MXPA06009000A - Rotor blade for a wind turbine - Google Patents

Abstract

The invention relates to a rotor blade for a wind turbine and to a wind turbine comprising a rotor with rotor blades of this type. The aim of the invention is to prevent the described disadvantages and to guarantee an improved overall performance. To achieve this, the invention provides a rotor blade with a drag ratio, in particular in the central or main board region of said rotor, whose value exceeds 80%and preferably 90%of the maximum value of said ratio in the range of±2°of the optimum pitch of said rotor.

Description

ROTOR ALABE FOR A WIND TURBINE FIELD OF THE INVENTION The invention relates to a rotor blade of a wind power installation and a wind power installation comprising a rotor having such rotor blades. BACKGROUND OF THE INVENTION The operation of a wind power installation and in particular the efficiency thereof is determined to a non-inconsiderable degree by the rotor blades or the rotor blade design.The rotor blades are described by a large number of parameters, in this respect attention is drawn to this situation generally as the state of the art to the book by Erich Hau, ind raftanlagen, 3rd edition, 2002, in particular pages 90 ff of it.The content of this book is also at the same time the basis of the present application and also the content of this application as far as is required for the present application.As mentioned, the operational efficiency and also the operation of regulation of wind power installations are governed to a non-existent degree. inconsiderable by the aerodynamic properties of the used rotor blade profiles.An important parameter of a rotor blade profile is characterized a for the ratio of the coefficient of lift ca and coefficient of resistance cw: Ref.174693 where E is referred to as the support-resistance relationship. Also an important parameter of a rotor blade is the high speed factor? where the high speed factor is defined by the quotient of the peripheral speed (u) of the tip of the rotor blade and the wind speed v. Figure 1 shows the known inflow flow conditions and air forces in the profile cross section of a blade element. If the profiles of the known rotor blades are investigated, a particular relationship is established between the lift-resistance ratio and the pitch angle. More specifically, it was found that the lift-resistance ratio is largely dependent on the respective step angle and typically a high lift-resistance relationship is achieved only in a fairly limited step angle range. Therefore, for example, a high lift-resistance ratio can be achieved if the pitch angle (of a rotor blade) is in the region of 6o and at the same time, however, the lift-resistance ratio drops severely then that the angle of the step slightly rises above or falls below the region of 6o.

If the value leaves the region of the optimum lift-resistance ratio, ie the pitch angle is markedly different from the optimum pitch angle, for example 6o, it can easily be seen that the complete efficient of the installation is smaller with the consequence that the wind power installation will have a tendency to adjust either the step angle to the optimum values again, for example by step control, and / or to adjust the full rotor in the wind at the optimum ratio by re-steer orientation. The size of the rotors of the wind power installations have increased steadily in recent years and the rotor areas of 10.00 square meters are not, meanwhile, more theory time but have become practical, for example in the case of an Enercon type E112 wind power installation. This involves a wind power installation whose rotor diameter is approximately 112 m. Now in practice it is impossible to achieve the optimum of the lift-resistance relationship on all regions of the rotor blade because, with the very large area of travel, it is not possible to assume that the wind is always flowing against the rotor. rotor blade from the same direction and always at the same speed. The consequence of this is that in some regions the blade or rotor blades admissibly operate in a relatively Optimal but in some other regions the rotor blades rather operate sub-optimally by virtue of the different nature of the flow-in-flow profile in the traveling rotor area. This results directly from the very close dependence of the lift-resistance ratio on the inflow angle and the consequence of this is that the loads in the rotor blade can fluctuate in an extreme way because the lift (Ca) of the blade The rotor is also approximately proportional to the lift-resistance ratio. It will be appreciated that, as a way to improve the problems indicated above and to avoid the disadvantages thereof, it is always possible to find an optimum adjustment by controlling the proper pitch of the rotor blades or by virtue of oscillating the entire rotor. It will be readily apparent to the man skilled in the art, however, that with this concept, the rotor blades must be, in practice, constantly adjusted in the wind (ie they must be calibrated) and / or the azimuth pulses must also be constantly steer the rotor without substantially improving the situation. DETAILED DESCRIPTION OF THE INVENTION The object of the invention is to avoid the disadvantages indicated above and to provide a better complete operation. The invention achieves the object by a rotor blade design having the features described in claim 1. Advantageous developments are described in the appended claims. One of the essential properties of the rotor blade design according to the invention is that the lift-resistance ratio remains virtually high during a fairly large step angle interval, but in this respect the highest value with respect to the ratio of sustentation-resistance now remains behind the optimum of the prior support-resistance relationship of the state of the art. Expressed in other terms, the lift-resistance ratio of the rotor blade according to the invention, with optimum adjustment of the pitch angle is - at a maximum - lower than in the state of the art, but at the same time a deviation of the Optimal adjustment does not immediately lead to a substantial reduction in the lift-resistance ratio and lift coefficient and therefore a lift, but deviations which are in the range of for example ± 0.5 to 3o of the optimum adjustment angle they do not lead to the substantial reduction in the lift-resistance ratio and consequently the reduction of lift with the consequence that the efficiency of full blast is improved. This also achieves a markedly better load distribution and a markedly lower load fluctuation (? L / dt). As can be seen from figure 2 the 'depression' of the lift-resistance ratio curve of the rotor blade according to the invention in the range between 4 and 8 °, the angle of the passage is remarkably wider than in the case of a known rotor blade. The claimed design configuration of the rotor blade will be found in particular in the central third of the rotor blade, that is to say in the so-called region of the rotor blade main board. This is the region which is between the junction region of the rotor blade or root region of the rotor blade on the one hand and the tip region, that is to say the outer end region, of the rotor blade. Figure 2 shows the variation of the lift coefficient or the lift-resistance ratio on the one hand relative to the angle of the passage. In particular, the curve diagrams relative to the pitch angle show that, in the case of a standard rotor blade, the lift-resistance ratio reaches its absolute maximum which is at about 170 in the region of the pitch angle. approximately 6th The support-resistance ratio already falls severely in a deviation of the angle of the passage of 6o or Io, that is to say either to 7o or 5o, and in particular with respect to greater step angles the support-resistance relationship is already divided when the angle of the step assumes a value of approximately 9o. With respect to lower step angles there is also a very sharp fall which however is not quite excessive as when the step angle differs with respect to larger step angles. The variation of the lift-resistance ratio in the case of a rotor blade according to the invention can also be seen in the diagram. The maximum is once again pronounced in the region of the pitch angle of approximately 6o and this maximum is below the maximum of the lift-reference ratio in the case of a standard rotor blade. It will be pointed, however, that the 'depression' of the optimum is now markedly wider as can be seen from the intersection curves and when for example the angle of the step is in the range of 4 to 8o, ie ± 2 ° from the Optimal step angle of 6o, the lift-resistance ratio is reduced only by approximately 10% from its optimum value. In the region of about 4.5 ° to -4 ° on the one hand and in the region of about 7 ° to 16 ° the lift-resistance ratio is always above the lift-resistance ratio curve for a known rotor blade. Also as can be seen the configuration of the rotor blade according to the invention completely improves the support coefficient of the complete rotor blade, which is realized by an increase in the efficiency of approximately 15% of the rotor blade. In particular, load fluctuations are also no longer longer than before, with some very small change in the angle of the passage, there is no need to carry out the corresponding measurements at the same time to re-adjust the angle of the passage to the optimum value desired, in the present example 6th. Figures 3a-3c show several views of a rotor blade tip, i.e. a rotor blade end portion. Figure 3a shows a perspective view of a rotor blade tip, Figure 3b shows a side view and Figure 3c shows a plan view. This rotor blade tip is also usually referred to as an edge arch. It can be seen from figure 3a that the edge arch is illustrated with three profile sections and three thread axes. The three different illustrations make it possible to show the rotation of the profile of the edge arc around the thread axis. In this respect the illustrated rotation is greater in terms of magnitude than the number of degrees specified in the description for reasons of illustration to render the representation in the illustration in the figure perceptible in any way to some degree. It should be particularly emphasized again at this juncture that the configuration according to the invention of the rotor blade refers in particular to the central portion, ie the so-called main board, ie the region which is between the root region of the rotor blade and the tip region. The main board can also be described generally as the 'central third' of a rotor blade, in this respect the specific dimensions on the main board may differ from this and the main board for example can also occupy approximately up to 60% of the length of rotor blade. Additionally or independently of the rotor blade configuration mentioned above, a further improvement can also be achieved - see Figures 3a to 3c - if the rotor blade tip, i.e. the tip end portion, is rotated in a given region about the thread axis, for example through approximately 4 to 8o, preferably approximately 5o, around the threaded (twisted) axis. The twisted then is at a so-called neutral inflow angle, ie the tip itself does not provide contribution to the lift. A typical configuration of a tip or a corresponding tip end section is known from the book mentioned earlier by Erich Hau, page 126 (Figure 535).

In accordance with the general school of thought, the sizing loads of a rotor blade are calculated as the product of the -width of the wind speed, the rotor blade area and the lift coefficient. Expressed as a formula the dimensioning load = V2 X A X CA, where the rotor area A is used to denote the area which the rotor covers (paths). This in consideration of textbooks is quite abrupt and does not always correspond to reality. The largest load of a rotor blade does not act on it in normal operation but when a burst once in 50 years so called 'traps' the rotor blade from the side. In this case the burst acts precisely on the entire rotor blade surface. In this respect it can be seen that the coefficient of support CA does not play a part, rather the coefficient of resistance Cw could be considered here. The coefficient of resistance, however, is always constant that more or less flat rotor blade surface, if the wind hits a blade, then hits precisely on a board. This situation, mainly full lateral inflow, is the worst case situation in which the largest load for which the rotor blade must be dimensioned, precisely a sizing load, occurs.

It will be evident from the foregoing that, with a constant coefficient of resistance, it is simply and only the area of the rotor blade that is crucial. This is also the reason for the unlikely configuration of rotor blades. However, it is known that the energy production of a wind power installation crucially depends on the length of the rotor blades. Therefore, the short long blades are hitherto preferred to the wide short blades. It will be noted, however, that the point will not be examined in this regard that this consideration does not apply to the inner region of alabe (main board) when the situation is fundamentally different. Finally, the relative speed of the rotor blade relative to the air flowing around it in the region of the blade root is the lowest and rises continuously towards the blade tip. Therefore, the rotor blade shape described herein with the narrow outer region and the optimized lift-resistor ratio is a particularly advantageous solution. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (4)

2. Having described the invention as above, the content of the following claims is claimed as property: 1. Rotor blade of a wind power installation, characterized in that the rotor blade, in particular in the central region of the rotor, the leading edge thus --called, has a lift-resistance ratio which in the region of about ± 2o from the optimum step angle has a lift-resistance ratio value of more than 80%, preferably 90% and more than the maximum value of the support-resistance relationship. 2. Rotor blade according to claim 1, characterized in that the characteristic curve of the lift-resistance ratio is of a configuration depending on the pitch angle as shown in figure 2.
3. 3. Wind power installation, characterized because it comprises a rotor which has at least one rotor blade having the characteristics according to one of the preceding claims.
4. 4. Rotor blade, characterized in that it has a tip or a tip end plate which rises out of the plane of the rotor blade in the manner of a small wing, where the end plate is rotated about the threaded shaft in its central plane by about 4 to 8o, preferably 4 to 6o, particularly preferably about 5o.