CN112572787B - Coaxial dual-rotor high-speed helicopter tip airfoil with low resistance and high divergence Mach number - Google Patents

Abstract

The invention designs a coaxial double-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number, the leading edge radius of the airfoil is 0.00679, the maximum thickness of the airfoil is 0.0700, it is located at 43.3% of the chord length of the airfoil, and the maximum camber is is 0.003260, which is located at 17.7% chord length of the airfoil, and the included angle of the trailing edge is 2.20 degrees. In the designed high, medium and low Mach number range, the airfoil of the present invention improves the high-speed characteristic significantly and is more robust under the condition that the low-speed characteristic loss is not large. Among them, in the high-speed zero-lift state and its vicinity, compared with the French classic OA series airfoil OA407, the airfoil has a very low drag coefficient, which is significantly lower and more robust. At the same time, the airfoil resistance divergence Mach number is significantly improved. It maintains a lower drag coefficient and low drag range in a wide Mach number range, and maintains better torque characteristics than the classic OA407 airfoil over the entire envelope range. It is a coaxial twin-rotor high-speed helicopter tip airfoil The design laid the foundation.

Description

A coaxial twin-rotor high-speed helicopter tip with low resistance and high divergence Mach number airfoil

technical field

The invention relates to the technical field of coaxial dual-rotor high-speed helicopter blade airfoil design, in particular to a coaxial dual-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number.

Background technique

The conventional configuration helicopter is subject to the high speed forward flight of about 300km/h, and there is a large separation flow phenomenon on the rear rotor blades. Lift and forward thrust, while the forward propeller and the rear propeller meet the matching of the aerodynamic characteristics of the rotor. Aerodynamic efficiency at high speed and large forward ratio in flight.

In order to break through the speed limit of helicopters, countries around the world have been exploring and researching new configurations and concepts of helicopters. Existing high-speed helicopter configurations mainly include compound, tilt and stop. The compound type includes coaxial twin-rotor helicopter, conventional rotor/advancing blade concept (Advancing Blade Concept, ABC) rotor configuration auxiliary propulsion or lift device. The ABC rotor system was proposed by the American Sikorsky Company in 1964. The system consists of a pair of counter-rotating, coaxial, completely rigid hingeless rotors. When flying forward at high speed, the forward blades of the upper and lower rotors provide the main force. Lift, the rearward blade is unloaded, and almost no lift is generated, thereby slowing or even eliminating the airflow separation in the reverse flow area of the rearward blade, ensuring the ability to fly forward at high speed. In the 50 years since the ABC rotor was proposed, Sikorsky has continuously developed and verified this configuration. In 1970, Sikorsky built a 40-foot ABC test rotor and tested it in the NASA-AMES wind tunnel. In 1972, the U.S. Army signed a contract with Sikorsky for the design, manufacture and test flight of the ABC rotor demonstrator XH-59A. The first flight was achieved in 1973, and the maximum level flight speed reached 238kt (about 441km/h) during a total of 170 hours of test flight. In 2008, Sikorsky launched the X2 demonstrator, which uses a coaxial rigid rotor and a propulsion propeller at the tail. In the test flight in 2010, the maximum level flight speed of X2 reached 250kt (about 460km/h), which is twice that of the current Black Hawk helicopter and 1.5 times that of the "Apache" helicopter. In 2015, the S-97 compound high-speed helicopter developed by Sikorsky based on the ABC rotor made its maiden flight successfully. A large number of wind tunnel tests and the demonstration of the verification machine show that the high-speed helicopter configuration with ABC rotor takes into account both the hovering and high-speed flight capabilities, and has the characteristics of compact structure, good aerodynamic performance, maneuverability and maneuverability, representing the development trend of high-speed helicopters .

The rotor is the key component of the helicopter to generate lift and thrust, and the performance of the rotor is mainly determined by the performance of the airfoil. Phase flight efficiency. The working mechanism of the coaxial rigid rotor is completely different from that of the traditional single rotor, and the requirements for the aerodynamic performance of the airfoil are also quite different. Helicopter rotors need to provide sufficient pulling force for hovering, maneuvering and forward flight operations. For a single-rotor helicopter, in order to maintain the balance of the fuselage, the resultant force of the pulling force generated by the forward side and the rear side of the blade needs to act on the rotating shaft. The incoming flow velocity on the forward side and the rear side is very different, so the conventional rotor airfoil needs to have both low-speed high-lift characteristics and high-speed low-drag characteristics. For the coaxial rigid rotor, the counter-rotating motion of the upper and lower rotors makes forward blades on both sides of the paddle disc, and the high dynamic pressure of the forward blades can be fully utilized to provide sufficient pulling force, while the backward blades do not need to provide pulling force. ; During high-speed forward flight, the rearward propellers can be unloaded to avoid the surge of drag and noise caused by the large-scale reversal zone, so the coaxial rigid rotor helicopter can usually obtain higher forward flight speed. The increase in the forward flight speed leads to a worse flow field environment where the backward propellers are located. When Sikorsky's X2TD demonstrator flies forward at high speed, more than 80% of the backward propellers are in the regurgitation zone. Therefore, the coaxial rigid rotor airfoil should have good high-speed and low-resistance characteristics, the tip airfoil should have a high resistance divergence Mach number, and the root airfoil should have anti-flow separation and low-resistance characteristics in the reversal region. The entire performance and working state of the rotor require that the rotor airfoil has a high maximum lift coefficient in the low Mach number to mid-subsonic state, and a small zero-lift drag coefficient and high drag divergence characteristics in the transonic state. At the same time, in order to reduce the torque and control load, the rotor airfoil also needs to have a small pitching moment. In addition, in order to ensure the hovering characteristics of the helicopter, it should also have a high lift-drag ratio in the hovering state. Therefore, the design of rotor airfoil is a comprehensive optimization design problem with multiple design points, multiple objectives and multiple constraints.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention designs a coaxial dual-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number. Flow and lower suction peak; the upper surface of the airfoil changes slowly from the leading edge and the leading edge camber drops significantly, so that the flow accelerates to the suction peak and begins to change gently, lower pressure recovery point and the designed "double weak shock wave" "The shape of the pressure distribution significantly reduces the shock wave drag and enhances the robustness of the airfoil drag characteristics to state changes such as Mach number, so that the drag divergence Mach number reaches 0.875, and the drag coefficient at the divergence point is 0.00710.

Compared with the classic high-speed rotor airfoil OA407 airfoil of the same thickness, the airfoil has a smaller leading edge radius, a smaller maximum camber, and a rearward shift in the maximum thickness, which makes the peak suction generated on the upper and lower surfaces of the airfoil not high, and the development of The typical weak shock pressure distribution pattern is obtained, which controls the development of the shock wave. At the same time, the camber decreases from the leading edge of the airfoil to 90% of the chord length, the camber of the trailing edge increases (reverse bend), and the position of the maximum thickness moves back, which makes the airfoil moment coefficient (absolute value) significantly smaller, and maintains the airfoil moment coefficient (absolute value) throughout the high and low speed. Good torque characteristics in the range.

Specifically, the technical scheme of the present invention is:

A coaxial twin-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number, the leading edge radius of the airfoil is 0.00679, the maximum thickness of the airfoil is 0.0700, the airfoil is located at 43.3% of the chord length, and the maximum camber is 0.003260, located in At 17.7% chord length of the airfoil, the trailing edge angle is 2.20 degrees.

Further, the geometric coordinate expressions of the upper and lower surfaces of the airfoil are respectively

where z _u (x) and z _l (x) are the ordinate positions of the upper and lower surfaces of the unit airfoil, respectively, x is the abscissa position of the unit airfoil shape point, A _u,i and A _l,i (i=0, 1,2...,7) are the fitting coefficients of the upper and lower surfaces of the airfoil in the above airfoil expression, respectively, z _te = 0.00100; the fitting coefficients of the upper and lower surfaces of the airfoil are

Further, the fitting coefficients of the upper and lower surfaces of the airfoil are preferably:

Further, the upper and lower surface data of the tip airfoil of the coaxial twin-rotor high-speed helicopter with low resistance and high divergence Mach number are given in the following table:

Airfoil upper surface data

lower surface coordinates

beneficial effect

The invention provides a coaxial double-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number. In the designed high, medium and low Mach number range, the airfoil of the present invention improves the high-speed characteristic significantly and is more robust under the condition that the low-speed characteristic loss is not large. Among them, in the high-speed zero-lift state and its vicinity, compared with the French classic OA series airfoil OA407, the invented airfoil has a very low drag coefficient, which is significantly lower and more stable. It maintains a lower drag coefficient and a low drag range in a wide Mach number range, and maintains better torque characteristics than the classic OA407 airfoil over the entire envelope range. The design laid the foundation.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is the geometric outline drawing of the airfoil of the present invention.

Fig. 2 is a pressure profile distribution diagram of an airfoil of the present invention at a design point.

FIG. 3 is a comparison between the airfoil geometric outline drawing of the present invention and the OA407 airfoil geometric outline drawing.

Figure 4 is a comparison of the camber of the airfoil geometry of the present invention and the OA407 airfoil geometry.

Figure 5 is a comparison of the thickness of the airfoil geometry of the present invention and the OA407 airfoil geometry.

FIG. 6 is a comparison diagram of the pressure distribution of the airfoil of the present invention and the airfoil of OA407 at the inspection point.

FIG. 7 is a comparison diagram of the drag divergence curves of the airfoil of the present invention and the airfoil of OA407 (CL=0.00, Re/Ma=7.20e6).

FIG. 8 is a comparison diagram of the moment characteristic curves of the airfoil of the present invention and the airfoil of OA407 (CL=0.00, Re/Ma=7.20e6).

FIG. 9 is a comparison diagram of the low-speed lift characteristic curves of the airfoil of the present invention and the OA407 airfoil (Ma=0.30, Re=2.16e6).

FIG. 10 is a comparison diagram of the low-speed lift characteristic curves of the airfoil of the present invention and the OA407 airfoil (Ma=0.40, Re=2.88e6).

FIG. 11 is a comparison diagram of the low-speed lift characteristic curves of the airfoil of the present invention and the OA407 airfoil (Ma=0.50, Re=3.60e6).

Detailed ways

The conventional configuration helicopter is subject to the high-speed forward flight of about 300km/h (large forward ratio), and there is a large separation flow phenomenon on the rear rotor blades. Very poor, unable to generate lift and forward thrust, and in order to meet the matching of rotor aerodynamic characteristics between the forward propeller and the rear propeller, the blade profile (airfoil) of the forward propeller cannot work under the high lift-drag ratio. The range of the angle of attack will seriously affect the aerodynamic efficiency of the helicopter when flying at a high speed and a large forward ratio.

To this end, according to the special mission requirements of different helicopters in different periods, according to the characteristics of the unsteady flow field of the helicopter rotor and the motion law of the blades, high-performance rotor airfoils that meet different performance requirements are designed. The coaxial rigid rotor high-speed helicopter based on the concept of advancing blades is a high-speed helicopter layout that was innovatively proposed and systematically studied by Sikorsky Corporation of the United States. Compared with conventional helicopters, the flight speed of coaxial twin-rotor helicopters is significantly improved. For example, the flight speed of S-97 helicopters can reach 482km/h, which has potential application value. Compared with fixed-wing aircraft airfoils, the research progress of rotor airfoil design is slow, mainly because of the complex design requirements and constraints of rotor airfoils. As the main element of the rotor blade, the airfoil determines the performance of the helicopter to a large extent. Therefore, in order to further improve the overall performance of the helicopter, the design of high-performance rotor airfoil is particularly important.

The coaxial twin-rotor high-speed helicopter tip airfoil with low resistance and high divergence Mach number proposed in this embodiment has a high-speed investigation state of Mach number of 0.87, lift coefficient of 0.00, Reynolds number of 6.264e6, and turbulence degree of 0.5. %, the turbulent viscosity ratio is 10. The radius of the leading edge of the airfoil is 0.00679, the maximum thickness of the airfoil is 0.0700, it is located at 43.3% chord length of the airfoil, the maximum camber is 0.003260, which is located at 17.7% chord length of the airfoil, and the included angle of the trailing edge is 2.20 degrees. It should be noted that in the field of airfoil design, the parameter descriptions are all described by dimensionless quantities, so the above-mentioned leading edge radius, maximum thickness, maximum camber and subsequent airfoil coordinate descriptions are described by dimensionless quantities. Based on the airfoil chord length c.

The specific geometric coordinate expressions of the upper and lower surfaces of the airfoil are:

Among them, z _u (x) and z _l (x) are the ordinate positions of the upper and lower surfaces of the unit airfoil, respectively, and x is the abscissa position of the unit airfoil shape point. Of course, in the field of airfoil design, it is expressed as a dimensionless quantity, The abscissa of the unit airfoil shape point ranges from 0 to 1; A _u,i and A _l,i (i=0,1,2...,7) are the fitting coefficients of the upper and lower surfaces of the above airfoil expression, respectively, z _te = 0.00100; the fitting coefficient of the above expression of airfoil is

Moreover, through numerical calculation, the airfoils obtained with the above coefficients within the range of not more than 0.5% have good performance.

The upper and lower surface data of the coaxial twin-rotor high-speed helicopter tip airfoil with low resistance and high divergence Mach number of this embodiment are given in Table 1 and Table 2 below

Table 1 Data on the upper surface of the airfoil

Table 2 lower surface coordinates

Comparing the aerodynamic performance of this embodiment with the classic OA407 airfoil, it can be seen that the airfoil of this embodiment has a significant improvement in the high-speed resistance divergence characteristics and significant basic resistance under the condition that the low-speed characteristic loss is not large at and near the design point. reduced, and torque characteristics are better in all conditions.

Table 3 Aerodynamic characteristics of the airfoil of the invention

Ma C_l C_d C_m 0.800 0.0000 0.00655 -0.00159 0.820 0.0000 0.00701 -0.00141 0.840 0.0000 0.00720 -0.00060 0.850 0.0000 0.00722 -0.00079 0.855 0.0000 0.00717 -0.00093 0.860 0.0000 0.00702 -0.00079 0.865 0.0000 0.00669 -0.00065 0.870 0.0000 0.00674 -0.00346 0.875 0.0000 0.00710 -0.00668 0.880 0.0000 0.00927 -0.00747 0.885 0.0000 0.01262 -0.00795 0.890 0.0000 0.01675 -0.00916

Table 4. Aerodynamic characteristics of the comparative airfoil (classic OA407 airfoil)

Ma C_l C_d C_m 0.800 0.0000 0.00775 -0.00584 0.820 0.0000 0.00794 -0.00600 0.840 0.0000 0.00787 -0.00758 0.850 0.0000 0.00782 -0.01098 0.855 0.0000 0.00800 -0.01419 0.860 0.0000 0.00853 -0.01870 0.865 0.0000 0.00944 -0.02400 0.870 0.0000 0.01084 -0.02948 0.875 0.0000 0.01289 -0.03468 0.880 0.0000 0.01559 -0.03879 0.885 0.0000 0.01913 -0.04364 0.890 0.0000 0.02318 -0.04685

As shown in the figure, the airfoil of this embodiment has a smaller leading edge radius (A) compared to the French classic high-speed rotor airfoil of the same thickness OA series airfoil OA407, so that the airflow around the leading edge of the airfoil remains relatively small after acceleration. A low suction peak, keeping the suction peak apex (A') in place helps reduce the pressure recovery point on the trailing edge of the airfoil. Then starting from the leading edge (A) of the airfoil of the present invention, the curve segment B where the upper surface of the airfoil is located maintains a small and relatively slow camber change and a suitable and low curvature increase, and the camber of the upper surface of the airfoil leading edge decreases significantly until it reaches the At the position of the maximum thickness, the pressure distribution on the upper surface of the airfoil changes gently from the A' position, and when it reaches the B' position, the classic "double weak shock wave" pressure distribution pattern appears, which significantly reduces the shock intensity. The corresponding airfoil The lower surface flow field shock is also weaker. The pressure distribution shape of this design not only significantly reduces the airfoil flow field resistance, but also greatly enhances the robustness of the airfoil flow field with changes in Mach number and angle of attack, thus maintaining the invention airfoil at a certain Mach number. Low drag characteristics of the range and significantly improved drag divergence Mach number.

The airfoil of the present invention is designed from the position C to the trailing edge of the airfoil until the thickness does not change, and the integral area generated by the pressure distribution at the position C' controls the increase of the airfoil bowing moment (the moment reference point is the 1/4 chord line position), The airfoil moment coefficient is better than that of the OA407 airfoil in the same state, and its absolute value is far less than 0.02, which effectively improves the moment characteristics of the high-speed rotor airfoil and reduces the trim resistance. The calculation of the natural transition state shows that in the high-speed zero-lift state (Ma=0.87, CL=0.00, Re=6.264e6) and its vicinity, the airfoil of the present invention has a very low drag coefficient, and the drag coefficient at the investigation point is 0.00673, a reduction of 41.1 counts relative to the drag coefficient of the comparative OA407 airfoil of 0.01084. At the same time, the airfoil of the present invention has a drag divergence Mach number of 0.875, which is 0.021 higher than that of the OA407 airfoil of 0.854, and maintains a lower drag coefficient and a low resistance range in a wide range of Mach numbers. And in the whole range of high, medium and low Mach numbers (Ma=0.2～Ma=0.87), it maintains better torque characteristics than the classic OA407 airfoil.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and those of ordinary skill in the art will not depart from the principles and spirit of the present invention Variations, modifications, substitutions, and alterations to the above-described embodiments are possible within the scope of the present invention without departing from the scope of the present invention.

Claims (3)

1. a coaxial twin-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number is characterized in that: the airfoil leading edge radius is 0.00679, the airfoil maximum thickness is 0.0700, and is located at the airfoil 43.3% chord length, The maximum camber is 0.003260, which is located at 17.7% of the chord length of the airfoil, and the included angle of the trailing edge is 2.20 degrees; The geometric coordinates of the upper and lower surfaces of the airfoil are expressed as

where z _u (x) and z _l (x) are the ordinate positions of the upper and lower surfaces of the unit airfoil, respectively, x is the abscissa position of the unit airfoil shape point, A _u,i and A _l,i (i=0, 1,2...,7) are the fitting coefficients of the upper and lower surfaces of the airfoil in the geometric coordinate expressions of the upper and lower surfaces of the airfoil respectively, z _te = 0.00100; the fitting coefficients of the upper and lower surfaces of the airfoil are

2. a kind of coaxial twin-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number according to claim 1 is characterized in that: the upper and lower surface fitting coefficients of the airfoil are:

3. a kind of coaxial twin-rotor high-speed helicopter blade tip airfoil with low resistance and high divergence Mach number according to claim 1, is characterized in that: the upper and lower surface data of airfoil is: Airfoil upper surface data

Airfoil lower surface data

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