Flexible wing structure design method based on aerodynamic optimization result

Abstract

The invention belongs to the field of aircraft structure design, and particularly relates to a flexible wing structure design method based on an aerodynamic optimization result. The method comprises the following steps: step 1, acquiring initial geometric parameters of a flapping-wing aircraft, and constructing a three-dimensional flapping-wing model based on the initial geometric parameters; 2, constructing a flapping wing motion model of the flapping wing three-dimensional model; 3, finite element aerodynamic force calculation is carried out according to the flapping wing three-dimensional model and the flapping wing motion model, and a torsion angle corresponding to the optimal aerodynamic state is obtained; 4, constructing a topological optimization model of the flapping wing according to the torsion angle, and carrying out topological optimization on the topological optimization model of the flapping wing; and 5, designing a flapping wing structure according to a topological optimization result. The advantages of computational fluid mechanics and computational structural mechanics simulation are fully exerted, the cost brought by a large amount of repeated experimental work in the flapping wing design is effectively reduced, and a more effective guiding means is provided for the design of the flapping wing with efficient aerodynamic performance.

Description

Technical Field

[0001] The present application belongs to the field of aircraft structure design, and in particular relates to a flexible wing structure design method based on aerodynamic optimization results. Background Art

[0002] Bionic flapping-wing aircraft have significant advantages and application potential in environmental monitoring and covert reconnaissance due to their unique flight mechanism and aerodynamic shape, as well as high maneuverability at small size and low Reynolds number.

[0003] Unlike traditional fixed-wing aircraft, flapping-wing aircraft rely on the flexible deformation of the wings during flapping to generate thrust and lift during forward flight. The flapping wings of flexible structures usually undergo chord-wise deformation distributed along the span direction, thereby changing the local angle of attack at different span-wise positions, thereby significantly increasing thrust. In recent years, a large number of studies on the flexible characteristics of flapping-wing structures have shown that flapping wings with suitable stiffness distribution and movement mode can generate ideal lift and thrust. In theory, there is a suitable structural deformation range for flapping wings, within which the aerodynamic characteristics can be effectively improved. In the design of flapping-wing aircraft, it is necessary to conduct a comprehensive study of aerodynamics, flight dynamics, kinematics, and flexible structural characteristics to obtain high-performance flapping-wing aircraft. However, the current design method of flapping-wing aircraft still has the problems of long design cycle and high cost.

[0004] Therefore, it is desired to have a technical solution to overcome or at least alleviate at least one of the above-mentioned defects of the prior art. Summary of the invention

[0005] The purpose of this application is to provide a flexible wing structure design method based on aerodynamic optimization results to solve at least one problem existing in the prior art.

[0006] The technical solution of this application is: A flexible wing structure design method based on aerodynamic optimization results, comprising: Step 1: obtaining initial geometric parameters of the flapping-wing aircraft, and constructing a flapping-wing three-dimensional model based on the initial geometric parameters; Step 2: constructing a flapping-wing motion model of the flapping-wing three-dimensional model; Step 3: performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain a torsion angle corresponding to an optimal aerodynamic state; Step 4: constructing a flapping wing topology optimization model according to the torsion angle, and performing topology optimization on the flapping wing topology optimization model; Step 5: Design the flapping wing structure based on the topology optimization results.

[0007] In at least one embodiment of the present application, in step 1, obtaining initial geometric parameters of the flapping-wing aircraft includes: Calculate the initial geometric parameters of the flapping-wing aircraft according to the bionic scaling law: ; in, m is the takeoff gross weight of the flapping-wing aircraft, b For the wingspan, S is the flapping wing area, f is the flapping frequency, V minp is the minimum power speed, V maxr is the maximum range speed, V cruise is the cruising speed; Calculate the initial geometric parameters of the flapping-wing aircraft according to the Strouhal number: ; in, S t is the Strouhal number, h is the wing-to-wing motion amplitude, and φ is the flapping amplitude angle.

[0008] In at least one embodiment of the present application, in step 2, a flapping wing motion model of the flapping wing three-dimensional model is constructed, and the flapping wing motion model is: ; ; in, α mb The flapping wingspan is y b The maximum value of the chordal torsion angle is y b is the flapping wing span position, α m is the maximum value of the chord-wise twist angle at the wing tip, α b is the spanwise twist angle, t For the flutter time.

[0009] In at least one embodiment of the present application, in step three, performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain the torsion angle corresponding to the optimal aerodynamic state includes: S31, performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain lift, thrust, torque coefficient, and flapping angular velocity; S32, respectively calculating the average lift coefficient, average thrust coefficient and average power coefficient within a flapping cycle; S33, calculating lift efficiency and propulsion efficiency according to the average lift coefficient, the average thrust coefficient and the average power coefficient; S34. Determine a torsion angle corresponding to an optimal aerodynamic state according to the lift efficiency and the propulsion efficiency.

[0010] In at least one embodiment of the present application, in S32, respectively calculating the average lift coefficient, the average thrust coefficient, and the average power coefficient within a flapping cycle includes: Calculate the instantaneous lift coefficient, instantaneous thrust coefficient and instantaneous power coefficient respectively: ; ; ; in, C L ( t ) is the instantaneous lift coefficient, C T ( t ) is the instantaneous thrust coefficient, C P ( t ) is the instantaneous power coefficient, L ( t ) is the instantaneous lift, T ( t ) is the instantaneous thrust, C mx ( t ) is the instantaneous torque coefficient, ω x ( t ) is the instantaneous flapping angular velocity, is the dynamic pressure, U is the incoming flow velocity; Calculate the average lift coefficient, average thrust coefficient, and average power coefficient in a flapping cycle respectively: ; ; ; in, is the average lift coefficient, is the average thrust coefficient, is the average power factor, T is the flapping cycle.

[0011] In at least one embodiment of the present application, in S33, the lift efficiency and the propulsion efficiency are calculated according to the average lift coefficient, the average thrust coefficient, and the average power coefficient, including: The lift efficiency is: ; The propulsion efficiency is: ; in, is the lift efficiency, To promote efficiency.

[0012] In at least one embodiment of the present application, in step 4, constructing a flapping wing topology optimization model according to the torsion angle, and performing topology optimization on the flapping wing topology optimization model, including: Constructing a flapping wing topology optimization model according to the torsion angle; Determine the topology optimization conditions of the flapping wing topology optimization model, wherein the topology optimization conditions include: The aerodynamic load is the lift and thrust obtained in step S31; The optimization target is the torsion angle corresponding to the optimal aerodynamic state obtained in step S34; The constraint range is that the leading edge of the flapping wing has no torsional deformation and the root of the flapping wing has no torsional deformation; The flapping wing topology optimization model is topologically optimized according to the topology optimization conditions.

[0013] The invention has at least the following beneficial technical effects: The flexible wing structure design method based on aerodynamic optimization results of the present application constructs a flapping wing motion model, conducts a study on the flexible deformation of the flapping wing when the flapping wing aircraft has the best aerodynamic efficiency, constructs a flapping wing topology optimization model, and obtains a flapping wing structure design scheme using topology optimization technology. The advantages of computational fluid dynamics and computational structural mechanics simulation are fully utilized, the cost of a large amount of repetitive experimental work in flapping wing design is effectively reduced, and a more effective guiding means is provided for the design of flapping wings with efficient aerodynamic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of a flexible wing structure design method based on aerodynamic optimization results according to an embodiment of the present application; Figure 2 is a schematic diagram of a flapping wing three-dimensional model of an embodiment of the present application; Figure 3 is a flapping wing motion model of one embodiment of the present application; Figure 4 It is a schematic diagram of the movement law of a flapping wing cross section according to an embodiment of the present application; Figure 5 This is a curve diagram showing the relationship between propulsion efficiency and torsion angle according to one embodiment of the present application. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the implementation of this application clearer, the technical scheme in the embodiment of this application will be described in more detail below in conjunction with the drawings in the embodiment of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of them. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be construed as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0016] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present application.

[0017] The following is combined with Figures 1 to 5 This application is described in further detail.

[0018] This application provides a flexible wing structure design method based on aerodynamic optimization results, such as Figure 1 As shown, the following steps are included: Step 1: obtaining initial geometric parameters of the flapping-wing aircraft, and constructing a flapping-wing three-dimensional model based on the initial geometric parameters; Step 2, constructing a flapping wing motion model of the flapping wing three-dimensional model; Step 3: Perform finite element aerodynamic calculation based on the flapping wing three-dimensional model and the flapping wing motion model to obtain the torsion angle corresponding to the optimal aerodynamic state; Step 4: construct a flapping wing topology optimization model according to the torsion angle, and perform topology optimization on the flapping wing topology optimization model; Step 5: Design the flapping wing structure based on the topology optimization results.

[0019] In the flexible wing structure design method based on aerodynamic optimization results of the present application, in step 1, first, the initial geometric parameters of the flapping-wing aircraft are obtained by two methods. In this embodiment, the bionic scaling law of flying organisms in nature is obtained, see Table 1.

[0020] Table 1

[0021] According to the practical experience of flapping-wing aircraft, the average value of the minimum power speed and the maximum range speed calculated by the bionic scaling law is used as the cruising speed of the flapping-wing aircraft to ensure that the flapping-wing aircraft can reach the selected cruising speed.

[0022] Specifically, the initial geometric parameters of the flapping-wing aircraft are calculated according to the bionic scaling law: ; in, m is the takeoff gross weight of the flapping-wing aircraft, b For the wingspan, S is the flapping wing area, f is the flapping frequency, V minp is the minimum power speed, V maxr is the maximum range speed, V cruise is the cruising speed; There is no calculation formula for the flapping amplitude angle in the bionic scaling law, so the Strouhal number is used. S t To do a rough calculation.

[0023] Calculate the initial geometric parameters of the flapping-wing aircraft according to the Strouhal number: ; in, S t is the Strouhal number, h is the wing-to-wing motion amplitude, and φ is the flapping amplitude angle.

[0024] Research shows S t = 0.2 to 0.4, the propulsion efficiency of the flapping motion is the highest. In this embodiment, S t =0.3 for calculation.

[0025] Take-off gross weight m =30g as an example, the initial geometric parameters of the flapping-wing aircraft obtained according to the above method are shown in Table 2.

[0026] Table 2

[0027] In this embodiment, the flapping wing three-dimensional model constructed based on the initial geometric parameters is as follows: Figure 2 As shown, the aerodynamic surface of the model is preferably designed with rounded corners.

[0028] In the flexible wing structure design method based on aerodynamic optimization results of the present application, in step 2, a flapping wing motion model of a flapping wing three-dimensional model is constructed. The flapping wing motion model is established according to the actual flapping deformation law of the flapping wing aircraft. In this embodiment, the flapping wing motion model has one degree of freedom, and the flapping wing performs a waving motion around the wing root. The flapping wing deformation mode is represented by a torsion angle. The torsion angle of the flapping wing gradually increases from the wing root to the wing tip, and as the span increases, the torsion angle increases linearly. Figure 3 It is the motion model of the flapping wing in the up-flapping and down-flapping stages respectively when the maximum value of the chord-wise twist angle at the wingtip position is 20°, wherein the incoming flow direction is consistent with the X-axis direction and the span direction of the flapping wing, and the flapping wing is twisted and deformed around the leading edge.

[0029] The motion law of the flapping wing three-dimensional model with spanwise torsion is explained by the change of the torsion angle with the span length and the change of the torsion angle with time. The flapping wing motion model is: ; ; in, α mb The flapping wingspan is y b The maximum value of the chordal torsion angle is y b is the flapping wing span position, α m is the maximum value of the chord-wise twist angle at the wing tip, α b is the spanwise twist angle, t For the flutter time.

[0030] The twist angle of a flapping wing with spanwise twist from the wing root to the wing tip at the same moment is proportional to the span, that is, the flapping wing has a chord-wise flexible deformation distributed along the span during the flapping motion, and the twist amplitude angle is the largest when the flapping wing is in the middle position between the upward and downward flaps. Figure 4 Schematic diagram of the flapping wing cross-sectional motion at the wing root and wing tip, where the cross-sectional deformation is a twist around the leading edge of the flapping wing.

[0031] In the flexible wing structure design method based on aerodynamic optimization results of the present application, in step three, finite element aerodynamic calculation is performed based on the flapping wing three-dimensional model and the flapping wing motion model to obtain the torsion angle corresponding to the optimal aerodynamic state. A flapping wing finite element model with different spanwise torsion is constructed based on the flapping wing three-dimensional model and the flapping wing motion model, and the CFD finite element solution method is used to analyze the aerodynamic force exerted on the aerodynamic surface of the flapping wing under the specified motion law. The dynamic mesh technology is used to calculate the unsteady aerodynamic force during the finite element solution. The effect of the torsion angle on the performance of the flapping wing three-dimensional model with spanwise torsion motion during flapping is analyzed, wherein the maximum torsion angle at the wingtip position gradually increases from 0° until the aerodynamic efficiency of the flapping wing reaches the optimal state. At this time, the flexible deformation of the flapping wing is the result after aerodynamic optimization, and the torsion angle corresponding to the optimal aerodynamic state is recorded.

[0032] Specifically, finite element aerodynamic calculation is performed based on the flapping wing three-dimensional model and the flapping wing motion model to obtain the torsion angle corresponding to the optimal aerodynamic state, including: S31, performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain lift, thrust, torque coefficient, and flapping angular velocity; The aerodynamic parameters of the flapping wing surface can be obtained through CFD finite element solution. When gliding with a fixed wingspan, the flapping wing area remains unchanged and the aerodynamic force will reach a stable value. S32, respectively calculating the average lift coefficient, average thrust coefficient, and average power coefficient within a flapping cycle, including: Calculate the instantaneous lift coefficient, instantaneous thrust coefficient and instantaneous power coefficient respectively: ; ; ; in, C L ( t ) is the instantaneous lift coefficient, C T ( t ) is the instantaneous thrust coefficient, C P ( t ) is the instantaneous power coefficient, L ( t ) is the instantaneous lift, T ( t ) is the instantaneous thrust, C mx ( t ) is the instantaneous torque coefficient, ω x ( t ) is the instantaneous flapping angular velocity, is the dynamic pressure, U is the incoming flow velocity; When flapping with a fixed wingspan, the flapping area remains unchanged, and flapping consumes power. Flapping wings generate lift and thrust at the same time. The aerodynamic force also changes periodically with periodic flapping. Considering the overall aerodynamic characteristics of the flapping wing, pay attention to the average lift, thrust and power characteristics; Calculate the average lift coefficient, average thrust coefficient, and average power coefficient in a flapping cycle respectively: ; ; ; in, is the average lift coefficient, is the average thrust coefficient, is the average power factor, T is the flapping cycle.

[0033] S33. Calculate lift efficiency and propulsion efficiency based on the average lift coefficient, average thrust coefficient and average power coefficient, including: In order to obtain the relationship between the aerodynamic force and input power generated by flapping wings with different geometric parameters, the lift efficiency and propulsion efficiency are calculated; The lift efficiency is: ; The propulsion efficiency is: ; in, is the lift efficiency, To promote efficiency.

[0034] S34. Determine the torsion angle corresponding to the optimal aerodynamic state according to the lift efficiency and the propulsion efficiency.

[0035] In this embodiment, the calculation result of the relationship between the propulsion efficiency and the chord-wise twist angle at the wing tip position is as follows: Figure 5 As shown in the figure, according to the calculation results, it can be concluded that the propulsion efficiency is the highest when the maximum value of the chord-wise twist angle at the wing tip is 20°. The maximum value of the chord-wise twist angle at the wing tip corresponding to the optimal aerodynamic state is recorded. α m , in the figure α is the chord-wise twist angle at the wingtip.

[0036] The flexible wing structure design method based on aerodynamic optimization results of the present application, in step 4, constructs a flapping wing topology optimization model according to the torsion angle, and performs topology optimization on the flapping wing topology optimization model, including: Construct a flapping wing topology optimization model based on the twist angle; Determine the topology optimization conditions of the flapping wing topology optimization model. The topology optimization conditions include: The aerodynamic load is the lift and thrust obtained in step S31; The optimization target is the torsion angle corresponding to the optimal aerodynamic state obtained in step S34; The constraint range is that the leading edge of the flapping wing has no torsional deformation and the root of the flapping wing has no torsional deformation; The flapping wing topology optimization model is topologically optimized according to the topology optimization conditions.

[0037] In a preferred embodiment of the present application, a flapping wing topology optimization model is constructed according to the torsion angle corresponding to the optimal aerodynamic state obtained in step 3. Under various topology optimization conditions, a structural optimization analysis is performed on the flexible deformation at the middle moment of the flapping cycle after stable flapping. At this time, the flexible flapping wing is at the moment of maximum deformation in the flapping cycle, and under this flexible deformation, the flapping wing has the best aerodynamic efficiency. In this embodiment, the motion state at the middle moment corresponding to the maximum value of the chord-wise torsion angle at the wing tip position of 20° is used as the topology optimization object. In this motion state, the aerodynamic load on the flapping wing surface is the lift calculated in step 3, the leading edge and the wing root are fixed constraints, and the optimization target is the maximum value of the chord-wise torsion angle at the wing tip position of 20°, and topology optimization is performed.

[0038] The present application discloses a flexible wing structure design method based on aerodynamic optimization results. In step five, the rib structure layout of the flapping wing is designed in combination with the topology optimization results, and a flapping wing with efficient aerodynamic performance is designed according to the force transmission results obtained by the topology optimization.

[0039] The flexible wing structure design method based on aerodynamic optimization results of the present application calculates the basic geometric design parameters of the flapping wing by observing the bionic scaling law of flying organisms in nature, summarizes the motion law of the flexible flapping wing and establishes the deformation equation of the flexible wing, establishes an unsteady aerodynamic model of the flexible flapping wing by CFD, analyzes the aerodynamic characteristics of the flapping wing during forward flight by CFD numerical simulation method, and obtains the influence of the flexible deformation of the flapping wing on the aerodynamic performance, and obtains the flexible deformation mode of the flapping wing with better aerodynamic characteristics by summarizing the influence law and mechanism of the parameters, proposes an optimization plan for the structural design of the flapping wing based on the aerodynamic optimization results, and obtains the force transmission plan of the flexible flapping wing in combination with the topology optimization technology, thereby providing guidance for the design of flexible flapping wing structures with better aerodynamic performance for flapping wing aircraft.

[0040] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A flexible wing structure design method based on aerodynamic optimization results, characterized in that: include: Step 1: obtaining initial geometric parameters of the flapping-wing aircraft, and constructing a flapping-wing three-dimensional model based on the initial geometric parameters; Step 2: constructing a flapping-wing motion model of the flapping-wing three-dimensional model; Step 3: performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain a torsion angle corresponding to an optimal aerodynamic state; Step 4: constructing a flapping wing topology optimization model according to the torsion angle, and performing topology optimization on the flapping wing topology optimization model; Step 5: Design the flapping wing structure based on the topology optimization results.

2. The flexible wing structure design method based on aerodynamic optimization results according to claim 1 is characterized in that: In step 1, the initial geometric parameters of the flapping-wing aircraft are obtained, including: Calculate the initial geometric parameters of the flapping-wing aircraft according to the bionic scaling law: ； in, m is the takeoff gross weight of the flapping-wing aircraft, b For the wingspan, S is the flapping wing area, f is the flapping frequency, V minp is the minimum power speed, V maxr is the maximum range speed, V cruise is the cruising speed; Calculate the initial geometric parameters of the flapping-wing aircraft according to the Strouhal number: ； in, S t is the Strouhal number, h is the wing-to-wing motion amplitude, and φ is the flapping amplitude angle.

3. The flexible wing structure design method based on aerodynamic optimization results according to claim 2 is characterized in that: In step 2, a flapping wing motion model of the flapping wing three-dimensional model is constructed, and the flapping wing motion model is: ； ； in, α mb The flapping wingspan is y b The maximum value of the chordal torsion angle is y b is the flapping wing span position, α m is the maximum value of the chord-wise twist angle at the wing tip, α b is the spanwise twist angle, t For the flutter time.

4. The flexible wing structure design method based on aerodynamic optimization results according to claim 3 is characterized in that: In step three, finite element aerodynamic calculation is performed according to the flapping wing three-dimensional model and the flapping wing motion model to obtain the torsion angle corresponding to the optimal aerodynamic state, including: S31, performing finite element aerodynamic calculation according to the flapping wing three-dimensional model and the flapping wing motion model to obtain lift, thrust, torque coefficient, and flapping angular velocity; S32, respectively calculating the average lift coefficient, average thrust coefficient and average power coefficient within a flapping cycle; S33, calculating lift efficiency and propulsion efficiency according to the average lift coefficient, the average thrust coefficient and the average power coefficient; S34. Determine a torsion angle corresponding to an optimal aerodynamic state according to the lift efficiency and the propulsion efficiency.

5. The flexible wing structure design method based on aerodynamic optimization results according to claim 4 is characterized in that: In S32, the average lift coefficient, average thrust coefficient, and average power coefficient within a flapping cycle are calculated respectively, including: Calculate the instantaneous lift coefficient, instantaneous thrust coefficient and instantaneous power coefficient respectively: ； ； ； in, C L ( t ) is the instantaneous lift coefficient, C T ( t ) is the instantaneous thrust coefficient, C P ( t ) is the instantaneous power coefficient, L ( t ) is the instantaneous lift, T ( t ) is the instantaneous thrust, C mx ( t ) is the instantaneous torque coefficient, ω x ( t ) is the instantaneous flapping angular velocity, is the dynamic pressure, U is the incoming flow velocity; Calculate the average lift coefficient, average thrust coefficient, and average power coefficient in a flapping cycle respectively: ； ； ； in, is the average lift coefficient, is the average thrust coefficient, is the average power factor, T is the flapping cycle.

6. The flexible wing structure design method based on aerodynamic optimization results according to claim 5 is characterized in that: In S33, the lift efficiency and the propulsion efficiency are calculated according to the average lift coefficient, the average thrust coefficient and the average power coefficient, including: The lift efficiency is: ； The propulsion efficiency is: ； in, is the lift efficiency, To promote efficiency.

7. The flexible wing structure design method based on aerodynamic optimization results according to claim 6 is characterized in that: In step 4, a flapping wing topology optimization model is constructed according to the torsion angle, and topology optimization is performed on the flapping wing topology optimization model, including: Constructing a flapping wing topology optimization model according to the torsion angle; Determine the topology optimization conditions of the flapping wing topology optimization model, wherein the topology optimization conditions include: The aerodynamic load is the lift and thrust obtained in step S31; The optimization target is the torsion angle corresponding to the optimal aerodynamic state obtained in step S34; The constraint range is that the leading edge of the flapping wing has no torsional deformation and the root of the flapping wing has no torsional deformation; The flapping wing topology optimization model is topologically optimized according to the topology optimization conditions.

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