Wind turbine rotor with the vertical rotation axis

The invention is a wind turbine rotor with the vertical rotation axis, used in the turbines applying the Darrieus' principle while processing the wind energy into the mechanical energy of the rotation movement.

Solutions of turbine rotors with the vertical rotation axis known e.g. from the patent descriptions US 4264279 and US 4430044 have, connected with the hub of the drive shaft, at least two horizontal supports with vertically mounted rotor blades on the ends.

Rotor blades have mostly a symmetrical aerodynamic profile and are connected with the support in the center zone of their height, with the division of the blade into the upper wing and the lower wing. During the rotor movement exerted by the wind pressure apart from the driving aerodynamic force, there is also centrifugal force. Both forces act in the centres of the mass of two wings. In the middle of the trajectory of the blade rotation movement, the aforementioned forces are directed to the same direction - resulting in the longitudinal deformation of the wings and high bending stress in the connection zone of the blade and the support. On the other half of the circle, at the side of the wind direction, there are both forces of reverse senses.

The appearing pulsating load changes, including polarity changes, have a significantly adverse effect on turbine wear and equipment efficiency. Known solutions consist in inserting additional elements into the construction of the rotor in order to stiffen the wings. For example, these may be the line tie rods - as in the rotor described in British Patent GB 2175350, or additional supports - as disclosed in the German Patent DE 3626917. The introduction of the strengthening elements results in the increase in the aerodynamic resistance and the decrease of the turbine efficiency, especially if they include the acutely angled forms, which facilitate the volumet

ric turbulence. The adverse effect of the centrifugal force leads to partial reduction in the application of the changeable profile on the rotor length, with the length of the chord and the thickness of the profile decreasing towards both wing ends. Such solution, among others, was applied in the rotor disclosed in the patent description EP 0046370. In the brief description of the working conditions and technical problems appearing in these kinds of rotors, it is necessary to indicate the diversity of the aerodynamic force on the upper and lower wing and the construction susceptibility to the self-excited aeroelastic vibrations, that is, the flutter of the wings at high speeds of the surrounding air. The characteristics of the area may often determine the substantial decrease of the wind speed at the lower wing level.

The aim of this invention is to draw up a simple construction of the rotor, which is characterised by the high stiffness and durability, low aerodynamic resistance and high efficiency of the wind pressure force transformation on the driving force of the rotor shaft.

In this invention, similarly to the above disclosed solutions, the rotor involves at least two horizontal supports connected with the hub. The rotor blades with the symmetric or concave-convex aerodynamic profile with the chord lenghts and profile thickness decreasing towards both wing ends are fixed tightly to the ends of the supports. The essence of the invention is that the upper and lower wing of the rotor blade deflect from the central zone radially outside at the angle relative to the rotating axis. At the same time, the chord lengths of the profile at both wings ends and the chord length in the centre zone are approximately inversely proportional to the radiuses of their location relative to the rotating axis. The use of the rotor with deflected and at the same time along profiled wings, provides the stable intensity of the wind power consumption along the length of the wings and the resistant centre zone. The substantial improvement of balance and decrease of pressing tension in the outer layers

of the wing is achieved by the getting closer the centres of wing masses to the support. The stretch tensions are generally generated in the support. The frequency of free vibrations of the blade with the deflected wings is higher then the one of the straight blade. This facilitating result is particularly visible during gust winds. The diversification of the air attack angle which appears in the central zone and at the ends of the wings in practice eliminates the danger of the flutter.

The aim of the further embodiments of the invention is to eliminate the influence of different wind speeds which appear at the upper and lower levels of the rotor.

For this purpose, it is advised that the angle of the lower wing deflection in the rotor should be larger than the angle of the upper wing deflection. The advised angle difference is in the range of 1°to 5°.

The solution in which the lower wing is longer than the upper one is also beneficial. The length difference in the range of 2 to 15% is recommended.

In accordance with the invention, in the rotor it would be advisable to use supports with the symmetrical aerodynamic profile and horizontally placed chord, as well as such connection with the hub that the longitudinal axes go through the profile's centre of inertia cut the rotating axis.

Referring to the fact that the rotor works with the highest possible efficiency at different wind speeds, it is also useful to connect the driving blades with the supports with the use of the known set point of the angle of attack, which enables the regulation in the range from -2° to +3°.

In order to completely understand the invention, the example of the schematic convention of the rotor is shown on the drawing. Particular figures on the drawing show: fig.1 - perspective view of the rotor with deflected wings, fig.2 - the view from the side, fig.3 - the view of the wing from the direction marked with the letter X on the fig.2, fig.4 - the view from the other rotor with wings of different length and varied deflection an-

-A- gles of upper and lower wings, whereas fig.5 shows the view from above on the rotor in its section according to the line Y-Y marked on the fig.4.

The rotor is fixed onto the hub 1 of the driving shaft bearing vertically in the tower of the fourth wind turbine. Two horizontal supports, with the symmetrical aerodynamic profile are fixed to hub 1. The profile chords of supports are horizontal and the longitudinal axis, which goes through the stiffness centre of the profile cuts the rotating axis of the rotor. The rotor blade 3 is fixed at the end of each support 2, the blade is connected with the support 2 by the centre zone 3c of its own length. The upper wing 3a and the lower wing 3b of the rotor blade 3 have the same length, both wings are deflected radially outside and the angle relative to the rotating axis is βi = β _2. The cross sections of the upper wing 3a and the lower wing 3b have the symmetrical or concave-convex aerodynamic profile with the chord lenghts from bi to b ₂ decreasing towards both wing ends and profile's thickness from Ci to C _2. The chord lengths of the profile at both wings ends 3a, 3b and the chord length bi in the centre zone 3c are inversely proportional to the radius Ri ₁ R ₂ of their location, relative to the rotating axis, as expressed in the relation: bi/b ₂ = R ₂ /R ₁ . When the land form features apply to such dimensional and shape relations, the wind power consumption is stable along the entire length of the wing and, at the same time, the angle of the air attack αi,α ₂ of speed resultant Ti, T ₂ of the air stream along the wing decreases. It is shown on the fig.3, where particular elementary surfaces of the wings, symbolically marked "1 cm" should generate the identical aerodynamic force, according to the formula:

Y = Cy _x Sx p x V ² /2, where

Cy - indicates the factor dependent on the shape of the aerodynamic profile,

S - the field of the elementary surface of the wing P - air density, V - the speed of the air flow

Nearby the central zone 3c the value of the product C _y S is higher than at the end of the wing, where V ² is a predominant value. In case of gust winds, the angle of the air attack α may exceed the critical value. In the rotor, in accordance with the invention, the angle of the air attack decreases continuously from α1 in the centre zone 3c to 0 ₂ at the ends of the wings 3a, 3b - which leads to exceeding the critical value also increasingly along the wings. The development process of the turbulence zone behind the wings has is continuous in nature; it does not result in the turbine pulsation or vibration of the tower 4 and supports 2, which appear in turbins with straight blade rotors.

When the assumed turbin power is maintained, the outside deflection of the wings 3a, 3b allows for shortening the support 2 appropriately - which reduces aerodynamic resistance of the turbine.

The rotor adapted to the balanced wind power consumption by the upper 3a and lower wing 3b is shown on the fig. 4, for the land conditions in which the wind speed is significantly diversified depending on the height above the ground level. The difference between aerodynamic powers appearing on the lower 3b and upper 3a wing creates the adverse torque moment of the supports.

The balance of the aerodynamic forces can be ensured with the use of the larger (by for example 3 ⁰⁾ deflection angle β ₂ of the lower wing 3b than the deflection angle of the upper wing 3a, maintainig equal lengths of the wings U = b _. The increase of the deflection angle value influences the circumferential speed of the wing and depends on the terrain damping aerodynamic profile. The load balance of the upper 3a and lower 3b wing can be also achieved at equal deflection angles βi = β2 but longer lower

wing 3b lengh 12 - for example about 10 % longer than the length h of the upper wing 3a.

The examinations of the rotor prototype, as specified in the invention, revealed that maximum efficiency of the power conversion for the different wind speeds W is achieved at different angles of attack v, between the centre zone chord 3c and the movement trajectory tangent to this section. For example, for the wind speed W=6 m/s, angle = -2°, for W= 9,5 m/s γ = 0° and for the W= 11 m/s Y = +2°. The rotor in the subject of the invention is equipped with one of the known solutions built-in to the support 2, which allows for changing the attack angle y, during the operation of the turbine.