CN103047079B - Efficient low-load wing section special for horizontal shaft wind turbine blade and designing method of wind section - Google Patents

Abstract

The patent of the present invention discloses a design method of a special airfoil for a horizontal axis wind turbine blade and a special airfoil for a horizontal axis wind turbine blade obtained based on the method. The design method is based on an inverse design method, and the designed airfoil has high efficiency and low Load, good variable working condition characteristics and smooth stall characteristics. The beneficial effects of the present invention are as follows: first, change the traditional airfoil design target, and propose a special airfoil for horizontal axis wind turbine blades with high efficiency and low load, good variable working condition characteristics and smooth stall characteristics. : It has a high maximum lift-to-drag ratio, a high design lift coefficient, a low maximum lift coefficient, a small drop in the design lift coefficient under rough leading edge conditions, good variable operating condition characteristics and smooth stall characteristics. Second, use the inverse design method to implement the special airfoil design of the horizontal axis wind turbine blade with high efficiency and low load, good variable working condition characteristics and smooth stall characteristics. Third, for the application of the airfoil with the relative thickness of the outer side of the wind turbine blade being less than or equal to 25%, the corresponding aerodynamic parameter design indicators are proposed.

Description

A high-efficiency low-load horizontal-axis wind turbine blade special airfoil and its design method

technical field

The present invention relates to a special airfoil design method for horizontal axis wind turbine blades, in particular to a special airfoil design for horizontal axis wind turbine blades with high efficiency and low load, good variable working condition characteristics and smooth stall characteristics based on the inverse design method design method.

Background technique

Wind turbine blades are the core components of wind turbines, and the performance of the special airfoil for wind turbine blades directly affects the performance of wind turbine blades. The blades not only have aerodynamic performance requirements but also load requirements. We hope that the wind turbine has a higher output power and a lower load at the same time, especially the increase of the ultimate load has a greater impact on the wind turbine blades.

The design of wind turbine blades has always required that the special airfoil of the wind turbine has a high maximum lift coefficient to increase the output power of the blade, especially the airfoil on the outer side of the blade. However, in practice, the blades mostly operate near the design operating point, not near the maximum lift coefficient, and a high design lift coefficient can reduce the chord length of the airfoil to reduce the weight of the blade and reduce the load. However, the maximum lift coefficient has little influence on the output power of the blade, and the increase of the maximum lift coefficient will cause the increase of the ultimate load of the blade instead.

During the operation of the wind turbine, due to various factors such as the influence of gusts or untimely control, the wind turbine cannot fully operate under the design conditions, and the airfoil of the wind turbine is required to have good variable operating condition characteristics and smooth stall characteristics.

Therefore, it is very necessary to develop a special airfoil for horizontal axis wind turbine blades with high efficiency and low load, good variable operating conditions and smooth stall characteristics. It should have a high maximum lift-to-drag ratio, a high design lift coefficient, and Low maximum lift coefficient, small drop in design lift coefficient under rough leading edge conditions, good variable operating condition characteristics and smooth stall characteristics.

Contents of the invention

In the prior art, there are many airfoil design methods, and various forms of intelligent optimization design methods are common, such as the optimization design method based on genetic algorithm, which is widely used at present. Another common airfoil design method is the inverse problem Design method, no matter which design method is used, a suitable airfoil can be obtained, but in the existing airfoil design methods, too much emphasis is placed on the improvement of the maximum lift coefficient, etc., and usually a larger maximum lift coefficient is taken as the design goal , Practice has proved that airfoils designed based on this concept often show shortcomings such as low efficiency and large loads in use, which greatly limits the development of wind turbine blades.

Aiming at the above-mentioned shortcomings and deficiencies of the prior art, the technical problem to be solved by the present invention is to propose a design method for a special airfoil for horizontal-axis wind turbine blades with high efficiency and low load, good variable working conditions and smooth stall characteristics and the above-mentioned Special airfoil for horizontal axis wind turbine blades.

Because wind turbines mostly operate near the design operating point (namely, the design angle of attack), rather than near the maximum lift coefficient. From the calculation formula of the following power p, it can be concluded that in terms of the aerodynamic performance of the airfoil, the maximum lift-to-drag ratio of the airfoil can be improved And the design lift coefficient C _l is the key to improve the output power of the blade. And a high design lift coefficient can reduce the chord length of the airfoil to reduce the weight of the blade and reduce the load.

$\mathrm{<span\; class="notranslate">\; dp</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&rho;</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c\&Omega;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; rdr</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&rho;</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c\&Omega;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}\mathrm{<span\; class="notranslate">\; tg\&phi;</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; rdr</span>}$

The shear force F _xb in the swinging direction of the aerodynamic load acting on the wind turbine blade is the main factor affecting the ultimate load of the blade. It can be seen from the calculation formula of F _xb that the higher the maximum lift coefficient of the airfoil, the greater the ultimate load will be, so the maximum lift coefficient of the airfoil should be limited in the design.

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; xb</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&rho;</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&rho;</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dr</span>}$

In addition, due to various factors such as the influence of gusts or untimely control during the operation of the wind turbine, the wind turbine cannot fully operate under the design conditions, and the airfoil of the wind turbine is required to have good variable operating condition characteristics and smooth stall characteristics. .

According to the above analysis, a special airfoil for horizontal axis wind turbine blades with high efficiency and low load, good variable working conditions and smooth stall characteristics should have the following aerodynamic characteristics: high maximum lift-to-drag ratio, high design lift coefficient, It has a low maximum lift coefficient, a small decrease in the design lift coefficient under the rough condition of the leading edge, and good characteristics of variable operating conditions and smooth stall characteristics.

The technical scheme that the present invention adopts for solving its technical problem is:

A design method for a special airfoil of a horizontal axis wind turbine blade, based on a general airfoil reverse design method, characterized in that the design method comprises the following steps:

Given airfoil target pressure distribution and initial basic airfoil;

Adjust the pressure distribution of the basic airfoil to obtain the intermediate airfoil;

Calculate the pressure distribution of the intermediate airfoil using the Euler equation;

Compare the pressure distribution of the intermediate airfoil with the target pressure distribution, judge whether it is necessary to continue to adjust the intermediate airfoil according to the degree of difference between the two, and if the degree of difference is within the allowable error range, terminate the adjustment to obtain the target airfoil , otherwise, continue to adjust the pressure distribution of the middle airfoil until the pressure distribution of the middle airfoil meets the requirements;

in,

The airfoil target pressure distribution includes the airfoil target pressure distribution under the design angle of attack and the airfoil target pressure distribution under the critical stall angle of attack: in the airfoil target pressure distribution under the design angle of attack, the suction surface The pressure peak is at the position of 1-25% of the chord length from the leading edge of the airfoil, and there is a gentle reverse pressure gradient from the suction leading edge of the airfoil to the position of 40% of the chord length, so as to obtain a smaller drag coefficient and a higher Design lift coefficient; in the airfoil target pressure distribution under the critical stall angle of attack, the pressure peak on the suction surface is at a position of 0-1% chord length from the leading edge point of the airfoil to control the maximum lift coefficient of the airfoil ;

During the design process, the maximum thickness of the constrained airfoil is at the position of 34.0%-37.0% of the chord length.

Preferably, for the airfoil applied to the outer side of the blade with a relative thickness less than or equal to 25%, in the step of judging whether to continue to adjust the intermediate airfoil, it is necessary to further determine whether each aerodynamic parameter of the intermediate airfoil meets the following conditions:

(a) Efficiency:

Maximum lift-to-drag ratio: ${\left(\frac{C_l}{C_d}\right)}_{\max }>150,$

Design lift coefficient: C _ldesign >1.16;

(b) Low load performance: the maximum lift coefficient C _lmax and the design lift coefficient C _ldesign satisfy

(c) Rough insensitivity: $0.85\&le;\frac{C_{\mathrm{ldesign}}^{\&prime;}}{C_{\mathrm{ldesign}}}\&le;1,$

(d) Good variable working condition characteristics:

Δα=α _stall -α _design ≥5, $0<\frac{C_{l\max }-C_{\mathrm{ldesign}}}{\mathrm{\&Delta;\&alpha;}}<0.05,$ $\frac{|{\left(\frac{C_l}{C_d}\right)}_{\mathrm{stall}}-{\left(\frac{C_l}{C_d}\right)}_{\max }|}{\mathrm{\&Delta;\&alpha;}}<\mathrm{twenty\; one};$

(e) Smooth stall characteristics:

${<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cl</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Cl</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; stall</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0.005</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; stall</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; ,</span>$

Among the above types:

C′ _ldesign is the design lift coefficient of the airfoil under rough conditions;

C _l , C _d , C _ldesign , C _lmax , The lift coefficient, drag coefficient, design lift coefficient, maximum lift coefficient, and maximum lift-to-drag ratio of the airfoil under the design angle of attack under smooth conditions; is the lift-to-drag ratio of the airfoil at the critical stall angle of attack under smooth conditions;

α, α _stall , Δα are angle of attack, stall angle of attack, and angle of attack difference, respectively.

Further, the step of calculating the design lift coefficient _C′ldesign of the airfoil under rough conditions is to set a fixed rotation speed at the position of 1% chord length of the upper surface and 10% chord length of the lower surface for the intermediate airfoil obtained in the design. The design lift coefficient calculated at peak time.

The design method of the special airfoil of the horizontal axis wind turbine blade of the present invention and the special airfoil of the wind turbine blade designed according to the method have the following advantages:

1. The special airfoil for wind turbine blades of the present invention has high efficiency and low load, good variable working conditions and smooth stall characteristics, and has changed the traditional airfoil design goal of one-sided pursuit of a larger maximum lift coefficient; 2. The wind turbine of the present invention The special airfoil for the blade has excellent aerodynamic characteristics, which effectively improves the performance of the blade. It has a high maximum lift-to-drag ratio, a high design lift coefficient, a low maximum lift coefficient, and a small drop in the design lift coefficient under rough leading edge conditions. 3. The wind turbine blade airfoil family of the present invention can increase the output power of the blade, reduce the load, reduce the weight of the blade, and reduce the cost of the blade.

Description of drawings

18%, 21%, 25% geometric profile diagrams of three airfoils of the present invention;

Fig. 2 is the pressure distribution of 25% airfoil at design point for the relative thickness of the present invention's design;

Fig. 3 is the pressure distribution of the airfoil with a relative thickness of 25% at the critical stall angle of attack for the design of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with examples and accompanying drawings.

The force on the airfoil is the resultant force of the distributed forces acting on the upper and lower surfaces. There are two types of surface forces, one is normal force and the other is tangential force. Define the resultant force perpendicular to the incoming flow in the far front as the lift force, and the resultant force in line with the direction of the incoming flow in the far side as the drag force. Lift and drag are usually expressed as dimensionless lift and drag coefficients. The lift coefficient and drag coefficient of the airfoil change with the angle of attack, which can form the lift characteristic and drag characteristic curve. At first, the lift coefficient of the airfoil increases with the angle of attack. When the angle of attack reaches a certain value, the lift coefficient reaches its maximum value, which is recorded as the maximum lift coefficient.

The lift-to-drag ratio is the ratio of the lift coefficient to the drag coefficient of an airfoil.

The design lift coefficient refers to the lift coefficient corresponding to the maximum lift-to-drag ratio.

The method for determining the design index of the present invention is: according to the aforementioned high efficiency, low load, rough insensitivity, good variable working condition characteristics and smooth stall characteristic evaluation formulas, the DU series airfoils and The NACA airfoil is analyzed, and the aerodynamic performance design index applied to the airfoil whose outer relative thickness of the wind turbine blade is less than 25% is proposed.

The design method of the special airfoil of the horizontal axis wind turbine blade proposed by the present invention is based on the general airfoil inverse design method, comprising the following steps: given the airfoil target pressure distribution and the initial basic airfoil; adjusting the pressure distribution of the basic airfoil to obtain Intermediate airfoil; use the Euler equation to calculate the pressure distribution of the intermediate airfoil; compare the pressure distribution of the intermediate airfoil with the target pressure distribution, and judge whether it is necessary to continue to adjust the intermediate airfoil according to the degree of difference between the two, if the degree of difference is allowed If within the error range, the adjustment is terminated to obtain the target airfoil, otherwise, continue to adjust the pressure distribution of the intermediate airfoil until the pressure distribution of the intermediate airfoil meets the requirements; wherein, the airfoil target pressure distribution includes the design Airfoil target pressure distribution at angle of attack and airfoil target pressure distribution at critical stall angle of attack: In the airfoil target pressure distribution at the design angle of attack, the pressure peak on the suction surface is at a distance from the airfoil leading edge point At the position of 1-25% of the chord length, there is a gentle reverse pressure gradient from the airfoil suction front edge to the position of 40% of the chord length, so as to obtain a smaller drag coefficient and a higher design lift coefficient; at the critical stall attack In the target pressure distribution of the airfoil under the angle, the pressure peak on the suction surface is at the position of 0-1% of the chord length from the leading edge of the airfoil to control the maximum lift coefficient of the airfoil; during the design process, the maximum thickness of the airfoil is constrained The position is at 34.0%-37.0% of the chord length.

For the airfoil applied to the outer side of the blade with a relative thickness less than or equal to 25%, in the step of judging whether it is necessary to continue adjusting the intermediate airfoil, it is necessary to further determine whether each aerodynamic parameter of the intermediate airfoil meets the following conditions:

(a) Efficiency:

Maximum lift-to-drag ratio: ${\left(\frac{C_l}{C_d}\right)}_{\max }>150,$

Design lift coefficient: C _ldesign >1.16;

(b) Low load performance: the maximum lift coefficient C _lmax and the design lift coefficient C _ldesign satisfy

(c) Rough insensitivity: $0.85\&le;\frac{C_{\mathrm{ldesign}}^{\&prime;}}{C_{\mathrm{ldesign}}}\&le;1,$

(d) Good variable working condition characteristics:

Δα=α _stall -α _design ≥5, $0<\frac{C_{l\max }-C_{\mathrm{ldesign}}}{\mathrm{\&Delta;\&alpha;}}<0.05,$ $\frac{|{\left(\frac{C_l}{C_d}\right)}_{\mathrm{stall}}-{\left(\frac{C_l}{C_d}\right)}_{\max }|}{\mathrm{\&Delta;\&alpha;}}<\mathrm{twenty\; one};$

(e) Smooth stall characteristics:

${<span\; class="notranslate">\; (</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Cl</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Cl</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; stall</span>}}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0.005</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; stall</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; ,</span>$

Among the above types:

C′ _ldesign is the design lift coefficient of the airfoil under rough conditions;

C _l , C _d , C _ldesign , _Clmax , The lift coefficient, drag coefficient, design lift coefficient, maximum lift coefficient, and maximum lift-to-drag ratio of the airfoil under the design angle of attack under smooth conditions; is the lift-to-drag ratio of the airfoil at the critical stall angle of attack under smooth conditions;

α, α _stall , Δα are angle of attack, stall angle of attack, and angle of attack difference, respectively.

In order to make the airfoil have a high design lift coefficient and a high maximum lift-to-drag ratio in the design, the pressure peak of the airfoil is restricted at the design point away from the leading edge of the airfoil to reduce the length of the unfavorable reverse pressure section of the airfoil. And it is controlled to have a low reverse pressure gradient from the suction front edge of the airfoil to the position of 40% of the chord length, so as to keep the airfoil with a longer laminar flow area, thereby obtaining a smaller drag coefficient.

In order to limit the maximum lift coefficient of the airfoil, the pressure peak is restricted near the critical angle of attack of the airfoil to be close to the leading edge of the airfoil, and the transition point moves forward rapidly, causing the airfoil to separate, thereby reducing its maximum lift coefficient. At the same time, the maximum thickness position of the airfoil is controlled at 34.0%-37.0% of the chord length.

The roughness of the leading edge will cause the laminar boundary layer of the airfoil to transition early, thereby separating early, resulting in a decrease in the lift coefficient. In the design, the thickness of the upper surface of the airfoil and the position of the maximum thickness are appropriately controlled to reduce the reverse pressure gradient, control the separation, and reduce the sensitivity of the design lift to the roughness of the leading edge. For the intermediate airfoil obtained in the design, the roughness insensitivity of the designed airfoil is analyzed by setting fixed transitions at 1% of the chord length on the upper surface and 10% of the chord length on the lower surface.

The present invention uses the above-mentioned design method and design means to design three airfoils with relative thicknesses of 18%, 21%, and 25% that meet the quantitative requirements of the design index proposed by the present invention. The developed airfoil is suitable for the middle and outer sides of wind turbines above MW level, and can achieve the purpose of increasing the output power of wind turbine blades and reducing the load on the blades.

Fig. 1 is the geometric profile of three airfoils of 18%, 21%, and 25% for the relative thickness that adopts the design method among the present invention and the means development. Taking the airfoil with a relative thickness of 25% as an example for analysis and verification, Figures 2 and 3 show the pressure distribution of the designed airfoil with a thickness of 25% at the design point and the critical angle of attack. It can be seen that the designed airfoil at the design point The pressure peak is far away from the leading edge, at the position of 1.4% of the chord length, and the pressure gradient changes smoothly from the leading edge to 40% of the chord length. At the critical angle of attack, the pressure peak is close to the leading edge at 0.22% of the chord length. At the same time, the maximum thickness of the airfoil is at 34.6% of the chord length. The aerodynamic parameters of the designed airfoil compared with the DU91-W-250 airfoil are shown in Table 1.

Table 1 Comparison of aerodynamic performance between the 25% airfoil designed by the present invention and the DU91-W-250 airfoil

It can be seen from Table 1 that the 25% airfoil of this design has the following characteristics compared with the DU91-W-250 airfoil:

(1) Efficiency: The maximum lift-to-drag ratio is over 150, the design lift coefficient 1.27 is greater than the design requirement value 1.16, and greater than the design lift coefficient 1.19 of the DU91-W1-250 airfoil;

(2) Low load: the ratio of the maximum lift coefficient to the design lift coefficient 1.14 is less than the design requirement value 1.25, and is less than 1.22 of the DU91-W1-250 airfoil;

(3) Rough insensitivity is slightly lower: its parameter value of 0.85 is slightly smaller than 0.89 of DU91-W1-250 airfoil, but meets the design index requirements;

(4) Good variable working condition characteristics: the corresponding parameter value 0.035 is less than the design requirement value 0.05, and 17.4 is less than the design requirement value 21;

(5) Smooth stall characteristics: the parameter value 0.0048 is less than the design requirement value 0.005, and less than 0.0066 of the DU91-W1-250 airfoil.

Through the above analysis, the various index parameters of the 25% airfoil designed by the present invention meet the design requirements, except for one roughness insensitivity which is slightly lower than that of the DU91-W1-250 airfoil, other performances are higher than the airfoil. Therefore, the overall aerodynamic performance of the airfoil with a relative thickness of 25% is better than that of the DU91-W1-250 airfoil.

In order to further verify the above implementation results, the designed 25% airfoil replaces the DU91-W1-250 airfoil and is applied to a 42.8m1.5MW wind turbine blade as an example to analyze its power and load. It is concluded that by replacing the airfoil, the output power of the wind turbine blades increases by 1% between 8m/s and 10.3m/s (10.3m is the rated wind speed). The maximum lift coefficient difference between the two airfoils at the ultimate load is only 0.01, and the ultimate load is slightly reduced, both of which are in the order of 1.83e5N, which achieves the purpose of controlling the load and increasing the power.

Claims (2)

1. A design method of special airfoil profile of a horizontal axis wind turbine blade is based on a general reverse design method of the airfoil profile, and is characterized by comprising the following steps:

giving an airfoil target pressure distribution and an initial base airfoil;

adjusting the pressure distribution of the basic airfoil profile to obtain a middle airfoil profile;

calculating the pressure distribution of the intermediate aerofoil using Euler equations;

comparing the pressure distribution of the middle wing profile with the target pressure distribution, judging whether the middle wing profile needs to be continuously adjusted according to the difference degree of the pressure distribution and the target pressure distribution, if the difference degree is within an allowable error range, terminating the adjustment to obtain the target wing profile, otherwise, continuously adjusting the pressure distribution of the middle wing profile until the pressure distribution of the middle wing profile meets the requirement;

wherein,

the airfoil target pressure distribution comprises an airfoil target pressure distribution under a design attack angle and an airfoil target pressure distribution under a critical stall attack angle: in the airfoil target pressure distribution under the design attack angle, the pressure peak value on the suction surface has a gentle adverse pressure gradient from the leading edge of the suction surface of the airfoil to the position of 40% of chord length at the position 1-25% of the chord length away from the leading edge point of the airfoil so as to obtain a small drag coefficient and a high design lift coefficient; in the airfoil target pressure distribution under the critical stall attack angle, the pressure peak value on the suction surface is at the chord length position 0-1% away from the leading edge point of the airfoil so as to control the maximum lift coefficient of the airfoil;

in the design process, the maximum thickness position of the airfoil is restrained at the position of 34.0% -37.0% chord length;

for the airfoil profile with the relative thickness less than or equal to 25% applied to the outer side of the blade, in the step of judging whether the middle airfoil profile needs to be continuously adjusted, whether each aerodynamic parameter of the middle airfoil profile meets the following condition needs to be further judged:

(a) high efficiency:

maximum lift-drag ratio: ${\left(\frac{C_l}{C_d}\right)}_{\max }>150,$

designing a lift coefficient: c_ldesign>1.16；

(b) Low load capacity: coefficient of maximum lift C_{l max}And design lift coefficient C_ldesignSatisfy the requirement of

(c) Roughness insensitivity:

(d) good variable working condition characteristics:

Δα＝α_stall-α_design≥5， <math> <mrow> <mn>0</mn> <mo>&lt;</mo> <mfrac> <mrow> <msub> <mi>C</mi> <mrow> <mi>l </mi> <mi>max</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>C</mi> <mi>ldesign</mi> </msub> </mrow> <mi>&Delta;&alpha;</mi> </mfrac> <mo>&lt;</mo> <mn>0.05</mn> <mo>,</mo> <mfrac> <mrow> <mo>|</mo> <msub> <mrow> <mo>(</mo> <mfrac> <msub> <mi>C</mi> <mi>l</mi> </msub> <msub> <mi>C</mi> <mi>d</mi> </msub> </mfrac> <mo>)</mo> </mrow> <mi>stall</mi> </msub> <mo>-</mo> <msub> <mrow> <mo>(</mo> <mfrac> <msub> <mi>C</mi> <mi>l</mi> </msub> <msub> <mi>C</mi> <mi>d</mi> </msub> </mfrac> <mo>)</mo> </mrow> <mi>max</mi> </msub> <mo>|</mo> </mrow> <mi>&Delta;&alpha;</mi> </mfrac> <mo>&lt;</mo> <mn>21</mn> <mo>;</mo> </mrow> </math>

(e) smoothed stall characteristics:

<math> <mrow> <msub> <mrow> <mo>(</mo> <mfrac> <msup> <mrow> <mo>(</mo> <msub> <mi>C</mi> <mi>l</mi> </msub> <mo>-</mo> <msub> <mi>C</mi> <mrow> <mi>l</mi> <mi>max</mi> </mrow> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mrow> <mi>&alpha;</mi> <mo>-</mo> <msub> <mi>&alpha;</mi> <mi>stall</mi> </msub> </mrow> </mfrac> <mo>)</mo> </mrow> <mi>max</mi> </msub> <mo>&lt;</mo> <mn>0.005,0</mn> <mo>&lt;</mo> <mi>&alpha;</mi> <mo>-</mo> <msub> <mi>&alpha;</mi> <mi>stall</mi> </msub> <mo>&lt;</mo> <mn>10</mn> <mo>,</mo> </mrow> </math>

in the above formulas:

C′_ldesigndesigning a lift coefficient for the airfoil under the rough condition;

C_l、C_d、C_ldesign、C_{l max}、designing a lift coefficient, a drag coefficient, a designed lift coefficient, a maximum lift coefficient and a maximum lift-drag ratio of the airfoil under an attack angle under a smooth condition;the lift-drag ratio of the airfoil under the critical stall attack angle under the smooth condition;

α、α_stall、Δα、α_designthe angle of attack, stall angle of attack, angle of attack difference, design angle of attack are respectively.

2. The design method of claim 1, whereinCalculating design lift coefficient C 'of airfoil profile under rough condition'_ldesignThe step (2) is to set a fixed transition position at the positions of 1% chord length on the upper surface and 10% chord length on the lower surface of the middle airfoil section obtained in the design so as to obtain a design lift coefficient.