hinge axis with angles even greater than 90° (with respect to the radial direction) and the torque was mainly generated by vane drag ("Panemone-like" rotor) . In a second stage, at the Department of Aeronautical

Engineering (DPA) of the University of Naples an ad hoc numerical code was readily developed, employed to predict the behavior of the turbine and the power generated by the latter in different operating conditions. The numerical activity was combined to an extended experimental activity conducted in wind tunnel on a larger and newer scale model of the turbine of the present invention. In fact, a second and much more advanced model was built and tested in the DPA wind tunnel. On this latter model the torque is generated by the vane-developed lift, and not by the drag as on the preceding model. It was modularly contrived, and built to be tested with a variable number of vanes and to optimize their pivot angle. This model has a 2.2m diameter, whereas the vane height (span) and chord are of 0.8m and 0.17m, respectively. The symmetric airfoil adopted for the vanes is a NACA 0018. The model was tested in different 2-, 3-, 4-, and β-vane configurations and, owing to the high number of parameters at issue, several in-tunnel tests had to be conducted. The first configuration tested exhibited a vane pivoting angle ranging from 0° to 90° (with respect to the radial direction) . In order to optimize these angles and the position of the counterweight, a specific contrivance allowing its movement was adopted. These vane articulation angles provided sufficient torque at the starting of the turbine, in fact the latter was capable of self-starting, by virtue of the torque generated by the drag of the vanes arranged at 90° with respect to the stream direction (see Figure 5) . Alas, the turbine was found not capable of increasing its angular velocity, since right after starting it operated within a range of angular velocities in which the output power was negative, (see Figure 5). Then, vane pivoting angle optimization was tackled, to overcome just the problems of negative output power at a low number of revolutions. In Figure 5 it is shown how the gross power outputted by the turbine for different values of the pivot angles of the vanes varies: apparently, letting the latter pivot at angles ranging from 80° to 90°, it is possible to increase the maximum gross power that the rotor is capable of generating, preserving the self-starting capabilities thereof. Lastly, the study of the effect of the number of vanes on the gross power outputted by the turbine led to the selection of a 3-vane rotor. This model was tested several times, modifying its features in accordance with the experimental and numerical results . All research aimed at singling out the best viable kinematic features of the turbine. The theoretical ratings performed take into account several mathematical models, capable of describing and foreseeing the behavior of the turbine of the present invention from a kinematic as well as from a dynamic viewpoint. After the wind tunnel testing and the numerical computation conducted on the model to scale employed in the tunnel, the study on a full size scale prototype began. Analyses and practical considerations on the dimensions of the prototype led to the selection of a 3- vane turbine having a 6m diameter. A 5m vane height (span) was selected, whereas the 0.4m chord provides a Reynolds number ranging from 0.8 x 10⁶ to 2.0 x 10⁶ depending on the operating conditions. Then, prior to the construction of the rotor, its performances were numerically predicted by using the aerodynamic data of a high-lift airfoil (thereafter employed in the construction of the vanes) called HL-18 and specifically designed, so as to prevent well-known cavitation phenomena thereto, concomitantly providing it with a high efficiency both at positive and negative angles of attack, since in a full revolution the vane operates in both conditions. Referring to Figures 1 and 2, the rotor and the vane of the hydraulic turbine of the present invention are illustrated. According to the invention there is provided a rotor 1 equipped with three vanes 2 and each vane 2 is supported by two arms 3 connected to the rotor 1. The arms 3 in turn are streamlined employing another symmetric airfoil designed ad hoc. The vanes 2 are made of an inner structure of longerons and ribs in steel, about which a Carbon-resin composite coating has been laminated. Also the supporting arms 3 have been streamlined, but by means of a structure in fiberglass reinforced plastic. Figure 2 shows a partial perspective view of the system for connecting the vane 2 onto the respective arm 3. More precisely, the vane 2 is pivotally mounted onto the arm 3 in a manner such that the former may pivot of 10° with respect to the direction orthogonal to that of the latter. The vane 2 is connected to each arm 3 by a counterweight member 4 integral to the former and hinged on the latter. The function of the member 4 is to balance the inertial torque of the vane during its rotation about the rotor, substantially shifting the center of gravity of the vane at its axis of rotation. Moreover, it is provided that the member 4 be hingedly mounted onto the arm 3, and pivoting (hence the vane 2 pivots too) within a range of 10° with respect to the direction orthogonal to the longitudinal direction of the arm 3, which is the radial direction of the rotor 1. Thus, the vane can pivot about the rotor of 10° with respect to the direction orthogonal to the axis of rotation of the latter. According to figure 3, it is provided that the turbine of the present invention be mounted on a floating structure forming the installation made of the turbine 1 and of a current generator 10. The entire installation is mounted on a floating platform 11. From a mechanical viewpoint, the turbine was designed following simple and effective principles, in order to attain a low level of maintenance interventions for the whole assembly. The turbine of the present invention entails the following advantages. A first advantage lies in that the direction of rotation of the rotor is independent from the direction of the marine stream. A second advantage lies in the elevated value of the torque at the starting, making the turbine capable of self-starting, even under load, with no need of any starting system. A third advantage lies in the excellent efficiency, simplicity of operation and low maintenance. Then, a pilot installation was implemented and tested on site in the presence of marine streams. The principal dimensions of the installation are as follows:

For sinker' it is meant a block working as anchoring or mooring means, or, optionally, an actual anchor. According to the installation of the present invention there is provided an overgear 13 (with a 1:90 ratio) . Moreover, there are provided distribution panels into the floating platform. The generator is of brushless type, 3-phase, synchronous, 4-pole, capable of generating a rated output of 128 kW and connected to a control unit capable of supplying power to the grid. The installation was located at a site where a marine stream maximum speed of about 2 m/s (4 knots), is predictable and the sea depth is of 20m, and moored 150m offshore. The stream never subsides, reversing its flowing sense approximately every 6 hours whereas its intensity varies with a 14-day interval. In figure 6 there are reported the power curves at different marine stream speeds, which were predicted with the aid of the numerical code developed. Then, the first set of tests conducted was aimed at systematic observation and data collection, in terms of stream speed as well as of output power. Moreover, the mechanical behavior of the turbine was carefully evaluated. It was observed that even with a slow (about 1.2 m/s) marine stream, the rotor quickly starts rotating with no external aid. Then, upon measuring the data the various parameters were computed, resulting in the graph of Figure 7. More precisely, it is defined as overall efficiency of the installation the ratio between the electric power output and the theoretical power related to the marine stream intercepted by the rotor. The expression of the efficiency is: η = Pel / 0.5 p V³ S

where p is the density of the water; V is the speed of the stream ; and S is the product between rotor diameter and vane height. According to experimental results the measured overall efficiency is equal to about the 23% (see Figure 7) . Such efficiency is comparable to (if not better than) that of wind turbines, which benefit from having been developed over more than three decades. Such a result is extremely encouraging. Lastly, there was conducted a study related to the quantity of power yieldable over a 1-year period from the site whereat the turbine was tested. Computing indicate at about 22000 kWh the useful power extractable by this installation over one full year. It should be considered that at this site, in view of the area interested by streams, the total extractable power is equal to 538 GWh.

Claims

Claims 1. A vertical axis hydraulic turbine of the kind comprising a vertical rotor (1) which comprises at least three vanes (2), each of which is pivotally connected to said rotor (1) by a pivoting connection onto a respective pair of arms (3) integral to the rotor (1) , characterized in that the arrangement is such that during the rotation of the rotor (1) each vane performs a an angular displacement comprised within a range from 80° to 90° with respect to the radial direction of the rotor

(1).

2. The vertical axis hydraulic turbine according to the preceding claim, wherein each vane (2) is integrally connected to a pair of counterweight members (4), said pair of counterweight members (4) being hinged with a limited pivoting of 10° to the respective pair of arms (3) of the rotor (1) for the pivoting connection of said vane (2) on said rotor (1) .

3. An installation for converting energy from hydraulic streams into electric energy, comprising the vertical axis hydraulic turbine according to the preceding claims, characterized in that it further comprises a floating platform (11) for the support of said turbine, and a electric generator (10) connected to said turbine rotor (1) .

4. The installation for converting energy according to the preceding claim, wherein said floating platform (11) comprises at least four sinkers for the mooring thereof to the depth underlying said platform.