GB2165008A

GB2165008A - Ian vertical-axis wind turbines with flexible blades

Info

Publication number: GB2165008A
Application number: GB08523566A
Authority: GB
Inventors: Vincenzo Gervasio
Original assignee: Tema SpA
Current assignee: Tema SpA
Priority date: 1984-09-25
Filing date: 1985-09-24
Publication date: 1986-04-03
Also published as: IT1176791B; GB2165008B; DK431885A; DK431885D0; IT8422813A0; GB8523566D0; IT8422813A1; NL8502608A

Abstract

To reduce torque oscillations in the turbines shaft (1) the wind rotor comprises flexible blades (2) which during operation twist into a helical configuration around the shaft as well as conforming to centrifugal forces such that the stresses in the blades are essentially tensile. The blades are preferably constituted by a set of shaped profiles, kept spaced apart from each other by ropes and sheathed within a sheath of air-tight material. <IMAGE>

Description

SPECIFICATION Eolian Vertical-Shaft Motor with Flexible Blades The present invention relates to an eolian verticalshaft motor with flexible blades, suitable to tbe coupled with electrical generators or other user machines, provided with particular characteristics of simpleness and cheapness.

It is known that one of the main problems which are to be faced in the manufacturing of eolian vertical-axis motors is that of the high stresses which the blades undergo due to the centrifugal force, which are often much higher than those due to the aerodynamic action by the wind and to the action by the gravity.

Among the possible structural shapes of an eolian vertical-axis motor, the first and most known one is that commonly known as the "Darrieus motor", from the name of its inventor, wherein the blades take, under the action by the centrifugal forces, such a shape as to reduce nearly to the pure traction the stresses which all the sections of the same blade undergo due to the action by the same forces.

In such a type of blades, the transmission of the motortorque, as generated by the action of the wind on the blades, to the vertical shaft around which the same blades rotate is accomplished, due to their particular stiffness, in the direction tangential to the motion and because of the stiffness, in the same direction, of the upper and lower blade supports.

In the rotors of the "Darrieus" type the blade must hence be rigid in the direction tangential relatively to the motion, but very elastic in the direction perpendicular to the first one, to the purpose of allowing it to turn, during its rotation, into the natural configuration reducing to the minimum the tension stresses inside the material, reducing them to the pure traction only.

The drawback of the Darrieus type motor is related to the presence of stresses of tangential type pulsating and of high value.

In all other rotor types, rigid blades are used, sometimes resorting to variable geometries, to the purpose of reducing the stresses acting on the structure of the eolian motor under conditions of extremely strong wind. In these cases, the strength of the centrifugal forces and the torque transmission are secured by the stiffness of the blades and of the structure supporting them, but it has become more complex the manufacturing of the blades, which require advanced mechanical solutions with the resorting to particular materials showing very good characteristics of strength to the mechanical stresses, with a mass as low as possible. One enters hence the field of the composite materials, whose use is typical of novel and sophisticated technologies.

From the above, it may be clearly seen that, whilst the adoption of the vertical shaft undoubtedly simplifies the overall structure of the wind motor, in particularly eliminating the need of orienting the equipment according to the direction of the wind, and easily allowing all the electrical equipment to be installed at ground's level, it complicates on the other side the construction of the blades, because generates greater stresses inside them and renders necessary more complex solutions.

On the other hand, if one regards to the eolian motors as the solution for rendering available energy in the Emergent Countries, wherein the technologies available are very simple and traditional, it can be seen that a simple solution of the problem of the blades would allow a type of vertical-shaft eolian motor to tbe accomplished, which would have to a nearly "ideal" extent the characteristics of strength, structural simplenesss and maintenance easiness which are necessary for the use in not highly industrialized Countries.

It has been surprisingly found that it is possible to reduce the tangential stresses typical of the Darrieus motor, without that it be needed to resort to variable-geometry blades, by using blades capable of deforming also helically during the motion, keeping their cross section substantially constant.

The eolian vertical-shaft motor with flexible blades according to the invention comprises: 1. A vertical shaft, linked at one of its ends directly or indirectly to one or more generators; 2. A set of blades positioned in a longitudinal fashion relatively to the shaft, flexible, radially and tangentially deformable during the operation, linked at their lower portion to the shaft, through a rigid connection bar, and at their upper portion always linked to the shaft through a tie-rod, it too of rigid character.

3. The rigid connection bars, each one of which has one of its ends rigidly linked to the shaft, or hinged on to a stationary support of the shaft, and its other end linked with the end of the blade.

4. The tie-rods, which are fastened to a ring slipped around the shaft and free to rotate by a certain angle around it and to move along the same downwards up to a shoulder.

We outline that by "radial deformability" the possibility should be intended of the blade to bend and to turn into a curved configuration relatively to the vertical shaft, with the generatrices of the blade and of the shaft always laying on the same plane. By "tangential deformability" it should be intended the possibility of the blade to turn into a helical configuration.

According to a preferred embodiment of the invention, the flexible and radially and tangentially deformable blades are constituted by a set of low-thickness shape profiles (ribs) spaced apart from each other, and linked with each other by means of a set of ropes or cables, in a number greater than two, and preferably comprised within the range of from 3 to 6, in particular of 4, said ropes or cables being firmly linked to said profiles so as to prevent them from sliding, the set of shaped profiles kept spaced apart from each other by the ropes or cables having their pointed ends linked with each other by ropes, and being sheathed within a sheath flexible, air-tight or substantially air-tight. The sheath is in particular and preferably of fabric, of non woven fabric, of rubbery material, or of deformable plastic material.

The shaped profiles have the shape of wing profile, as it can be seen from the drawings too. The distance between two adjacent profiles must be shorter than, or of the same order of magnitude of the span of the shaped profile The number of blades is comprised within the range of from 1 to 4, and is preferably of two.

The invention shall now be explained with the aid of the attached drawings; the embodiments shown in them are in no way to be considered as limitative of the invention.

In Fig. 1 a two-blades rotor according to the invention is shown, wherein with 1 the vertical shaft has been indicated, with 2 the blades constituted by shaped profiles, spaced apart from each other by ropes and coated with fabric, with 3 the rigid connection bars between the shaft and the blades, with 4 the hinges of the bars with the fixed shaft support, with 5 the rigid tie-rod, with 6 the annular element, with 7 the shoulder. The blades (2) are linked both to the bars (3) and to the tie-rods (5) by tying the end ropes of the blades to the free ends of said bars and tie-rods.

In Fig. lathe blade deformation type is shown allowing the transmission of the torque to the central shaft.

In order to be able to accomplish a type of blade with these characteristics, a structure as shown in Fig. 2 has been conceived. It can be clearly seen how the structure of the blade is constituted by four cables (actually, more than two cables are needed, and they must be so positioned as not to lay on a single plane), with caracteristics of not extendibility and of good flexibility; on said cables, by means of screw sleeves, or by any other suitable devices preventing them from sliding along the same cables, flat plates provided with holes or slots for the passage of the cables are installed at a suitable distance from each other. The aerodynamic profile of the blade is then secured by a tube of flexible fabric slided on to the disclosed structure. A wire connects the points of the flat plates.

In such a way the blade is constituted by many elements, interconnected to each other by the cables, which can get deformed (on cables pulled taut) while maintaining the parallelism between the plates forming its ends and hence maintaining, for deformations of limited extent, the initial aerodynamic shape, with good fidelity. It is of course important that the fabric be free of sliding on the edge of the plates, so as to prevent the formation of wrinkles during the deformation of the blade.

In this structural conception no theoretical limits exist as for the types of materials to be used for the plates, the cables and the fabric; the first ones must however be rigid and strong enough not to break under the action of the centrifugal forces counteracted by the reactions by the cables, and must have a high enough mass to guarantee a good positioning of the blade under the action by the centrifugal forces; the second ones must only be quite non-extendible and very flexible, and must be capable to withstand the stresses which however can be easily computated: the fabric may be of the same type as that used for the boat sails, with a good wear strength and a good unshrinkability under the action by the weathering.

Moreover, no theoretical limits exist as for the size of the rotor, which can be made as large as desired, possibly using Intermediate stiffening tie-rods reducing the free length of the blade (Fig. 3).

It is finally evident the easiness of blade manufacturing even on spots wherein the availability of technologies is extremely poor and traditional, and as much evident is how easily possible breakings of any structural elements of the same blade can be repaired.

It is important to observe that during the movement of the eolian rotor according to the invention, the blades assume a helical configuration developed on the surface of a rotation paraboloid and that, notwithstanding the bending of the blades in the radial directions, they are able to perferctly transmit the driving motion. As for the coating, in case it is of fabric, it is preferably that the weft and the warp thereof be respectively parallel to the ropes or cables the first one and to the profiles the other, or vice-versa, so as to favour the helical deformation. Among the fabrics, the sail fabrics have their weft and warp yarns perpendicular and allow hence the application as mentioned above.

An advantage which can be obtained with the rotor according to the invention consists in that, due to the high helical deformation of the blades, a reduction is obtained in the oscillatory components of the torques, as the zero-torque points are eliminated.

Claims

1. Vertical-shaft eolian motor with flexible blades comprising a vertical shaft either directly or indirectly linked at one of its ends to one or more generators, a set of blades positioned longitudinally relatively to the shaft, flexible, linked to the shaft at their lower portion, by means of a rigid linking bar, and at their upper portion linked always to the shaft, by means of a tie-rod, wherein the rigid linking bars have one of their ends rigidly connected to the shaft, or hinged on to a support stationary on the same, and their other end linked to the end of the blade, characterized in that the blades are radially and tangentially deformable during the operation, the tie-rod is rigid and the rigid tie-rod is fastened on to an annular element slipped on to the shaft, free of rotating by a certain angle freely around it, and of shifting downwards down to a shoulder.

2. Eolian motor according to claim 1, characterized in that the flexible blades, radially and tangentially deformable, are constituted by a set of low-thickness shaped profiles, spaced apart from each other and linked to each other by means of a set of ropes or cables, said ropes or cables being firmly fastened on to said profiles, the set of shaped profiles, kept spaced apart from each other by the ropes or cables having their pointed ends mutually connected by wires and being enclosed within an air-tight or substantially air-tight sheath.

3. Eolian motor according to claim 2, wherein the flexible sheath is of a material selected among fabrics, non-woven fabrics, rubbery materials, deformable plastic materials.

4. Eolian motor according to claims 1 and 3, wherein the weft and the warp of the fabric are respectively parallel to the ropes or cables the first one, and to the profiles the other one, or vice-versa.

5. Eolian motor according to claim 2, wherein the profiles have a distance between each other lower than or of the same order of magnitude of the span of the profile.

6. Vertical shaft eolian motor, substantially as hereinbefore described with reference to, and as shown in, Figure 1 or 3 of the accompanying drawings, optionally in association with Figure 2.