阅读说明：本技术 用于高速直升机旋翼桨根的非对称双钝头翼型及设计方法 (Asymmetric double-blunt-tip airfoil profile for rotor root of high-speed helicopter and design method ) 是由 韩少强 宋文萍 韩忠华 许建华 于 2020-06-29 设计创作，主要内容包括：本发明提供一种用于高速直升机旋翼桨根的非对称双钝头翼型及设计方法,翼型上表面前缘倒圆半径为0.044C,翼型上表面后缘倒圆半径为0.015C；翼型下表面前缘倒圆半径为0.034C,翼型下表面后缘倒圆半径为0.032C；翼型的最大厚度为26％C,最大厚度位置为42％C；弯度为0.84％C；C为翼型弦长。本发明根据反流区的实际流动特性,设计出用于高速直升机旋翼桨根的非对称双钝头翼型,与桨叶外段头钝尾尖的常规翼型具有很好的几何相容性,顺流和反流状态下都具有更低的气动阻力和更高的升阻比,能有效抑制流动分离现象的发生,同时具备良好的力矩特性,从而提高直升机巡航效率,适应新一代高速直升机的使用需求。(The invention provides an asymmetric double-blunt-nose wing profile for a rotor root of a high-speed helicopter and a design method, wherein the radius of the front edge of the upper surface of the wing profile is 0.044C, and the radius of the rear edge of the upper surface of the wing profile is 0.015C; the radius of the front edge of the lower surface of the airfoil is 0.034C, and the radius of the rear edge of the lower surface of the airfoil is 0.032C; the maximum thickness of the airfoil is 26% C, and the maximum thickness position is 42% C; camber of 0.84% C; c is the airfoil chord length. According to the actual flow characteristics of the counter-flow area, the asymmetric double-blunt-nose wing type for the rotor root of the high-speed helicopter is designed, has good geometric compatibility with the conventional wing type with the blunt-nose tail tip at the outer section of the blade, has lower aerodynamic resistance and higher lift-drag ratio in both a forward flow state and a counter-flow state, can effectively inhibit the occurrence of flow separation, and has good torque characteristics, so that the cruising efficiency of the helicopter is improved, and the use requirements of a new generation of high-speed helicopters are met.)

1. An asymmetric double-blunt-nose airfoil for a rotor root of a high-speed helicopter is characterized in that the radius of a front edge of the upper surface of the airfoil is 0.044C, and the radius of a rear edge of the upper surface of the airfoil is 0.015C; the radius of the front edge of the lower surface of the airfoil is 0.034C, and the radius of the rear edge of the lower surface of the airfoil is 0.032C;

the maximum thickness of the asymmetric double-blunt-end airfoil for the rotor root of the high-speed helicopter is 26% C, and the maximum thickness position is 42% C; camber of 0.84% C; wherein C is the airfoil chord length.

Therefore, the asymmetric double-blunt-nose wing profile for the rotor root of the high-speed helicopter is a front-back asymmetric double-blunt-nose wing profile applied to a back flow area of the rotor root of the high-speed helicopter, the radius of the front edge of the upper surface of the wing profile is larger than the radius of the rear edge of the upper surface of the wing profile, the radius of the front edge of the lower surface of the wing profile is larger than the radius of the rear edge of the lower surface of the wing profile, the maximum thickness position is close to the front edge, and the wing profile and the blade outer-section blunt-; the wing profile has small camber, which is beneficial to simultaneously reducing the resistance in the downstream and reverse flow states; the radius of the front edge of the upper surface of the wing profile, the radius of the rear edge of the upper surface of the wing profile, the radius of the front edge of the lower surface of the wing profile and the radius of the rear edge of the lower surface of the wing profile are all larger than those of the same wing profile, so that the negative pressure peak value under the condition of forward flow and backflow is improved, the lift performance is improved, and the lift-drag ratio is improved.

2. The asymmetric double blunt profile for a high speed helicopter rotor root according to claim 1 wherein said asymmetric double blunt profile for a high speed helicopter rotor root has the following aerodynamic characteristics:

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the lift coefficient is determined to be 0.5, the drag coefficient is 0.022, and the lift-drag ratio is 22.7;

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the fixed lift coefficient is 0.85, the drag coefficient is 0.028, and the lift-drag ratio is 30.4;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.45, the drag coefficient is 0.027, and the lift-drag ratio is 16.7;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.85, the drag coefficient is 0.035, and the lift-drag ratio is 24.2.

3. The asymmetric double blunt profile for a rotor root of a high speed helicopter according to claim 1 wherein said airfoil upper surface of said asymmetric double blunt profile for a rotor root of a high speed helicopter has geometric coordinate data as set forth in table 2; the geometrical coordinate data of the lower surface of the airfoil are shown in Table 3:

TABLE 2 NPU-ASEA-260 Airfoil Upper surface geometric coordinate data

Serial number X_up/C Y_up/C Serial number X_up/C Y_up/C 1 0.000000 0.000000 18 0.554568 0.125106 2 0.001530 0.012579 19 0.614521 0.119979 3 0.005792 0.022872 20 0.671777 0.113899 4 0.012149 0.033252 21 0.725297 0.107081 5 0.021197 0.044441 22 0.774266 0.099703 6 0.033532 0.056415 23 0.818113 0.091874 7 0.049898 0.069017 24 0.856529 0.083674 8 0.071086 0.081897 25 0.889492 0.075194 9 0.097584 0.094423 26 0.917164 0.066533 10 0.129703 0.105919 27 0.939870 0.057784 11 0.167682 0.115768 28 0.958126 0.048991 12 0.211410 0.123375 29 0.972394 0.040218 13 0.260425 0.128531 30 0.983119 0.031549 14 0.314077 0.131486 31 0.990966 0.022810 15 0.371548 0.132438 32 0.996557 0.013302 16 0.431686 0.131561 33 1.000000 0.000000 17 0.493164 0.129045

TABLE 3 geometric coordinate data of NPU-ASEA-260 Airfoil lower surface

Wherein: x_upthe/C represents the upper surface abscissa of the airfoil; y is_upthe/C represents the upper surface ordinate of the airfoil; x_lowthe/C represents the lower surface abscissa of the airfoil; y is_lowand/C represents the lower surface ordinate of the airfoil.

4. A design method of asymmetric double blunt point airfoil for rotor root of high-speed helicopter according to any of claims 1-3, characterized in that the design method is a multi-objective multi-constraint global optimization design method cooperating with forward flow and reverse flow conditions, and simultaneously taking airfoil CST parameter, airfoil upper surface leading edge radius control parameter, airfoil upper surface trailing edge radius control parameter, airfoil lower surface leading edge radius control parameter and airfoil lower surface trailing edge radius control parameter as design variables, and using a proxy optimization algorithm to optimize the airfoil by weight cooperating with asymmetric forward flow and reverse flow conditions, comprising the following steps:

step 1, parameterizing the upper surface and the lower surface of the wing profile respectively by adopting a CST parameterization method, wherein the parameterization expression is as follows:

y_{on the upper part}＝C_{On the upper part}(x)·S_{On the upper part}(x)

y_{Lower part}＝C_{Lower part}(x)·S_{Lower part}(x)

Wherein:

y_{on the upper part}Is the airfoil vertical coordinate of the upper surface of the airfoil;

y_{lower part}Is the airfoil longitudinal coordinate of the airfoil lower surface;

x is the airfoil abscissa;

C_{on the upper part}(x) Being a function of the class of the upper surface of the airfoil, C_{Lower part}(x) A class function of the lower surface of the airfoil; the definition is as follows:

wherein:

controlling parameters for the radius of the front edge of the upper surface of the airfoil;

controlling parameters for the trailing edge radius of the upper surface of the airfoil;

controlling parameters for the radius of the leading edge of the lower surface of the airfoil;

controlling parameters for the radius of the trailing edge of the lower surface of the airfoil;

S_{on the upper part}(x) Is a profile function of the upper surface of the airfoil, S_{Lower part}(x) The profile function for the lower surface of the airfoil is defined as follows:

wherein:

S_i(x) Is a Bernstein polynomial, i is the serial number of the Bernstein polynomial, and is also a variable in the Bernstein polynomial;

n is the order of the type function;

the undetermined coefficients of the upper surface of the airfoil are 9 undetermined coefficients of the upper surface of the airfoil in total, which are respectively as follows:

for undetermined coefficient of airfoil lower surface, totally 9 airfoil lower surfaces undetermined coefficients are:

step 2, determining a design variable X as:

step 3, designing a target function:

the forward flow design state is Mach number 0.53 and Reynolds number 3.7 × 10⁶Taking the lift coefficient of-0.5, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

the reflux design state is Mach number of 0.21 and Reynolds number of 1.47 × 10⁶Taking the lift coefficient of-0.6, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

under a certain weight, taking the minimum value of the sum of the resistance coefficient under the forward flow design state and the resistance coefficient under the reverse flow design state as an objective function, wherein the expression of the (x) of the objective function f is as follows:

wherein:

W_Sthe weight coefficient of a fixed lift design point when representing a downstream design state is 0.5;

W_Fthe weight coefficient of a fixed lift design point in the reflux design state is represented, and is taken as 0.5;

respectively representing four fixed lift design points in a reverse flow design stateA target drag coefficient of (d);

step 4, designing constraint conditions:

constraint 1: the absolute values of the moment coefficients of the 4 fixed lift design points in the downstream design state are not more than 1.1 times of the absolute values of the moment coefficients of the corresponding fixed lift design points of the reference airfoil profile;

constraint 2: the moment coefficient absolute values of the 4 fixed lift design points in the reverse flow design state are not more than 1.1 times of the moment coefficient absolute values of the corresponding fixed lift design points of the reference airfoil profile;

constraint 3: the maximum thickness of the airfoil is not less than 26% C;

constraint 4: the maximum thickness position is between 40% ± 3% C;

and 5, performing wing profile optimization design by adopting a proxy optimization algorithm, and outputting a design variable value which meets constraint conditions and minimizes the objective function, namely: output of

To ultimately determine the designed airfoil profile.

5. The method of claim 4, wherein the proxy optimization algorithm is configured to:

the proxy model comprises the following steps: a Kriging model;

and (3) point adding criterion: EI, MSP, LCB, PI and MSE are used in parallel;

number of initial sample points: 20, the number of the cells is 20;

total number of sample points: 500 pieces.

Technical Field

The invention belongs to the technical field of wing profile design, and particularly relates to a front-back asymmetric double-blunt-nose wing profile for a rotor root back-flow area of a high-speed helicopter and a corresponding design method thereof.

Background

When the helicopter flies forward at a certain forward ratio mu, the forward blade area and the backward blade area of the rotor are asymmetrical relative to the air flow speed due to the superposition effect of the incoming flow. Assuming that the radius of the rotor disk is R, a phenomenon that relative airflow blows from the trailing edge to the leading edge occurs in a region where the radial position of the root of the trailing blade is smaller than μ R | sin ψ |, and the region where such a phenomenon exists is called a "reverse flow region". In the counter-flow region, the aerodynamic efficiency of the blade is low, serious flow separation and stall phenomena exist, and the attack angle, the lift force, the resistance and the pitching moment characteristics of each section of the blade are obviously different from those outside the counter-flow region. The blade root section airfoil profile is required to be capable of reducing resistance and improving lift-drag ratio within a larger lift coefficient range in a forward flow state and a reverse flow state.

Coaxial rigid rotors are key components of the "abc (active blade concept)" rotor system, and their performance directly affects the high-speed helicopter flight performance. The performance of the wing profile, which is the basic component of a coaxial rigid rotor, significantly affects the aerodynamic properties of the coaxial rigid rotor. Take two versions of coaxial rigid rotorcraft verification engines XH-59A and X2, West Kesky, USA, as examples: XH-59A suffers severe type drag losses at the trailing edge of its rotor at high speeds. This is because at high speeds, the trailing blade has up to 85% of the reverse flow area and the blade root is more in deep reverse flow. Such airflow is prone to separation, resulting in a sharp increase in the drag of the trailing blades and a substantial reduction in cruise efficiency. By analyzing the flow field characteristics of the coaxial rigid rotors, the western costa corporation has developed intensive research into the design of new blades and has adopted several advanced wing profiles designed on the blades of the next generation of prover X2. Most particularly, a special double-blunt-nose wing type which is symmetrical front and back is adopted at the root of the blade, tests prove that the wing type can effectively relieve the flow separation phenomenon of the backward blade in a reverse flow area, and the efficiency of the improved XH-59A rotor wing adopting the wing type is improved compared with that of a reference rotor wing at each flight speed.

In the field of aviation, research is less dedicated to coaxial rigid high-speed rotor root airfoils, and the airfoils disclosed so far include three types: firstly, the method comprises the following steps: a standard elliptical airfoil profile; secondly, the method comprises the following steps: DBLN526 airfoil used by western corsky corporation on X2 high-speed coaxial rigid rotor technology validators; thirdly, the method comprises the following steps: the NPU-EA-260 airfoil filed by northwest university of industry, the patent number of which is: ZL 201811236180.8. The three solutions consider that the flow separation phenomenon of the backward blades can be effectively inhibited by using the blunt trailing edge airfoil profile, the pneumatic efficiency of the blades in the reverse flow area is improved, and the dynamic stall phenomenon is avoided.

In the three schemes, the standard elliptical wing type is not specially designed, and the requirements of a high-speed helicopter cannot be met. The DBLN526 airfoil and the NPU-EA-260 airfoil are designed to be large-thickness and blunt-trailing-edge front-back symmetrical airfoils with the relative thickness of 26%, and the corresponding design method only considers the shape design of the front half part of the airfoil in the downstream direction. Therefore, the occurrence of the flow separation phenomenon cannot be effectively inhibited in the reverse flow state, and the defects of high aerodynamic resistance and low lift resistance are overcome, so that the cruise efficiency of the helicopter is limited.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides an asymmetric double-blunt-nose airfoil profile for a rotor root of a high-speed helicopter and a design method, which can effectively solve the problems.

The technical scheme adopted by the invention is as follows:

the invention provides an asymmetric double-blunt-nose wing profile for a rotor root of a high-speed helicopter, wherein the radius of the front edge of the upper surface of the wing profile is 0.044C, and the radius of the rear edge of the upper surface of the wing profile is 0.015C; the radius of the front edge of the lower surface of the airfoil is 0.034C, and the radius of the rear edge of the lower surface of the airfoil is 0.032C;

the maximum thickness of the asymmetric double-blunt-end airfoil for the rotor root of the high-speed helicopter is 26% C, and the maximum thickness position is 42% C; camber of 0.84% C; wherein C is the airfoil chord length.

Therefore, the asymmetric double-blunt-nose wing profile for the rotor root of the high-speed helicopter is a front-back asymmetric double-blunt-nose wing profile applied to a back flow area of the rotor root of the high-speed helicopter, the radius of the front edge of the upper surface of the wing profile is larger than the radius of the rear edge of the upper surface of the wing profile, the radius of the front edge of the lower surface of the wing profile is larger than the radius of the rear edge of the lower surface of the wing profile, the maximum thickness position is close to the front edge, and the wing profile and the blade outer-section blunt-; the wing profile has small camber, which is beneficial to simultaneously reducing the resistance in the downstream and reverse flow states; the radius of the front edge of the upper surface of the wing profile, the radius of the rear edge of the upper surface of the wing profile, the radius of the front edge of the lower surface of the wing profile and the radius of the rear edge of the lower surface of the wing profile are all larger than those of the same wing profile, so that the negative pressure peak value under the condition of forward flow and backflow is improved, the lift performance is improved, and the lift-drag ratio is improved.

Preferably, the asymmetric double blunt airfoil for the rotor root of the high-speed helicopter has the following aerodynamic characteristics:

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the lift coefficient is determined to be 0.5, the drag coefficient is 0.022, and the lift-drag ratio is 22.7;

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the fixed lift coefficient is 0.85, the drag coefficient is 0.028, and the lift-drag ratio is 30.4;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.45, the drag coefficient is 0.027, and the lift-drag ratio is 16.7;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.85, the drag coefficient is 0.035, and the lift-drag ratio is 24.2.

Preferably, the geometric coordinate data of the upper surface of the airfoil of the asymmetric double-blunt-end airfoil for the rotor root of the high-speed helicopter are shown in a table 2; the geometrical coordinate data of the lower surface of the airfoil are shown in Table 3:

TABLE 2 NPU-ASEA-260 Airfoil Upper surface geometric coordinate data

TABLE 3 geometric coordinate data of NPU-ASEA-260 Airfoil lower surface

Serial number	Xup/C	Yup/C	Serial number	Xup/C	Yup/C
						1	0.000000	0.000000	18	0.555495	-0.115196
2	0.001382	-0.013867	19	0.613864	-0.112224
						3	0.006400	-0.024832	20	0.669741	-0.108360
4	0.014017	-0.035012	21	0.722086	-0.103727
						5	0.024517	-0.045117	22	0.770125	-0.098421
6	0.038327	-0.055264	23	0.813376	-0.092483
						7	0.056132	-0.065493	24	0.851596	-0.085933
8	0.078617	-0.075641	25	0.884760	-0.078809
						9	0.106162	-0.085347	26	0.912985	-0.071159
10	0.139100	-0.094255	27	0.936516	-0.063032
						11	0.177485	-0.101985	28	0.955745	-0.054445
12	0.221108	-0.108195	29	0.970996	-0.045442
						13	0.269503	-0.112779	30	0.982590	-0.036098
14	0.322045	-0.115873	31	0.991065	-0.026249
						15	0.377952	-0.117580	32	0.996938	-0.015115
16	0.436263	-0.117979	33	1.000000	0.000000
						17	0.495862	-0.117153

Wherein: x_upthe/C represents the upper surface abscissa of the airfoil; y is_upthe/C represents the upper surface ordinate of the airfoil;X_lowthe/C represents the lower surface abscissa of the airfoil; y is_lowand/C represents the lower surface ordinate of the airfoil.

The invention also provides a design method of the asymmetric double blunt point wing profile for the rotor root of the high-speed helicopter, which is a multi-objective multi-constraint global optimization design method for cooperation of forward flow and reverse flow states, and simultaneously takes the wing profile CST parameter, the wing profile upper surface front edge radius control parameter, the wing profile upper surface rear edge radius control parameter, the wing profile lower surface front edge radius control parameter and the wing profile lower surface rear edge radius control parameter as design variables, adopts a proxy optimization algorithm, and carries out wing profile optimization by considering the asymmetric forward flow and reverse flow states in weight cooperation, and specifically comprises the following steps:

step 1, parameterizing the upper surface and the lower surface of the wing profile respectively by adopting a CST parameterization method, wherein the parameterization expression is as follows:

y_{on the upper part}＝C_{On the upper part}(x)·S_{On the upper part}(x)

y_{Lower part}＝C_{Lower part}(x)·S_{Lower part}(x)

Wherein:

y_{on the upper part}Is the airfoil vertical coordinate of the upper surface of the airfoil;

y_{lower part}Is the airfoil longitudinal coordinate of the airfoil lower surface;

x is the airfoil abscissa;

C_{on the upper part}(x) Being a function of the class of the upper surface of the airfoil, C_{Lower part}(x) A class function of the lower surface of the airfoil; the definition is as follows:

wherein:

is in front of the upper surface of the wingAn edge blending radius control parameter;

controlling parameters for the trailing edge radius of the upper surface of the airfoil;

controlling parameters for the radius of the leading edge of the lower surface of the airfoil;

controlling parameters for the radius of the trailing edge of the lower surface of the airfoil;

S_{on the upper part}(x) Is a profile function of the upper surface of the airfoil, S_{Lower part}(x) The profile function for the lower surface of the airfoil is defined as follows:

wherein:

S_i(x) Is a Bernstein polynomial, i is the serial number of the Bernstein polynomial, and is also a variable in the Bernstein polynomial;

n is the order of the type function;

the undetermined coefficients of the upper surface of the airfoil are 9 undetermined coefficients of the upper surface of the airfoil in total, which are respectively as follows:

is the lower surface of the wing profileConstant coefficients, there are 9 wing section lower surfaces in total to be undetermined coefficients, and the coefficients are respectively:

step 2, determining a design variable X as:

step 3, designing a target function:

the forward flow design state is Mach number 0.53 and Reynolds number 3.7 × 10⁶Taking the lift coefficient of-0.5, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

the reflux design state is Mach number of 0.21 and Reynolds number of 1.47 × 10⁶Taking the lift coefficient of-0.6, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

under a certain weight, taking the minimum value of the sum of the resistance coefficient under the forward flow design state and the resistance coefficient under the reverse flow design state as an objective function, wherein the expression of the (x) of the objective function f is as follows:

wherein:

W_Sthe weight coefficient of a fixed lift design point when representing a downstream design state is 0.5;

W_Fthe weight coefficient of a fixed lift design point in the reflux design state is represented, and is taken as 0.5;

respectively showing downstream designFour design points of constant lift force in state

A target drag coefficient of (d);

respectively representing four fixed lift design points in a reverse flow design state

A target drag coefficient of (d);

step 4, designing constraint conditions:

constraint 1: the absolute values of the moment coefficients of the 4 fixed lift design points in the downstream design state are not more than 1.1 times of the absolute values of the moment coefficients of the corresponding fixed lift design points of the reference airfoil profile;

constraint 2: the moment coefficient absolute values of the 4 fixed lift design points in the reverse flow design state are not more than 1.1 times of the moment coefficient absolute values of the corresponding fixed lift design points of the reference airfoil profile;

constraint 3: the maximum thickness of the airfoil is not less than 26% C;

constraint 4: the maximum thickness position is between 40% ± 3% C;

and 5, performing wing profile optimization design by adopting a proxy optimization algorithm, and outputting a design variable value which meets constraint conditions and minimizes the objective function, namely: output of

To ultimately determine the designed airfoil profile.

Preferably, the proxy optimization algorithm is set as follows:

the proxy model comprises the following steps: a Kriging model;

and (3) point adding criterion: EI, MSP, LCB, PI and MSE are used in parallel;

number of initial sample points: 20, the number of the cells is 20;

total number of sample points: 500 pieces.

The asymmetric double-blunt-nose airfoil profile for the rotor root of the high-speed helicopter and the design method have the following advantages:

(1) according to the actual flow characteristics of the counter-flow area, the asymmetric double-blunt-nose wing type for the rotor root of the high-speed helicopter is designed, has good geometric compatibility with the conventional wing type with the blunt-nose tail tip at the outer section of the blade, has lower aerodynamic resistance and higher lift-drag ratio in both a forward flow state and a counter-flow state, can effectively inhibit the occurrence of flow separation, and has good torque characteristics, so that the cruising efficiency of the helicopter is improved, and the use requirements of a new generation of high-speed helicopters are met.

(2) The wing profile design method adopts a parameterization method considering the change of the radius of the front edge and the rear edge of the upper surface and the lower surface of the wing profile, so that the design space of the wing profile can be effectively expanded, and the better appearance can be searched; by adopting a Kriging model-based agent optimization algorithm, the airfoil optimization problem under asymmetric downstream and reverse flow states is cooperatively considered, the method has better global property, is suitable for the aerodynamic optimization design problem of complex target constraint under complex design spaces such as asymmetric double blunt-tip airfoil design and the like, and provides powerful technical support for the aerodynamic design of a new generation of high-speed helicopters.

Drawings

FIG. 1 is a schematic view of the flow-around state and the flow-in direction of an asymmetric double-blunt-tip airfoil of the present invention;

FIG. 2 is a flow chart of a method for designing an asymmetric double blunt tip airfoil provided by the present invention;

FIG. 3 is a comparison of the geometry of the airfoil of the present invention, the NPU-EA-260 airfoil, and the DBLN526 airfoil;

FIG. 4 is a downstream Mach number of 0.53 for an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at a Reynolds number of 3.7 × 10⁶Calculating a lift force-resistance characteristic curve comparison diagram in a state;

FIG. 5 is a downstream Mach number of 0.53 for an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at a Reynolds number of 3.7 × 10⁶Calculating a comparison graph of lift force-lift drag ratio characteristic curves in a state;

FIG. 6 is a downstream Mach number of 0.53 for an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at a Reynolds number of 3.7 × 10⁶Calculating a lift force-moment characteristic curve comparison diagram in a state;

FIG. 7 is a graph of an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at reverse flow, Mach number 0.21, Reynolds number 1.47 × 10⁶Calculating a lift force-resistance characteristic curve comparison diagram in a state;

FIG. 8 is a graph of an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at reverse flow, Mach number 0.21, Reynolds number 1.47 × 10⁶Calculating a comparison graph of lift force-lift drag ratio characteristic curves in a state;

FIG. 9 is a graph of an airfoil of the present invention, a comparative NPU-EA-260 airfoil, and a DBLN526 airfoil at reverse flow, Mach number 0.21, Reynolds number 1.47 × 10⁶Calculating a lift force-moment characteristic curve comparison diagram in a state;

wherein:

1 represents the geometric or aerodynamic characteristic of the NPU-ASEA-260 airfoil of the present invention;

2 represents the geometric or aerodynamic characteristic of the NPU-EA-260 airfoil for comparison;

3 represents the geometrical profile or aerodynamic characteristic of the DBLN526 airfoil for comparison.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As helicopter speed increases, the reverse flow area of the rotor gradually increases. In this region, a phenomenon occurs in which relative airflow blows from the trailing edge to the leading edge of the rotor blade. For rotors using conventional airfoils, the flow separation phenomenon is severe, the aerodynamic efficiency of the rotor is reduced, and stall is likely to occur due to the presence of the backward flow zone of the retreating blade. The conventional standard elliptical airfoil profile, DBLN526 airfoil profile and NPU-EA-260 airfoil profile can solve the problem that the aerodynamic performance of the conventional airfoil profile in a reverse flow area is deteriorated, but the three airfoil profiles are symmetrical in front and rear edges, the asymmetry of the profile in an asymmetrical forward/reverse flow state cannot be considered, and the corresponding design method only considers the profile design of the front half part of the airfoil profile in the forward flow direction. In actual coaxial rotor flow, the forward flow Mach number of the blade root airfoil profile is far larger than the reverse flow Mach number, so that the front-back asymmetric double-blunt-end airfoil profile designed according to different characteristics of forward flow and reverse flow is more favorable for improving the aerodynamic performance of the coaxial rotor blade.

The composite high-speed helicopter adopting the coaxial rigid rotor technology is one of the important directions for the development of the future helicopters. Aiming at the flowing characteristics of the root part of the backward blade of the practical coaxial rigid rotor, the wing section optimization problem under the asymmetric downstream and reverse flow states is cooperatively considered through weight optimization, and through large-range multi-point multi-constraint drag reduction optimization design, the front and back asymmetric double blunt-nose wing section which gives consideration to the downstream and reverse flow aerodynamic efficiency and has better geometric compatibility with the blade outer section wing section is obtained.

The invention relates to an asymmetric double-blunt-nose wing profile for a high-speed helicopter rotor blade root, which is a blade root wing profile for a high-speed coaxial rigid ABC rotor blade. The invention aims to design a new airfoil profile with smaller resistance of a forward/reverse flow region, higher lift-drag ratio and good torque characteristic according to the actual flow characteristic of the reverse flow region, thereby improving the cruising efficiency of a helicopter and simultaneously providing a new design method for the design of a new generation of high-speed helicopter rotor blade root airfoil profile.

Specifically, the invention designs a front-back asymmetric double-blunt-nose airfoil suitable for a rotor root aiming at a coaxial rigid rotor blade. Referring to fig. 3, which is shown by a solid line, it is an airfoil geometric feature diagram of the present invention, and its salient features include the following three points:

(1) the radius of the front edge of the upper surface of the airfoil is obviously greater than the radius of the rear edge of the upper surface of the airfoil, the radius of the front edge of the lower surface of the airfoil is obviously greater than the radius of the rear edge of the lower surface of the airfoil, the maximum thickness position of the front edge of the lower surface of the airfoil is close to the front edge, the good transition of the profile shape and the conventional profile with the blunt tail tip of the outer section head of the blade is ensured, the geometrical compatibility is good, the maximum thickness of the profile is 26.

(2) The wing section camber is less, is favorable to reducing simultaneously the resistance under the forward flow and the backward flow state, and wing section camber is 0.84% C.

(3) The radius of the front edge of the upper surface of the wing profile, the radius of the rear edge of the upper surface of the wing profile, the radius of the front edge of the lower surface of the wing profile and the radius of the rear edge of the lower surface of the wing profile are all larger than those of the same wing profile, so that the negative pressure peak value in a downstream and reverse flow state can be improved, the lift loss caused by smaller camber can be compensated, and the lift-drag ratio can be improved; specifically, the radius of the front edge of the upper surface of the airfoil is 0.044C, and the radius of the rear edge of the upper surface of the airfoil is 0.015C; the radius of the front edge of the lower surface of the airfoil is 0.034C, and the radius of the rear edge of the lower surface of the airfoil is 0.032C.

The asymmetric double-blunt-end airfoil profile for the rotor root of the high-speed helicopter is named as NPU-ASEA-260, and specific geometric characteristic parameters are shown in a table 1. C is the airfoil chord length.

TABLE 1 geometrical characteristics of NPU-ASEA-260 Airfoil

The invention provides an asymmetric double-blunt-nose airfoil profile for a rotor root of a high-speed helicopter, which has the following aerodynamic characteristics:

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the lift coefficient is determined to be 0.5, the drag coefficient is 0.022, and the lift-drag ratio is 22.7;

at forward flow Mach number 0.53, Reynolds number 3.7 × 10⁶When the fixed lift coefficient is 0.85, the drag coefficient is 0.028, and the lift-drag ratio is 30.4;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.45, the drag coefficient is 0.027, and the lift-drag ratio is 16.7;

at reflux Mach number 0.21, Reynolds number 1.47 × 10⁶When the lift coefficient is fixed to be 0.85, the drag coefficient is 0.035, and the lift-drag ratio is 24.2.

The geometric coordinate data of the upper surface of the airfoil profile of the asymmetric double-blunt-nose airfoil profile for the rotor root of the high-speed helicopter provided by the invention is shown in a table 2; the geometrical coordinate data of the lower surface of the airfoil are shown in Table 3:

TABLE 2 NPU-ASEA-260 Airfoil Upper surface geometric coordinate data

TABLE 3 geometric coordinate data of NPU-ASEA-260 Airfoil lower surface

Serial number	Xup/C	Yup/C	Serial number	Xup/C	Yup/C
						1	0.000000	0.000000	18	0.555495	-0.115196
2	0.001382	-0.013867	19	0.613864	-0.112224
						3	0.006400	-0.024832	20	0.669741	-0.108360
4	0.014017	-0.035012	21	0.722086	-0.103727
						5	0.024517	-0.045117	22	0.770125	-0.098421
6	0.038327	-0.055264	23	0.813376	-0.092483
						7	0.056132	-0.065493	24	0.851596	-0.085933
8	0.078617	-0.075641	25	0.884760	-0.078809
						9	0.106162	-0.085347	26	0.912985	-0.071159
10	0.139100	-0.094255	27	0.936516	-0.063032
						11	0.177485	-0.101985	28	0.955745	-0.054445
12	0.221108	-0.108195	29	0.970996	-0.045442
						13	0.269503	-0.112779	30	0.982590	-0.036098
14	0.322045	-0.115873	31	0.991065	-0.026249
						15	0.377952	-0.117580	32	0.996938	-0.015115
16	0.436263	-0.117979	33	1.000000	0.000000
						17	0.495862	-0.117153

Wherein, X_upthe/C represents the upper surface abscissa of the airfoil; y is_upthe/C represents the upper surface ordinate of the airfoil; x_lowthe/C represents the lower surface abscissa of the airfoil; y is_lowand/C represents the lower surface ordinate of the airfoil.

The asymmetric double blunt point airfoil NPU-ASEA-260 for the rotor root of the high-speed helicopter requires that the airfoil profile of the blade root can simultaneously reduce resistance and improve lift-drag ratio in a larger lift coefficient (or pitch angle) range in a forward flow state and a reverse flow state, the design space is very complex, an effective global design method is required, and a better design effect is difficult to achieve by adopting a traditional design method.

The invention adopts a multi-objective multi-constraint global optimization design method of forward/reverse flow state cooperation to design NPU-ASEA-260 wing profile, the method adopts a parameterization method considering the change of the radius of the front and rear edges of the upper and lower surfaces and a proxy optimization algorithm based on a Kriging model, and cooperatively considers the wing profile optimization problem under the asymmetric forward flow and reverse flow states, and the flow of the design method is shown in figure 2.

The specific design method comprises the following steps:

step 1, parameterizing the upper surface and the lower surface of the wing profile respectively by adopting a CST parameterization method, wherein the parameterization expression is as follows:

y_{on the upper part}＝C_{On the upper part}(x)·S_{On the upper part}(x)

y_{Lower part}＝C_{Lower part}(x)·S_{Lower part}(x)

Wherein:

y_{on the upper part}Is the airfoil vertical coordinate of the upper surface of the airfoil;

y_{lower part}Is the airfoil longitudinal coordinate of the airfoil lower surface;

x is the airfoil abscissa;

C_{on the upper part}(x) Being a function of the class of the upper surface of the airfoil, C_{Lower part}(x) As a function of the airfoil lower surface(ii) a The definition is as follows:

wherein:

controlling parameters for the radius of the front edge of the upper surface of the airfoil;

controlling parameters for the trailing edge radius of the upper surface of the airfoil;

controlling parameters for the radius of the leading edge of the lower surface of the airfoil;

controlling parameters for the radius of the trailing edge of the lower surface of the airfoil;

S_{on the upper part}(x) Is a profile function of the upper surface of the airfoil, S_{Lower part}(x) The profile function for the lower surface of the airfoil is defined as follows:

wherein:

S_i(x) Is a Bernstein polynomial, i is the serial number of the Bernstein polynomial, and is also a variable in the Bernstein polynomial;

n is the order of the type function;

the undetermined coefficients of the upper surface of the airfoil are 9 undetermined coefficients of the upper surface of the airfoil in total, which are respectively as follows:

for undetermined coefficient of airfoil lower surface, totally 9 airfoil lower surfaces undetermined coefficients are:

step 2, determining a design variable X as:

step 3, designing a target function:

streamwise design conditions (flow from leading edge to trailing edge) were Mach 0.53, Reynolds number 3.7 × 10⁶Taking the lift coefficient of-0.5, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

the reverse flow design conditions (flow from trailing edge to leading edge) were Mach number 0.21, Reynolds number 1.47 × 10⁶Taking the lift coefficient of-0.6, -0.1, 0.3 and 0.85 as 4 fixed lift design points respectively, and expressing the values as follows:

under a certain weight, taking the minimum value of the sum of the resistance coefficient under the forward flow design state and the resistance coefficient under the reverse flow design state as an objective function, wherein the expression of the (x) of the objective function f is as follows:

wherein:

W_Sthe weight coefficient of a fixed lift design point when representing a downstream design state is 0.5;

W_Fthe weight coefficient of a fixed lift design point in the reflux design state is represented, and is taken as 0.5;

respectively represents four fixed lift design points under the condition of downstream design

A target drag coefficient of (d);

respectively representing four fixed lift design points in a reverse flow design stateA target drag coefficient of (d);

step 4, designing constraint conditions:

constraint 1: the absolute values of the moment coefficients of the 4 fixed lift design points in the downstream design state are not more than 1.1 times of the absolute values of the moment coefficients of the corresponding fixed lift design points of the reference airfoil profile;

constraint 2: the moment coefficient absolute values of the 4 fixed lift design points in the reverse flow design state are not more than 1.1 times of the moment coefficient absolute values of the corresponding fixed lift design points of the reference airfoil profile;

constraint 3: the maximum thickness of the airfoil is not less than 26% C;

constraint 4: the maximum thickness position is between 40% ± 3% C;

and 5, performing wing profile optimization design by adopting a proxy optimization algorithm, and outputting a design variable value which meets constraint conditions and minimizes the objective function, namely: output of

To ultimately determine the designed airfoil profile.

Wherein: the proxy optimization algorithm is set as follows:

the proxy model comprises the following steps: a Kriging model;

and (3) point adding criterion: EI, MSP, LCB, PI and MSE are used in parallel;

number of initial sample points: 20, the number of the cells is 20;

total number of sample points: 500 pieces.

The invention provides a forward/reverse flow state cooperative multi-objective multi-constraint global optimization design method for front and back asymmetric double blunt tip airfoil design.

Has the advantages that: the parameterization method can effectively control the change of the radius of the front edge and the rear edge while fitting the airfoil profile line with high precision; the optimization algorithm has better global property and is suitable for the pneumatic optimization design problems with complex design space and complex target constraint, such as front-back asymmetric double blunt tip airfoil design.

The novel wing profile and the corresponding novel design method provided by the invention can effectively improve the aerodynamic performance of the coaxial dual-rotor helicopter blades, thereby improving the cruise efficiency of the helicopter and providing powerful technical support for the aerodynamic design of a new generation of high-speed helicopters.

FIG. 3 is a geometric profile of an airfoil designed according to the present invention. As can be seen from the figure 3, the invention adopts the design idea of the front-back asymmetric double blunt-tip airfoil profile, and ensures that the airfoil profile can show better aerodynamic characteristics when facing forward flow and reverse flow under different Mach numbers; the wing profile has small camber, which is beneficial to simultaneously reducing the resistance in the downstream and reverse flow states; the radius radiuses of the front and rear edges of the upper and lower surfaces of the wing profile are large, so that the negative pressure peak values in a downstream state and a reverse flow state are improved, the lift loss caused by small camber is compensated, and the lift-drag ratio is improved; the radius of the front edge of the airfoil is obviously larger than that of the rear edge, the maximum thickness position is close to the front edge, the good transition of the profile of the airfoil and the conventional airfoil with blunt tip at the outer section of the blade is ensured, and the good geometric compatibility is realized.

Therefore, the NPU-ASEA-260 airfoil profile meets design requirements of low resistance, high lift-drag ratio and good moment characteristics.

By taking a DBLN526 airfoil profile and an NPU-EA-260 airfoil profile as references, in a design state, the NPU-ASEA-260 airfoil profile has excellent aerodynamic performance, obvious drag reduction, larger lift-drag ratio and good moment characteristic. The main aerodynamic characteristics at some of the design points are shown in tables 4 and 5, in comparison to airfoils DBLN526 and NPU-EA-260.

TABLE 4 resistance and lift-drag characteristics of NPU-ASEA-260 airfoils and comparative airfoils DBLN526, NPU-EA-260 at partial design points (Ma 0.53, Re 3.7 × 10⁶)

TABLE 5 drag and lift-drag characteristics of NPU-ASEA-260 airfoils and comparative airfoils DBLN526, NPU-EA-260 at some design points (Ma 0.21, Re 1.47 × 10⁶)

Comparative example:

the inventors evaluated the aerodynamic performance of the NPU-ASEA-260 airfoil of the present invention using a Computational Fluid Dynamics (CFD) numerical simulation method and compared it to a DBLN526 airfoil and an NPU-EA-260 airfoil.

The evaluation calculation state is:

1) forward flow (flow from leading edge to trailing edge), Ma is 0.53 and reynolds number is 3.7 × 10⁶

2) In the reverse flow state (flow from trailing edge to leading edge), Ma is 0.21 and reynolds number is 1.47 × 10⁶

And (3) carrying out turbulence simulation by adopting a k-omega SST model.

3-9, the solid lines represent aerodynamic data for an NPU-ASEA-260 airfoil of the present invention, the dashed lines represent aerodynamic data for a comparative DBLN526 airfoil, and the dotted lines represent aerodynamic data for a comparative NPU-EA-260 airfoil.

Specifically, FIG. 4 shows a comparison of the drag-lift characteristics of an NPU-ASEA-260 airfoil of the present invention versus a DBLN526 airfoil for comparison at forward flow conditions. The NPU-ASEA-260 airfoil profile is in a lift coefficient range of-0.5-1.0, the drag coefficients are obviously smaller than those of the NPU-EA-260 airfoil profile and the DBLN526 airfoil profile, and the NPU-ASEA-260 airfoil profile has obvious low-resistance characteristics.

FIG. 5 shows a comparison of lift-to-drag ratio profiles for an NPU-ASEA-260 airfoil of the present invention and a comparative NPU-EA-260 airfoil and a DBLN526 airfoil at forward flow conditions. The NPU-ASEA-260 airfoil profile has the optimal wide working condition characteristic within the lift coefficient range of-0.5-1.0, the lift-drag ratio is remarkably larger than that of the NPU-EA-260 airfoil profile and that of the DBLN526 airfoil profile within a larger lift coefficient range, and the NPU-ASEA-260 airfoil profile has obvious high lift-drag ratio characteristics.

FIG. 6 shows a comparison of lift-moment characteristics for an NPU-ASEA-260 airfoil of the present invention and a comparative NPU-EA-260 airfoil and DBLN526 airfoil at forward flow conditions. The NPU-ASEA-260 airfoil profile is in a lift coefficient range of-0.5-1.0, and the moment coefficient is equivalent to that of the NPU-EA-260 airfoil profile and is slightly superior to that of a DBLN526 airfoil profile.

FIG. 7 shows a comparison of the drag-lift characteristics of an NPU-ASEA-260 airfoil of the present invention and a comparative NPU-EA-260 airfoil and DBLN526 airfoil in a counter-current condition. The NPU-ASEA-260 airfoil profile is in a lift coefficient range of-1.0-1.2, and drag coefficients are all obviously smaller than those of a DBLN526 airfoil profile; in the lift coefficient range of-0.7-0.5, the NPU-ASEA-260 airfoil drag coefficient is greater than that of the NPU-EA-260 airfoil; in the range of lift coefficient more than 0.5, the NPU-ASEA-260 airfoil drag coefficient is obviously smaller than that of the NPU-EA-260 airfoil.

FIG. 8 shows a comparison of lift-to-drag ratio characteristics of an NPU-ASEA-260 airfoil of the present invention and a comparative NPU-EA-260 airfoil and a DBLN526 airfoil in a reverse flow condition. The lift coefficient of the NPU-EA-AS-260 airfoil is in the range of-1.0-1.2, and the lift-drag ratio is remarkably larger than that of the NPU-EA-260 airfoil and that of the DBLN526 airfoil; in the range of lift coefficient larger than 0.5, the lift-drag ratio of the NPU-ASEA-260 airfoil is obviously larger than that of the NPU-EA-260 airfoil. The stall characteristics under positive lift conditions are significantly better than the NPU-EA-260 airfoil and the DBLN526 airfoil.

FIG. 9 shows a comparison of lift-moment characteristics of an NPU-ASEA-260 airfoil of the present invention and a comparative NPU-EA-260 airfoil and DBLN526 airfoil in a reverse flow condition. The NPU-ASEA-260 airfoil profile is in a lift coefficient range of-1.0-1.2, and the moment coefficient is equivalent to that of the NPU-EA-260 airfoil profile and is slightly superior to that of a DBLN526 airfoil profile.

The comprehensive design and calculation results show that:

1) the NPU-ASEA-260 wing type has obvious drag reduction effect under the conditions of forward flow high-speed flow and reverse flow low-speed flow;

2) compared with an NPU-EA-260 airfoil and a DBLN526 airfoil, the NPU-ASEA-260 airfoil has the advantages that the lift coefficient of a linear section is remarkably increased in a forward flow state, the stall characteristic is improved in a reverse flow state, and the overall lift-drag ratio is higher;

3) the moment characteristic of the NPU-ASEA-260 airfoil is equivalent to that of the NPU-EA-260 airfoil and slightly superior to that of a DBLN526 airfoil;

4) compared with an NPU-EA-260 wing profile and a DBLN526 wing profile, the NPU-ASEA-260 wing profile has smaller camber and is beneficial to drag reduction; the radius of the front edge and the rear edge are larger, so that the negative pressure peak value in a forward/reverse flow state is improved, and the lift force is improved; the radius of the front edge is larger than that of the rear edge, the maximum thickness position is more forward, and the vane airfoil has better geometrical compatibility with the conventional airfoil with the blunt tail tip of the outer section head of the vane.

5) The design result also verifies the effectiveness of the multi-objective multi-constraint global optimization design method for forward and backward asymmetric double blunt tip airfoil design forward/backward flow state cooperation.

In conclusion, the invention carries out targeted airfoil drag reduction optimization design of the rotor flow reversal area according to the flow field characteristics of the rotor flow reversal area. Has the following characteristics:

first, the NPU-ASEA-260 airfoil of the present invention has geometrically distinct features compared to the NPU-EA-260 airfoil and the DBLN526 airfoil, namely: the front and rear edges are asymmetric, the radius of the front and rear edges is larger, the camber is smaller, and the difference with the prior similar airfoil profile is obvious.

Secondly, on the aspect of aerodynamic performance, the NPU-ASEA-260 airfoil profile has overall improvement compared with the existing similar front-back symmetrical airfoil profile, has lower resistance and better lift-drag ratio characteristic and good moment characteristic, and ensures that the aerodynamic performance of the airfoil profile is comprehensively superior to the NPU-EA-260 airfoil profile and the DBLN526 airfoil profile in a design state.

Finally, the NPU-ASEA-260 airfoil of the invention has better combination compatibility and excellent aerodynamic characteristics, so that the airfoil is very suitable for a high-speed rotor blade reverse flow area. The wing profile can effectively improve the cruising efficiency of the helicopter, and the corresponding design method can provide technical support for the design of the root wing profile of the rotor wing of the new-generation high-speed helicopter.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements should also be considered within the scope of the present invention.