CN208123004U - A kind of ellipse blunt trailing edge aerofoil profile - Google Patents

Abstract

A kind of ellipse blunt trailing edge aerofoil profile, for about the symmetrical oval blunt trailing edge aerofoil profile of chord length；The relative thickness of the ellipse blunt trailing edge aerofoil profile is 50%；Rear is with a thickness of 27.27% chord length.Maximum relative thickness position is 54.54% chord length away from leading edge point.The blunt trailing edge that the utility model is taken can effectively improve the rigidity of blade, reduce the barometric gradient of airfoil suction side back segment, delay turbulence separation, be conducive to improve the lift coefficient and stall angle of aerofoil profile, and preceding edge roughness sensibility is low, therefore the utility model can be as the substitute for the pneumatic equipment bladess root aerofoil profile being commonly used.

Description

An elliptical blunt trailing edge airfoil

technical field

The invention belongs to the technical field of fan blade section airfoil design, and in particular relates to a large-thickness wind turbine blade root airfoil capable of bearing relatively large loads, having a large stall attack angle and low front edge roughness sensitivity.

Background technique

As the world's energy problems become increasingly prominent, wind energy has been rapidly developed as an environmentally friendly renewable resource. Blade design is the core technology of fan design. Blade performance determines wind energy utilization, load characteristics, and noise levels. It is the most important factor to determine the performance of the blade. Therefore, the airfoil design of high-performance wind turbines is of great significance for improving the wind energy capture capacity of the blades and reducing the weight of the blades and the system load.

Many institutions at home and abroad have carried out design research on advanced airfoil families of wind turbine blades. The United States and Europe have successively developed airfoil families such as S series, DU series, RIS series, FFA series, and AH series. Among these airfoils, some The airfoil lacks experimental verification at high Reynolds numbers, and the aerodynamic performance of some airfoils deteriorates seriously when the roughness is large. These airfoil families are all airfoils with different thicknesses designed for different positions of the blade from the root to the tip. Generally speaking, the main indicators of wind turbine airfoil are structural characteristics, geometric compatibility, aerodynamic characteristics, stall characteristics and leading edge roughness sensitivity. Specifically, structural characteristics refer to the ability to withstand load and fatigue, and geometric compatibility refers to The transition between different thickness airfoils from the root to the tip of the wind turbine blade. The aerodynamic characteristics refer to the lift-drag coefficient and the lift-drag ratio of the airfoil in the blade. The stall characteristics refer to the changes in the aerodynamic characteristics of the airfoil before and after the stall. Leading edge roughness sensitivity refers to the extent to which contamination at the leading edge of the airfoil causes turbulent flow separation to occur early on the airfoil and leads to a decrease in the maximum lift coefficient. For the airfoil at the root of the wind turbine blade, it is necessary to provide lift stably and bear the load on the entire blade, so the airfoil here needs to have good structural characteristics and geometric compatibility, high aerodynamic characteristics, slow stall characteristics And the characteristics of low sensitivity to leading edge roughness.

Domestic research on airfoil design of wind turbines started relatively late, but developed rapidly by absorbing advanced foreign experience. Northwestern Polytechnical University proposed an airfoil for megawatt-scale wind turbine blades in the invention patent with the patent number CN2011100023215.1, and disclosed a family of airfoils for megawatt-scale wind turbine blades, including 7 airfoils in total Type, the relative thickness of the airfoil used for the root of the blade is 40%, and the relative thickness is not large.

Northwestern Polytechnical University proposed an airfoil suitable for 5-10 MW wind turbine blades in the invention with the application number 201610164779.X, including 8 airfoils in total, and the relative thickness of the transitional airfoil used for the root is 50% and 60%, the thickness of the trailing edge is 12% and 15%, with high lift and high lift-to-drag ratio, and also has a large maximum lift coefficient and lift-to-drag ratio at high Reynolds numbers, but the stall characteristics are average.

The Institute of Engineering Thermophysics of the Chinese Academy of Sciences proposed a family of wind turbine blade airfoils in the invention and creation of the application number CN201020677153.7, and proposed a family of large-thickness blunt trailing edge wind force Airfoil and its design method, the airfoil family includes four airfoils with relative thicknesses of 45%, 50%, 55% and 60%, and trailing edge thicknesses of 7%, 9%, 12% and 16% , is designed for the root of the blade to replace the traditional cylindrical structure, thereby improving the performance of the blade. The maximum stall angle of attack of these four airfoils is only 8 degrees.

In the invention with the application number CN201610546194.4, a family of thick airfoils for large wind turbine blades is proposed, including 8 airfoils with relative thicknesses of 35%, 40%, 45%, 50%, and 55%. , 60%, 65% and 70%, the thickness of the trailing edge is 2.8%, 4.5%, 8.0%, 12%, 16%, 20%, 24% and 28%, in which the relative thickness of 35% of the airfoil stall angle of attack The largest, can reach 12.5°, followed by an airfoil with a relative thickness of 50%, with a stall angle of attack of 11.5°.

Beijing Guodian United Power Technology Co., Ltd. proposed a large-thickness blunt trailing edge airfoil blade for a large fan in the invention with the application number CN201310283675.7, and disclosed a wind force with a root airfoil relative thickness of 65%-75%. The thickness of the airfoil trailing edge is 25%-35%, and the stall angle of attack is 10°. The above-mentioned large-thickness wind turbine airfoil has high precision requirements due to camber or negative loading, and is difficult to manufacture. Once there is a deviation, it will have a certain impact on the aerodynamic performance of the airfoil, and generally the stall angle of attack is small.

In 2008, Professor Gao Zhenghong from the School of Aeronautics of Northwestern Polytechnical University published "Research on the Low-speed Aerodynamic Characteristics of Elliptical Airfoils" in "Aeronautical Computing Technology" Volume 38, Issue 3, and studied the elliptical airfoil with a relative thickness of 16%. The advantages of symmetry, continuous curvature, and simple manufacture, and the greater the relative thickness, the greater the stall angle of attack. Due to the large thickness of the airfoil at the root of the wind turbine blade, the flow there is often in a flow separation flow state with a large angle of attack. Therefore, a large stall angle of attack is beneficial to the improvement of the aerodynamic performance of the airfoil at the root of the wind turbine. However, the lift coefficient of the pure elliptical airfoil will decrease rapidly after stalling, and it does not have slow-stall characteristics. Moreover, due to the small thickness of the airfoil, the stall angle of attack is only 8°, and the maximum lift coefficient is also small.

Contents of the invention

In order to overcome the disadvantages in the prior art that the stall angle of attack of the thick airfoil is small, and the lift coefficient of the pure elliptical airfoil will drop rapidly after stalling, does not have slow stall characteristics, and the maximum lift coefficient is also small, the present invention proposes An elliptical blunt trailing edge airfoil.

The elliptical blunt trailing edge airfoil proposed by the present invention is symmetrical about the chord length; the relative thickness of the elliptical blunt trailing edge airfoil is 50%; the thickness of the trailing edge is 27.64% of the chord length. The maximum relative thickness position is 54.54% of the chord length from the leading edge point.

The coordinate points of the upper airfoil y _up and the lower airfoil y _down of the elliptical obtuse trailing edge airfoil in the dimensionless coordinate system are shown in Table 1.

Table 1 The coordinate points of the upper and lower airfoils of the airfoil in the dimensionless coordinate system

In Table 1, C is the chord length of the airfoil, x/C represents the dimensionless abscissa point of the upper or lower surface of the airfoil, y _up /C represents the dimensionless ordinate point of the upper surface of the airfoil, and y _down / C represents the dimensionless ordinate point of the lower airfoil.

The dimensionless coordinate system is the leading edge vertex as the coordinate origin, the chord line direction is the x-axis, and the y-axis of the dimensionless coordinate system is perpendicular to the x-axis.

The dimensionless two-dimensional coordinate data of the elliptical obtuse trailing edge airfoil described in Table 1 can keep the shape of the airfoil unchanged when it is enlarged or reduced. When it is necessary to obtain airfoils with different chord lengths, the dimensionless x-coordinates and y-coordinates in the table are multiplied by the chord length C respectively, so as to obtain the upper airfoil coordinates (x, y _up ) and lower airfoil coordinates

(x, y _down ), connect these coordinate points with B-spline curves to obtain an airfoil that meets the design requirements.

Compared with the prior art, the airfoil proposed by the present invention has the following advantages:

1. The airfoil is an elliptical airfoil with smooth curvature and a blunt trailing edge, which greatly reduces the manufacturing difficulty and production cost in terms of manufacturing process;

2. The maximum thickness of the airfoil is 50%C, and the thickness of the trailing edge is 27.27%C. The cross-sectional area and moment of inertia of the airfoil are large, which can effectively improve the stiffness of the blade and improve the structural performance of the blade. Sandia Laboratories in the United States are also researching It is found that by increasing the thickness of the blunt trailing edge airfoil, its structural performance can be significantly improved, and the increase in blade weight can be better limited, and the weight can be reduced by up to 15%;

3. The airfoil has a thicker trailing edge, which reduces the pressure gradient at the rear section of the suction surface of the airfoil, delays the separation of turbulent flow, and is conducive to improving the lift coefficient and stall angle of attack of the airfoil;

4. The roughness sensitivity of the leading edge of this airfoil is low. For wind turbine blades working in the field, pollutants often stick to the leading edge, which will have a great impact on the aerodynamic characteristics of the general airfoil. However, this airfoil simulates this In the first state, a rough strip is pasted at the position of 5%C of the leading edge, the aerodynamic characteristics are not significantly changed compared with the original airfoil, the maximum lift coefficient does not change much, and the aerodynamic characteristics are very stable.

Description of drawings

Fig. 1 is the outline schematic diagram of the ellipse airfoil provided by the present invention;

Fig. 2 is the structural representation of the elliptical airfoil provided by the present invention;

Figure 3 is a schematic diagram of the stationary transition state in the experiment. In the picture:

1. Leading edge; 2. Upper airfoil; 3. Lower airfoil; 4. Trailing edge; 5. Rough belt.

Detailed ways

This embodiment is an elliptical obtuse trailing edge airfoil symmetrical about the chord length.

The maximum relative thickness position of the elliptical blunt trailing edge airfoil relative to the general wind turbine airfoil is relatively backward, so that the maximum relative thickness position is 54.54% of the chord length from the leading edge 1 apex; the relative thickness is 50%; the thickness of the trailing edge 4 is 27.64% of the chord length. In this embodiment, the chord length C of the elliptical obtuse trailing edge airfoil is 0.55m.

The elliptical blunt trailing edge airfoil is placed in a dimensionless coordinate system, the dimensionless coordinate system is the origin of the coordinates, the chord direction is the x-axis, and the y-axis of the dimensionless coordinate system is perpendicular to the x-axis.

The coordinate points of the upper airfoil 2 and the lower airfoil 3 in this embodiment in the dimensionless coordinate system are shown in Table 1.

Table 1 The coordinate points of the upper and lower airfoils of the airfoil in the dimensionless coordinate system

In Table 1, C is the chord length of the airfoil, x/C represents the dimensionless abscissa point of the upper or lower surface of the airfoil, y _up /C represents the dimensionless ordinate point of the upper surface of the airfoil, and y _down / C represents the dimensionless ordinate point of the lower airfoil.

In order to verify the aerodynamic characteristics of this embodiment, experiments were carried out in the NF-3 low-speed two-dimensional airfoil wind tunnel of Northwestern Polytechnical University. The length of the experimental model is 1.6m, and the airfoil section is the elliptical obtuse trailing edge airfoil of this embodiment.

In this experiment, under two conditions of natural transition and fixed transition, the Reynolds numbers are 1×10 ⁶ , 2×10 ⁶ , and 3×10 ⁶ under three different experimental conditions, and a static pressure measuring hole is drilled in the central section of the model. Static pressure test was carried out on the model, and the lift characteristics and stall characteristics of the model were obtained.

It is a traditional experimental method for wind turbine airfoils to carry out wind tunnel experiments on the airfoil under two different conditions: natural transition and fixed transition. The experimental state of pasting the rough strip 5 at the position of 5%C from the front edge and 10%C from the lower airfoil to the front edge is used to simulate the situation of pollutants on the leading edge of the airfoil, as shown in Figure 3. In addition, the Reynolds number is also a parameter that must be simulated in the wind turbine airfoil experiment. The Reynolds number is a dimensionless number that can be used to characterize the fluid situation. It is also a similar parameter that expresses the effect of viscosity in fluid mechanics. It is represented by Re, defined for:

Among them, ρ represents the density of the fluid, v represents the flow velocity of the fluid, c represents the chord length of the airfoil, and μ represents the viscosity of the fluid.

Taking the experimental results with a Reynolds number of 1×10 ⁶ as an example, the stall angle of attack under natural transition conditions is as high as 25 degrees, and the stall angle of attack under fixed transition conditions is 23 degrees, and the airfoil is symmetrical about the chord length, negative The stall angle of attack of the angle is also above 20 degrees, which is much larger than that of ordinary thick airfoils. After the stall, the lift coefficient does not drop rapidly, and the stall characteristic is moderate. In addition, the maximum lift coefficient under natural transition conditions is 1.403, and the maximum lift coefficient under fixed transition conditions is 1.068. The maximum lift coefficient under fixed transition conditions has decreased by 23.88%, that is, the leading edge roughness sensitivity is 23.88%. For the airfoil at the root of the wind turbine, the leading edge roughness sensitivity is generally less than 25%. Therefore, it proves again that the airfoil provided by the present invention has low sensitivity to the leading edge roughness and stable aerodynamic characteristics.

Claims (1)

1. An ellipse blunt trailing edge airfoil is characterized in that the ellipse blunt trailing edge airfoil is symmetrical about the chord length; the relative thickness of the ellipse blunt trailing edge airfoil is 50%; the trailing edge thickness is 27.64% of the chord length; the maximum The relative thickness position is 54.54% of the chord length from the leading edge point.