CN114593010A - A high lift-to-drag ratio wind turbine airfoil and its design method at a large angle of attack - Google Patents

Abstract

The invention belongs to the technical field of wind power generation, and in particular relates to a design method for a high lift-to-drag ratio wind turbine airfoil under a large angle of attack. shape profile, the leading edge point of the reference airfoil profile is coincident with the coordinate origin, and a slot is set on the reference airfoil profile; two points are selected at the lower airfoil surface as the entrance of the slot, denoted as point a and point b; Select two points on the upper airfoil as the exit of the slit, denoted as point c and point d; point e between point a and point c, point f between point b and point d; aec and bfd constitute the opening. The shape of the slot, forming a channel in the middle of the airfoil; ae and bf are straight lines, ec and fd are arcs, and ae and bf are parallel. A larger stall angle of attack and smaller resistance are achieved, which significantly improves its lift-to-drag ratio at a large angle of attack, thereby improving the wind energy absorption efficiency of the wind rotor of the wind turbine.

Description

A high lift-to-drag ratio wind turbine airfoil and its design method at a large angle of attack

technical field

The invention belongs to the technical field of wind power generation, and in particular relates to a high lift-to-drag ratio wind turbine airfoil and a design method thereof under a large attack angle.

Background technique

系列翼型、瑞典航空研究院设计的FFA系列翼型等，并被众多的风电企业采用，对风力发电机性能的改善起到了至关重要的作用。For the geometric shape of the wind blade, the airfoil is the "gene" of the blade, and its aerodynamic performance directly affects the aerodynamic performance of the wind turbine blade. Therefore, the design of the aerodynamic shape of the wind turbine blade of the wind turbine cannot be separated from the airfoil design. Before the 1980s, the airfoils of wind turbines often used aviation airfoils. However, aviation airfoils are usually designed under the condition of subsonic speed, and the aerodynamic performance cannot be effectively guaranteed under low speed conditions. In addition, there are disadvantages of small thickness and inability to meet structural requirements. At the same time, the airfoil stalls at high angles of attack. serious. Therefore, the current research on aviation airfoils has been difficult to meet the design requirements of wind turbines. Therefore, since the 1980s, under the trend of increasing wind turbine blades, the demand for special airfoils for high-performance wind turbines has become more and more urgent. Many foreign institutions have carried out research on special airfoils for large wind turbines in the last century, and achieved fruitful results, forming several series of special airfoils for wind turbines, such as the NACA series airfoils designed by the National Aeronautics and Space Administration (NASA). , the NREL S series airfoil designed by the National Renewable Energy Laboratory (NREL) in the United States, the DU series airfoil designed by Delft University in the Netherlands, the Danish airfoil

A series of airfoils, FFA series airfoils designed by the Swedish Aeronautical Research Institute, etc., have been adopted by many wind power companies, and have played a crucial role in improving the performance of wind turbines.

The current wind turbine airfoil design scheme, for example, the existing vertical axis wind turbines mostly use the reference airfoil, and the smooth transition near the trailing edge of the airfoil suction surface, its aerodynamic performance can effectively improve the wind turbine's absorption efficiency of wind energy, thereby improving wind power economic efficiency of the machine. However, although this type of airfoil can ensure a low drag coefficient at a small angle of attack, it is prone to airflow separation at a large angle of attack, thereby reducing the lift coefficient, increasing the drag coefficient, and reducing the wind turbine rotor. Economic benefits, so the aerodynamic efficiency of vertical axis wind turbines is not high at low wind speeds.

At present, the slit shapes of domestic and foreign patents and documents are designed with full straight and full arc. They can only improve a limited lift-to-drag ratio (less than 100%) at a limited large angle of attack (greater than 16°), and the split The seam shape and parameters do not give a perfect design method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high lift-to-drag ratio wind turbine airfoil and a design method thereof under a large angle of attack, which solves the problem that airflow separation is easy to occur at a large angle of attack, thereby reducing the lift coefficient, increasing the drag coefficient, reducing the In view of the economic benefits of the wind turbine rotor, the aerodynamic efficiency of the vertical axis wind turbine is not high at low wind speeds.

The present invention is achieved through the following technical solutions:

A design method for a high lift-to-drag ratio wind turbine airfoil under a large angle of attack, the high lift-to-drag ratio wind turbine model is described as follows with its formation process:

Project the reference airfoil profile on the XY coordinate system to obtain the reference airfoil profile, coincide the leading edge point of the reference airfoil with the coordinate origin, and set a slit on the reference airfoil profile;

Select two points at the lower airfoil as the entrance of the slot, denoted as point a and point b; select two points at the upper airfoil as the exit of the slot, denoted as point c and point d;

Take point e between point a and point c, and point f between point b and point d;

aec and bfd form a slotted shape that forms a channel in the middle of the airfoil;

ae and bf are straight lines, ec and fd are arcs, ae and bf are parallel;

A valve is provided at the entrance of the slit.

Further, when the angle of attack is 0-8°, the valve is in a closed state; when the angle of attack is greater than 8°, the valve is in an open state.

Further, the chord length of the reference airfoil profile is C, the abscissa corresponding to point a is 0.05C-0.08C, the abscissa corresponding to point b is 0.07C-0.1C, and the abscissa corresponding to point c is 0.55C -0.65C, the horizontal width of ab is 0.07C-0.1C, and the horizontal width of cd is 0.08C-0.1C.

Further, ec is an arc with a radius of 0.5C-0.55C, and fd is an arc with a radius of 0.4C-0.45C.

Further, the position of the slit entrance is offset from the rear end of the wing at the stagnation point of the airfoil.

Further, the trailing end of the ec is tangent to the upper airfoil.

Further, the position of the slotted outlet is on the side of the front end of the wing in the separation area of the upper airfoil, and the slotted outlet is parallel to the upper airfoil.

Further, the included angle between ae and the X axis is 10°˜20°.

Further, the S809 airfoil is used as the reference airfoil.

The invention also discloses a high lift-to-drag ratio wind turbine airfoil under a large attack angle obtained based on the design method for a high lift-to-drag ratio wind turbine airfoil under a large attack angle.

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention provides a design method of a high lift-to-drag ratio wind turbine airfoil under a large attack angle. The airfoil has a smooth slit in the middle, and the slit introduces the high-speed airflow on the lower surface to the upper surface, increasing the upper surface. Air flow kinetic energy, thereby inhibiting the air flow separation, so that the airfoil has a larger lift coefficient at a large angle of attack, a larger stall angle of attack, and less resistance, and can improve the lift at a large angle of attack (greater than 8°). coefficient, to achieve a larger stall angle of attack and smaller resistance, which significantly improves its lift-to-drag ratio at a large angle of attack, thereby improving the wind energy absorption efficiency of the wind turbine rotor. There is a valve at the entrance of the slit. In the case of a small attack angle (less than 8°), the valve closes the slit at a small attack angle and uses the basic contour, which ensures better performance under the small attack angle. lift-to-drag ratio.

Description of drawings

Fig. 1 is the geometrical shape of the airfoil of the present invention;

Figure 2 is the geometric shape of the reference airfoil;

3 is a comparison of the lift curves of the airfoil of the present invention and the reference airfoil when the angle of attack is 2°-20°, and S809-1 represents the airfoil of the present invention;

4 is a comparison of the drag curves of the airfoil of the present invention and the reference airfoil when the angle of attack is 2°-20°, and S809-1 represents the airfoil of the present invention;

5 is a comparison of the lift-drag ratio curves of the airfoil of the present invention and the reference airfoil when the angle of attack is 2°-20°, and S809-1 represents the airfoil of the present invention;

6 is the comparison of Mach number distribution and flow field when the airfoil of the present invention and the reference airfoil are at an angle of attack of 6°, wherein FIG. 6A is the airfoil of the present invention, and FIG. 6B is the reference airfoil;

7 is the comparison of Mach number distribution and flow field when the airfoil of the present invention and the reference airfoil are at an angle of attack of 8°, wherein FIG. 7A is the airfoil of the present invention, and FIG. 7B is the reference airfoil;

Fig. 8 is the comparison of Mach number distribution and flow field between the airfoil of the present invention and the reference airfoil when the angle of attack is 10°, wherein Fig. 8A is the airfoil of the present invention, and Fig. 8B is the reference airfoil;

Fig. 9 is the comparison of Mach number distribution and flow field between the airfoil of the present invention and the reference airfoil when the angle of attack is 16°, wherein Fig. 9A is the airfoil of the present invention, and Fig. 9B is the reference airfoil;

Fig. 10 is the Mach number distribution comparison and flow field comparison between the airfoil of the present invention and the reference airfoil when the angle of attack is 18°, wherein Fig. 10A is the airfoil of the present invention, and Fig. 10B is the reference airfoil;

Figure 11 shows the geometric shape of a straight-line slotted airfoil, named S809-2,

Figure 12 shows the geometry of the slotted airfoil with a circular arc slotted airfoil, named S809-3;

Figure 13 is the lift-drag ratio variation curve of different shapes of slotted airfoils when the angle of attack is greater than 8°;

Figure 14 is the lift-drag ratio change curve of slotted airfoil S809-4 and S809-5 when the angle of attack is greater than 8°.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and embodiments, wherein the embodiments are theoretical calculation analysis of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The invention discloses a high lift-to-drag ratio wind turbine airfoil at a large angle of attack. A valve is provided at the entrance of the slit. In the case of a small angle of attack (less than 8°), the valve makes the slit at a small angle of attack. Close down and use its base profile, which ensures a better lift-to-drag ratio at a small angle of attack. In the case of a large angle of attack (greater than 8°), the valve opens, making it have a good lift-drag ratio and lift coefficient at a large angle of attack.

The valve can use a solenoid valve. The solenoid valve is connected to the control unit. A measurement unit for measuring the angle of attack is arranged on the airfoil. The measurement unit is connected to the control unit. In the case of a large angle of attack (greater than 8°), the control unit triggers the valve to open.

With reference to Figure 1, the structure of the high lift-to-drag ratio wind turbine airfoil is based on the curve profile of the reference airfoil S809 shown in Figure 2 as a prototype. The structure of the high lift wind turbine airfoil is described as follows:

Make the frontal projection of the reference airfoil profile respectively in the X and Y coordinate system to obtain the reference airfoil profile, and coincide the leading edge point of the reference airfoil profile with the coordinate O point;

Make abcdef on the profile of the reference airfoil and connect aec and bfd, where ae and bf are parallel straight lines, ec is an arc, and fd is an arc. upper wing surface.

In the embodiment of the present invention, the main design indicators of the high lift-to-drag ratio wind turbine airfoil are as follows: (1) the design Reynolds number is in the order of 1 million, and the design Mach number is 0.2; Stall at high angle of attack; (3) Good lift-drag characteristics; (4) Stall characteristics are moderate. According to these indicators, the slitting parameters of different performances can be set.

In the practical application process of the present invention, the outer surface of the high lift-to-drag ratio wind turbine airfoil at a large angle of attack is divided into two parts by slits, the front section and the rear section, the front section is composed of aec and leading edge, and the rear section is composed of bdf and The trailing edge composition, aec and bdf form the shape of the slot, and the aerodynamic characteristics of the slotted airfoil vary with the variation of the slot parameters.

For this inventive airfoil, the slotted design is the key. The function of the slit is to introduce the high-speed airflow of the lower airfoil into the upper airfoil, increase the kinetic energy of the airflow on the upper airfoil, so as to slow down the airflow separation of the upper airfoil, increase its stall angle of attack, reduce the drag, and increase the lift. , thereby significantly increasing the lift-to-drag ratio at large angles of attack.

The empirical design parameters of the slit are as follows: ab is the airflow inlet, cd is the airflow outlet, the length and coordinates of ab and cd are variable, in general, ae, bf should be straight lines and the angle with the x-axis should be 10° to 20° °, ec and fd should be arcs and ec should be tangent to the upper wing surface as much as possible, ab should be at a position behind the stagnation point of the wing, point a should be between 0.05C and 0.08C, and the width of ab should be 0.07C Between -0.1C, cd should be in front of the upper airfoil separation area, c point should be between 0.55C-0.65C, and the width of cd should be as small as possible, between 0.08C-0.1C, ec is an arc with a radius of 0.5C-0.55C, and fd is an arc with a radius of 0.4C-0.45C.

Example 1

In the high lift-to-drag ratio wind wing model provided by the present invention, the front section of the slit is linear, and the rear section is circular. ae and bf are two line segments, ec and fd are two arcs, and the chord length of the reference airfoil profile is C, where a _x =0.05C, b _x =0.13C, c _x =0.59c, d _x =0.66 C, the width of ab is 0.08C, ae is parallel to bf, the lateral distance of ae is 0.34C, bf=0.32C, the angle between ae and the x-axis is 16°, ec is an arc with a radius of 0.52Cmm, and the The airfoils are tangent and fd is an arc with a radius of 0.41C and a cd width of 0.07C. It is named S809-1 after this.

Example 2

In the high lift-to-drag ratio wind wing model provided by the present invention, the front section of the slit is linear, and the rear section is circular. ae and bf are two line segments, ec and fd are two arcs, and the chord length of the reference airfoil profile is C, where a _x =0.05C, b _x =0.12C, c _x =0.55C, d _x =0.63 C, ab width is 0.07C, ae is parallel to bf, the lateral distance of ae is 0.34C, bf=0.32C, the angle between ae and the x-axis is 10°, ec is an arc with a radius of 0.51Cmm, and the The airfoil is tangent, fd is an arc with a radius of 0.41C, and the width of cd is 0.07C, denoted as S809-4.

Example 3

In the high lift-to-drag ratio wind wing model provided by the present invention, the front section of the slit is linear, and the rear section is circular. ae and bf are two line segments, ec and fd are two arcs, and the chord length of the reference airfoil profile is C, where a _x =0.08C, b _x =0.18C, c _x =0.65C, d _x =0.75 C, the width of ab is 0.1C, ae is parallel to bf, the lateral distance of ae is 0.34C, bf=0.32C, the angle between ae and the x-axis is 20°, ec is an arc with a radius of 0.53Cmm, and the The airfoil is tangent, fd is an arc with a radius of 0.42C, and the width of cd is 0.1C, denoted as S809-5.

As can be seen from Figure 14, compared with the reference airfoil, the slotted airfoil will have a better lift-drag ratio, but the position and shape of the slot are the key.

The advantages of a wind turbine airfoil with a high lift-to-drag ratio of the present invention are verified by comparing the following different inflow angles of attack. The airfoil aerodynamic analysis software is used to analyze the aerodynamic performance. The calculated state parameters are: incoming flow angle of attack: 6°, 8°, 10°, 16°, 18°, Mach number 0.2, Reynolds number 1×106.

Take the classic wind turbine airfoil S809 as the reference airfoil, compare it with the airfoil of the present invention, and analyze and compare the aerodynamic performance difference between the airfoil of the present invention and the reference airfoil.

It can be seen from FIG. 3 that the airfoil S809-1 of the present invention stalls when the angle of attack is 18°, and the reference airfoil stalls when the angle of attack is 10°, and the airfoil of the present invention obviously delays the stall.

It can be seen from FIG. 4 that when the angle of attack is 0-8°, the resistance of the present invention is slightly increased, but when the angle of attack is greater than 8°, the resistance of the airfoil of the present invention is greatly reduced.

It can be seen from FIG. 5 that when the angle of attack is greater than 8°, the lift-to-drag ratio of the airfoil of the present invention is significantly larger than that of the reference airfoil, and has greater lift and less resistance.

It can be seen from Figures 6, 7 and 8 that the role of the slits in the airfoil of the present invention is to introduce the high-speed airflow from the lower surface to the upper surface to increase lift and reduce drag.

It can be seen from Figures 9 and 10 that when the angle of attack is greater than 16°, a large separation area has appeared on the upper airfoil of the reference airfoil, but the airfoil of the present invention introduces the high-speed airflow from the lower airfoil to the upper airfoil because of the slits. There is no separation zone on the airfoil and the upper airfoil. The airfoil of the present invention has good aerodynamic characteristics under the condition of large attack angle (when the attack angle is 20°, it is improved by more than 10 times compared with the reference airfoil), and has a large airfoil. lift-drag ratio and lift coefficient, and greatly delayed separation.

For the slotted airfoil, the design of the slotting parameters is the key, and the influence of different slotted shapes on the design of the airfoil of the present invention is analyzed and compared.

Comparative Example 1

As shown in Figure 11, the slot shape is designed as the geometric shape of a linear slot airfoil, named S809-2, that is, ae and bf are parallel straight lines, ec is a straight line, fd is a straight line, aec is a straight line, bfd as a straight line.

Comparative Example 2

As shown in Figure 12, the slot shape is designed as the geometric shape of the arc-shaped slot airfoil, named S809-3.

As shown in Figure 13, the lift-drag ratio curve of different shapes of slotted airfoils when the angle of attack is greater than 8° shows that the S809-1 airfoil has the largest lift-drag ratio when the angle of attack is greater than 8°.

Table 1 is the increment table of the maximum lift-to-drag ratio of the airfoil of the present invention and S809 under different slot shapes (Example 1 of the present invention and Comparative Documents 1 and 2) when the angle of attack is 18°;

Table 1. Comparison of maximum lift-drag ratio and its lift-drag ratio increment table

S809 S809-1 S809-2 S809-3 Cl/Cd 5.122 60.0097 15.3129 16.4982 Incremental 0% 1071.6% 199% 222.1%

As can be seen from Figures 11-13 and Table 1, the unsealing parameters have many influences on the airfoil of the present invention, which are summarized as follows:

The inlet should be as large as possible, and the direction of the inlet should be as parallel as possible to the direction of the incoming flow; the outlet should be as small as possible, and the direction of the outlet should be as parallel to the upper airfoil as possible.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. a design method of a high lift-to-drag ratio wind turbine airfoil under large angle of attack, is characterized in that, described high lift-to-drag ratio wind turbine model is described as with its formation process: Project the reference airfoil profile on the XY coordinate system to obtain the reference airfoil profile, coincide the leading edge point of the reference airfoil profile with the coordinate origin, and set a slit on the reference airfoil profile; Select two points at the lower airfoil as the entrance of the slot, denoted as point a and point b; select two points at the upper airfoil as the exit of the slot, denoted as point c and point d; Take point e between point a and point c, and point f between point b and point d; aec and bfd form a slotted shape that forms a channel in the middle of the airfoil; ae and bf are straight lines, ec and fd are arcs, ae and bf are parallel; A valve is provided at the entrance of the slit. 2. the design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1, is characterized in that, when the angle of attack is 0-8°, the valve is in a closed state; when the angle of attack is 0-8° When greater than 8°, the valve is in the open state. 3. the design method of a kind of high lift-to-drag ratio wind turbine airfoil under large angle of attack according to claim 1, it is characterized in that, the chord length of the reference airfoil profile is C, and the abscissa corresponding to point a is 0.05C-0.08C, the abscissa corresponding to point b is 0.07C-0.1C, the abscissa corresponding to point c is 0.55C-0.65C, the horizontal width of ab is 0.07C-0.1C, and the horizontal width of cd is 0.08C-0.1C. 4. the design method of a kind of high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 3, is characterized in that, ec is the arc of radius 0.5C-0.55C, and fd is radius 0.4C -0.45C arc. 5 . The design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1 , wherein the slot entrance is located at the rear end side of the wing at the stagnation point of the airfoil. 6 . 6 . The design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1 , wherein the tail end of the ec is tangent to the upper airfoil. 7 . 7. The design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1, characterized in that, the slotted outlet position is on the side of the front end of the wing in the separation area of the upper airfoil, and the opening The slot outlet is parallel to the upper wing surface. 8 . The design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1 , wherein the included angle between ae and the X axis is 10° to 20°. 9 . 9 . The design method of a high lift-to-drag ratio wind turbine airfoil under a large angle of attack according to claim 1 , wherein the S809 airfoil is used as the reference airfoil. 10 . 10. A high lift-to-drag ratio wind turbine airfoil under a large attack angle obtained based on the design method for a high lift-to-drag ratio wind turbine airfoil at a large attack angle according to any one of claims 1-9.

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