阅读说明：本技术 一种仿生扑翼飞行器柔性扑翼气动特性分析方法、计算机设备及存储介质 (Bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method, computer equipment and storage medium ) 是由 欧阳一农 方群 王小龙 王明超 于 2021-08-03 设计创作，主要内容包括：本发明属于飞行器气动特性分析技术领域,特别涉及一种仿生扑翼飞行器柔性扑翼气动特性分析方法,包括以下步骤：设计扑翼的运动规律；计算扑翼运动产生的空气动力；利用升力和推力计算扑翼在空气动力作用下的柔性变形特征；利用柔性变形特征对初级扑翼的扑动角和扭转角进行修正,从而计算出考虑扑翼柔性变形效果的空气动力特性。本发明能有效分析仿生扑翼飞行器在飞行过程中扑翼的柔性变形,从而计算出考虑扑翼柔性变形效果的空气动力特性,为扑翼飞行器动力学特性建模和控制器设计建立基础,简化了对扑翼柔性变形问题的气动特性分析方法,满足了考虑扑翼柔性变形的扑翼飞行器的精度要求,为未来扑翼柔性气动力特性分析提供了新的思路和技术途径。(The invention belongs to the technical field of aircraft aerodynamic characteristic analysis, and particularly relates to a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method, which comprises the following steps: designing the motion law of the flapping wings; calculating aerodynamic force generated by the movement of the flapping wings; calculating the flexible deformation characteristic of the flapping wing under the aerodynamic action by utilizing the lift force and the thrust force; and correcting the flapping angle and the torsion angle of the primary flapping wing by utilizing the flexible deformation characteristic, thereby calculating the aerodynamic characteristics considering the flexible deformation effect of the flapping wing. The method can effectively analyze the flexible deformation of the flapping wings of the bionic flapping wing aircraft in the flying process, thereby calculating the aerodynamic characteristics of the flapping wing aircraft considering the flexible deformation effect, establishing a foundation for modeling the dynamic characteristics of the flapping wing aircraft and designing a controller, simplifying the aerodynamic characteristic analysis method for the problem of the flexible deformation of the flapping wings, meeting the precision requirement of the flapping wing aircraft considering the flexible deformation of the flapping wings, and providing a new thought and technical approach for the future analysis of the flexible aerodynamic characteristics of the flapping wings.)

1. A bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method is characterized in that a flapping wing aircraft with a double-section wing structure is used as a research object, a flapping wing directly connected with a fuselage is called as a secondary flapping wing (1), and a non-directly connected section is a primary flapping wing (2), and comprises the following steps:

s1, designing the motion rule of the flapping wing:

establishing a flapping law of the flapping wings in the flapping process to obtain a flapping angle of the primary flapping wing (2) at the current moment in the flapping process;

establishing a flapping wing torsion rule in the flapping process to obtain a torsion angle of the primary flapping wing (2) at the current moment in the flapping process;

s2, calculating aerodynamic force generated by the movement of the flapping wings:

obtaining aerodynamic force generated by the flapping wing moving in the state at a certain moment according to the surface element relative to the wind speed and the aerodynamic coefficient of the incoming flow;

converting the aerodynamic force on each surface element to a flapping wing coordinate system to obtain a lift force parallel to the direction of the flapping wing coordinate system and a thrust force along the direction of the flapping wing coordinate system, and obtaining the lift force and the thrust force generated by the movement of the whole flapping wing plane through the integration of each surface element on the flapping wing plane;

s3: calculating the flexible deformation characteristic of the flapping wing under the aerodynamic action by utilizing the lift force and the thrust force;

s4: the flapping angle and the torsion angle of the primary flapping wing (2) are corrected by utilizing the flexible deformation characteristics, so that the aerodynamic characteristics of the flapping wing in consideration of the flexible deformation effect are calculated.

2. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 1, wherein in S1, the flapping process comprises an upper flapping and a lower flapping, and the flapping law of the flapping wings in the lower flapping process is established to obtain the flapping angle of the secondary flapping wing (1) at the current moment and the flapping angle of the primary flapping wing (2) at the current moment in the lower flapping process; the method specifically comprises the following steps:

in the lower flapping process, the flapping angle of the secondary flapping wing (1) at the current moment is as follows:

β_s＝β_si-A_βs+A_βs cos(2πf_dT)；

the flapping angle of the primary flapping wing (2) at the current moment is as follows:

β_p＝β_s+β_pi

wherein, beta_sThe flapping angle of the secondary flapping wing (1) at the current moment;β_siis the initial flapping angle of the secondary flapping wing (1); a. the_βsIs the flapping amplitude of the secondary flapping wing (1); beta is a_pIs the flapping angle of the primary flapping wing (2) at the current moment; beta is a_piIs the initial flapping angle of the primary flapping wing (2); f. of_dThe flapping frequency of the lower flapping process; and T represents the corresponding time of the current time in a single flapping cycle.

3. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 1, wherein in S1, the flapping process comprises an upper flapping and a lower flapping, and a flapping wing torsion rule in the lower flapping process is established to obtain a torsion angle of the primary flapping wing (2) at the current moment and a torsion angle of the secondary flapping wing (1) at the current moment in the lower flapping process; the method specifically comprises the following steps:

in the lower flapping process, the torsion angle of the secondary flapping wing (1) at the current moment is theta_sThe torsion angle of the primary flapping wing (2) at the current moment is theta_pThe moment of changing the torsion angle is e_p；

When T is more than or equal to 0 and less than or equal to e_pThe calculation formula is as follows:

when in useThe calculation formula is as follows:

θ_s＝θ_sd；

θ_p＝θ_pd；

when in useThe calculation formula is as follows:

wherein the content of the first and second substances,

wherein, theta_sdThe torsion angle amplitude of the secondary flapping wing (1) in the lower flapping stage is obtained; theta_suThe torsion angle amplitude of the secondary flapping wing (1) in the upper flapping stage is obtained; theta_pdThe torsion angle amplitude of the primary flapping wing (2) at the lower flapping stage; theta_puThe torsion angle amplitude of the primary flapping wing (2) in the upper flapping stage is obtained; and T represents the corresponding time of the current time in a single flapping cycle.

4. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 1, wherein in S1, the flapping process comprises an upper flapping and a lower flapping, and the flapping law of the flapping wings in the upper flapping process is established to obtain the flapping angle of the secondary flapping wing (1) at the current moment in the upper flapping process and the flapping angle of the primary flapping wing (2) at the current moment; the method specifically comprises the following steps:

in the upper flapping process, the flapping angle of the secondary flapping wing (1) at the current moment is as follows:

the calculation formula of the flapping angle of the primary flapping wing (2) at the current moment is as follows:

in the formula: beta is a_sFor the secondary flapping wing (1) at the present momentFlapping angle; beta is a_siIs the initial flapping angle of the secondary flapping wing (1); a. the_βsIs the flapping amplitude of the secondary flapping wing (1); beta is a_pIs the flapping angle of the primary flapping wing (2) at the current moment; beta is a_piIs the initial flapping angle of the primary flapping wing (2); and T represents the corresponding time of the current time in a single flapping cycle.

5. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 1, wherein in S1, the flapping process comprises an upper flapping and a lower flapping, and a flapping wing torsion rule in the upper flapping process is established to obtain a torsion angle of the primary flapping wing (2) at the current moment in the upper flapping process and a torsion angle of the secondary flapping wing (1) at the current moment; the method specifically comprises the following steps:

in the upper flapping process, the torsion angle of the primary flapping wing (2) at the current moment is theta_sThe torsion angle of the secondary flapping wing (1) at the current moment is theta_p；

When in useThe calculation formula is as follows:

wherein the content of the first and second substances,

when in useThe calculation formula is as follows:

θ_s＝θ_su；

θ_p＝θ_sp；

when (P-e)_p) When T is less than or equal to P, the calculation formula is as follows:

wherein the content of the first and second substances,

in the formula: theta_sdThe torsion angle amplitude of the secondary flapping wing (1) in the lower flapping stage is obtained; theta_suThe torsion angle amplitude of the secondary flapping wing (1) in the upper flapping stage is obtained; theta_pdThe torsion angle amplitude of the primary flapping wing (2) at the lower flapping stage; theta_puIs the torsion angle amplitude of the primary flapping wing (2) in the upper flapping stage.

6. The method of claim 1, wherein in S2, the aerodynamic force generated by the flapping wing moving in this state at a certain time includes a lift force F perpendicular to the incoming flow direction_NAnd a resistance F parallel to the direction of the incoming flow_D；

Wherein, C_N,C_DIs the aerodynamic coefficient; v is the velocity of the bin relative to the incoming flow.

7. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 6, wherein S3 specifically comprises the following steps: determining the deformation degree of the primary flapping wing (2) in the moving process by adopting a finite element calculation method, adding load on the wing surface, calculating the average lift force generated by the movement of the primary flapping wing (2) in the lower flapping process and the upper flapping process, regarding the lift force as uniformly distributed load and loading the uniformly distributed load on the plane of the primary flapping wing (2), wherein the calculation formula of the torsional deformation angle of any point in the plane of the flapping wing in two directions is as follows:

α_flex(x,z,t)＝α_tip(x/λ_p)²(z/l_p)² (32)

β_flex(x,z,t)＝β_tip(x/λ_p)²(z/l_p)² (33)

in the formula: alpha is alpha_flexThe angle of torsional deformation of any point on the plane of the primary flapping wing (2) around the front edge (3); beta is a_flexThe angle of torsional deformation of any point on the plane of the primary flapping wing (2) around the wing root is set; alpha is alpha_tipThe torsional deformation angle of the wing tip of the primary flapping wing (2) around the leading edge (3); beta is a_tipThe primary flapping wing (2) is in a torsional deformation angle around the wing root; lambda [ alpha ]_pIs the chord length of the primary flapping wing (2); l_pIs the expansion length of the primary flapping wing (2).

8. The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft according to claim 7, wherein S4 specifically comprises the following steps: the torsional deformation angle around the leading edge (3) is superposed into the torsional angle of the primary flapping wing (2), the torsional deformation angle around the wing root is superposed into the flapping angle of the primary flapping wing (2), and the calculation formula of the flapping angle and the torsional angle of the corrected primary flapping wing (2) is as follows:

θ_pflex＝θ_p+α_flex

β_pflex＝β_p+β_flex

wherein, theta_pflexRepresenting the corrected primary flapping wing twist angle, beta_pflexRepresenting the corrected primary flapping angle, alpha_flexRepresenting the torsional deformation angle, beta, around the leading edge (3)_flexRepresenting torsional variations around the wing rootForm angle, θ_pIs the torsion angle, beta, of the primary flapping wing (2)_pIs the flapping angle of the primary flapping wing (2).

9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor when executing the computer program performs the steps of the method of analyzing the aerodynamic characteristics of a flexible flapping wing of a bionic flapping wing aircraft according to any one of claims 1 to 8.

10. A computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the method for analyzing the aerodynamic characteristics of a flexible flapping wing of a bionic flapping wing aircraft according to any one of claims 1 to 8.

Technical Field

The invention belongs to the technical field of aircraft aerodynamic characteristic analysis, and particularly relates to a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method, computer equipment and a storage medium.

Background

From the beginning of the last century to the present, the aviation technology has been rapidly developed for over 100 years, and various aircrafts have been developed, which far surpass the natural flying creatures in the aspects of flying speed, internal space, transportation bearing capacity and the like. However, the artificial aircraft cannot match the flying biological phase in nature in the above aspects under the same physical scale. Flying organisms in the nature select flapping wings as a flying propulsion mode after billions of years of evolution, and have incomparable excellent flying performance compared with an artificial aircraft. The flapping wing aircraft is a novel aircraft which appears in the last 30 years and simulates the shape, structure and flying mode of birds and flying insects. The flapping wing air vehicle is characterized in that a main body part of the flapping wing air vehicle comprises a flapping wing capable of moving in multiple degrees of freedom, and required lift force and thrust force are generated through the movement of the flapping wing. Flapping wing flight is the most common flight mode for flying organisms in nature, has higher biological rationality, flexible flight control and high pneumatic efficiency, and has more obvious advantages under the microminiature scale. The prior flapping wing air vehicle can be divided into a bird-imitating flapping wing air vehicle and an insect-imitating flapping wing air vehicle according to different flapping modes. The bird-imitating ornithopter and the insect-imitating ornithopter mainly differ in three aspects of flapping motion, flapping frequency and direction of a flapping surface of the flapping wings. The flapping wing air vehicle has similar flying mode to birds, and can generate flexible flying thrust and lift force through the movement of the flapping wings, so that the aerodynamic efficiency of the flapping wing air vehicle is much higher than that of a normal fixed wing air vehicle.

Li xi Ji researches the aerodynamic characteristics of the flapping wings and the empennage of a multi-section bionic flapping wing aircraft in the document 'multi-section bionic flapping wing aircraft flexible wing and empennage aerodynamic analysis', analyzes the aerodynamic change condition generated by the motion of the flapping wings under different parameter combinations, and provides a reference basis for the research on the aerodynamic characteristics of the flapping wing aircraft; the stroke ratio influence factor, the chord direction torsion function and the spread direction torsion function are introduced into an original constant-speed motion flapping wing model in the literature 'research on aerodynamic characteristics of flexible flapping wings', and the comparison simulation result shows that the aerodynamic characteristics of the flapping wings can be improved by the flexible change of the flapping wings; huminglan analyzes the action of inertia force of wings with different masses in the wing inertia force analysis of the imitation kun flapping wing aircraft, contrasts and analyzes the change condition of aerodynamic force generated by flapping wings under the condition of considering the inertia force or not, and provides a foundation for multi-body dynamics modeling.

In summary, the main problems in the analysis of aerodynamic characteristics of flapping wing aircraft are: the degree of deformation of the flapping wings cannot be quantitatively described; the influence of the flexible deformation effect of the flapping wings on the aerodynamic characteristics of the flapping wings is not considered; the time consumption of the calculation of the flexible deformation effect of the flapping wing is long, and the real-time requirement of control cannot be met.

Disclosure of Invention

The invention aims to provide a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method, computer equipment and a storage medium, and solves the main problems existing in the aspect of flapping wing aircraft aerodynamic characteristic analysis at present.

The invention is realized by the following technical scheme:

a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method takes a flapping wing aircraft with a double-section wing structure as a research object, a flapping wing directly connected with a fuselage is called a secondary flapping wing, and a non-directly connected section is a primary flapping wing, and comprises the following steps:

s1, designing the motion rule of the flapping wing:

establishing a flapping law of the flapping wings in the flapping process to obtain a flapping angle of a primary flapping wing at the current moment in the flapping process;

establishing a flapping wing torsion rule in the flapping process to obtain a torsion angle of a primary flapping wing at the current moment in the flapping process;

s2, calculating aerodynamic force generated by the movement of the flapping wings:

obtaining aerodynamic force generated by the flapping wing moving in the state at a certain moment according to the surface element relative to the wind speed and the aerodynamic coefficient of the incoming flow;

converting the aerodynamic force on each surface element to a flapping wing coordinate system to obtain a lift force parallel to the direction of the flapping wing coordinate system and a thrust force along the direction of the flapping wing coordinate system, and obtaining the lift force and the thrust force generated by the movement of the whole flapping wing plane through the integration of each surface element on the flapping wing plane;

s3: calculating the flexible deformation characteristic of the flapping wing under the aerodynamic action by utilizing the lift force and the thrust force;

s4: and correcting the flapping angle and the torsion angle of the primary flapping wing by utilizing the flexible deformation characteristic, thereby calculating the aerodynamic characteristics considering the flexible deformation effect of the flapping wing.

Further, in S1, the flapping process includes upper flapping and lower flapping, and a flapping law of the flapping wings in the lower flapping process is established to obtain a flapping angle of the secondary flapping wing at the current time and a flapping angle of the primary flapping wing at the current time in the lower flapping process; the method specifically comprises the following steps:

in the lower flapping process, the flapping angle of the secondary flapping wing at the current moment is as follows:

β_s＝β_si-A_βs+A_βs cos(2πf_dT)；

the flapping angle of the primary flapping wing at the current moment is as follows:

β_p＝β_s+β_pi

wherein, beta_sThe flapping angle of the secondary flapping wing at the current moment; beta is a_siIs the initial flapping angle of the secondary flapping wing; a. the_βsThe flapping amplitude of the secondary flapping wing; beta is a_pThe flapping angle of the primary flapping wing at the current moment; beta is a_piIs the initial flapping angle of the primary flapping wing; f. of_dThe flapping frequency of the lower flapping process; and T represents the corresponding time of the current time in a single flapping cycle.

Further, in S1, the flapping process comprises an upper flapping and a lower flapping, and a flapping wing torsion rule in the lower flapping process is established to obtain a torsion angle of a primary flapping wing at the current moment and a torsion angle of a secondary flapping wing at the current moment in the lower flapping process; the method specifically comprises the following steps:

in the lower flapping process, the torsion angle of the secondary flapping wing at the current moment is theta_sPrimary flapping wing twist at presentThe angle of rotation being theta_pThe moment of changing the torsion angle is e_p；

When T is more than or equal to 0 and less than or equal to e_pThe calculation formula is as follows:

when in useThe calculation formula is as follows:

θ_s＝θ_sd；

θ_p＝θ_pd；

when in useThe calculation formula is as follows:

wherein the content of the first and second substances,

wherein, theta_sdThe torsion angle amplitude of the secondary flapping wing in the lower flapping stage; theta_suThe torsion angle amplitude of the secondary flapping wing in the upper flapping stage; theta_pdThe torsion angle amplitude of the primary flapping wing at the lower flapping stage; theta_puThe torsion angle amplitude of the primary flapping wing in the upper flapping stage; and T represents the corresponding time of the current time in a single flapping cycle.

Further, in S1, the flapping process comprises upper flapping and lower flapping, and a flapping law of the flapping wings in the upper flapping process is established to obtain a flapping angle of a secondary flapping wing at the current moment and a flapping angle of a primary flapping wing at the current moment in the upper flapping process; the method specifically comprises the following steps:

in the upper flapping process, the flapping angle of the secondary flapping wing at the current moment is as follows:

the calculation formula of the flapping angle of the primary flapping wing at the current moment is as follows:

in the formula: beta is a_sThe flapping angle of the secondary flapping wing at the current moment; beta is a_siIs the initial flapping angle of the secondary flapping wing; a. the_βsThe flapping amplitude of the secondary flapping wing; beta is a_pThe flapping angle of the primary flapping wing at the current moment; beta is a_piIs the initial flapping angle of the primary flapping wing; and T represents the corresponding time of the current time in a single flapping cycle.

Further, in S1, the flapping process comprises an upper flapping and a lower flapping, and a flapping wing torsion rule in the upper flapping process is established to obtain a torsion angle of a primary flapping wing at the current moment and a torsion angle of a secondary flapping wing at the current moment in the upper flapping process; the method specifically comprises the following steps:

in the upward flapping process, the torsion angle of the primary flapping wing at the current moment is theta_sThe torsion angle of the secondary flapping wing at the current moment is theta_p；

When in useThe calculation formula is as follows:

wherein the content of the first and second substances,

when in useThe calculation formula is as follows:

θ_s＝θ_su；

θ_p＝θ_sp；

when (P-e)_p) When T is less than or equal to P, the calculation formula is as follows:

wherein the content of the first and second substances,

in the formula: theta_sdThe torsion angle amplitude of the secondary flapping wing in the lower flapping stage; theta_suThe torsion angle amplitude of the secondary flapping wing in the upper flapping stage; theta_pdThe torsion angle amplitude of the primary flapping wing at the lower flapping stage; theta_puThe amplitude of the torsion angle of the primary flapping wing in the upper flapping stage.

Further, in S2, the aerodynamic force generated by the flapping wing moving in this state at a certain time includes a lift force F perpendicular to the incoming flow direction_NAnd a resistance F parallel to the direction of the incoming flow_D；

Wherein, C_N,C_DIs the aerodynamic coefficient; v is the velocity of the bin relative to the incoming flow.

Further, S3 specifically is: determining the deformation degree of the primary flapping wing in the moving process by adopting a finite element calculation method, adding loads on the wing surface, calculating the average lift force generated by the movement of the primary flapping wing in the lower flapping process and the upper flapping process, regarding the lift force as uniformly distributed loads and loading the uniformly distributed loads on the plane of the primary flapping wing, wherein the calculation formula of the torsional deformation angle of any point in the plane of the flapping wing in two directions is as follows:

α_flex(x,z,t)＝α_tip(x/λ_p)²(z/l_p)² (32)

β_flex(x,z,t)＝β_tip(x/λ_p)²(z/l_p)² (33)

in the formula: alpha is alpha_flexThe torsional deformation angle of any point on the primary flapping wing plane around the front edge; beta is a_flexThe torsional deformation angle of any point on the primary flapping wing plane around the wing root; alpha is alpha_tipThe torsional deformation angle of the wing tip of the primary flapping wing around the leading edge; beta is a_tipThe primary flapping wing is in a torsional deformation angle around the wing root; lambda [ alpha ]_pIs the chord length of the primary flapping wing; l_pIs the spread length of the primary flapping wing.

Further, S4 specifically is: and (2) superposing the torsional deformation angle around the leading edge into the torsional angle of the primary flapping wing, superposing the torsional deformation angle around the wing root into the flapping angle of the primary flapping wing, and calculating the corrected flapping angle and torsional angle of the primary flapping wing by the following formula:

θ_pflex＝θ_p+α_flex

β_pflex＝β_p+β_flex

wherein, theta_pflexRepresenting the corrected primary flapping wing twist angle, beta_pflexRepresenting the corrected primary flapping angle, alpha_flexRepresenting the torsional deformation angle, beta, around the leading edge_flexRepresenting torsion around the wing rootTransformation angle, θ_pIs the torsion angle of the primary flapping wing, beta_pIs the flapping angle of the primary flapping wing.

The invention also discloses computer equipment which comprises a memory, a processor and a computer program which is stored in the memory and can run on the processor, and is characterized in that the processor realizes the steps of the bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method when executing the computer program.

The invention also discloses a computer readable storage medium, which stores a computer program, and is characterized in that the computer program is executed by a processor to realize the steps of the bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method.

Compared with the prior art, the invention has the following beneficial technical effects:

the invention discloses a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method which can be used for effectively analyzing the flexible deformation of a flapping wing of a bionic flapping wing aircraft in the flying process, thereby calculating the aerodynamic characteristic considering the flexible deformation effect of the flapping wing and establishing a foundation for modeling the dynamics characteristic of the flapping wing aircraft and designing a controller. The method simplifies the aerodynamic characteristic analysis method for the flapping wing flexible deformation problem, meets the precision requirement of the flapping wing air vehicle considering the flapping wing flexible deformation, and provides a new thought and technical approach for the future analysis of the flapping wing flexible aerodynamic characteristics.

Drawings

FIG. 1 is a schematic view of a flapping wing segment of a bionic flapping wing aircraft;

FIG. 2 is a view of the flapping wing coordinate system definition;

FIG. 3 is a view of the flapping wing motion angle definition; FIG. 3(a) is the flapping angle and FIG. 3(b) is the twist angle;

FIG. 4 is a simplified aerodynamic model of an flapping wing;

FIG. 5 is a diagram of aerodynamic changes in flapping motion without taking into account primary compliance deformation;

FIG. 6 is a schematic view of the flexible deformation of the flapping wings;

FIG. 7 is a diagram of aerodynamic changes of flapping wing motion, which is obtained by the method for analyzing aerodynamic characteristics of flexible flapping wings and takes primary flexible deformation into consideration.

Wherein, 1 is a secondary flapping wing, 2 is a primary flapping wing, and 3 is a leading edge.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

As shown in fig. 1, the bionic object of the bionic flapping wing aircraft used in the invention is young gold carving, so the studied flapping wing aircraft has a double-section wing structure, wherein the flapping wing directly connected with the aircraft body is called as a secondary flapping wing 1, and the non-directly connected section is a primary flapping wing 2.

As shown in fig. 2, the present invention takes the right secondary flapping wing 1 as an example to define a flapping wing coordinate system, which is defined as: the original point is the connection point of the secondary flapping wing 1 and the fuselage; the x axis is parallel to the chord line direction of the flapping wings and points to the head of the fuselage to be positive; the y axis is vertical to the flapping wing plane and points upwards to be positive; the z-axis is perpendicular to the plane.

Fig. 3 is a view defining the flapping wing motion angle, and the present invention is illustrated with the right secondary flapping wing 1 as an example: angle of oscillation beta_rsO of coordinate system of secondary flapping wing 1 on right side₃z₃Axis and frame coordinate system O₁x₁z₁Angle between planes, when O₃z₃The axis is located at O₁x₁z₁Beta when lying below the plane_rsPositive and negative otherwise. Torsion angle theta_rsO of coordinate system of secondary flapping wing 1 on right side₃x₃Axis and frame coordinate systemAngle between planes, when O₃x₃The axis is located at O₁x₁z₁Theta when above the plane_rsPositive and negative otherwise.

The invention regards the leading edges 3 and the wing roots of the secondary flapping wing 1 and the primary flapping wing 2 as rigid skeletons, so that the secondary flapping wing 1 does not generate flexible deformation in the moving process, and only the influence of the flexible deformation of the primary flapping wing 2 on the aerodynamic force generated by the flapping wing needs to be considered for this purpose.

On the basis of the premise, the invention provides a bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method, which comprises the following steps:

1) designing flapping wing motion law

Since the flapping wing aircraft mainly generates upward lift force and forward thrust force by flapping of the flapping wings, it is very important to design a proper motion law of the flapping wings. The motion rule of the flapping wing designed by the invention mainly comprises two motions: flapping and twisting.

The flapping wing movement is mainly divided into a lower flapping process and an upper flapping process, wherein the lower flapping process accounts for 60% of the whole flapping cycle, and the upper flapping process accounts for 40% of the whole flapping cycle. Let the average flapping frequency of the whole process be f.

The flapping frequency of the lower flapping process is:

the frequency of the upper flapping process is as follows:

p represents an average flapping cycle, T represents the flight time, Q represents the number of flapping cycles experienced, and T represents the corresponding time of the current time in a single flapping cycle, then:

T＝t-Q·P (4)

in formula (3): floor is an integer function.

The following is an illustration of the flapping process:

in the lower flapping processThe flapping law of the middle flapping wing is as follows:

β_s＝β_si-A_βs+A_βscos(2πf_dT) (5)

β_p＝β_s+β_pi (6)

in formulae (5) and (6): beta is a_sThe flapping angle/degree of the secondary flapping wing 1 at the current moment; beta is a_siIs the initial flapping angle/° of the secondary flapping wing 1; a. the_βsIs the flapping amplitude/° of the secondary flapping wing 1; beta is a_pThe flapping angle/degree of the primary flapping wing 2 at the current moment; beta is a_piIs the initial flapping angle/° of the primary flapping wing 2.

The torsion law of the wings in the flapping process is shown in formulas (7) to (13):

when T is more than or equal to 0 and less than or equal to e_pWhen e is present_pRepresents the moment of changing the torsion angle;

when in useWhen the temperature of the water is higher than the set temperature,

θ_s＝θ_sd (9)

θ_p＝θ_pd (10)

when in useWhen the temperature of the water is higher than the set temperature,

in the formulae (11) to (12),

the following is an explanation of the process of the upper flapping:

in the process of putting onThe flapping law of the middle flapping wing is as follows:

in formulae (14) and (15): beta is a_sThe flapping angle/degree of the secondary flapping wing 1 at the current moment; beta is a_siIs the initial flapping angle/° of the secondary flapping wing 1; a. the_βsIs the flapping amplitude/° of the secondary flapping wing 1; a. the_βpIs the flapping amplitude/° of the primary flapping wing 2; beta is a_pThe flapping angle/degree of the primary flapping wing 2 at the current moment; beta is a_piIs the initial flapping angle/° of the primary flapping wing 2.

The torsion law of the flapping wing in the flapping process is shown in formulas (16) to (23):

when in useWhen the temperature of the water is higher than the set temperature,

in the formulae (16) to (17),

when in useWhen the temperature of the water is higher than the set temperature,

θ_s＝θ_su (19)

θ_p＝θ_sp (20)

when (P-e)_p) When T is less than or equal to P,

in formulae (7) to (23): theta_sThe torsion angle/° of the secondary flapping wing 1 at the current moment; theta_pIs the torsion angle/° of the primary flapping wing 2 at the current moment; theta_sdThe torsion angle amplitude/degree of the secondary flapping wing 1 at the lower flapping stage; theta_suThe torsion angle amplitude/degree of the secondary flapping wing 1 in the upper flapping stage is shown; theta_pdThe torsion angle amplitude/degree of the primary flapping wing 2 at the lower flapping stage; theta_puThe torsion angle amplitude/° of the primary flapping wing 2 of the upper flapping stage.

2) Calculating aerodynamic forces generated by flapping wings

In the process of flapping under the flapping wing, the speed of each calculation surface element in the flapping wing relative to air consists of two parts: one part is the flying speed V of the flapping wing aircraft_∞And the other part is the flapping speed Vwown at which the flapping wings face downwards. The velocity of the bin with respect to the incoming flow is:

the calculated bin is then:

α_att＝α_b+θ+arctan((V_down cos(α_b))/(V_∞+V_down sin(α_b)) (25)

wherein alpha is_bIs the flight angle of attack of the fuselage; theta is the torsion angle of the primary flapping wing 2, and the latter half of equation (25) is the influence of the surface element flapping velocity on the angle of attack.

Therefore, the aerodynamic force generated by the flapping wings moving in this state at a certain time is as follows:

in formulae (26) and (27), C_N,C_DThe calculation formula of (2) is as follows:

C_N＝0.225+1.58sin(2.13α_att-7.2) (28)

C_D＝1.92-1.55cos(2.04α_att-9.82) (29)

in formulae (26) to (29): alpha is alpha_ttCalculating the attack angle of the surface element; c_N,C_DIs the aerodynamic coefficient; v is the velocity of the calculation bin relative to the incoming flow; f_NBeing lift perpendicular to the direction of incoming flow, F_DIs the resistance parallel to the incoming flow direction. The aerodynamic force on each surface element is converted into the coordinate system of the flapping wing to obtain the coordinate system O parallel to the flapping wing₃y₃Directional lifting force F_LAnd along the flapping wing coordinate system O₃x₃Thrust in the direction F_M. The lift force and the thrust force generated by the movement of the whole flapping wing plane are obtained by integrating all surface elements on the flapping wing plane and are respectively:

L＝∫∫F_Lds (30)

M＝∫∫F_Mds (31)

3) taking into account the flexible deformation of the flapping wings

As the primary flapping wing 2 of the real birds has larger area than the secondary flapping wing 1 and has less supporting skeleton, the flapping wing of the real birds which generates torsional deformation in the flying process is mainly the primary flapping wing 2, and the secondary flapping wing 1 hardly generates torsional deformation.

Therefore, the invention only considers the flexible deformation effect of the primary flapping wing 2, and the front edge 3 and the wing root of the primary flapping wing 2 are considered to be rigid skeletons, so that the flexible deformation at the front edge 3 and the wing root is not considered. And determining the deformation degree of the primary flapping wing 2 in the motion process by adopting a finite element calculation method. Adding loads on the airfoil surface, calculating the average lift force generated by the movement of the primary flapping wing 2 in the lower flapping process and the upper flapping process, and taking the lift force as uniform load to be loaded on the plane of the primary flapping wing 2. The torsion angle of one point on the flapping wing plane along the spanwise direction and the chordwise direction is changed in a manner similar to a parabola, and the calculation formula of the torsion deformation angle of any point in the flapping wing plane in two directions is as follows:

α_flex(x,z,t)＝α_tip(x/λ_p)²(z/l_p)² (32)

β_flex(x,z,t)＝β_tip(x/λ_p)²(z/l_p)² (33)

in the formula: alpha is alpha_flexThe torsional deformation angle/degree around the leading edge 3 at any point on the plane of the primary flapping wing 2; beta is a_flexThe torsional deformation angle/degree of any point on the plane of the primary flapping wing 2 around the wing root; alpha is alpha_tipIs the twist deflection angle/° of the wing tip of the primary flapping wing 2 around the leading edge 3; beta is a_tipThe torsional deformation angle/degree of the primary flapping wing 2 around the wing root; lambda [ alpha ]_pIs the chord length/m of the primary flapping wing 2; l_pIs the span length/m of the primary flapping wing 2.

The flexible deformation of the flapping wings is periodically varied with a period equal to the flapping period, but with a phase lead of 1/4 periods of the flapping angle. The flapping of the primary flapping wing 2 is divided into two phases: the primary flapping wings 2 of the first stage at a frequency f_dLower flap 1/2 cycle, second stage is 2f_uThe flapping continues for one cycle. The expression of the torsional deformation angle of the wing tip is obtained as follows:

the first stage is as follows:

and a second stage:

in formulae (34) to (37): alpha is alpha_max1The maximum value/° of the chord-direction deformation angle of the primary flapping wing in the first stage; beta is a_max1Is the maximum value/° of the spanwise deformation angle of the primary flapping of the first stage; alpha is alpha_max2The maximum value/° of the chord-wise deformation angle of the primary flapping wing in the second stage; beta is a_max2Is the maximum value/° of the spanwise deformation angle of the primary flapping at the second stage. The average lift force generated by the primary flapping wing in the lower flapping process is calculated to be 13.49N, and the average lift force generated by the primary flapping wing in the upper flapping stage is calculated to be 20.78N. And loading the result on the primary flapping wing plane as the uniform load of the finite element analysis, wherein the finite element calculation result is as follows: in the first flapping stage, the maximum deformation angle of the wing tip about the wing root is about-10.4 ° and the maximum deformation angle about the leading edge is about-15.8 °; in the second flapping phase, the maximum deflection angle of the tip about the root is about 16.71 ° and the maximum deflection angle about the leading edge is about 21.16 °.

4) Correction of motion law of flapping wings by using flexible deformation characteristics

In view of the flexible deformation of the primary flapping wings 2, the law of motion of the primary flapping wings 2 needs to be corrected. The torsional deformation angle around the leading edge 3 is superposed into the torsional angle of the primary flapping wing 2, the torsional deformation angle around the wing root is superposed into the flapping angle of the primary flapping wing 2, and the calculation formula of the flapping angle and the torsional angle of the corrected primary flapping wing 2 is as follows:

θ_pflex＝θ_p+α_flex (38)

β_pflex＝β_p+β_flex (39)

wherein, theta_pflexRepresenting the corrected primary flapping wing twist angle, beta_pflexRepresenting the corrected primary flapping angle, alpha_flexRepresenting the torsional deformation angle, beta, around the leading edge 3_flexRepresenting the torsional deflection angle around the root.

The torsional deformation angle of the leading edge 3 and the torsional deformation angle of the wing root are obtained by equation (32) and equation (33).

FIG. 4 is a simplified aerodynamic model of flapping wings, which is a modified quasi-stationary model used in the present invention to discretize the flapping motion process into a series of time points, each time point generating aerodynamic forces equal to those generated by the translational motion of the flapping wings at the same attitude in a quasi-stationary state.

FIG. 5 is a diagram of aerodynamic changes in flapping motion without regard to primary compliance deformation showing that lift and thrust are periodically varied, the lift having one peak and one valley during the flapping cycle, the thrust having two peaks and two valleys during the flapping cycle; the maximum value of the lift force occurs at the moment when the flapping angle is zero in the lower flapping process, and the minimum value occurs at the moment when the flapping angle is zero in the upper flapping process; the maximum value of the thrust occurs at the moment when the flapping angle is zero during the up-and down-flapping process, and the minimum value occurs at the moment when the flapping angle is maximum and minimum.

Fig. 6 is a schematic view of the flexible deformation of the flapping wing, showing the primary flapping wing 2 undergoing torsional deformation in two directions, namely torsional deformation around the leading edge 3 and torsional deformation around the wing root, both torsional deformation angles being zero at the wing root and the leading edge 3, and both torsional deformation angles being at a maximum at the wing tip.

FIG. 7 is a view of aerodynamic changes of flapping wing movement considering primary flexible deformation, which shows that the flexible deformation effect of the flapping wing mainly has great influence on the lift force of the flapping wing in the lower flapping process and the thrust force of the flapping wing in the upper flapping process, and the changes are that in the lower flapping stage, the lift force is increased and the thrust force is almost unchanged; in the upper flapping stage, the lift force is almost unchanged, and the thrust force is increased.

The method for analyzing the aerodynamic characteristics of the flexible flapping wings of the bionic flapping wing aircraft can adopt the forms of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The bionic flapping wing aircraft flexible flapping wing aerodynamic characteristic analysis method can be stored in a computer readable storage medium if the method is realized in the form of a software functional unit and sold or used as an independent product. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of the method embodiments may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. Computer-readable storage media, including both non-transitory and non-transitory, removable and non-removable media, may implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. It should be noted that the computer readable medium may contain content that is subject to appropriate increase or decrease as required by legislation and patent practice in jurisdictions, for example, in some jurisdictions, computer readable media does not include electrical carrier signals and telecommunications signals as is required by legislation and patent practice. The computer storage medium may be any available medium or data storage device that can be accessed by a computer, including but not limited to magnetic memory (e.g., floppy disk, hard disk, magnetic tape, magneto-optical disk (MO), etc.), optical memory (e.g., CD, DVD, BD, HVD, etc.), and semiconductor memory (e.g., ROM, EPROM, EEPROM, nonvolatile memory (NANDFLASH), Solid State Disk (SSD)), etc.

In an exemplary embodiment, there is also provided a computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the method for analyzing the aerodynamic properties of a flexible flapping wing of a bionic flapping wing aircraft when executing the computer program. The processor may be a Central Processing Unit (CPU), other general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, etc.

The above description is only a general example of the present invention, and does not limit the present invention in any way, although the present invention is demonstrated in the general example that the present invention not only provides a flapping wing flexible deformation characteristic analysis and aerodynamic characteristic simplified calculation method of flapping wing aircraft considering flexible deformation, but also can be easily generalized to the problem of aerodynamic characteristic analysis of other different aircraft. Accordingly, those skilled in the art can readily devise many modifications and equivalents of the disclosed methods and techniques without departing from the spirit and scope of the invention. However, any simple modification, equivalent change and modification made to the above general embodiments or similar works according to the technical essence of the present invention are still within the scope of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.