A laminar supercritical rotor airfoil suitable for the heavy-weight high-speed characteristics in the middle of the blade of a high-speed helicopter

Abstract

The present invention proposes a laminar supercritical rotary wing airfoil suitable for the heavy weight and high-speed characteristics in the middle of the blade of a high-speed helicopter. The leading edge radius of the airfoil is 0.00377, the maximum thickness of the airfoil is 0.12, which is located at the 41% chord length of the airfoil, the maximum camber is 0.0122, which is located at the 18.6% chord length of the airfoil. This 12% thickness airfoil is used near 0.5R of the blade and is located in the main lift section. While improving its high-speed drag divergence characteristics, it also has a high lift-to-drag ratio at medium Mach numbers and high lift characteristics at low speeds. Compared with the classical OA312 airfoil, the designed airfoil has a 0.4 increase in the drag divergence Mach number and an 11.1% increase in the maximum lift coefficient without significant loss in low-speed characteristics. The high-speed characteristics are improved significantly and more robustly. Considering the special design requirements of the rotary wing airfoil of a high-speed helicopter, the designed airfoil shows significant advantages compared with the classical OA312 airfoil.

Description

Technical Field

[0001] The present invention relates to the field of airfoils for high-speed helicopter rotor blades, and specifically to a laminar supercritical rotary airfoil with high-speed characteristics and a bias towards high speed in the middle of the blades suitable for high-speed helicopters. Background Art

[0002] The motion law of helicopter rotors during flight is extremely complex. The airfoil is an important factor in the shape of the rotor blades. Its shape design directly determines the unsteady aerodynamic performance of the rotor, thus greatly affecting key performance indicators such as the aerodynamic efficiency, flight speed, and handling quality of the helicopter. Conventional aircraft airfoils cannot be directly used in the design of high-performance rotors, and it is necessary to conduct research on the special airfoils for rotors aiming at the special aerodynamic environment of the rotors.

[0003] The biggest reason that makes the design of helicopter blades face difficulties is that the oncoming flow velocity and angle of attack of the sectional airfoil are in different oncoming flow conditions. The wide-speed-range oncoming flow velocity results in different design requirements and emphasis characteristics at different stations along the span of the helicopter blade airfoil. In the high-speed flight state of the helicopter, the forward-side blades are in an airflow with a very large dynamic pressure, and shock stall is likely to occur. Moreover, there will be a large-scale reverse flow area in the high-speed forward flight state of the rotor. The subsequent negative lift and flow separation phenomena cause significant loss of helicopter performance. As the rotating lift surface of the helicopter, each blade of the rotor is in the wake of the previous blade. The high-speed rotation motion makes the linear velocity on the blade continuously change from low speed to high speed along the radius, and it may reach transonic speed at the blade tip. This makes the aerodynamic interference between the rotor blades very intense, facing complex aerodynamic characteristics such as high compressibility and strong radial flow, and should have good high-speed characteristics. The blade root is in deep reverse flow and should have anti-flow separation and low-drag characteristics.

[0004] For the airfoil at the 50% position of the helicopter blade, while focusing on its high-speed characteristics, its low-speed characteristics should also be taken into account. Therefore, the dynamic aerodynamic characteristics of the rotary airfoil pose extremely high requirements for the design of the airfoil. Summary of the Invention

[0005] To solve the problems existing in the prior art and improve the aerodynamic characteristics of the airfoil in the middle of the helicopter blade, the present invention designs and proposes a laminar supercritical rotary airfoil with high-speed characteristics and a bias towards high speed in the middle of the blades suitable for high-speed helicopters through a high-dimensional multi-objective airfoil robust design method. While improving its high-speed drag divergence characteristics, this airfoil also has a high lift-to-drag ratio at medium Mach numbers and high lift characteristics at low speeds.

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

[0007] The laminar supercritical rotary wing airfoil suitable for the heavy high-speed characteristics in the middle of the blade of a high-speed helicopter has a leading edge radius of 0.00377, a maximum airfoil thickness of 0.12, which is located at the 41% chord length of the airfoil, and a maximum camber of 0.0122, which is located at the 18.6% chord length of the airfoil. It should be noted that in the field of airfoil design, parameter descriptions are all carried out using dimensionless quantities. Therefore, the above leading edge radius, maximum thickness, maximum camber, and subsequent airfoil coordinate descriptions are all carried out using dimensionless quantities, and the dimensionless process is based on the airfoil chord length c.

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

[0009]

[0010] where x represents the abscissa of the upper or lower surface of the airfoil, y represents the corresponding ordinate of 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 airfoil root;

[0011] The fitting coefficients for the upper surface of the airfoil are:

[0012]

[0013] The fitting coefficients for the lower surface of the airfoil are:

[0014]

[0015] Furthermore, the preferred fitting coefficients for the upper and lower surfaces of the airfoil are:

[0016] The fitting coefficients for the upper surface of the airfoil are:

[0017]

[0018]

[0019] The fitting coefficients for the lower surface of the airfoil are:

[0020]

[0021] Furthermore, the positions of the coordinate points on the upper and lower surfaces of the laminar supercritical rotary wing airfoil suitable for the heavy high-speed characteristics in the middle of the blade of a high-speed helicopter are:

[0022] Upper surface coordinates:

[0023]

[0024]

[0025] Lower surface coordinates:

[0026]

[0027]

[0028] Compared with the classical OA312 airfoil with a thickness of 12%, the upper surface camber of this airfoil moves downward, the leading-edge radius decreases, the slope of the leading-edge change reduces, and the mean camber line descends, which is beneficial to further increase the divergence Mach number; the maximum thickness moves backward, and a reverse camber appears at the trailing edge, which can reduce the drag at medium and high Mach numbers and improve the lift-to-drag ratio.

[0029] Beneficial effects

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] The present invention provides a laminar supercritical rotary airfoil suitable for the middle part of the blade of a high-speed helicopter, which emphasizes high-speed characteristics. This 12%-thickness airfoil is used near 0.5R (±0.1R) of the blade, located in the main lift section. While improving its high-speed drag divergence characteristics, it also has a high lift-to-drag ratio at medium Mach numbers and high lift characteristics at low speeds. The present invention uses an efficient multi-objective robust optimization method to optimize the design of a 12%-thickness high-speed rotary airfoil. The aerodynamic performance of the designed airfoil is compared in detail with that of the classical OA312 airfoil at high, medium, and low Mach numbers. The results show that compared with the classical airfoil, without significant loss of low-speed characteristics, the designed opt airfoil has an increase of 0.4 in the drag divergence Mach number and an increase of 11.1% in the maximum lift coefficient. The high-speed characteristics are significantly improved and more robust. Considering the special design requirements of the rotary airfoil of a high-speed helicopter, the designed airfoil shows significant advantages compared with the classical OA312 airfoil.

[0032] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. Description of the drawings

[0033] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0034] Figure 1 Geometric shape diagram of the airfoil of the present invention;

[0035] Figure 2 Comparison of the geometric shape diagram of the airfoil of the present invention and the geometric shape diagram of the OA312 airfoil;

[0036] Figure 3 Comparison of the mean camber line of the airfoil of the present invention and the mean camber line of the OA312 airfoil;

[0037] Figure 4Comparison diagram of moment characteristics curves between the airfoil of the present invention and OA312 airfoil (CL = 0.00, Re = 4.4e6);

[0038] Figure 5 Comparison diagram of drag divergence curves between the airfoil of the present invention and OA312 airfoil (CL = 0.00, Re = 4.4e6);

[0039] Figure 6 Comparison diagram of low-speed lift characteristics curves between the airfoil of the present invention and OA312 airfoil (Ma = 0.4, Re = 2.2e6);

[0040] Figure 7 Comparison diagram of mid-Mach lift characteristics curves between the airfoil of the present invention and OA312 airfoil (Ma = 0.6, Re = 3.3e6). Detailed implementation manners

[0041] The embodiments of the present invention will be described in detail below. The embodiments are exemplary and are intended to explain the present invention, rather than being construed as a limitation to the present invention.

[0042] When a large coaxial rotor helicopter is in a high-speed forward flight state, the oncoming flow from the middle to the tip of the blade is in a transonic state. The shock wave generated by the acceleration of the airflow on the upper surface of the blade significantly increases the blade drag, seriously affecting the aerodynamic characteristics of the helicopter. 50% of the blade station is in the main lift section, and the flight condition is at medium to high Mach numbers. In this range, a laminar supercritical airfoil is mainly used to take into account the aerodynamic characteristics at medium and high Mach numbers, so as to improve the cruise efficiency of the whole machine.

[0043] Therefore, according to the aerodynamic problems and design objectives faced by the helicopter blade, on the basis of improving the traditional single-point deterministic optimization design, the present invention uses a high-dimensional multi-objective robust optimization design method to design and propose a laminar supercritical rotor airfoil with a bias towards high-speed characteristics, which is applicable to the middle part of the high-speed helicopter blade.

[0044] The design requirements for this airfoil are high drag divergence characteristics, a large range of low drag and robustness at high Mach numbers (Ma = 0.7 - 0.85), a high lift-to-drag ratio at medium Mach numbers (Ma = 0.5 - 0.6), high lift at low Mach numbers (Ma = 0.3 - 0.4), and moment characteristics in all states should be taken into account. Therefore, based on these design requirements, the design model is a typical high-dimensional multi-objective complex constraint optimization problem, which makes it difficult for general multi-objective optimization algorithms to obtain an effective solution set. So we optimize with the goal of reducing the mean and variance of the airfoil drag at high-speed states, making the optimized airfoil have robust high drag divergence characteristics. At the same time, we optimize the mean and variance of the drag in the constant-lift state at medium Mach numbers to maintain a good lift-to-drag ratio and take into account the moment characteristics. Through multiple rounds of optimization and compromise selection of the multi-objective optimization algorithm, we select an aerodynamic shape that takes into account the moment coefficients at high, medium, and low Mach numbers and all states.

[0045] The lift-drag aerodynamic characteristics of the optimized airfoil are analyzed within a wide Mach number range. The Mach numbers under investigation are 0.4, 0.6, 0.7 to 0.85, and the corresponding Reynolds numbers are 3.2e6, 4.8e6, 5.6e6 to 6.8e6. The results show that the airfoil meets the design requirements well under the condition of meeting the constraints.

[0046] (1) Optimization model

[0047] According to the design requirements, the drag divergence Mach number is high, the moment characteristics are low, and the lift-drag ratio is high at low speeds. The constraint conditions focus on optimizing the drag divergence characteristics and moment characteristics.

[0048] Table 1 Design point conditions of the low-subsonic high-lift and low-drag rotor blade airfoil

[0049]

[0050] Search range X ∈ R n , X ∈ [X L , X U , Design objectives and constraints:

[0051] Table 2 Design objectives and constraints of the low-subsonic high-lift and low-drag rotor blade airfoil

[0052]

[0053]

[0054] (2) Optimized airfoil data

[0055] As Figure 2 shown by the comparison between the airfoil geometric shape diagram of the present invention and the geometric shape diagram of the reference airfoil OA312, compared with the classical OA312 airfoil with a thickness of 12%, the upper surface of this airfoil moves downward, the leading edge radius decreases, the slope of the leading edge change decreases, and the mean camber line descends, which is beneficial to further increase the divergence Mach number. The maximum thickness moves backward, and a reverse bend appears at the trailing edge, which can reduce the drag at medium and high Mach numbers and improve the lift-drag ratio.

[0056] Specifically, the laminar supercritical rotor blade airfoil applicable to the middle part of the high-speed helicopter blade and emphasizing high-speed characteristics in this embodiment has the following airfoil characteristics:

[0057] Leading edge radius Airfoil area Maximum thickness Maximum thickness position Maximum camber Maximum camber position 0.00377 0.08465 12％ 0.410 0.0122 0.186

[0058] It should be noted that in the field of airfoil design, parameter descriptions are all carried out using dimensionless quantities. Therefore, the above leading edge radius, maximum thickness, maximum camber, and subsequent airfoil coordinate descriptions are all carried out using dimensionless quantities, and the dimensionless process is based on the airfoil chord length c.

[0059] Furthermore, the unified expressions obtained by fitting the upper and lower surfaces of the airfoil using 7th-order CST parameterization are as follows:

[0060]

[0061] where x represents the abscissa of the upper or lower surface of the airfoil, y represents the corresponding ordinate of 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 airfoil root;

[0062] The fitting coefficients for the upper surface of the airfoil are:

[0063]

[0064] The fitting coefficients for the lower surface of the airfoil are:

[0065]

[0066]

[0067] The specific positions of the coordinate points on the upper and lower surfaces are: Coordinates of the upper surface:

[0068] Coordinates of the upper surface:

[0069]

[0070]

[0071] Coordinates of the lower surface:

[0072]

[0073]

[0074] (3) Comparison of aerodynamic data

[0075] As Figure 4 shown by the comparison of the moment characteristic curves of the airfoil of the present invention and the reference airfoil OA312 airfoil, and Figure 5 shown by the comparison of the drag divergence curves of the airfoil of the present invention and the reference airfoil OA312 airfoil, it can be clearly seen that the drag divergence Mach number of the optimized airfoil has increased by 0.4 compared to the reference airfoil, and the moment characteristics have been significantly improved. This is because compared with the reference airfoil, the camber of the optimized airfoil is reduced, and the position of the maximum thickness is shifted backward, which weakens the shock wave or shifts the shock wave position backward, which is beneficial to improving the drag divergence characteristics. Moreover, compared with the initial airfoil, there is a certain anti-loading characteristic at the trailing edge of the optimized airfoil, which provides a certain nose-up moment and balances with its nose-down moment, reducing the absolute value of the moment and enhancing the moment characteristics. However, due to the reduction of the camber on the upper surface, there is a loss of low-speed characteristics within a certain range, which can be seen fromFigure 6 As can be seen from the comparison of the low-speed lift characteristic curves between the airfoil of the present invention and the reference airfoil OA312 airfoil, the low-speed lift characteristic of the optimized airfoil is reduced compared to the reference airfoil. However, since its operating point is mainly at medium to high Mach numbers, a slight reduction in the low-speed lift characteristic of the airfoil is acceptable. From Figure 7 As can be seen from the comparison diagram of the medium Mach number lift characteristic curves between the airfoil of the present invention and the reference airfoil OA312 airfoil, the lift characteristic of the optimized airfoil is improved compared to the reference airfoil at the operating point.

[0076] Based on the above analysis, a laminar supercritical rotary wing airfoil with a bias towards high-speed characteristics applicable to the middle part of the blades of high-speed helicopters proposed by the present invention can take into account high drag divergence characteristics, low moment characteristics, and high lift and low drag characteristics at medium and high speeds. It can meet the special aerodynamic design requirements of high-speed helicopters.

[0077] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. A laminar supercritical rotor airfoil suitable for the heavy-weight high-speed characteristics in the middle of the blade of a high-speed helicopter, characterized in that: The leading-edge radius of the airfoil is 0.00377, the maximum thickness of the airfoil is 0.12, which is located at the 41% chord length of the airfoil, the maximum camber is 0.0122, which is located at the 18.6% chord length of the airfoil; the leading-edge radius, maximum thickness, maximum camber and subsequent airfoil coordinate descriptions are all described using dimensionless quantities, and the dimensionless process is based on the airfoil chord length c; The airfoil is used at the position of 0.5R±0.1R of the high-speed helicopter blade, where R is the blade span; The airfoil is designed using a high-dimensional multi-objective robust optimization design method, with the OA312 airfoil as the baseline airfoil, and the design point conditions are: In design state 1, with the minimum mean and variance of the airfoil drag as the objective, the constraints are that compared with the baseline airfoil, the thickness does not decrease, the area does not decrease, and the moment does not increase; in design state 2, with the minimum mean and variance of the airfoil drag as the objective, the constraint is that compared with the baseline airfoil, the moment does not increase; The geometric coordinate expressions of the upper and lower surfaces of the designed airfoil are: where x represents the abscissa of the upper or lower surface of the airfoil, y represents the corresponding ordinate of 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 airfoil root; The fitting coefficients of the upper surface of the airfoil are: The fitting coefficients of the lower surface of the airfoil are:

2. The laminar supercritical rotary wing airfoil with heavy high-speed characteristics applicable to the middle part of the high-speed helicopter blade according to claim 1, characterized in that: The fitting coefficients of the upper surface of the airfoil are: The fitting coefficients of the lower surface of the airfoil are:

3. The laminar supercritical rotor airfoil suitable for the heavy-high-speed characteristics in the middle of the blade of a high-speed helicopter according to claim 1, wherein: The positions of the coordinate points on the upper and lower surfaces of the airfoil are: Upper surface coordinates: Lower surface coordinates:

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