A high-speed natural laminar airfoil with low torque, high drag and divergence Mach number suitable for rotors

Abstract

The present invention proposes a natural laminar airfoil with low torque and high drag divergence Mach number suitable for a rotor. The leading edge radius of the airfoil is large, which accelerates the leading edge flow speed and improves the suction peak, and can still have good torque characteristics and maintain a wide range of laminar flow at high speed. In addition, it also has excellent drag divergence characteristics and can be used for high-speed helicopter rotor design. Compared with the OA407 airfoil, the zero lift torque in the transonic state of the present invention has been significantly reduced while ensuring that the loss of low-speed aerodynamic performance is not large, so that the available Mach number range of the airfoil controlled by torque is significantly increased. Within the designed Mach number range, the zero lift torque coefficient of the airfoil is close to 0, with good low torque characteristics, and the drag divergence Mach number reaches 0.875, which is 0.018 higher than that of OA407. It has obvious low torque and high drag divergence Mach number and low drag characteristics, laying a foundation for the design of high-speed helicopter rotors.

Description

Technical Field

[0001] The invention belongs to the technical field of high-speed natural laminar airfoils, and in particular relates to a natural laminar airfoil with low torque, high drag and divergence Mach number suitable for a rotor. Background Art

[0002] Helicopters are widely used in civil and military fields due to their flexibility and strong adaptability, and have made great contributions to the development of the national economy. However, the complex working state of the rotor leads to a low speed of the helicopter, and increasing the flight speed has always been the primary goal of helicopter development. The key to improving the forward flight speed of the helicopter lies in the rotor design, and the core of which is the airfoil design.

[0003] Unlike fixed-wing aircraft, when a helicopter is flying forward, the rotor has both forward speed and rotation speed, so the speed of the forward blades may even exceed the speed of sound, while the backward blades face problems such as flow separation caused by backflow. Carefully designed airfoils are needed to alleviate the above problems and provide support for increasing the flight speed of helicopters.

[0004] The typical natural laminar airfoil mainly maintains a larger laminar area by shifting the maximum thickness position backward, which makes its leading edge radius smaller and the pressure recovery area smaller. In addition, the traditional laminar airfoil design is mainly used for fixed-wing aircraft, and torque constraints are rarely considered, which is not enough for rotary-wing aircraft. The above design features make the traditional natural laminar airfoil have a small drag divergence Mach number and strong flow separation phenomenon when cruising at high speed, which greatly restricts the increase of helicopter flight speed. Summary of the invention

[0005] In order to solve the problem that the existing airfoil cannot meet the requirements of rotor airfoil design, the present invention takes into account high-speed performance, torque constraints and drag reduction requirements at the same time, and proposes a high-speed natural laminar airfoil with low torque, high drag divergence Mach number suitable for the rotor. The leading edge radius of the airfoil is large, which accelerates the leading edge flow speed and improves the suction peak, and can still have good torque characteristics at high speeds and maintain a large range of laminar flow. In addition, it also has excellent drag divergence characteristics and can be used in high-speed helicopter rotor design.

[0006] The technical solution of the present invention is:

[0007] The invention discloses a high-speed natural laminar airfoil with low torque, high drag and divergent Mach number suitable for a rotor, wherein the leading edge radius of the airfoil is 1.8%, the maximum thickness of the airfoil is 7.72% and is located at 48.8% of the chord length of the airfoil, the maximum camber is 0.27% and is located at 1.8% of the chord length of the airfoil, and the trailing edge angle is 1.21 degrees; the leading edge radius, the maximum thickness and the maximum camber are described by dimensionless quantities, with the chord length c of the airfoil as a reference.

[0008] Furthermore, the geometric coordinate expressions of the upper and lower surfaces of the airfoil are:

[0009]

[0010] Where x represents the horizontal coordinate of the upper or lower surface of the airfoil, y represents the vertical coordinate corresponding to the upper or lower surface of the airfoil, n represents the order of the CST parameterization method, and y tail represents the y coordinate of the step at the root of the airfoil;

[0011] The fitting coefficient of the upper surface of the airfoil is:

[0012]

[0013] The fitting coefficient of the lower surface of the airfoil is:

[0014]

[0015] Furthermore, the fitting coefficients of the upper and lower surfaces of the airfoil are optimized as follows:

[0016] The fitting coefficient of the upper surface of the airfoil is:

[0017]

[0018] The fitting coefficient of the lower surface of the airfoil is:

[0019]

[0020] Furthermore, the coordinate positions of the upper and lower surfaces of the high-speed natural laminar airfoil suitable for the rotor with low torque and high drag divergence Mach number are:

[0021] Upper surface coordinates:

[0022]

[0023]

[0024]

[0025] Bottom surface coordinates:

[0026]

[0027]

[0028]

[0029] This airfoil effectively controls the development of shock waves, thereby significantly improving the airfoil drag divergence characteristics; compared with the classic rotor airfoil OA407, it has a smaller slope on the upper surface of the leading edge and a larger slope on the lower surface of the leading edge; compared with OA407, the maximum thickness position of this airfoil is moved backward, it has a smaller maximum curvature, and the maximum curvature position is moved forward, and it is fuller at the trailing edge of the airfoil. In the high-speed Mach number range of 0.7-0.9 and zero-lift state, the airfoil drag divergence Mach number is increased by 0.018 relative to OA407, and a very low drag coefficient and good torque characteristics are maintained in the range of 0.78-0.9. The robustness of the aerodynamic characteristics is further enhanced, and better torque characteristics are maintained relative to the OA407 airfoil in the entire envelope range.

[0030] Beneficial Effects

[0031] The present invention proposes a high-speed natural laminar airfoil with low torque and high drag divergence Mach number suitable for a rotor. While ensuring that the loss of low-speed aerodynamic performance is not large, the zero-lift torque in the transonic state is significantly reduced compared with the OA407 airfoil, so that the available Mach number range of the airfoil controlled by torque is significantly increased. Within the designed Mach number range, the zero-lift torque coefficient of the airfoil is close to 0, with good low-torque characteristics, and the drag divergence Mach number reaches 0.875, which is 0.018 higher than that of OA407. It has obvious low-torque and high-drag divergence Mach number and low drag characteristics, laying a foundation for the design of high-speed helicopter rotors.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 It is the geometrical appearance diagram of the airfoil of the present invention.

[0035] Figure 2 The geometrical appearance of the airfoil of the present invention is compared with the geometrical appearance of the airfoil of OA407.

[0036] Figure 3 It is a comparison diagram of the pressure shape distribution of the airfoil of the present invention and the OA407 airfoil at the inspection point.

[0037] Figure 4 It is a comparison diagram of the drag divergence curves of the airfoil of the present invention and the airfoil of OA407.

[0038] Figure 5 It is a comparison diagram of the moment curves of the airfoil of the present invention and the airfoil of OA407.

[0039] Figure 6 It is a comparison diagram of lift coefficient curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.3.

[0040] Figure 7 It is a comparison diagram of the lift-to-drag ratio curves of the airfoil of the present invention and the airfoil of OA407 at a low speed state of Ma=0.3.

[0041] Figure 8 It is a comparison diagram of lift coefficient curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.4.

[0042] Fig. 9 It is a comparison diagram of lift-to-drag ratio curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.4.

[0043] Fig.10 It is a comparison diagram of lift coefficient curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.5.

[0044] Fig.11 It is a comparison diagram of lift-to-drag ratio curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.5.

[0045] Fig.12 It is a comparison diagram of lift coefficient curves of the airfoil of the present invention and the airfoil of OA407 at low speed state Ma=0.6.

[0046] Fig.13 It is a comparison diagram of the lift-to-drag ratio curves of the airfoil of the present invention and the airfoil of OA407 at a low speed state of Ma=0.6. DETAILED DESCRIPTION

[0047] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0048] High-speed flight is a bottleneck that advanced helicopters need to break through. As the core component of helicopters, rotors need to meet the requirements of high-speed flight through carefully designed airfoils. The airfoils at the tips of rigid coaxial twin-rotor blades need to have low torque, high drag divergence Mach number and low drag characteristics. However, when traditional rotor airfoils are used at the tips of rigid coaxial twin-rotor high-speed helicopter blades, the shock wave drag is large and the nose-up torque is high, which completely fails to meet the drag divergence requirement of Ma=0.9, thereby limiting the forward flight speed of such helicopters and greatly limiting their overall performance.

[0049] In order to solve the above problems, the present invention proposes a high-speed natural laminar airfoil with low torque and high drag divergence Mach number suitable for the rotor, and the airfoil is used for the tip of the rigid coaxial twin rotor. The design idea of ​​the airfoil is based on the proxy optimization method to constrain the drag of the rotor airfoil in the low-speed state Ma=0.3, Ma=0.4, Ma=0.5 and Ma=0.6 to ensure that its aerodynamic performance at low speed is not seriously lost. On this basis, its transonic aerodynamic characteristics are further optimized to reduce the drag and torque of the airfoil and increase the drag divergence Mach number. The above is the optimization method of this airfoil. This optimization takes into account both torque balancing and high-speed performance, and also considers reducing drag. It is a typical multi-objective problem, which is achieved by current numerical optimization methods. It does not belong to the characteristic parameters of the airfoil, so it will not be repeated here.

[0050] The invention proposes a high-speed natural laminar airfoil with low torque and high drag divergence Mach number suitable for a rotor, and the high-speed Mach number is 0.78-0.90 Mach, and the sonic Reynolds number is 7.2e6. The airfoil is drawn according to a drawing with a horizontal and vertical coordinate ratio of 1 as shown in FIG. Figure 1 shown.

[0051] The leading edge radius of the airfoil is 1.8%, the maximum thickness of the airfoil is 7.72%, located at 48.8% of the chord length of the airfoil, the maximum camber is 0.27%, located at 1.8% of the chord length of the airfoil, and the trailing edge angle is 1.21 degrees. It should be noted that in the airfoil design, the parameter description is dimensionless, so the above geometric features are the result of dimensionless treatment of the airfoil chord length C.

[0052] The specific analytical expression of the coordinates of the upper and lower surfaces of the airfoil is:

[0053]

[0054] Where x represents the horizontal coordinate of the upper or lower surface of the airfoil, y represents the vertical coordinate corresponding to the upper or lower surface of the airfoil, and n represents the order of the CST parameterization method. For this embodiment, the 7th-order CST parameterization method is used, n is 7, and y is tail Represents the y coordinate of the step at the root of the airfoil.

[0055] The specific fitting coefficients of the upper and lower surfaces of the airfoil are:

[0056] The relevant parameters of the upper surface of this airfoil are described as:

[0057]

[0058] The relevant parameters of the lower surface of this airfoil are described as follows:

[0059]

[0060] The coordinates of the upper and lower surfaces of the airfoil in this embodiment are:

[0061] Upper surface coordinates:

[0062]

[0063]

[0064]

[0065] Bottom surface coordinates:

[0066]

[0067]

[0068]

[0069] Compare this example to the classic 7% thick OA407 airfoil:

[0070] Figure 2 It is a comparison diagram of the geometric shapes of the two airfoils. In order to better observe the difference between them, the aspect ratio of the coordinate axis is set to 0.25. It can be seen that the airfoil of this embodiment (named OPT in the figure legend) has a larger leading edge radius than the reference airfoil (named OA407 in the figure legend); compared with the reference airfoil, this embodiment has a smaller slope on the upper surface of the leading edge and a larger slope on the lower surface of the leading edge; compared with the reference airfoil, the maximum thickness position of this embodiment is moved backward; compared with the reference airfoil, this embodiment has a smaller maximum curvature, and the maximum curvature position is moved forward, and it is fuller at the trailing edge of the airfoil.

[0071] The difference in geometry will inevitably lead to aerodynamic changes. Firstly, the aerodynamic performance of the present invention is analyzed under the high-speed zero-lift design state (Ma=0.86, Re=6.912e6, CL=0.00). Figure 3 The pressure distribution morphology diagram of the airfoil of the present invention and the airfoil of OA407 at high speed and zero lift is given. The slope of the upper surface of the leading edge decreases, and the slope of the lower surface of the leading edge increases, so that the pressure transition of the airfoil of the present invention is smoother. Compared with the suction peak of the upper surface of OA407, the upper surface of the airfoil of the present invention has three low-pressure areas in the front, middle and rear, which makes the airfoil of the present invention have excellent low-drag characteristics and drag divergence characteristics within a certain Mach number range.

[0072] Figure 4This is a comparison diagram of the drag divergence curves of the airfoil of the present invention and the OA407 airfoil in the transonic state. It can be seen that the airfoil of the present invention has lower zero-lift drag between Mach 0.865 and Mach 0.90 than the OA407 airfoil, and the drag divergence Mach number is increased from 0.857 to 0.875, an increase of 0.018 Mach, and an obvious transonic spoon-shaped area appears. Figure 5 This is a comparison diagram of the moment curves of the airfoil of the present invention and the OA407 airfoil in the transonic state. It can be seen that the absolute value of the moment of the airfoil of the present invention is greatly reduced compared with the OA407 airfoil, meeting the low moment, high drag divergence Mach number and low drag characteristics.

[0073] The lift coefficient curves and lift-to-drag ratio curves of the present invention at low speeds Ma=0.3, Ma=0.4, Ma=0.5 and Ma=0.6 are respectively as follows: Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 , Fig.11 , Fig.12 and Fig.13 As shown, it can be observed that the low-speed lift characteristics of the present invention are reduced compared with OA407, the low-speed lift-to-drag ratio characteristics are equivalent to OA407 within a small angle of attack, and the lift-to-drag ratio characteristics at a large angle of attack are reduced, but this is acceptable for a rotor.

[0074] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for designing a high-speed natural laminar airfoil with low torque and high drag divergence Mach number suitable for a rotor, characterized by: Aiming at the design requirements of low moment, high drag divergence Mach number and low drag characteristics of the airfoil at the tip of the rigid coaxial twin-rotor blade, based on the proxy optimization method, the drag of the airfoil at low speed Ma=0.3, Ma=0.4, Ma=0.5 and Ma=0.6 is constrained, and on this basis, the transonic aerodynamic characteristics of the airfoil are further optimized, the drag and moment of the airfoil are reduced, and the drag divergence Mach number is increased; finally, the high-speed natural laminar airfoil with low moment and high drag divergence Mach number suitable for the rotor is obtained: the leading edge radius of the airfoil is 1.8%, the maximum thickness of the airfoil is 7.72%, located at 48.8% of the chord length of the airfoil, the maximum camber is 0.27%, located at 1.8% of the chord length of the airfoil, and the trailing edge angle is 1.21 degrees; the leading edge radius, maximum thickness and maximum camber are described by dimensionless quantities, with the chord length c of the airfoil as the reference; The airfoil is used for the tip position of a coaxial helicopter; The geometric coordinate expressions of the upper and lower surfaces of the airfoil are: Where x represents the horizontal coordinate of the upper or lower surface of the airfoil, y represents the vertical coordinate corresponding to the upper or lower surface of the airfoil, n represents the order of the CST parameterization method, and y tail represents the y coordinate of the step at the root of the airfoil; The fitting coefficient of the upper surface of the airfoil is: The fitting coefficient of the lower surface of the airfoil is: The obtained high-speed natural laminar airfoil with low torque and high drag divergence Mach number suitable for the rotor has three low-pressure areas in the front, middle and rear on the upper surface of the airfoil under the high-speed zero-lift design state of Ma=0.86, Re=6.912e6, and CL=0.00, and the drag divergence Mach number reaches 0.

875.

2. A high-speed natural laminar airfoil with low torque, high drag and divergence Mach number suitable for a rotor according to claim 1, characterized in that: The coordinate points of the upper and lower surfaces of the airfoil are: Upper surface coordinates: Bottom surface coordinates:

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