CN111611652A - Flapping wing aerodynamic characteristic analysis method based on active flexible deformation - Google Patents

Flapping wing aerodynamic characteristic analysis method based on active flexible deformation Download PDF

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CN111611652A
CN111611652A CN202010498481.9A CN202010498481A CN111611652A CN 111611652 A CN111611652 A CN 111611652A CN 202010498481 A CN202010498481 A CN 202010498481A CN 111611652 A CN111611652 A CN 111611652A
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汪忠来
张晏玮
郑皓
路腾
岳宁远
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University of Electronic Science and Technology of China
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Abstract

The invention discloses a flapping wing aerodynamic characteristic analysis method based on active flexible deformation, which comprises the following steps of: s1, establishing a wing three-dimensional model and a flow field grid of flapping wing motion; s2, dividing grids and refining fit grids; s3, selecting a turbulence model according to the actual situation of the flight environment, determining boundary conditions, and performing UDF editing and moving grid setting according to the coupled motion of flapping wing heave-pitch and the active flexible deformation rule of the trailing edge; s4, calculating lift force and drag coefficient; and S5, changing different flapping wing frequencies and flexible deformation coefficients, and performing comparative analysis on lift resistance coefficients. The invention obtains the aerodynamic characteristics of the biological thin wing under the actual condition by bionic simulation of the composite motion of the combination of the heave-pitch of the real wing and the active flexible deformation of the trailing edge. And the relation between the average lift-drag coefficient and the frequency and the flexible deformation coefficient is calculated and analyzed by comparing different flapping wing frequencies and flexible deformation coefficients, so that the most suitable flapping wing frequency and flexible deformation coefficient are selected preferably.

Description

Flapping wing aerodynamic characteristic analysis method based on active flexible deformation
Technical Field
The invention belongs to the field of flight mechanics, and particularly relates to an analysis method for aerodynamic characteristics of a flapping wing based on active flexible deformation.
Background
With the rapid development of scientific technology, the aviation industry technology has been widely applied in the fields of civilian use, military use, national defense and the like. Aircrafts, represented by airplanes, have become an important tool indispensable to human life and civilization development. The design direction of the present and future aircrafts is to expect that the aircrafts are small, portable and carried about, can realize low-altitude flight like insects or birds, and can skillfully complete self reconnaissance or search tasks and the like. For many years, research on unmanned aerial vehicles with military use as a main background has been active, and the unmanned aerial vehicles realize task planning and track generation of the unmanned aerial vehicles through ground base remote control navigation or through self intelligent control algorithms to complete preset flight tasks.
At present, three flight modes of a micro aircraft are provided, namely a fixed wing flight mode, a rotor wing flight mode and a flapping wing flight mode. The flapping wing flight is a bionic flapping wing flight mode of a novel aircraft which is designed and manufactured based on the bionics principle and simulates bird and insect flight. If the aircraft is developed successfully, compared with the aircraft which is fixed and flies with a rotor wing, the aircraft has unique advantages: such as take-off in situ or in small field, excellent flight maneuverability and hovering performance and low flight cost, can integrate the lifting, hovering and propelling functions into a flapping wing system, can complete long-distance flight by using less energy, and is more suitable for completing flight tasks under the conditions of no energy supplement for a long time and long distance. However, the flapping wing flying mode is adopted in the natural flying creatures without exception, so that the flapping wing flying is more advantageous than the fixed wing flying and the rotor wing flying according to the research results of bionics and aerodynamics, and the micro bionic flapping wing aircraft has a dominant position in the research field. From the above, in the micro aircraft, the unique advantages of the bionic flapping wing aircraft determine that the bionic flapping wing aircraft has wide application potential space in the future civil, military and national defense fields.
The huge application prospect stimulates the continuous exploration of the human beings on the natural creatures and the movement capacity thereof, so as to develop more advanced aircrafts and underwater vehicles. The numerical simulation has the advantages of strong repeatability, simple force measurement, capability of obtaining more flow field information and the like, makes up for the defects of experimental research and theoretical analysis, and gradually becomes a hotspot of the current bionic motion research. The aerodynamics of the micro aircraft and the large aircraft are greatly different, the flying Reynolds number of the conventional aircraft is in the order of magnitude, the aerodynamic design of the conventional aircraft tends to be mature, but the flying speed of the micro aircraft is only dozens of kilometers, the flying Reynolds number is only in the order of magnitude of 1000, even lower, the micro aircraft flies at such a low Reynolds number, and the aerodynamic characteristics of the micro aircraft are highlighted as follows: the pneumatic viscous force and the resistance are more outstanding; the negative surface layer of the machine body tends to the laminar flow characteristic easily; the phenomenon that the boundary layer of the wing is separated from the wing is easy to occur, so that the lift force is lost; aerodynamic stability and control of its attitude are difficult to achieve, etc. Conventional fixed-wing and rotor flight mechanisms and design methods are not suitable for micro-aircraft, so new conditions must be considered to study the flapping situation.
The aerodynamic characteristics of the flapping wings have been studied as early as the 20 th century. Knoller and Betz explain the ability of a bird to produce thrust through flapping wings, so the first realized that a flapping wing can produce lift as well as thrust. This phenomenon is now also referred to as the Knoller-Betz effect. However, due to the strong unsteady characteristic of the flapping wing flow field, it is very difficult to find an accurate analytic solution of the flow field. One begins to seek an approximate solution for the flapping wing flow field. One uses a simplified model based on the assumption of a quasi-steady (quasi-steady) to approximately analyze the aerodynamic force of the flapping wings. In the quasi-stationary model, the motion of the flapping wing is dispersed into a series of stationary postures according to time, and at each moment, the instantaneous aerodynamic force of the flapping wing at the moment is assumed to be equal to the aerodynamic force generated by the stationary wing with the same posture under the stationary condition, and finally, the aerodynamic force at each moment is calculated according to the time to be regarded as the variation condition of the aerodynamic force of the flapping wing. The method for calculating by discretizing the abnormal flow field into the continuous constant flow field does not consider the abnormal influence of the flow field, which is exactly the most important part of the flapping wing flow field and can not be ignored absolutely. Theodorseen et al studied the application of unsteady flow theory in the field of unsteady aerodynamic forces of fixed wings. The theory assumes that the vortices at the airfoil surface and wake zone are infinitely thin. This assumption is also applicable to high Reynolds number flows where the effect on vortices is mainly concentrated in the boundary layer, but as the Reynolds number decreases, the viscous effect and diffusion increases and the theory no longer applies to large amplitude unsteady motion. In recent years, with the development of cfd (computed Fluid dynamics) technology, the non-compressible flow through an arbitrary shape of flapping wing is calculated by surface element method of eddy and dipole on the surface of the flapping wing, so that the influence of the thickness and camber of the flapping wing can be considered, thereby replacing the previous Theodorsen flapping theory of thin wings. Binning, while taking into account the effects of airfoil thickness and removing the assumption of infinitely thin wake regions, the singularity distribution of the vortices still limits the effects of the vortices to near the airfoil and in the wake regions and small areas. And with the rapid development of the computer technology, the computing capability of the computer is greatly enhanced, and the method for solving the N-S equation can be used for analyzing the flapping wing flow field, so that the viscous influence of the flapping wing flow field can be considered. Meanwhile, researchers begin to try to analyze the flow field difference of flapping wing flight by a method of solving a complete N-S equation, and certain achievement is achieved.
In conclusion, the rigidity experiment and numerical research have achieved some valuable results, but in the flying process of actual insects or birds, the wings will deform flexibly due to the aerodynamic effect. However, the present numerical calculation method for the propulsion efficiency of the flexible flapping wing has not been systematically and completely described, and the understanding of the intrinsic mechanism of the propulsion performance changing with parameters is lacked. On the other hand, the numerical simulation of bionic flow such as flapping wings often involves a complex moving boundary problem, and the efficient and accurate solution of the problem is always a difficult point of computational fluid mechanics.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for obtaining the aerodynamic characteristics of a biological thin wing under the actual condition by biomimetically simulating the combined compound motion of heave-pitch of a real wing and active flexible deformation of a trailing edge; and comparing different flapping wing frequencies and flexible deformation coefficients, and calculating and analyzing the relation between the average lift drag coefficient and the frequency and the flexible deformation coefficient, thereby optimizing the most suitable flapping wing frequency and flexible deformation coefficient and optimizing the flapping wing aerodynamic characteristic analysis method based on the active flexible deformation.
The purpose of the invention is realized by the following technical scheme: an active flexible deformation-based flapping wing aerodynamic characteristic analysis method comprises the following steps:
s1, establishing a wing three-dimensional model and a flow field grid of flapping wing motion, selecting a bionic standard wing profile to construct the wing three-dimensional model, and simultaneously performing flow field modeling according to the flow field simulation requirement;
s2, dividing grids and refining fit grids, carrying out grid division on the wing three-dimensional model and the whole flow field by using a tetrahedral grid, establishing a wing fit grid by using a thincut, and carrying out fairing treatment and gradient correction on the wing fit grid;
s3, setting solving parameters; selecting a turbulence model according to the actual situation of the flight environment, determining boundary conditions, and performing UDF editing and moving grid setting according to the coupled motion of flapping wing heave-pitch and the active flexible deformation rule of the trailing edge;
s4, calculating lift force and drag coefficient: calculating lift and drag coefficients on a fluid-solid interaction surface of the wing and surrounding air;
and S5, processing data, changing different flapping wing frequencies and flexible deformation coefficients, and performing comparative analysis on lift resistance coefficients.
Further, the airfoil model in step S1 is selected from standard airfoil NACA0012 in a low speed airfoil series established by NACA in the united states, and the material is selected as solid with a density of 2719kg/m3The selection standard of the flow field model is based on the numerical simulation requirement that the ratio of the length to the chord length of the left flow field and the right flow field of the wing is greater than 20: 1, the size of a three-dimensional cuboid region for constructing the flow field is 10(m) × 6(m) × 3.5.5 (m), the material is air, and the density is 1.225kg/m3The viscosity was 1.7894e-05 kg/m-s.
Further, the specific implementation method of step S3 is as follows: the turbulence model selects an equation model based on vorticity: the entry boundary condition of the Spalart-Allmoras model is a velocity entry boundary condition, the velocity is 0.1m/s, and the turbulence is 0.0001m2The outlet is a pressure boundary condition, and the rest are non-slip boundaries;
the wing motion is the combination of heave-pitch coupled motion and trailing edge active flexible deformation, namely the trailing edge active flexible deformation is given on the basis of the wing coupled motion, the characteristic that the set chordwise deformation only occurs in the rear half part is represented, the wing Y direction completes the integral heave-pitch coupled motion, and the rear 2/3 part simulates the flexible deformation on the basis of the coupled motion to form integral bionic composite motion; wherein the heave motion is expressed as:
h(t)＝h0sin(ωt)
in the formula: h is0In order to obtain heave amplitude, omega is the circular frequency of the flapping wing, the relation between omega and the frequency f of the flapping wing is 2 pi f, and t is time;
compound motion the pitch motion among them is represented as:
θ(t)＝θ0sin(ωt-ψ)
in the formula: theta0Psi is the phase difference between heave and pitch motion, being the pitch amplitude;
establishing an XYZ satellite coordinate system, the motion of the flapping wing along with the flapping wing and an XYZ fixed coordinate system, and expressing the active flexible deformation motion of the trailing edge in the compound motion as follows:
l(t)＝(x-0.04)/*c*sin(ωt)
in the formula: l (t) represents the displacement difference between the Y direction of the trailing edge and the leading edge, and is the wing deformation coefficient, and c is the wing chord length;
the UDF function is written by combining the coupled motion law of the flapping wings, and the trailing edge motion of the UDF function is expressed as:
l(t)＝(-115*pow(x,4)+35.2*pow(x,3)-4.682*pow(x,2)+0.1984*x+0.0034)+(x-0.04)/c**sin(ωt)
y＝l(t)+h0sin(ωt)
its leading edge motion is expressed as:
l(t)＝0.05633*pow(x,0.5)-60.76*pow(x,4)+17.07*pow(x,3)-2.111*pow(x,2)-0.07558*x
y＝l(t)+h0*sin(ωt)
in the formula: pow (a, b) represents the power of b of a;
selecting a corresponding UDF model for each wing part in the dynamic grid area module setting, loading corresponding grid motion UDF functions for the front section and the rear section of the upper surface of the wing and the front section and the rear section of the lower surface of the wing respectively, and setting the rest model parts into a 'Deforming' type; and performing diffusion type smoothing treatment on the moving grid, wherein the diffusion factor is set to be 0.2.
Further, the lift resistance coefficient calculation method in step S4 includes:
CL＝FY/(0.5ρU2Ap)
CD＝FX/(0.5ρU2Ap)
in the formula: fX，FYRespectively drag and lift, ρ air density, U incoming flow velocity, ApIs the characteristic cross-sectional area of the airfoil.
Further, the average rise and resistance coefficient in the data statistics in step S5 is represented as:
Figure BDA0002523772620000041
Figure BDA0002523772620000042
in the formula: t is the motion period of the flapping wings.
The invention has the beneficial effects that: the invention provides an active flexible deformation-based flapping wing aerodynamic characteristic analysis method aiming at the defects in the conventional flapping wing numerical simulation method. The method obtains the aerodynamic characteristics of the biological thin wing under the actual condition by bionic simulation of the composite motion of the combination of the heave-pitch of the real wing and the active flexible deformation of the trailing edge. Comparing different flapping wing frequencies and flexible deformation coefficients, and calculating and analyzing the relation between the average lift-drag coefficient and the frequency and the flexible deformation coefficient, thereby optimizing the most suitable flapping wing frequency and flexible deformation coefficient; provides an important theoretical basis for the design of the prior micro bionic flapping wing air vehicle for the understanding of the flight characteristics of insects and birds in the nature under the condition of low Reynolds number.
Drawings
FIG. 1 is a flow chart of the method for analyzing aerodynamic characteristics of a flapping wing based on active flexible deformation of the present invention;
FIG. 2 is a schematic diagram of meshing optimization of a portion of a wing in contact with a flow field;
FIG. 3 is a schematic diagram of the combined motions of heave-pitch and active compliant deformation;
FIG. 4 is a graph showing the variation of lift coefficient with time at an flapping wing circle frequency of 100.
Detailed Description
The scheme of the invention is as follows: firstly, establishing a wing three-dimensional model and a flow field grid of flapping wing motion, determining a heave-pitch motion rule and a motion rule of flexible active deformation of a wing trailing edge, then combining commercial CFD software FLUENT calculated by using mainstream hydrodynamics, using a user-defined function UDF technology and a dynamic grid technology bound in the FLUENT to set a solver, finally performing monitor setting of residual error, lift coefficient and resistance coefficient on post-processing, and controlling variables to change multiple groups of parameters to analyze the average lift coefficient and the resistance coefficient of the flapping wing under different flapping wing frequencies and different flexible deformation coefficients.
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in FIG. 1, the invention relates to a method for analyzing the aerodynamic characteristics of a flapping wing based on active flexible deformation, which comprises the following steps:
s1, establishing a wing three-dimensional model and a flow field grid of flapping wing motion, selecting a bionic standard wing profile to construct the wing three-dimensional model, and simultaneously performing flow field modeling according to the flow field simulation requirement;
the airfoil model is selected from standard airfoil NACA0012 in a low-speed airfoil series built by NACA, and the material is selected from solid with a density of 2719kg/m3The selection standard of the flow field model is based on the numerical simulation requirement that the ratio of the length to the chord length of the left flow field and the right flow field of the wing is greater than 20: 1, the size of a three-dimensional cuboid region for constructing the flow field is 10(m) × 6(m) × 3.5.5 (m), the material is air, and the density is 1.225kg/m3The viscosity was 1.7894e-05 kg/m-s.
S2, dividing meshes and refining fit meshes, and as shown in figure 2, using tetrahedral meshes to divide the meshes of the wing three-dimensional model and the whole flow field; establishing a wing skin grid by utilizing the thincut, and performing fairing treatment and gradient correction on the wing skin grid; the total number of tetrahedral mesh units adopted by the flow field division exceeds 20 ten thousand.
S3, setting solving parameters; selecting a turbulence model according to the actual situation of the flight environment, determining boundary conditions, and performing UDF editing and moving grid setting according to the coupled motion of flapping wing heave-pitch and the active flexible deformation rule of the trailing edge;
the solution is selected as transient state, based on pressure method, the turbulence model selects equation model based on vorticity: the spalar-almiras model, which is designed for the aeronautical field, is mainly wall-bound flow and has shown good results. The inlet boundary conditions were velocity inlet boundary conditions, velocity 0.1m/s, turbulence 0.0001m2The outlet is a pressure boundary condition, and the rest are non-slip boundaries;
the wing motion is the combination of heave-pitch coupled motion and trailing edge active flexible deformation, namely the trailing edge active flexible deformation is given on the basis of the wing coupled motion, the characteristic that the set chordwise deformation only occurs in the rear half part is represented, the wing Y direction completes the integral heave-pitch coupled motion, and the rear 2/3 part simulates the flexible deformation on the basis of the coupled motion to form integral bionic composite motion; wherein the heave motion is expressed as:
h(t)＝h0sin(ωt)
in the formula: h is0In order to obtain heave amplitude, omega is the circular frequency of the flapping wing, the relation between omega and the frequency f of the flapping wing is 2 pi f, and t is time; preferably, the heave amplitude is set to 0.02 and the circle frequency is set to 50-150.
Compound motion the pitch motion among them is represented as:
θ(t)＝θ0sin(ωt-ψ)
in the formula: theta0Psi is the phase difference between heave and pitch motion, being the pitch amplitude; preferably, the pitch amplitude is set to pi/12 and the phase difference is set to 0.
Establishing an XYZ satellite coordinate system, the motion of the flapping wing along with the flapping wing and an XYZ fixed coordinate system, and expressing the active flexible deformation motion of the trailing edge in the compound motion as follows:
l(t)＝(x-0.04)/*c*sin(ωt)
in the formula: l (t) represents the displacement difference between the Y direction of the trailing edge and the leading edge, and is the wing deformation coefficient, and c is the wing chord length; preferably, the deformation coefficient is set to 0.01 to 0.09, and the chord length is 0.1.
The UDF function is written by combining the coupled motion law of the flapping wings, and the trailing edge motion of the UDF function is expressed as:
l(t)＝(-115*pow(x,4)+35.2*pow(x,3)-4.682*pow(x,2)+0.1984*x+0.0034)+(x-0.04)/c**sin(ωt)
y＝l(t)+h0sin(ωt)
its leading edge motion is expressed as:
l(t)＝0.05633*pow(x,0.5)-60.76*pow(x,4)+17.07*pow(x,3)-2.111*pow(x,2)-0.07558*x
y＝l(t)+h0*sin(ωt)
in the formula: pow (a, b) represents the power of b of a;
selecting a corresponding UDF model for each wing part in the dynamic grid area module setting, loading corresponding grid motion UDF functions for the front section and the rear section of the upper surface of the wing and the front section and the rear section of the lower surface of the wing respectively, and setting the rest model parts into a 'Deforming' type; and performing diffusion type smoothing treatment on the moving grid, wherein the diffusion factor is set to be 0.2. At this point, the compiled UDF function is introduced into FLUENT, and the wing motion configuration is completed in combination with the dynamic grid setting, and the motion diagram is shown in fig. 3.
S4, calculating lift force and drag coefficient: calculating lift and drag coefficients on a fluid-solid interaction surface of the wing and surrounding air;
and the lift coefficient and the resistance coefficient monitor are arranged, so that the graph window can dynamically display the change of the lift coefficient and the resistance coefficient along with the iteration process in real time. And setting the calculation time step length and the step number for solving. The lift resistance coefficient calculation method comprises the following steps:
CL＝FY/(0.5ρU2Ap)
CD＝FX/(0.5ρU2Ap)
in the formula: fX，FYRespectively drag and lift, ρ air density, U incoming flow velocity, ApIs the characteristic cross-sectional area of the airfoil. Preferably, the time step size is set to 5e-4, the number of time steps is set to 1000 steps, the maximum number of iterations per time step is 20, the incoming flow speed is 0.1m/s, ApIs 0.04. A lift coefficient plot is obtained, which is shown in figure 4, and figure 4 shows a schematic representation of the change in lift coefficient with time at a flapping wing circle frequency of 100.
S5, processing data, changing different flapping wing frequencies and flexible deformation coefficients, and performing comparative analysis on lift resistance coefficients;
the average rise and resistance coefficient in data statistics is represented as:
Figure BDA0002523772620000071
Figure BDA0002523772620000072
in the formula: t is the motion period of the flapping wings.
The invention provides the relation between different frequencies and flexible deformation coefficients and the average lift coefficient and the resistance coefficient, the control variables are flapping wing circle frequency and flexible deformation coefficient, one group of calculation is that the deformation coefficient is controlled at 0.03, and the circle frequency is respectively taken at five levels of 50, 75, 100, 125 and 150; the other group is calculated by taking the circle frequency as 100 and the deformation coefficients as 0.01, 0.03, 0.05, 0.07 and 0.09 respectively, as shown in the following tables 1 and 2:
TABLE 1 mean lift coefficient and drag coefficient at different frequencies
ω CLA CDA
50 0.34 0.21
75 0.43 0.28
100 0.55 0.38
125 0.61 0.42
150 0.69 0.47
TABLE 2 different flexural deformation coefficients, mean lift coefficient and drag coefficient
Figure BDA0002523772620000073
Figure BDA0002523772620000081
The invention finds out that the average lift coefficient and the resistance coefficient are increased along with the increase of the flapping wing circle frequency through numerical calculation; the influence of the flexible deformation coefficient on the lift coefficient is that the flexible deformation coefficient rises firstly and then falls, an optimal value is obtained near 0.05, and the resistance coefficient is continuously reduced along with the increase of the deformation coefficient, which shows that the thrust generation and the lift generation are weakened when the flexibility is too high, so that the optimal flexible deformation coefficient corresponding to the micro flapping wing air vehicle is required to be found to improve the flight efficiency.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims (5)

1. The flapping wing aerodynamic characteristic analysis method based on active flexible deformation is characterized by comprising the following steps of:
s1, establishing a wing three-dimensional model and a flow field grid of flapping wing motion, selecting a bionic standard wing profile to construct the wing three-dimensional model, and simultaneously performing flow field modeling according to the flow field simulation requirement;
s2, dividing grids and refining fit grids, carrying out grid division on the wing three-dimensional model and the whole flow field by using a tetrahedral grid, establishing a wing fit grid by using a thincut, and carrying out fairing treatment and gradient correction on the wing fit grid;
s3, setting solving parameters; selecting a turbulence model according to the actual situation of the flight environment, determining boundary conditions, and performing UDF editing and moving grid setting according to the coupled motion of flapping wing heave-pitch and the active flexible deformation rule of the trailing edge;
s4, calculating lift force and drag coefficient: calculating lift and drag coefficients on a fluid-solid interaction surface of the wing and surrounding air;
and S5, processing data, changing different flapping wing frequencies and flexible deformation coefficients, and performing comparative analysis on lift resistance coefficients.
2. The method as claimed in claim 1, wherein the airfoil model is selected in step S1 as standard airfoil NACA0012 in a low speed airfoil series created by NACA in usa, and the material is selected as solid with a density of 2719kg/m3The selection standard of the flow field model is based on the numerical simulation requirement that the ratio of the length to the chord length of the left flow field and the right flow field of the wing is greater than 20: 1, the size of a three-dimensional cuboid region for constructing the flow field is 10(m) × 6(m) × 3.5.5 (m), the material is air, and the density is 1.225kg/m3The viscosity was 1.7894e-05 kg/m-s.
3. The flapping wing aerodynamic characteristic analysis method based on active flexible deformation of claim 2, wherein the step S3 is realized by the following specific method: the turbulence model selects an equation model based on vorticity: the entry boundary condition of the Spalart-Allmoras model is a velocity entry boundary condition, the velocity is 0.1m/s, and the turbulence is 0.0001m2The outlet is a pressure boundary condition, and the rest are non-slip boundaries;
the wing motion is the combination of heave-pitch coupled motion and trailing edge active flexible deformation, namely the trailing edge active flexible deformation is given on the basis of the wing coupled motion, the characteristic that the set chordwise deformation only occurs in the rear half part is represented, the wing Y direction completes the integral heave-pitch coupled motion, and the rear 2/3 part simulates the flexible deformation on the basis of the coupled motion to form integral bionic composite motion; wherein the heave motion is expressed as:
h(t)＝h0sin(ωt)
in the formula: h is0In order to obtain heave amplitude, omega is the circular frequency of the flapping wing, the relation between omega and the frequency f of the flapping wing is 2 pi f, and t is time;
compound motion the pitch motion among them is represented as:
θ(t)＝θ0sin(ωt-ψ)
in the formula: theta0Psi is the phase difference between heave and pitch motion, being the pitch amplitude;
establishing an XYZ satellite coordinate system, the motion of the flapping wing along with the flapping wing and an XYZ fixed coordinate system, and expressing the active flexible deformation motion of the trailing edge in the compound motion as follows:
l(t)＝(x-0.04)/*c*sin(ωt)
in the formula: l (t) represents the displacement difference between the Y direction of the trailing edge and the leading edge, and is the wing deformation coefficient, and c is the wing chord length;
the UDF function is written by combining the coupled motion law of the flapping wings, and the trailing edge motion of the UDF function is expressed as:
l(t)＝(-115*pow(x,4)+35.2*pow(x,3)-4.682*pow(x,2)+0.1984*x+0.0034)+(x-0.04)/c**sin(ωt)
y＝l(t)+h0sin(ωt)
its leading edge motion is expressed as:
l(t)＝0.05633*pow(x,0.5)-60.76*pow(x,4)+17.07*pow(x,3)-2.111*pow(x,2)-0.07558*x
y＝l(t)+h0*sin(ωt)
in the formula: pow (a, b) represents the power of b of a;
selecting a corresponding UDF model for each wing part in the dynamic grid area module setting, loading corresponding grid motion UDF functions for the front section and the rear section of the upper surface of the wing and the front section and the rear section of the lower surface of the wing respectively, and setting the rest model parts into a 'Deforming' type; and performing diffusion type smoothing treatment on the moving grid, wherein the diffusion factor is set to be 0.2.
4. The method for analyzing aerodynamic characteristics of an flapping wing based on active flexural deformation of claim 1, wherein the lift drag coefficient calculation method in step S4 comprises:
CL＝FY/(0.5ρU2Ap)
CD＝FX/(0.5ρU2Ap)
in the formula: fX，FYRespectively drag and lift, ρ air density, U incoming flow velocity, ApIs the characteristic cross-sectional area of the airfoil.
5. The method for analyzing aerodynamic characteristics of flapping wings based on active flexural deformation of claim 1, wherein the average lift and drag coefficients during data statistics in step S5 are represented as:
Figure FDA0002523772610000021
Figure FDA0002523772610000022
in the formula: t is the motion period of the flapping wings.
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