Bird-like flapping wing design method based on momentum theorem analysis to analyze lift influencing factors

Abstract

The application provides a bird flapping wing design method based on momentum theorem analysis of factors influencing lift, which comprises the following steps: firstly, determining basic thrust and lift design constraints according to task requirements; secondly, according to the momentum theorem, converting design parameters influencing the thrust and lift into contributions to the horizontal thrust and vertical lift of the flapping wing, and screening the design parameters according to the constraints; considering the influence of power consumption, determining corresponding design measures for reducing the power consumption; analyzing the realizability of the design measures to obtain the design parameters and corresponding design measures considering the realizability; sorting the importance of the design parameters, optimizing the design measures of the corresponding design parameters, and obtaining the preliminary design scheme of the bird flapping wing. The application converts complicated design constraints into simple requirements for the thrust and lift of the flapping wing, greatly shortens the design time of the flapping wing vehicle for different flight requirements, standardizes the overall design idea of the flapping wing, and has high theoretical support and engineering practical significance.

Description

Technical Field

[0001] This invention relates to the field of flapping wing design technology for flapping wings of flapping-wing aircraft, specifically a bird-inspired flapping wing design method based on momentum theorem analysis of thrust influencing factors. Background Technology

[0002] Bird-inspired flapping-wing aircraft are characterized by high maneuverability, higher propulsion efficiency at low Reynolds numbers, and strong environmental stealth. When performing aerial inspection, information acquisition, and strike missions in special areas and time zones, they possess capabilities that other types of aircraft do not have, making their role in both civilian and military fields increasingly important.

[0003] For bird-inspired flapping-wing aircraft, the aerodynamic characteristics of the flapping wing directly determine the aircraft's performance and mission capabilities. Currently, the factors affecting the lift and thrust of flapping wings can be broadly categorized into four types:

[0004] 1) Geometric parameters of the wing: airfoil (divided into static airfoil and dynamic airfoil), planform (divided into static planform and dynamic planform); among them, the flexible deformation of the wing, the bending of the wing along the span, the expansion and contraction within the wing surface, the chordal torsion of the wing along the span direction and other flapping modes will be mainly reflected in the changes of the dynamic airfoil and planform.

[0005] 2) Wing flapping parameters: including flapping amplitude and flapping frequency;

[0006] 3) Flow parameters: including wind speed, angle of attack, etc.;

[0007] 4) Micro-flow control structures: including wingtip slot parameters, small wing feather parameters, etc.

[0008] Designing a high-thrust, high-lift flapping wing requires a thorough understanding of the aerodynamics of various design parameters and alternative design measures. The goal is to find an optimal design that meets the aircraft's performance and functional requirements, achieves low energy consumption, and possesses biomimetic feasibility. Unfortunately, while there has been considerable research both domestically and internationally, it primarily relies on comparing and selecting a better design based on a large sample size of calculations or experiments involving various combinations of design parameters and alternative design measures. On one hand, even if large-scale CFD calculations or experiments are feasible, the resulting design may not be the optimal solution, leaving no way to determine its full potential. On the other hand, current limitations in CFD and wind tunnel testing technologies make it impossible to complete such large-scale calculations and experiments due to insufficient computational and experimental capabilities, as well as the time and resource costs involved. Summary of the Invention

[0009] To address the problems existing in current flapping wing design methods, this invention, based on the analysis of the influencing factors of thrust and lift generation by flapping wings using momentum theory, proposes a bird-inspired flapping wing design method based on the momentum theorem to analyze the influencing factors of thrust. This aims to solve the problems of blind and trial-and-error approaches in current flapping wing design both domestically and internationally, which make it difficult to achieve optimal thrust and lift effects, as well as the problems of lengthy design processes and wasted design and testing resources. This invention can provide a preliminary flapping wing design scheme that meets macroscopic requirements, narrowing down the range of design parameters for subsequent detailed design.

[0010] The technical solution of this invention is as follows:

[0011] A bird-inspired flapping wing design method based on momentum theorem analysis of thrust influencing factors includes the following steps:

[0012] Step 1: Determine the basic thrust and lift design constraints based on the mission requirements, and determine the priority of lift and thrust considerations during the design process;

[0013] Step 2: Based on the momentum theorem, the design parameters affecting thrust and lift are transformed into contributions to the horizontal thrust and vertical lift of the flapping wing. Based on the thrust and lift design constraints determined in Step 1, design parameters that satisfy the thrust and lift design constraints are selected.

[0014] Step 3: For the design parameters selected in Step 2, considering the impact of power consumption, further filter the design parameters and determine the corresponding design measures to reduce power consumption;

[0015] Step 4: Perform a feasibility analysis on the design measures corresponding to the design parameters further selected in Step 3 to obtain the design parameters and corresponding design measures after considering feasibility.

[0016] Step 5: Based on the priority of lift and thrust considerations determined in Step 1, sort the design parameters obtained in Step 4 by importance, optimize the design measures of the corresponding design parameters according to their importance, and obtain the preliminary design scheme of the bird flapping wing.

[0017] Furthermore, in step 2, the design parameters affecting thrust and lift include: passive / active dynamic airfoil and planform shape, flapping wing twist angle, flapping frequency and flapping amplitude, descent time ratio, angle of attack and velocity, and small-scale flow control.

[0018] Furthermore, the design measures corresponding to each design parameter are as follows:

[0019] Passive / active dynamic airfoils and planforms: Maximize thrust and / or lift by designing airfoils and planforms; improve thrust by designing flexible airfoils; reduce negative lift and power consumption during flapping by designing spanwise folding wings to improve lift;

[0020] Flapping wing twist angle: By designing twisting motion, thrust and lift are improved, and power consumption is reduced;

[0021] Flapping frequency and amplitude: Within a certain range, increasing the flapping frequency and amplitude can increase the thrust, but it will lead to a significant increase in power consumption.

[0022] Dive time percentage: The power consumption is lowest when the dive time percentage is equal to 0.5 ± 0.05.

[0023] Angle of attack and speed: Increasing wind speed and angle of attack can increase lift, but will correspondingly increase drag and power consumption;

[0024] Small-scale flow control includes small winglets and wingtip slots; using small winglets can increase lift, while using wingtip slots can reduce lift-induced drag, thereby increasing residual thrust.

[0025] Furthermore, the design measures to reduce power consumption include:

[0026] (1) Control the flapping frequency and flapping amplitude, and minimize the flapping frequency and flapping amplitude as much as possible while meeting the thrust and lift design requirements;

[0027] (2) Design passive / active dynamic airfoils and planform shapes to reduce the weight of flapping wings while meeting lift design requirements;

[0028] (3) By designing the torsion angle, the downward and upward torsion can be achieved, thereby reducing the projected wing area during the up-and-down flapping and reducing power consumption;

[0029] (4) By designing the flapping wing to bend along the span and to contract the wing surface inward, the projected wing area during the flapping motion is changed, thereby reducing the work done by the negative lift.

[0030] (5) Control the angle of attack and wind speed while meeting the lift design requirements.

[0031] Furthermore, in step 4, the feasibility analysis considers factors such as: achieving the design function, energy conversion rate per unit weight, structural reliability, and control difficulty brought about by multi-degree-of-freedom design.

[0032] Furthermore, after conducting a feasibility analysis, the ease or difficulty of implementing the corresponding design measures for each design parameter is as follows:

[0033]

[0034] Furthermore, in step 5, considering the importance of design factors affecting lift, the order is: angle of attack and wind speed >> passive / active dynamic airfoil and plane shape = flapping twist > flapping frequency and flapping amplitude = descent time percentage; considering the importance of design factors affecting thrust, the order is: flapping frequency and flapping amplitude >> passive / active dynamic airfoil and plane shape = flapping twist = angle of attack > descent time percentage.

[0035] Further optimization measures to increase lift include:

[0036] (1) Under the constraints of drag and power consumption, increase wind speed and angle of attack to increase lift;

[0037] (2) Design passive / active dynamic airfoils and planform shapes to maximize lift;

[0038] (3) Considering the resistance constraint, design the torsional motion;

[0039] (4) Use small wing feathers to increase lift;

[0040] Optimization measures to increase thrust include:

[0041] (1) Under the condition of power consumption constraint, increase the flapping frequency and flapping amplitude to increase thrust;

[0042] (2) Adopt an upward thrust and upward twist, and a downward thrust and downward twist method to increase thrust;

[0043] (3) Maximize thrust by designing passive / active dynamic airfoils and planar shapes;

[0044] (4) By reducing the angle of attack, lift drag is reduced, thereby increasing the remaining thrust;

[0045] (5) Reduce lift drag by designing wingtip slots, thereby increasing residual thrust.

[0046] Beneficial effects

[0047] The beneficial effects of this invention are as follows: Through momentum theorem analysis, this invention transforms the cumbersome design constraints into simple requirements for the thrust of flapping wings. Based on this, by analyzing known factors affecting thrust, a general design scheme and improvement ideas for flapping wing parameters are derived, which greatly shortens the design time for flapping wing aircraft with different flight requirements and standardizes the overall design concept of flapping wings. It has high theoretical support and engineering practical significance.

[0048] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0049] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0050] Figure 1 : Flowchart of the theoretical analysis of this invention;

[0051] Figure 2 : Frequency and amplitude of the flapping wing model;

[0052] Figure 3 Force diagram of airfoil profile with free flow and angle of attack (during airfoil downdraft motion);

[0053] Figure 4 Force diagrams of airfoil profiles under torsional motion only; (a) airfoil flapping downwards and twisting downwards, (b) airfoil flapping upwards and twisting upwards;

[0054] Figure 5 : Planar shape of flapping wing. Detailed Implementation

[0055] The purpose of this invention is to address the problems of blind and trial-and-error approaches in the current design of flapping wings, both domestically and internationally, which make it difficult to achieve optimal thrust and lift effects, as well as the problems of lengthy design processes and wasted design and testing resources. This invention proposes a new bird-inspired flapping wing design method to obtain a flapping wing design scheme that meets the requirements on a macroscopic level, thereby narrowing the range of design parameters for subsequent detailed design.

[0056] The basic research idea of ​​this invention is:

[0057] First, based on the reasoning of the momentum theorem, the influence of various design parameters on thrust and lift during the flapping wing motion is qualitatively explained. By analyzing the momentum increments of the air generated by the flapping of the wing along the thrust and lift directions, the possible contribution of each design parameter or design measure to thrust and lift is qualitatively analyzed and explained.

[0058] Then, the energy consumption of each design parameter and design measure is analyzed, and the feasibility of implementing these design parameters and design measures on the corresponding biomimetic aircraft is considered, and a set of design parameters and design measures is established.

[0059] Subsequently, based on the mission requirements, the priority of considering lift and thrust in the design was determined: either lift should be the primary consideration with thrust as a secondary consideration, or thrust should be the primary consideration with lift as a secondary consideration, or both thrust and lift need to be considered. For the three different design requirements, feasible design parameters and design measures were determined.

[0060] The final design flow yields an effective combination of design parameters or design measures for biomimetic flapping wings that consider both high thrust and high lift, as well as low power consumption and feasibility, tailored to specific performance and functional requirements. Based on this flow, one can obtain the aerodynamic design of a high-thrust and high-lift flapping wing that macroscopically meets the performance and functional requirements of a biomimetic aircraft, relying on less CFD calculations and detailed experimental analysis.

[0061] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0062] First, based on the basic flapping wing model, the momentum theorem is used to analyze the influence of each design parameter on thrust and lift.

[0063] Here is a summary of the meanings of the parameter variables:

[0064] Table 1. Meaning of Parameter Variables

[0065]

[0066]

[0067] like Figure 2 As shown, assume the flapping wing model is a thin flat wing with a chord length of c and a half-span of l. The wing root is on the x-axis and rotates around the x-axis. The flapping amplitude is φ, the frequency is f, and the free-flow velocity is V. ∞ In the case of only flapping, V ∞ =0.

[0068] Taking the following half-cycle as an example, the following inferences can be drawn:

[0069]

[0070]

[0071]

[0072] p=ΔmΔυ=φ 2 lcfρ

[0073] Where Δm is the total mass of air affected by the flapping motion, and Δυ is the average downward velocity of the air affected by Δm.

[0074] According to the momentum theorem:

[0075] LΔt=ΔmΔυ

[0076] L=4φ 2 f 2 lcρ

[0077] This shows that the vertical lift L is directly proportional to the square of the flapping frequency f and the square of the flapping amplitude φ. The use of folding wings is also to reduce the wing area S during upward flapping, thereby reducing the negative lift; where...

[0078] S=(l-Δl)c

[0079] Δl is the change in the length l of the thin plate after folding.

[0080] exist Figure 2 Adding free flow and angle of attack to the basics, such as Figure 3 As shown in the figure, the force diagram of the airfoil during its downward flapping motion considers the free flow and the airfoil profile shape at the angle of attack. The angle between the flapping axis and the x-axis is α, and the direction of the free flow is parallel to the x-axis in the opposite direction. Let the downward impulse applied to the air be p = ΔmΔυ. Then, according to the momentum theorem, the force acting on the airfoil is F = 4φ. 2 f 2 lcρ can be decomposed into F along the lift direction. y and F along the direction of free flow x Considering the lift coefficient C L Then we have:

[0081] C L =aα

[0082]

[0083]

[0084] D = -4φ 2 f 2 lcρsinα≈-4φ 2 f 2 lcρα

[0085] It can be seen that while increasing the angle of attack increases lift, it also increases drag.

[0086] If in Figure 2 Adding torsional motion to the base, such as Figure 4 As shown, the figure illustrates the force diagram of the airfoil cross-section during torsional motion only. Assuming a downward impulse p = ΔmΔυ applied to the air, the force acting on the airfoil, derived from the momentum theorem, is F = 4φ. 2 f 2 lcρ can be decomposed into F along the lift direction. y and F along the direction of free flow x Assuming the twist angle is θ, then:

[0087] Pounce and twist:

[0088] Lift F y =4φ 2 f2 lcρcosθ

[0089] Thrust F x =4φ 2 f 2 lcρsinθ

[0090] Pounce and twist:

[0091] negative lift F y =-4φ 2 f 2 lcρcosθ

[0092] Thrust F x =4φ 2 f 2 lcρsinθ

[0093] It can be seen that if only in Figure 2 The addition of torsional motion on top of this increases thrust by changing the direction of impulse, reduces negative lift during the upward lunge, and indirectly increases the effective angle of attack, thus further increasing lift.

[0094] Furthermore, the design measures for small-scale flow control structures, such as small winglets and wingtip slots, are analyzed in detail below:

[0095] Winglets exhibit a lift-enhancing effect similar to vortex generators. By inducing a downwash, they inject momentum from the free flow into the boundary layer, increasing momentum within the boundary layer and thus suppressing flow separation and increasing lift. At high angles of attack, the streamwise vortices formed at the tips of the winglets induce a strong downwash on the upper surface of the wing. This downwash transfers momentum from the free flow to the lower-velocity near-wall boundary layer, further suppressing flow separation and increasing lift.

[0096] The wingtip slots have a drag-reducing effect. The relationship between the induced drag coefficient k and the wingspan coefficient M is as follows:

[0097] M = 1 / k 1 / 2 , where k is the induced drag coefficient;

[0098] k = dD / dL 2 πqb 2 Where D is drag, L is lift, q is dynamic pressure, and b is wingspan.

[0099] Next, we will analyze the power consumption impact of design parameters and design measures:

[0100] Regarding power consumption, when other conditions are the same, the higher the flapping frequency, the greater the power consumption. If the flapping frequency remains unchanged, according to the power consumption formula P=FV, the greater the wing loading and inertial force on the flapping wing, the greater the energy consumption. To put it more intuitively, the greater the instantaneous lift generated, whether positive or negative, the more work is consumed.

[0101] Among the design measures, those that can reduce power consumption include:

[0102] (1) Control the flapping frequency and flapping amplitude. When meeting the thrust design requirements, the flapping frequency and flapping amplitude should be as small as possible.

[0103] (2) Design passive / active dynamic airfoils and planar shapes to reduce the weight of flapping wings while ensuring the lift meets the design requirements.

[0104] (3) Design appropriate torsional motion, and after superimposing the torsion angle, realize the downward torsion and upward torsion, reduce the projected wing area when flapping up and down, so as to reduce power consumption.

[0105] (4) By designing the flapping wing to bend along the span and to contract the wing surface inward, the projected wing area during the flapping motion is changed, thereby reducing the work done by the negative lift.

[0106] (5) Appropriately control the angle of attack and wind speed.

[0107] (6) Energy consumption is lowest when the time spent falling is about 0.5, but the actual impact is small.

[0108] After considering power consumption limitations, the next step for the aforementioned design measures is to assess their feasibility for implementation on corresponding biomimetic aircraft. Some design measures, while effective and with acceptable power consumption, are difficult to implement; or, even if implemented, the negative impacts are too great to offset their original aerodynamic gains. Factors to consider in the feasibility analysis include: achieving the designed function, energy conversion efficiency per unit weight, structural reliability, and the control difficulties arising from multi-degree-of-freedom design, etc.

[0109] Achieving design functionality: This directly reflects the feasibility of the design measure and the extent to which the design effect can be achieved.

[0110] Energy conversion efficiency per unit weight: This is used to evaluate the efficiency of a new design mechanism in converting energy into thrust.

[0111] Structural reliability: Theoretically, the simpler the structure, the higher the reliability and the higher the transmission efficiency.

[0112] The control challenges brought about by multi-degree-of-freedom design: In order to achieve better flight performance, more complex flight modes may be introduced, which in turn puts forward higher requirements for control design.

[0113] Furthermore, since increasing thrust increases speed, which in turn increases lift, the margin of thrust can be converted into a lift gain. Based on this understanding, in addition to ensuring basic lift, we focused on adopting measures to increase thrust during the design process.

[0114] The final set of design parameters and measures, taking feasibility into account, is derived, with the difficulty of implementation ranging from easy to moderate to difficult.

[0115] Table 2 Design Parameters and Design Measures (Aggregate)

[0116]

[0117]

[0118] The lift and drag generation mechanisms of flapping wings are similar to those of fixed wings, primarily relying on speed and angle of attack. While flapping parameters also play a role in lift generation, they are not the dominant factor. Almost all forms of flapping serve to increase thrust and generate a small amount of lift. The arm sections of a flapping wing mainly generate lift, while the arm sections mainly generate thrust. This decouples lift and thrust through two wing sections, reducing the design complexity of flapping wings, which is important in the design of passive / active dynamic airfoils and planforms. Therefore, for concentrated design parameters and measures, the following order of importance of influencing factors is given.

[0119] Considering the order of importance of factors affecting lift:

[0120] Angle of attack and wind speed >> Passive / active dynamic airfoil and planform = flapping twist > flapping frequency and flapping amplitude = percentage of downpour time

[0121] Corresponding optimization measures to increase lift include:

[0122] (1) Increasing wind speed and angle of attack is the simplest and most effective way to increase lift. However, wind speed and angle of attack will increase drag and power consumption. Therefore, considering the constraints of drag and power consumption, increasing wind speed and angle of attack can increase lift.

[0123] (2) Design passive / active dynamic airfoils and planform shapes to maximize lift;

[0124] (3) Design a suitable torsional motion, such as using a downward-thrusting and upward-torsional motion to increase lift, but this will also increase drag. Therefore, torsional motion design should be carried out under drag constraints.

[0125] (4) Use small wing feathers to increase lift.

[0126] Considering the order of importance of the factors affecting thrust:

[0127] Flapping frequency and amplitude >> Passive / active dynamic airfoil and planform = Flapping twist = Angle of attack > Flutter time percentage

[0128] Corresponding optimization measures to increase thrust include:

[0129] (1) Increasing the flapping frequency and flapping amplitude is the simplest and most effective measure to increase thrust, but it will increase power consumption. Therefore, under the condition of power consumption constraint, increasing the flapping frequency and flapping amplitude can increase thrust.

[0130] (2) Maximize thrust by designing passive / active dynamic airfoils and planar shapes;

[0131] (3) By reducing the angle of attack, lift drag is reduced, thereby increasing the remaining thrust;

[0132] (4) The flapping wing twists upward during the upward flapping motion and downward during the downward flapping motion, which can increase thrust;

[0133] (5) Reduce lift drag by designing wingtip slots, thereby increasing residual thrust.

[0134] To simultaneously increase lift and thrust, the following design measures can be taken:

[0135] (1) By designing the torsional motion, it is possible to find a state in which the lift and thrust of the flapping wing increase simultaneously, while having a smaller impact on power consumption.

[0136] (2) By designing the airfoil and planar shape, there will be static airfoil and static planar shape that are optimal for lift, as well as passive / active dynamic airfoil and dynamic planar shape, or static airfoil and static planar shape and passive / active dynamic airfoil and dynamic planar shape that are optimal for thrust.

[0137] (3) Designing appropriate small wing feathers and wingtip slots can also increase lift and thrust at the same time.

[0138] Furthermore, the requirements for lift and thrust can be reduced equivalently through overall shape modification and partial redesign:

[0139] (1) The overall shape design of the aircraft is conducive to reducing pressure difference and frictional resistance, which is equivalent to reducing the requirements for wing thrust, and only incurring some weight costs.

[0140] (2) The partial modification design at the wing-body junction creates an additional fixed lifting surface by connecting the fuselage and flapping wing, which increases lift and is equivalent to reducing the lift requirements of the wing.

[0141] Based on the above analysis, we present a design flow for biomimetic aircraft flapping wing design parameters or measures that effectively combine thrust and lift while maintaining low power consumption and feasibility, tailored to specific performance and functional requirements. Based on this flow, one can obtain a high-thrust, high-lift flapping wing design scheme that macroscopically best meets the performance and functional requirements of the biomimetic aircraft, relying on less CFD calculation and detailed experimental analysis.

[0142] Step 1: Determine the basic thrust and lift design constraints based on the mission requirements, and determine the priority of lift and thrust considerations during the design process;

[0143] The requirements here include user requirements or experimental verification requirements; the basic thrust and lift design constraints mentioned above include weight (such as takeoff weight, payload weight), size (such as maximum span), performance (such as cruise speed, maximum speed, wind resistance, flight distance, mission time, and endurance), attitude change capability (such as hovering, high-speed dive, and level flight), feasibility, and the impact of phased goals (i.e., the current design goals of the prototype, excluding future upgrade performance indicators).

[0144] Step 2: Based on the momentum theorem, the design parameters affecting thrust and lift are transformed into contributions to the horizontal thrust and vertical lift of the flapping wing. Based on the thrust and lift design constraints determined in Step 1, design parameters that satisfy the thrust and lift design constraints are selected.

[0145] Step 3: For the design parameters selected in Step 2, considering the impact of power consumption, further filter the design parameters and determine the corresponding design measures to reduce power consumption;

[0146] Step 4: Perform a feasibility analysis on the design measures corresponding to the design parameters further selected in Step 3 to obtain the design parameters and corresponding design measures after considering feasibility.

[0147] Step 5: Based on the priority of lift and thrust considerations determined in Step 1, sort the design parameters obtained in Step 4 by importance, optimize the design measures of the corresponding design parameters according to their importance, and obtain the preliminary design scheme of the bird flapping wing.

[0148] To better explain the purpose and advantages of the present invention, the present invention is described below with reference to a specific embodiment:

[0149] Step 1: Determine the basic thrust and lift design constraints based on the mission requirements, and determine the priority of considering lift and thrust during the design process.

[0150] In this embodiment, the mission requirement is long-duration flight; therefore, the aircraft weight *m* is determined first, and the lift during cruise is designed to be *L*. The design philosophy is to minimize power consumption *P* while meeting the lift requirement. Under size constraints, the following structure is constructed: Figure 5 The flapping wing planform is shown. The root chord length of the flapping wing is 1.0c (c = 0.082m), the wingtip chord length is 0.4c, the span is 3.6c, and the inner arm section and the outer hand section are the same length, both 1.8c.

[0151] Step 2: Based on the momentum theorem, the design parameters affecting thrust and lift are transformed into contributions to the horizontal thrust and vertical lift of the flapping wing. Based on the thrust and lift design constraints determined in Step 1, design parameters that satisfy the thrust and lift design constraints are selected.

[0152] Here, based on the wing model established in step 1, kinematic modeling of the flapping wing motion is performed to determine the kinematic parameters describing the wing. According to the momentum theorem, the influence of each design parameter on thrust and lift is analyzed, and design parameters and measures that satisfy the thrust and lift design constraints are selected, including the angle of attack α and wind speed V. ∞ The parameters include: passive / active dynamic airfoil and planform shape, twist angle θ, flapping frequency f and flapping amplitude φ, and the proportion of flapping time.

[0153] The sources of lift during cruise can be roughly determined, specifically as follows:

[0154]

[0155] In the formula, "-" represents the upward movement and "+" represents the downward movement. Considering the design measures of the passive / active dynamic airfoil and plane shape, the airfoil area during upward movement becomes S=(l-Δl)c, which reduces the negative lift.

[0156] Step 3: For the design parameters selected in Step 2, considering the impact of power consumption, further filter the design parameters and determine the corresponding design measures to reduce power consumption;

[0157] Since the mission requires minimizing power consumption during extended flight and the flapping parameters have a relatively small impact on lift, the first consideration is to appropriately limit the flapping frequency f and flapping amplitude φ, and select a suitable twist angle θ to reduce the projected wing area during vertical flapping. Secondly, the passive / active dynamic airfoil and planform shape are optimized, particularly the arm wings, which are the main lift-generating components, including airfoil shape, chord length, and materials. Furthermore, designs such as spanwise bending and in-plane contraction are considered to further reduce the projected wing area during upward flapping.

[0158] Step 4: Perform a feasibility analysis on the design measures corresponding to the design parameters further selected in Step 3 to obtain the design parameters and corresponding design measures after considering feasibility.

[0159] In this embodiment, the flapping frequency f and flapping amplitude φ, passive / active dynamic airfoil and planar shape are used as design parameters, and the corresponding design measures have a high degree of feasibility.

[0160] Step 5: Based on the priority of lift and thrust considerations determined in Step 1, the design parameters obtained in Step 4 are ranked by importance, and the design measures for the corresponding design parameters are optimized according to their importance. In this embodiment, the main design consideration is to increase thrust, and finally the preliminary design scheme of the bird-like flapping wing is obtained.

[0161] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A bird-inspired flapping wing design method based on momentum theorem analysis of thrust influencing factors, characterized in that: Includes the following steps: Step 1: Determine the thrust and lift design constraints based on the mission requirements, and determine the priority of considering lift and thrust during the design process; Step 2: Based on the momentum theorem, the design parameters affecting thrust and lift are transformed into contributions to the horizontal thrust and vertical lift of the flapping wing. Based on the thrust and lift design constraints determined in Step 1, design parameters that satisfy the thrust and lift design constraints are selected. Step 3: For the design parameters selected in Step 2, considering the impact of power consumption, further filter the design parameters and determine the corresponding design measures to reduce power consumption; Step 4: Perform a feasibility analysis on the design measures corresponding to the design parameters further selected in Step 3 to obtain the design parameters and corresponding design measures after considering feasibility. Step 5: Based on the priority of lift and thrust considerations determined in Step 1, sort the design parameters obtained in Step 4 by importance, optimize the design measures of the corresponding design parameters according to their importance, and obtain the preliminary design scheme of the bird flapping wing.

2. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 1, characterized in that: In step 2, the design parameters that affect thrust and lift include: passive / active dynamic airfoil and planform shape, flapping wing twist angle, flapping frequency and flapping amplitude, descent time ratio, angle of attack and velocity, and small-scale flow control.

3. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 2, characterized in that: The design measures corresponding to each design parameter are as follows: Passive / active dynamic airfoils and planforms: Maximize thrust and / or lift by designing airfoils and planforms; improve thrust by designing flexible airfoils; reduce negative lift and power consumption during flapping by designing spanwise folding wings to improve lift; Flapping wing twist angle: By designing twisting motion, thrust and lift are improved, and power consumption is reduced; Flapping frequency and amplitude: Within a certain range, increasing the flapping frequency and amplitude can increase the thrust, but it will lead to a significant increase in power consumption. Dive time percentage: The power consumption is lowest when the dive time percentage is equal to 0.5 ± 0.

05. Angle of attack and speed: Increasing wind speed and angle of attack can increase lift, but will correspondingly increase drag and power consumption; Small-scale flow control includes small winglets and wingtip slots; using small winglets can increase lift, while using wingtip slots can reduce lift-induced drag, thereby increasing residual thrust.

4. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 2, characterized in that: The design measures to reduce power consumption include: (1) Control the flapping frequency and flapping amplitude. While meeting the design requirements for thrust and lift, reduce the flapping frequency and flapping amplitude. (2) Design passive / active dynamic airfoils and planform shapes to reduce the weight of flapping wings while meeting lift design requirements; (3) By designing the torsion angle, the downward and upward torsion can be achieved, thereby reducing the projected wing area during the up-and-down flapping and reducing power consumption; (4) By designing the flapping wing to bend along the span and to contract the wing surface inward, the projected wing area during the flapping motion is changed, thereby reducing the work done by the negative lift. (5) Control the angle of attack and wind speed while meeting the lift design requirements.

5. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 1, characterized in that: In step 4, the feasibility analysis considers factors such as: achieving the design function, energy conversion rate per unit weight, structural reliability, and control difficulty brought about by multi-degree-of-freedom design.

6. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 5, characterized in that: After conducting a feasibility analysis, the ease or difficulty of implementing the corresponding design measures for each design parameter is as follows: 。 7. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 1, characterized in that: In step 5, considering the importance of design factors affecting lift, the order is: angle of attack and wind speed >> passive / active dynamic airfoil and plane shape = flapping twist > flapping frequency and flapping amplitude = descent time percentage; considering the importance of design factors affecting thrust, the order is: flapping frequency and flapping amplitude >> passive / active dynamic airfoil and plane shape = flapping twist = angle of attack > descent time percentage.

8. The bird-like flapping wing design method based on momentum theorem analysis of thrust influencing factors as described in claim 7, characterized in that: Optimization measures to increase lift include: (1) Under the constraints of drag and power consumption, increase wind speed and angle of attack to increase lift; (2) Design passive / active dynamic airfoils and planforms to maximize lift; (3) Considering the resistance constraint, design the torsional motion; (4) Use small wing feathers to increase lift; Optimization measures to increase thrust include: (1) Under the condition of power consumption constraint, increase the flapping frequency and flapping amplitude to increase thrust; (2) Adopt an upward-thrusting and downward-thrusting method to increase thrust; (3) Maximize thrust by designing passive / active dynamic airfoils and planar shapes; (4) By reducing the angle of attack, lift drag is reduced, thereby increasing the remaining thrust; (5) By designing wingtip slots, lift-induced drag is reduced, thereby increasing residual thrust.

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