High subsonic tiltrotor airfoil and wing based on the retreating blade theory

Abstract

The invention discloses a high subsonic tilt-rotor airfoil and a wing based on the backward blade theory, belonging to the field of tilt-rotor helicopter rotor airfoil design; the camber of the leading edge of the upper surface of the airfoil is 0.202-0.242, and the camber of the trailing edge of the upper surface is 0.079-0.099; the camber of the leading edge of the lower surface of the airfoil is 0.146-0.176, and the camber of the trailing edge of the lower surface is 0.026-0.046; the slope of the trailing edge of the upper surface of the airfoil is The slope of the trailing edge of the lower surface is 0.0057~0.0077; the airfoil is set at 60%-85% of the span of the tilt-rotor helicopter blade. The airfoil can alleviate the large angle of attack separation phenomenon at subsonic speed, improve the stall characteristics, weaken the shock wave on the upper surface of the airfoil at transonic speed, and delay the divergence Mach number. Compared with the NACA64212 retreating blade airfoil, it has better lift, drag and torque characteristics in the subsonic and transonic ranges.

Description

Technical Field

[0001] The invention relates to the field of rotor blade airfoil design of a tilt-rotor helicopter, in particular to a high subsonic tilt-rotor airfoil and a wing based on a retreating blade theory. Background Art

[0002] The airfoil is the basic component of the rotor. The aerodynamic characteristics of the airfoil have a key impact on the performance of the rotor, directly affecting the load, speed, range, noise and vibration level of the tilt-rotor helicopter. The wide Mach number, variable angle of attack and unsteady characteristics of the rotor airfoil make its design more complicated than that of the fixed-wing. At the same time, the special states of the rotor such as forward flight, maneuvering and unsteady flight lead to the rotor design goal of increasing the maximum divergence Mach number and reducing the torque coefficient, while still maintaining high lift.

[0003] The performance of a tilt-rotor helicopter mainly includes maneuverability, propeller efficiency in cruise state, compressible drag characteristics of the propeller, and hovering efficiency in helicopter mode. As the basic element of the rotor, the performance of the propeller blade airfoil directly affects the performance of the helicopter, especially the performance of the tilt-rotor helicopter. Early helicopter rotors generally directly adopted simple aircraft wing airfoils. However, compared with fixed-wing aircraft wings, helicopter rotors have complex coupling phenomena of multiple motions such as pitch change, flapping, shimmy, and elastic deformation on the basis of rotational motion. The unsteady changes of the forward flow further lead to unsteady and asymmetric complex flow phenomena in the rotor blades, causing the rotor blades to simultaneously experience transonic flow at the wing tip, low-speed flow at the wing root, and even reverse flow, accompanied by dynamic stall and blade vortex interference. Therefore, the design of the tilt-rotor helicopter blade airfoil must consider the flow mechanisms at different stations and meet the multidisciplinary design requirements of aerodynamics, control stability characteristics, and other multi-modal motions. Due to the cyclic pitch control of the rotor, the retreating blade is generally in a large angle of attack state, causing boundary layer separation in front of the suction front edge of the blade, resulting in divergent dynamic stall of the rotor blade, causing a sudden drop in lift, an increase in drag and nose-down moment, and a strong aerodynamic load hysteresis effect, which in turn causes rotor aerodynamic load oscillation and blade vibration, seriously restricting the improvement of the helicopter's flight speed and flight capability.

[0004] In order to alleviate the shock wave separation and divergent dynamic stall problems caused by the high angle of attack of the retreating blades of a high-speed helicopter, it is necessary to consider designing an airfoil that can delay the generation of shock waves, suppress the dynamic stall characteristics of the rear and tip of the helicopter blades, and increase the nose-up moment. Summary of the invention

[0005] In response to the problems existing in the prior art, the present invention provides a high subsonic tilt-rotor airfoil and wing based on the trailing blade theory. The airfoil has a relatively large leading edge thickness, which can effectively improve the subsonic lift characteristics and stall characteristics, and at the same time can balance the zero-lift moment at high subsonic speeds.

[0006] The present invention is achieved through the following technical solutions:

[0007] A high subsonic tilt-rotor airfoil based on the retreating blade theory, wherein the camber of the leading edge of the upper surface of the airfoil is 0.202-0.242, and the camber of the trailing edge of the upper surface is 0.079-0.099;

[0008] The camber of the leading edge of the lower surface of the airfoil is 0.146-0.176, and the camber of the trailing edge of the lower surface is 0.026-0.046;

[0009] The slope of the trailing edge of the upper surface of the airfoil is -0.09 to -0.11, and the slope of the trailing edge of the lower surface is 0.0057 to 0.0077.

[0010] Preferably, the maximum thickness T of the airfoil is 0.12 m, and the maximum thickness position is at 0.289 times the chord length.

[0011] Preferably, the maximum camber of the airfoil is 0.0137 times the chord length, and the maximum camber position is at 0.6085 times the chord length.

[0012] Preferably, the airfoil is arranged at a position between 60% and 85% in the span direction of the blade.

[0013] Preferably, the surface of the airfoil is n The surface coordinates are fitted by the order CST parameterization as follows:

[0014]

[0015] in, x is the surface abscissa of the airfoil, y is the surface ordinate of the airfoil, i is the order sequence, n is the order of the CST parameterization method, For the airfoil root step y coordinate, is the fitting coefficient, For order sequence i The fitting coefficient of , ! is the factorial.

[0016] Preferably, the radius of the leading edge of the upper surface of the airfoil is 0.00575 m, and the radius of the leading edge of the lower surface of the airfoil is 0.000121 m.

[0017] Preferably, the leading edge of the upper surface and the leading edge of the lower surface are connected at one end close to the chord line of the airfoil and smoothly transition to form the leading edge of the airfoil, the trailing edge of the upper surface is smoothly connected to the other end of the leading edge of the upper surface, the trailing edge of the lower surface is smoothly connected to the other end of the leading edge of the lower surface, and the trailing edge of the upper surface and the trailing edge of the lower surface are intersected at one end close to the trailing edge of the airfoil.

[0018] A wing, the airfoil of which at the 60%-85% position of the wing span is a high subsonic tilt-rotor airfoil based on the retreating blade theory.

[0019] A helicopter, the wing of the helicopter is the wing described above.

[0020] Preferably, the helicopter is a tilt-rotor helicopter.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The invention provides a high subsonic tiltrotor airfoil based on the theory of retreating blades. The airfoil is arranged at 60%-85% of the span of a tiltrotor helicopter blade. When the large tiltrotor helicopter is in the cruise and hovering stages, the middle and rear sections of the blades along the span are in a transonic state. Due to the increase in the leading edge camber and the decrease in the trailing edge camber of the tiltrotor airfoil, the drag characteristics of the transonic state are improved while ensuring that the loss of low-pressure sonic aerodynamic performance is controllable, and the tiltrotor airfoil has excellent torque characteristics. In the high subsonic hovering stage of the tiltrotor helicopter, due to the increase in the camber of the tiltrotor airfoil, the blades greatly improve the stall characteristics and maximum lift characteristics of the tiltrotor helicopter while ensuring a small nose-down torque. The aerodynamic performance of the tiltrotor airfoil was compared with that of the NACA64212 (NACA National Advisory Committee for Aeronautics) retreating blade airfoil. The tiltrotor airfoil can alleviate the large angle of attack separation phenomenon at high subsonic speed, improve the stall characteristics, weaken the shock wave on the upper surface of the airfoil at transonic speed, and delay the divergence Mach number. Compared with the NACA64212 retreating blade airfoil, it has better lift, drag and torque characteristics in the subsonic and transonic ranges. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a geometrical shape diagram of the high subsonic tilt-rotor airfoil of the present invention;

[0024] Figure 2 A comparison diagram of the geometrical appearance of the tiltrotor airfoil of the present invention and the NACA64212 airfoil;

[0025] Figure 3A comparison diagram of the camber of the tiltrotor airfoil of the present invention and the NACA64212 airfoil;

[0026] Figure 4 A comparison diagram of the pressure distribution of the tiltrotor airfoil of the present invention and the NACA64212 airfoil at the design point;

[0027] Figure 5 It is a comparison diagram of the drag characteristic curves of the tiltrotor airfoil of the present invention and the NACA64212 airfoil under transonic speed;

[0028] Figure 6 It is a comparison diagram of the moment characteristic curves of the tiltrotor airfoil of the present invention and the NACA64212 airfoil under transonic speed;

[0029] Figure 7 This is a comparison diagram of the lift characteristic curves of the tilt-rotor airfoil of the present invention and the NACA64212 airfoil at low speed at 0.45 Ma;

[0030] Figure 8 It is a comparison diagram of the lift characteristic curves of the tilt-rotor airfoil of the present invention and the NACA64212 airfoil at low speed at 0.5 Ma.

[0031] In the figure: 1, leading edge of upper surface; 2, trailing edge of upper surface; 3, leading edge of lower surface; 4, trailing edge of lower surface. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings, which are intended to explain the present invention rather than to limit it.

[0033] Definition: The airfoil is the shape of the wing's cross section. The front end of the wing's cross section is called the leading edge, and the rear end is called the trailing edge.

[0034] See also Figure 1 , a high subsonic tilt-rotor airfoil based on a retreating blade theory, comprising an upper surface leading edge 1, an upper surface trailing edge 2, a lower surface leading edge 3 and a lower surface trailing edge 4;

[0035] The upper surface leading edge 1 and the lower surface leading edge 3 are connected at one end close to the airfoil chord line and smoothly transition to form the leading edge of the airfoil, the upper surface trailing edge 2 is smoothly connected to the other end of the upper surface leading edge 1 at one end close to the leading edge of the airfoil, the lower surface trailing edge 4 is smoothly connected to the other end of the lower surface leading edge 3 at one end close to the leading edge of the airfoil, and the upper surface trailing edge 2 and the lower surface trailing edge 4 are intersected at one end close to the trailing edge of the airfoil.

[0036] The radius of the leading edge 1 of the upper surface of the airfoil is 0.00575m, the slope of the leading edge 1 of the upper surface is 0.195~0.235, the curvature of the leading edge 1 of the upper surface is 0.202~0.242, the slope of the trailing edge 2 of the upper surface is -0.09~-0.11, and the curvature of the trailing edge 2 of the upper surface is 0.079~0.099.

[0037] The radius of the lower surface leading edge 3 of the airfoil is 0.000121 m, the slope of the lower surface leading edge 3 is -0.19~-0.21, the curvature of the lower surface leading edge 3 is 0.146~0.176, the slope of the lower surface trailing edge 4 is 0.0057~0.0077, and the curvature of the lower surface trailing edge 4 is 0.026~0.046.

[0038] The included angle of the trailing edge 2 of the upper surface of the airfoil is 1.8°, and the included angle of the trailing edge 4 of the lower surface is 0.9°.

[0039] The maximum thickness T of the airfoil is 0.12 m, the maximum thickness position is at 0.289 times the chord length, the maximum camber is 0.0137 times the chord length, and the maximum camber position is at 0.6085 times the chord length.

[0040] The airfoil is arranged at a position between 60% and 85% in the span direction of the blade.

[0041] When a large tilt-rotor helicopter is in a backward state, the backward blade is generally in a state of large angle of attack, causing boundary layer separation at the leading edge of the blade suction surface, resulting in divergent dynamic stall of the tilt-rotor backward blade, causing a sudden drop in lift, an increase in drag and nose-down moment, and a strong aerodynamic load hysteresis effect, thereby causing tilt-rotor aerodynamic load oscillation and blade vibration, seriously affecting the flight characteristics of the tilt-rotor helicopter. The high subsonic tilt-rotor airfoil based on the backward blade theory provided in the present application is arranged at 60%-85% of the span direction of the tilt-rotor helicopter blade. % position, the airfoil has a relatively large leading edge thickness, which can effectively improve the lift characteristics and stall characteristics of the tilt-rotor at subsonic speeds; at the same time, the leading edge camber of the airfoil is increased, and the trailing edge camber of the airfoil is reduced, which can balance the zero lift moment of the tilt-rotor at high subsonic speeds; in addition, the slope of the leading edge 1 of the upper surface of the airfoil changes more gently, which can weaken the shock wave and reduce the wave drag at transonic speeds. Therefore, the airfoil is applied to a tilt-rotor helicopter, which can significantly improve the lift characteristics, moment characteristics and drag characteristics of the tilt-rotor helicopter at high subsonic speeds.

[0042] The surface of the tiltrotor airfoil is n The surface coordinates are fitted by parametric fitting of the class function / shape transformation (CST). The expression of the surface coordinates is as follows:

[0043]

[0044] in, x is the surface abscissa of the airfoil, y is the surface ordinate of the airfoil, i is the order sequence, A is the fitting coefficient, n is the order of the CST parameterization method, For order sequence i The fitting coefficient of n is 7, that is, the 7th-order CST parameterization method is used. For the airfoil root step y Coordinates, ! is the factorial.

[0045] It should be noted that in the present application, the calculation method of the upper surface and the lower surface of the tilt-rotor airfoil are the same. Therefore, when calculating the upper surface of the tilt-rotor airfoil, x is the horizontal coordinate of the upper surface of the airfoil, y is the ordinate of the upper surface of the airfoil. When calculating the lower surface of the tilt-rotor airfoil, x is the horizontal coordinate of the lower surface of the airfoil, y is the ordinate of the lower surface of the airfoil.

[0046] The fitting coefficients of the upper surface of the tiltrotor airfoil are shown in Table 1.

[0047] Table 1

[0048]

[0049] The fitting coefficients of the lower surface of the tiltrotor airfoil are shown in Table 2.

[0050] Table 2

[0051]

[0052] In Table 1 and Table 2, A 0, A 1, A 2, A 3. A 4. A 5， A 6 are different fitting coefficients.

[0053] The upper surface coordinates of the above-mentioned tilt-rotor airfoil are shown in Table 3, where x is the abscissa of the upper surface data and y is the ordinate of the upper surface data.

[0054] Table 3

[0055]

[0056] The lower surface coordinates of the above-mentioned tilt-rotor airfoil are shown in Table 4, where x is the abscissa of the lower surface data and y is the ordinate of the lower surface data.

[0057] Table 4

[0058]

[0059] The NACA64212 airfoil is used as a reference airfoil to compare its performance with the tilt-rotor airfoil of the present application.

[0060] See also Figure 2 , is a geometric comparison diagram of the tiltrotor airfoil and the NACA64212 airfoil. In the figure, the tiltrotor airfoil of the present application is named Opt. In order to better observe the difference in the geometric shapes of the two airfoils, the aspect ratio of the coordinate axis is set to 0.15. From a geometric point of view, the tiltrotor airfoil of the present application has a relatively large leading edge radius compared to the NACA64212 airfoil, and the leading edge of the tiltrotor airfoil has a larger slope than the NACA64212 airfoil.

[0061] See also Figure 3 , a comparison diagram of the camber of the tilt-rotor airfoil and the NACA64212 airfoil. It can be seen that the tilt-rotor airfoil of the present application has a larger maximum camber than the NACA64212 airfoil.

[0062] according to Figure 2 and Figure 3 It can be clearly seen that the tilt-rotor airfoil of the present application and the NACA64212 airfoil have obvious geometric differences in appearance, and this geometric difference will inevitably change the aerodynamic performance of the airfoil. The aerodynamic performance of the tilt-rotor airfoil is compared with that of the NACA64212 airfoil in the transonic state. The Mach number Ma=0.75, the lift coefficient CL=0.20, and the Reynolds number Re=6.6e6 in the transonic state.

[0063] Figure 4 This is a comparison diagram of the pressure distribution of the tilt-rotor airfoil of this application and the NACA64212 airfoil at the design point. Figure 5 This is a comparison diagram of the drag characteristic curves of the tiltrotor airfoil of the present application and the NACA64212 airfoil under transonic conditions. Under transonic conditions, the leading edge radius of the tiltrotor airfoil increases, and the upper surface of the airfoil tends to be flat, which greatly weakens the shock wave on the upper surface and can improve the drag divergence characteristics.

[0064] Figure 6 This is a comparison diagram of the drag characteristic curves of the tiltrotor airfoil of the present application and the NACA64212 airfoil under transonic conditions. Due to the increase in the leading edge camber of the tiltrotor airfoil and the decrease in the positive camber of the trailing edge, the nose-down moment characteristics of the tiltrotor airfoil are significantly improved.

[0065] Figure 7 This is a comparison chart of the lift characteristic curves of the tilt-rotor airfoil of this application and the NACA64212 airfoil at low speed at 0.45 Ma. Figure 8 This is a comparison of the lift characteristic curves of the tilt-rotor airfoil and the NACA64212 airfoil at low speed at 0.5 Ma. Figure 7 and Figure 8 It can be seen that due to the increase in the camber of the tilt-rotor airfoil, the tilt-rotor airfoil has good lift characteristics and stall characteristics compared with the NACA64212 airfoil at Mach numbers of 0.45 and 0.50, respectively.

[0066] The aerodynamic performance parameters of the tilt-rotor airfoil of the present application and the NACA64212 airfoil at different Mach numbers are described below, see Table 5.

[0067] Table 5

[0068]

[0069] The aerodynamic performance parameters of the tilt-rotor airfoil of the present application and the NACA64212 airfoil at a Mach number of 0.45 are described below, see Table 6.

[0070] Table 6

[0071]

[0072] In Tables 5 and 6, Ma is the Mach number, C is the d is the drag coefficient, C m is the moment coefficient, C l is the lift coefficient and Alpha is the angle of attack.

[0073] Figure 1-Figure 4 Where X is the streamwise coordinate, Y is the spanwise coordinate, C is the chord, and C P is the trim lift coefficient, Figure 5 Baseline is the baseline.

[0074] According to Tables 5 and 6, the aerodynamic characteristics of the tilt-rotor airfoil of the present application are comprehensively analyzed. Compared with the NACA64212 airfoil of the leading blade with a thickness of 12%, the leading edge radius of the tilt-rotor airfoil is increased, and at 0.45 and 0.50 Mach, it has a larger lift coefficient and stall angle of attack under the same incoming flow. The tilt-rotor airfoil has a smaller maximum curvature than the NACA64212 airfoil, which effectively weakens the shock wave intensity and improves the drag divergence characteristics of the airfoil. At the same time, the increase in the leading edge curvature and the decrease in the trailing edge curvature reduce the head-down moment relative to the NACA64212 airfoil, which can effectively improve the balancing characteristics of the blades. Therefore, the tilt-rotor airfoil significantly improves the high subsonic characteristics of the tilt-rotor helicopter, and lays a technical foundation for the design of the middle and rear sections of the tilt-rotor helicopter blades.

[0075] Example 1

[0076] The present invention also provides a wing, wherein 60% to 85% of the airfoil in the span direction of the wing is the high subsonic tilt-rotor airfoil based on the retreating blade theory.

[0077] Example 2

[0078] The present invention also provides a helicopter, the wings of the helicopter are the wings described in Example 1, and the helicopter is a tilt-rotor helicopter.

[0079] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A high subsonic tiltrotor airfoil based on the retreating blade theory, characterized in that: The radius of the leading edge (1) of the upper surface of the airfoil is 0.00575 m, the slope of the leading edge (1) of the upper surface is 0.195-0.235, the curvature of the leading edge (1) of the upper surface of the airfoil is 0.202-0.242, the slope of the trailing edge (2) of the upper surface is -0.09--0.11, and the curvature of the trailing edge (2) of the upper surface is 0.079-0.099; The radius of the leading edge (3) of the lower surface of the airfoil is 0.000121 m, the slope of the leading edge (3) of the lower surface is -0.19 to -0.21, the curvature of the leading edge (3) of the lower surface of the airfoil is 0.146 to 0.176, the slope of the trailing edge (4) of the lower surface is 0.0057 to 0.0077, and the curvature of the trailing edge (4) of the lower surface is 0.026 to 0.046; The included angle of the trailing edge (2) of the upper surface of the airfoil is 1.8°, and the included angle of the trailing edge (4) of the lower surface is 0.9°; The maximum thickness T of the airfoil is 0.12 m, the maximum thickness position is at 0.289 times the chord length, the maximum camber is 0.0137 times the chord length, and the maximum camber position is at 0.6085 times the chord length; The airfoil is arranged at 60%-85% of the blade span; The surface of the airfoil adopts n The surface coordinates are fitted by the order CST parameterization as follows: in, x is the surface abscissa of the airfoil, y is the surface ordinate of the airfoil, i is the order sequence, n is the order of the CST parameterization method, For the airfoil root step y coordinate, is the fitting coefficient, For order sequence i The fitting coefficient of , ! is the factorial; The fitting coefficients for the upper surface of the tiltrotor airfoil are as follows: The fitting coefficients of the lower surface of the tiltrotor airfoil are as follows: in, A 0, A 1, A 2, A 3. A 4. A 5， A 6 are different fitting coefficients.

2. A high subsonic tiltrotor airfoil based on the retreating blade theory according to claim 1, characterized in that: The leading edge (1) of the upper surface and the leading edge (3) of the lower surface are connected at one end close to the chord line of the airfoil and smoothly transition to form the leading edge of the airfoil; the trailing edge (2) of the upper surface is connected at one end close to the leading edge of the airfoil to the other end of the leading edge (1) of the upper surface; the trailing edge (4) of the lower surface is connected at one end close to the leading edge of the airfoil to the other end of the leading edge (3); the trailing edge (2) of the upper surface and the trailing edge (4) of the lower surface intersect at one end close to the trailing edge of the airfoil.

3. A wing, characterized in that: The airfoil at the position of 60%-85% of the wing span is a high subsonic tilt-rotor airfoil based on the retreating blade theory as described in any one of claims 1-2.

4. A helicopter, characterized in that: The wing of the helicopter is a wing as described in claim 3, and the helicopter is a tilt-rotor helicopter.

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