CH706919B1 - Savonius rotor with six blades. - Google Patents

Abstract

The invention relates to a Savonius rotor with six blades and a vertical wind turbine of which it is the main component. The rotor can capture fluid from any direction and rotate at low incident velocities due to its high torque. Having a slow rotation speed, this rotor is almost inaudible. Simple in construction, requiring no complicated manufacturing process and can even be done with recovery equipment; it is ideal for rural areas. The invention also relates to a stator having four guide vanes-caches enveloping said rotor; can significantly improve the rotor efficiency for four major incident directions. The stator only captures the fluid from these directions so it should not be mounted if, for example in the case of the wind turbine, the wind blowing in the area has no preferential direction.

Description

Description [0001] The invention consists of a six-blade Savonius-type rotor according to claim 1; the conventional Savonius rotor geometry has been modified according to claim 2 such that the rotor has a relatively constant moment of force throughout the rotation and can start with fluid from any direction. This results in a higher yield than the classic Savonius rotor. The invention also relates to a stator provided for this rotor according to claim 3, the stator prevents air from striking the convex faces of the blades and forces the fluid in the concave faces, which also locally increases the pressure and therefore increases significantly yield. The stator has only four air intakes, so it is installed only when the incident fluid aligns frequently with the air inlets. The present invention also relates to a wind device according to one of claims 4, 5 and 6 formed by the Savonius rotor with six blades with or without stator, connected to a rotation shaft which can be coupled to a generator or a another device for transforming or transmitting mechanical energy.

[0002] Vertical-axis wind turbines are preferred to those with horizontal axes in inhabited areas; indeed, they accept wind from any direction and therefore do not need to adapt to wind direction changes. In addition, their low rotational speed ensures a very low noise level or even inaudible and a longer life.

[0003] In inhabited areas, many obstacles are found on the windward path; this generates turbulence and decreases the average wind speed. Indeed, the average flow is degraded and the turbulence increases while the speed decreases. This turbulence can manifest itself in the form of bursts, eddies, changes of direction. Horizontal-axis wind turbines must always be oriented towards the wind and all these turbulences have a particularly detrimental effect on the efficiency of the installation. Indeed, the response time of the system facing a change of direction is often too long and the wind turbine can not effectively capture the wind.

[0004] Vertical axis wind turbines separate into two families: the lift rotors and the drag rotors. The lift rotors consist of wing profiles positioned vertically and at a certain distance from the axis of rotation (Darrieus type). The drag rotors (Savonius type) have an undeniable advantage: the simplicity of their design. On the other hand, their yield is the lowest. Indeed, their operating principle is based on the difference in drag between the concave and convex faces. Each blade being a cylindrical half-tube, the concave face having a drag coefficient of about 2.3 and the convex face of about 1.2 (a convex body moves with less resistance than a concave body); when the air simultaneously strikes the convex and concave faces, it exerts a greater force on the concave face than on the convex face and thus follows a moment of force which breaks the static equilibrium and there is then rotation. The low efficiency is due to the drag force exerted on the convex face of the blade throughout the rotation. This force comes to somehow brake the rotor.

List of Figures [0005]

Fig. 1: Steps for tracing the geometry of the rotor, blades and free space inside.

Fig. 2: Drawing of manufacture of the rotor.

Fig. 3: 3D model (CAD) of the rotor mounted on a permanent magnet generator; rotor mounted with the stator wrapping the rotor.

Fig. 4: 3D rotor model and rotor cut with stator.

DETAILED DESCRIPTION OF THE INVENTION [0006] The present invention is in fact a solution to the main problem of the "classical" Savonius rotor. The moment of force is certainly high but is not constant along the rotation, it depends on the angle between the rotor and the incident wind. In operation, this results in a low efficiency and an impulse every 180 degrees that can also cause fatigue. When the rotor is stopped, it may be difficult to start if the wind is blowing from an unfavorable angle: this is a fundamental problem. There are several methods to solve this problem: to give a helical shape to the blades by twisting them longitudinally, to superpose Savonius rotors on each other but with an angular offset, to increase the number of blades. These changes are often at the expense of performance even if they standardize the moment of strength. This loss of efficiency is due to the increase in the inertia of the rotor as well as a non optimal flow of air in the rotor. Thus, a difficult optimization work is necessary if one wishes to improve the efficiency and simultaneously to have a moment of force relatively homogeneous with the angle of the wind.

The invention then consists of a Savonius-type rotor modified so as to remedy the defects of the conventional rotor Savonius. This six blade rotor is simple and cheap constitution. It is ideal for rural areas. Indeed, it can be manufactured with recovery equipment; machining, formatting and assembly operations are simple.

All geometric factors influence the flow in the rotor and therefore the yield. However, the optimization lies mainly in the ratio between the outside diameter D and the inside diameter Di (see Fig. 2). The inside diameter defines the free space inside the rotor. The role of this inner diameter is to allow the air circulating in the rotor not to remain prisoner but rather to pass from blade to blade thus increasing the dynamic pressure on the concave face of each blade and finally increasing the moment of global force generated. This inner diameter has an optimum value related to the number of blades. The shape of the blades also plays a crucial role in the aerodynamic properties of the rotor. The determination of the optimum values can be done by means of experiments on prototypes or simulations. Here, the geometry has been defined according to claim 2.

The ratio between the outside diameter and the height of the rotor also plays a role in the efficiency. In the case of the prototypes made by the author, a ratio of 2 was used; the height of the blades H is thus twice the outer diameter D.

The main reason for the low efficiency of the Savonius rotor is the force exerted along the rotation on the convex face of the blade. The most direct way to increase the yield is therefore to hide the convex faces of the blades behind a shield. Better yet, to force the air into the concave faces of the blades. We would therefore use fixed vanes sheltering the convex faces and revealing the concave faces. These fixed blades thus constitute a stator (see Fig. 3) directing the air in the concave faces and preventing the air from striking on the convex faces. Theoretically, the efficiency of such an installation increases significantly.

According to the results of the simulations, the maximum aerodynamic efficiencies (at optimum rotation speed and ignoring any mechanical friction) are the following: - 0.2 for the "classical" rotor of Savonius - 0.3 for the rotor six-blade rotor shown here - 0.5 for rotor with stator at optimal pick-up angle.

The main disadvantage of the stator is that it removes the independence of the wind direction, in fact in the case here, it directs the wind in the concave faces for certain preferred angles 90 ° apart . The other angles do not constitute optimal inlet conditions for the air in the rotor and the efficiency therefore decreases. Thus, the efficiency and rotation of the rotor are both dependent on the direction of the incident wind. The efficiency of the wind turbine is improved by the stator only if the wind blowing in the wind turbine aligns with the air intakes of the stator. If the wind blowing on the site is relatively uniform in intensity in each direction; the stator will not be installed.

The stator must be fixed and therefore independent of the rotor, it is fixed relative to the ground robustly. A space must be left between the stator and the rotor to prevent the blades from touching the stator in case of oscillations in the vertical plane. Embodiment of the Invention [0014] The 3D drawings used to produce the plans for manufacture are shown in FIG. 3. Plans can be easily made with CAD software and Figs. 1 and 2.

Tracking blades according to FIG. 1: [0016] To better understand the following lines, it is ideal to have under the eyes figs. 1a and 1b. Define the diameter of the rotor (two prototypes made at 0.5 m and 1 m in diameter). Draw six circles of diameter equal to the radius of the rotor arranged at 60 degrees intervals. The centers of the six circles are placed on a circle of diameter equal to the radius of the rotor. Thus, the circles are perfectly inscribed in the circle of the rotor, they are tangent to it. Then, for each of the six circles, keep only one half. Draw the circle representing the inside diameter (0.35 m for a 1 m diameter rotor and 0.175 m for a 0.5 m diameter rotor). Finally, remove the part of the semicircles inside the circle representing the inside diameter, which amounts to truncating the blades to create the free space in the middle of the rotor.

Before describing the manufacture, it is important to remember that it is necessary to minimize the inertia of the rotor so that it can rotate in low winds. For this, it is necessary to choose light materials. It is also important to remember that the rotor is placed in height and that its surface perpendicular to the wind undergoes a clear force in the direction of the wind: it thus creates an important moment of force compared to the ground. It goes without saying that it is necessary to ballast or stow the structure supporting the rotor. When the permanent magnet generator is connected, it creates a resistive magnetic torque that the rotor must overcome to be able to rotate and produce electricity. It is precisely this resistive torque that affects the structure supporting the generator as a torsion moment. Again, the structure supporting the rotor must be able to withstand tipping and twisting. For the structure, rigid and heavier materials will be chosen.

Steps in the manufacture of the rotor: [0019] 1) Lower and upper disc supporting the blades:

With reference to FIG. 2, two discs (1) and (3) with a diameter slightly greater than the diameter of the rotor must be cut off, the fractions of registered circles representing the blades must be traced faithfully on the lower disc

Claims (6)

(1) and higher (3). The necessary holes in the center of the disc must be made to connect to the generator or to a rotating shaft. 2) Realization of the blades: Referring to FIG. 2, the blades (2) can be made from aluminum sheets folded in a fraction of circles. They must therefore be cut to the length of the circular arc L (previously drawn) and fold them respecting the radius of curvature. The width of the sheets is equal to the length of the circular arc L and their height H determines the height of the rotor. As for the thickness, it depends on the chosen material and the method of fixing on the disc. In the case of aluminum, the author chose 2 mm thick for prototypes 1 m in diameter and 0.5 m in diameter. 3) Fixing the blades: The blades (2) are placed on the corresponding tracings on the lower disk and then they can be welded by points. Care must be taken not to deform the blades during welding. Some points are enough, it is not necessary to make a weld seam. With materials that do not lend themselves to welding, mechanical or chemical fixing means will be considered. 4) Attachment to the upper disk 3: The lower disk assembly (1) more blades (2) is returned (placed upside down) and kept suspended above the upper disk (3) which has been previously drawn in the same way as the lower disk (1). Once the blades (2) placed correctly with respect to the disk and the tracing, they are brought into contact with the disk and then welded or fixed in the same manner as before. Stator according to FIGS. 3a and 3b: The stator consists of four guide vanes-caches. Cache means the curved portion enveloping the rotor and guide blade inclined rectilinear part focusing the flow. The four sets are arranged uniformly every 90 ° thus giving four preferential directions of wind (0 °, 90 °, 180 °, 270 °). When the wind blows from one of the four preferred directions, the efficiency of the turbine increases due to the sharp decrease in pressure on the convex faces of the blades. The pressure exerted on the guide vanes-caches can be considerable in case of strong wind; it is obvious that it will be necessary to use rigid and robust materials. Since they are not moving parts, their inertia does not need to be minimized (heavier materials can be chosen). The guide vanes may be simple sheets folded so as to obtain the desired geometric shape. They are then welded or mechanically fixed to the support ring. It is recalled that the support ring has an inner diameter of a value greater than the diameter of the upper and lower disks: to avoid contact with the rotor in rotation. Since the guide vanes are fixed only at one end (support ring at the base of the structure), there is a large overhang and it is therefore necessary to use robust materials or more thick so that it has no noticeable deformation under the pressure of the wind. It will be necessary to consider the case of a storm with extreme gusts of wind as criterion of dimensioning. The support ring has any fastening means robust relative to the ground so that the stator remains firmly fixed in case of extreme gusts. claims A six-blade Savonius type rotor consisting of an upper disk (3), a lower disk (1) and six curved blades (2) attached to the disks, all constituting a rigid cylindrical body and empty to the interior of which the walls are formed by the blades which are dimensioned so that there is a free space in the center of the rotor allowing the flow of a fluid inside the rotor. 2. Rotor according to claim 1, characterized in that: - the six blades (2) describe identical fractions of six circles inscribed in the lower and upper discs whose centers of six circles are uniformly distributed every 60 degrees and positioned on a circle concentric with the lower and upper disks of radius equivalent to half the radius of the rotor; the end of the six blades (2) is tangent to an imaginary circle of diameter D which represents the diameter of the rotor; - The free space in the center of the rotor is represented by an imaginary circle of diameter Di inside which the blades must not penetrate; the value of Di is 0.35D; the six blades (2) have an arc length L and a height H. 3. rotor-stator assembly comprising a rotor according to claim 1 or 2, characterized in that said rotor is enveloped by a stator composed by: - four guide vanes fixed to a fixed support ring which are distributed 90 degrees apart around the rotor, all forming four identical air inlets surrounding the rotor and positioned at 90 degrees intervals; the guide vanes being constituted by a circular part confined in the support ring and an oblique part open towards the outside, said oblique part of the guide vane being arranged to focus the wind in the inlet of air and said circular portion of the guide vane being dimensioned so as to mask the convex face of the rotor blade without hindering the air inlet in the concave faces; the inside diameter of the support ring is chosen so that the rotor never comes into contact with the guide vanes. 4. Vertical axis wind turbine, characterized in that it comprises a rotor according to claim 1 or 2, connected to the center of the lower disk or the center of the upper disk to a rotation shaft, the rotor-rotating shaft assembly being likely to rotate under the action of the wind. 5. A vertical axis wind turbine, characterized in that it comprises a rotor-stator assembly according to claim 3, said rotor is connected to the center of the lower disk or to the center of the upper disk to a rotation shaft, the rotor-rotor assembly rotating shaft being able to rotate under the action of the wind. 6. Vertical axis wind turbine according to one of claims 4 and 5, characterized in that the rotation shaft is coupled to an electric generator or to another device for transforming or transmitting the rotational energy of the rotor.