KR101454260B1 - 35% Thickness Airfoil for Large Scale Wind Turbine Blade - Google Patents

Abstract

The present invention relates to a 35% thickness airfoil for a large scale wind turbine blade. The 35% thickness airfoil for a large scale wind turbine blade according to one embodiment of the present invention is used for a wind turbine. According to one embodiment of the present invention, the airfoil has an upper surface and a lower surface. The thickness is 35% of a cord length. According to one embodiment of the present invention, a maximum ratio (lift coefficient/drag coefficient) in free transition is 155. A maximum ratio in forced transistor is 69. More particularly, in an aspect of the present invention, the 35% thickness airfoil for a large scale wind turbine blade can include other embodiments.

Description

35% Thickness Airfoil for Large Scale Wind Turbine Blade for Large Capacity Wind Turbine Blades with 35%

The present invention relates to an airfoil for a wind turbine, and more particularly to an airfoil for a wind turbine having a thickness ratio of 35%.

Wind power generators that generate electric energy by using wind power are being studied as alternative energy sources due to depletion of natural resources such as petroleum, coal and natural gas due to development of industry and population increase.

Wind power generation is a technology to convert kinetic energy of air flow into mechanical energy and then to produce electric energy again. Since it uses natural wind as an energy source, it is eco-friendly without increasing cost. .

In the structure of a conventional wind turbine generator, a nacelle for rotatably supporting a rotor blade is rotatably installed on the upper end of a tower of a high-rise tower on the ground. Inside the nacelle, a gearbox, a generator, To the generator via the main shaft. On the other hand, a wind direction anemometer is disposed at the upper end of the nacelle corresponding to the air flow wake. This is to control the entire system optimally according to the speed of the wind and to monitor the power generation. It adjusts the pitch angle of the rotor blades based on the wind direction and wind speed measured in the wind direction anemometer, Maximize.

On the other hand, the rotor blade obtains a three-dimensional shape by distributing a plurality of airfoil shapes along the span direction (longitudinal direction). The root side of the rotor blades should be thicker airfoils for structural stiffness and thinner on the tip of the rotor blades should be airfoils with better drag ratio (drag coefficient / drag coefficient) to be.

The airfoil is composed of an upper surface 63 and a lower surface 64 that are distributed along the cord 65 as shown in FIG. 1 and the front portion of the airfoil 6 is joined to the front surface 61, leading edge, and the trailing edge is referred to as trailing edge 62. The maximum thickness 66 and the cord length (see FIG. 2) of the airfoil 6 are important variables that determine the performance of the airfoil 6 . The maximum thickness 66 is usually used by dimensionlessly dividing by the cord length.

As is well known, the performance and efficiency of a wind turbine depend on the shape of each airfoil 6 that forms a cross section of the rotor blade, and the selection of an appropriate airfoil 6 is important for a wind turbine, Do.

However, most of the airfoils 6 currently used in wind power generators are usually developed for aircraft. For example, the Reynolds number (= density * code length * wind velocity / air viscosity coefficient), which is an important hydrodynamically variable parameter, is about 500,000-1,600,000 for wind turbines And the airfoil 6 in an area completely different from the operating condition is used as the rotor blade cross-sectional shape of the wind power generator, so that a considerable performance deterioration has to be taken.

Furthermore, the rotor blade of the wind turbine is large with a span of 10 m or more and is continuously exposed to pollution of the external environment (dust, insect body, moisture, freezing), but cleaning is not easy, It is expected that a higher efficiency rotor blade could not be expected by using the airfoil developed for aircraft without considering the above effects.

Airfoils used for wind turbines include the DU-W series of Delft University of Technology in the Netherlands, the RIS0-A and RIS0-B series of RIS0-DTU in Denmark, the FFA-W series of Sweden Aeronautical Research Institute, The NREL S series and the NACA 6 series. In order to develop an airfoil, it takes a lot of time and a lot of time and patience and effort to budget for a year or two. As a result, some of the above-mentioned airfoil series have to pay for their use according to the patent application. Efforts have also been made to maintain structural rigidity by receiving strong bending moments at the hub portion of the wind turbine blades. As a result, efforts have been made to reduce the weight of the hub by increasing the stiffness of the air foil by increasing the cross-sectional area of the air foil to 50% of the length of the airfoil cord. Among these airfoils, there is a flatback airfoil that allows the trailing edge of the airfoil to have a constant thickness. Particularly, in the case of a conventional airfoil, the thickness is thin and the tip is sharp. However, since the structure is difficult to design due to a strong bending moment in the vicinity of the hub, a flatback airfoil can be used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an airfoil family applicable to large-capacity wind turbine blades of a megawatt scale. Specifically, each of the airfoils belonging to the airfoil group must have a similar shape to each other and aerodynamic characteristics, and the advantage of such a structural design and a smooth and smooth blade shape can be achieved with a naked eye. The second is to provide an airfoil with low roughness sensitivity. Providing an airfoil in which the transition ratio when the transition point moves as far as possible through the forced transition reflecting the surface roughness is greater than 50% of the leg ratio obtained from the free transition process in the smooth airfoil . The airfoil having a thickness ratio of more than 30% is intended to provide not only the port ratio but also a high lift coefficient. In particular, it is an object of the present invention to provide an airfoil having a small roughness sensitivity by maximizing aerodynamic characteristics of an airfoil in a smooth state, and comparing the ratio of the forced transition to the free transition state in a wide range of angle of attack angles.

The present invention provides the following means for solving the above problems.

The present invention relates to an airfoil for use in a wind turbine blade, wherein the airfoil has an upper surface and a lower surface, the thickness ratio is 35% of the cord length, and the upper surface has a vertical coordinate value (x / (y / c) has a positive value, and the bottom surface has an absolute value of the vertical coordinate value (y / c) increased and decreased when the horizontal coordinate value (x / c) is in the range of more than 0.00 to 0.932, 1.0, the absolute value of the vertical coordinate value (y / c) increases again.

The airfoil has a shape of a horizontal coordinate value (x / c) and a vertical coordinate value (y / c) corresponding to the following table.

The present invention has the following effects.

1. Each airfoil belonging to the group of airfoils must have a similar shape and aerodynamic characteristics to each other, providing the advantage of such a structural design and a smooth blade shape that is also visually appealing.

2. Provides airfoil with low roughness sensitivity. Providing an airfoil in which the transition ratio when the transition point moves as far as possible through the forced transition reflecting the surface roughness is greater than 50% of the leg ratio obtained from the free transition process in the smooth airfoil It is effective.

3. The airfoil having a thickness ratio of more than 30% has an effect of providing a high lift coefficient as well as a lift ratio. Particularly, there is an effect of maximizing the aerodynamic characteristics of the airfoil in a smooth state, but providing an airfoil having a small roughness sensitivity by comparing the positive and negative ratios of the forced transition and the free transition state in a wide range of angle of attack angle.

1 and 2 are views for explaining the shape of an airfoil.
3 is a table of aerodynamic characteristics data of an airfoil group according to the present invention.
4 is a view showing each individual airfoil shape of an airfoil group according to the present invention;
FIG. 5 and FIG. 6 are tables of airfoils according to the present invention and the conventional airfoil (DU) group, which are based on the maximum angle of incidence and lift coefficients under the free transition and enforced conditions based on the angle of attack at which the maximum amount of airflow is generated.
7 is a graph of the resultant of the lift ratio and the lift ratio of the airfoil according to the present invention.
Figure 8 is a graph of the resultant of the airspeed < Desc / Clms Page number 10 >
9 is a view showing the shape of an airfoil according to the present invention.
10 is an elevation curve of an airfoil according to the present invention.
11 is a drag curve of an airfoil according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. Even if the terms are the same, it is to be noted that when the portions to be displayed differ, the reference signs do not coincide.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

The terms first, second, etc. in this specification may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

The aerodynamic performance of airfoils used in wind turbine blades can have a significant impact on annual power generation. As the operation time increases after installing the wind turbine generator, foreign matter such as dust or insect is fixed on the surface of the wind turbine blade and the surface roughness is increased. This roughness change affects the boundary layer transition and causes the aerodynamic performance to deteriorate. A well-designed airfoil with a low roughness sensitivity can minimize the degradation of the port ratio by less influencing the surface roughness increase due to blade operation. The airfoil designed in this way is an important factor that can lead to the improvement of the capacity factor of the wind turbine. The effect of roughness on aerodynamic performance can be found in the variation of cloth advantage. Particularly in the outboard of the blade, it requires an airfoil having a thin thickness and excellent in terms of the cost ratio. Therefore, the development of airfoil with less than 25% thickness and low roughness sensitivity is the main objective, and in the case of thicker airfoil, the goal is development of airfoil with maximum lift coefficient and lift performance.

The present invention provides an airfoil family applicable to large-capacity wind turbine blades of a megawatt scale. To this end, the design of the airfoil focused on the following points. The first is that each airfoil belonging to the airfoil group should be similar in shape and aerodynamic characteristics to each other. This will allow you to complete the geometry of the structure and the shape of the blade, which is also visually pleasing to the naked eye. The second is to design airfoils with low roughness sensitivity. The aim is to design the load ratio to be more than 50% of the load ratio obtained from the free transition process in the smooth airfoil when the transition point is moved to the front as far as possible through the forced transition reflecting the surface roughness do. It is also aimed to design the airfoil having a thickness ratio of more than 30% so as to have a high lift coefficient as well as a port ratio. The XFOIL program was used for the numerical calculation. The focus of the design was to maximize the aerodynamic characteristics of the airfoil in a smooth state, and to compare the ratio of the forced transition to the free transition state in a wide range of angle of attack, It aims to develop.

Hereinafter, a method for airfoil design will be described.

Airfoils having a thickness ratio of 18% used for the blade tip were made using NACA64-618, and airfoils having different thickness ratios were designed by inputting XFOIL to the basic shape from the thickness and the Kember distribution as shown in Fig. The Reynolds number is set to 10 × 10 ⁶ considering the shape and operating conditions of a large wind turbine of 5 MW or more. By adopting the flatback airfoil design concept, the thickness of the airfoil after 21% Respectively.

The comparison of aerodynamic performance is focused on designing the aerofoil group of DU-W series so that aerodynamic characteristics are similar or superior. XFOIL can handle transitions from a laminar boundary layer to a turbulent boundary layer. At this time, the transition condition applies the e ⁿ method. This method can be applied to predicting the transition advantage only when the two-dimensional Tollmien-Schlichting wave grows due to the linear instability of the flow, if it has a transition inducing structure. Here, n = 9 is used as a typical value to match the wind tunnel test results on average. In this case, when the surface is smooth, the point ^{where the} e ⁿ condition is satisfied before or after the trailing edge of the wing due to the free transition phenomenon is a transition point. For a rough surface airfoil, a cloth edge is forcibly given to any position before the airfoil . In the present invention, 5% of the cord is positioned at the top of the wing, and 10% of the cord is positioned at the bottom of the wing. The method of designing the external shape of the airfoil can maximize the design variables by presenting design variables and constraints through optimum design. However, in the case of determining the shape of a plurality of airfoils for use in a blade as in the present invention, the outer shape of the airfoil should preferably be similar to that of the airfoil so that the structure can be designed easily and smoothly. That is, the advance radius, the maximum thickness position, the camber, the camber position, the trailing edge thickness, the weight of the upper surface of the airfoil, and the weight occupied by the lower surface should be gradually changed as the thickness ratio increases. Therefore, it was not easy to optimize the shape of six airfoils with a simple optimization technique, and we focused on determining the airfoil shape by combining various functions provided by XFOIL. However, there is no specific standard for determining the initial shape to speed up the design. However, to reflect the aerodynamic inspiration, the negative camber is placed in the front part to reduce the roughness sensitivity as the thickness ratio increases, Compensation. The shape of the airfoil group obtained as a result of such efforts is shown in Fig. Particularly in the case of 40% airfoil, the front portion of the NACA63-040 airfoil with the maximum thickness was deformed to have an elliptical shape in order to obtain a smooth transition with the circular cylinder.

Fig. 5 and Fig. 6 summarize the maximum airspeed and lift coefficients under the conditions of free transition and forced draft in the designed airfoil and DU airfoil group based on the angle of attack at which the maximum airspeed ratio is generated.

As shown in FIGS. 5 to 8, the newly developed airfoil exhibits excellent overall air portability in a comparatively thin airfoil having a thickness ratio of 30% or less as compared with the DU airfoil group. When the thickness ratio exceeds 30%, the airfoil is relatively high It shows the lift coefficient and meets the design goal.

In conclusion, we developed a group of airfoils for horizontal wind turbines suitable for large-capacity wind turbines of 5 MW and above. The developed airfoil satisfies the target of high lift ratio and lift coefficient if it is insensitive to the initially set roughness. For airfoils thinner than 30% of thickness, the forced airfoil reflects the surface roughness, The proportion was over 50%. The newly developed airfoil showed better overall aerodynamic performance than the DU airfoil with relatively thin airfoils with a thickness ratio of less than 30% and showed a relatively high lift coefficient when the thickness ratio exceeded 30%.

Hereinafter, the airfoil having a thickness ratio of 35% will be described in more detail.

The present invention provides the shape coordinates of an airfoil developed for the purpose of increasing the aerodynamic efficiency of a wind turbine blade and the aerodynamic characteristics of the airfoil. Here, efficiency refers to the ratio of conversion from a given wind speed to electrical output, and an airfoil for a wind turbine having an aerodynamically superior shape has an effect of increasing the capacity factor of a wind turbine. Power generation companies that operate wind turbines prefer wind turbines with high utilization rates because utilization rates are directly linked to the import of wind turbines.

The most important technique here is the shape of the airfoil constituting the blade. The well-designed airfoil shape should have characteristics such that the output is not significantly reduced even if the roughness of the blade surface increases due to dust, worms, or freezing. Since the surface roughness of the blades reduces the power output by as much as 50%, the use of excellent airfoils plays an important role in increasing the market share of wind turbines.

는 받음각을 의미하며, 자유천이(free transition)에서 받음각은 8.5이며, 강제천이(forced transition)에서 받음각은 6.0이다.
도 3에 표시된 TE t(%)는 에어포일 뒷전의 두께를 코드길이(c)로 나눈 값의 퍼센티지이며, 두께비가 코드길이(c)의 35%인 경우, 뒷전의 두께를 코드길이(c)로 나눈 값의 퍼센티지는 2.0%이다.
도 3에 표시된 바와 같이,

는 에어포일의 두께가 최대가 되는 위치를 앞전에서 코드길이(c)의 몇 퍼센트인지 나타내는 값으로, 본 발명에서는 에어포일의 두께가 최대가 되는 위치는 앞전으로부터 코드길이(c) 대비 30%에 위치한다. Airfoils used in wind turbine blades should be similar in shape to each other as the airfoil family. Here, similar shape refers to chord position, camber distribution, radius of curvature of leading edge, thickness ratio of trailing edge, etc. where the maximum thickness of airfoil exists, As the faces of the members resemble each other, the shape of the various airfoils used in the blades must be similar to each other so that the blades are smooth and aerodynamically superior. The KW1-35 airfoil according to the present invention is a relatively thin airfoil having a thickness ratio of 35% of the cord length and used on the tip side of the blade, and has been developed to have a high Reynolds number of 10 ⁷ , The airfoil has an operating range three times higher than the Reynolds number of the airfoil for airflow. This airfoil has a lift-to-drag ratio of up to 155 under free transition conditions, and a forced transition reflecting the roughness effect (5% at the front and 5% at the top) The transition ratio is 69).
On the other hand, as shown in Fig. 5

Means the angle of attack, the angle of attack at free transition is 8.5, and the angle of attack at 6.0 for forced transition.
The TEt (%) shown in Fig. 3 is a percentage of the thickness of the rear airfoil divided by the cord length c. If the thickness ratio is 35% of the cord length c, Is 2.0%. ≪ / RTI >
As shown in Figure 3,

In the present invention, the position where the thickness of the airfoil reaches the maximum is 30% of the cord length (c) from the leading edge. Located.

The shape coordinates of the KW1-35 airfoil according to the present invention are as follows.

Referring to FIG. 9, values of y / c (c is a code length), which is a value in the y-axis in the counterclockwise direction starting from a point where x / c (c is a code length) Respectively.

10 and 11 show the lift curve and the drag curves of the KW1-35 airfoil according to the present invention.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

6: Airfoil
t: maximum thickness
c: Code length
c _l : lift
c _d : Drag
α: Angle of attack

Claims (2)

delete An airfoil for use in a wind turbine blade, the airfoil having an upper surface and a lower surface, wherein the thickness ratio is 35% of the cord length,
The Reynolds number is 10 ⁷ , and the percentage of the thickness of the trailing edge divided by the cord length is 2.0%
In the free transition, the maximum heading ratio is 155, the angle of attack is 8.5,
In the forced transition, the maximum heading ratio is 69, the angle of attack is 6.0,
The position where the thickness of the airfoil reaches the maximum is located at 30% of the cord length from the front side,
Airfoil for large-capacity wind turbine blades with a thickness ratio of 35% with the form of horizontal coordinate value (x / c) and vertical coordinate value (y / c) corresponding to the table below.

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