1. A multi-rotor unmanned aerial vehicle blade optimization design method comprises the following steps:

s1, determining working condition parameters and selecting a reference wing profile;

s2, parameterizing the reference airfoil profile to obtain a basic airfoil profile;

s3, optimizing the basic airfoil profile to obtain the optimal airfoil profile;

and S4, carrying out optimal airfoil three-dimensional simulation verification.

2. The method of claim 1, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S1, the operating condition parameters include a blade rotation speed n (rpm), and a pulling force, an inflow speed V, and an inflow angle α at the rotation speed;

and the selection reference wing section is an wing section which meets the working condition use condition or is close to the working condition use condition and is selected from a wing section library.

3. The method of claim 1, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S2, the base airfoil is parameterized by the PARSEC method, and the upper and lower surfaces of the airfoil are described using a weighted linear combination fit of polynomials to obtain the base airfoil.

4. The method of claim 1, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S3, the basic airfoil profile is optimized by a genetic algorithm, including the following sub-steps:

s31, encoding and group initializing;

s32, selecting operation, cross operation and mutation operation;

s33, detecting and evaluating the individual fitness to obtain an ideal wing profile;

and S34, optimizing the ideal airfoil profile to obtain the optimal airfoil profile.

5. The method of claim 4, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S31, the encoding is to encode the obtained curve expression of the basic airfoil, the population initialization includes setting a population scale, a variable string length, an evolution algebra, a cross probability and a variation probability, preferably, the population scale is 10 to 200, the variable string length is 11, and the evolution algebra is 100 to 200;

preferably, the optimization objective function is the airfoil lift-drag ratio y:

wherein alpha is airfoil angle of attack, T is airfoil tension, D is airfoil resistance, C_LIs the coefficient of airfoil lift, C_dIs the airfoil drag coefficient.

6. The method of claim 4, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S32, applying selection, crossover, and mutation operations to the population to obtain a next generation population;

wherein a selection operator of the selection operation selects for optimal reservation:

the operator or the cross probability of the cross operation is 0.5-0.9;

the operator mutation probability of the mutation operation is 0.1-0.3.

7. The method of claim 4, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S33, the fitness function is set to:

wherein y is airfoil lift-drag ratio, y₀The lift-drag ratio of the original airfoil shape is obtained.

8. The method of claim 4, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S34, the chord length of the ideal airfoil profile is again varied by the genetic algorithm to generate a new airfoil profile library, and the variable of the genetic algorithm is the chord length c of the airfoil profile, and the aerodynamic data of the airfoil profile is encoded.

9. The method of claim 8, wherein the rotor blade is a rotor blade of a multi-rotor drone,

the aerodynamic data is obtained by integrating the phyllo-pixel along the airfoil span.

10. The method of claim 8, wherein the rotor blade is a rotor blade of a multi-rotor drone,

the optimization in the genetic algorithm takes the blade force effect as an optimization objective function, and the blade force effect can be expressed as follows:

wherein eta is the force effect of the blades, and omega is the rotating speed of the blades.

Background

Most of the traditional blade designs are based on past empirical data, and by determining the relationship between the maximum output tension and the input power, the number, the diameter, the average chord length and other geometric parameters of the blades are preliminarily selected, and the radial distribution mode of the blade thickness and the proper airfoil profile are selected.

However, this single line design approach requires constant design of propeller geometry and calculations: and (3) calculating and evaluating the performance of the propeller under various working conditions by utilizing knowledge of the strip theory according to the preliminarily determined geometric parameters of the blades, and if the calculation result cannot meet the design target, reselecting the geometric parameters and performing modeling calculation until the performance meets the design requirement. Due to the fact that the design mode has a plurality of repeated verification links, the design efficiency of the paddle is low, and the task amount is large.

In addition, most of the existing blade optimization design researches are only optimized and designed aiming at a certain parameter or a certain working condition so as to improve the pneumatic performance of the blade, the universality is poor, the design dimension is low, the universal applicability is not available, and the blade optimization design researches are difficult to adapt to various requirements.

For the reasons, the inventor provides a general optimal design method for blades of a multi-rotor unmanned aerial vehicle.

Disclosure of Invention

In order to overcome the problems, the inventor of the invention carries out intensive research and designs an optimal design method for blades of a multi-rotor unmanned aerial vehicle, which comprises the following steps:

s1, determining working condition parameters and selecting a reference wing profile;

s2, parameterizing the reference airfoil profile to obtain a basic airfoil profile;

s3, optimizing the basic airfoil profile to obtain the optimal airfoil profile;

and S4, carrying out optimal airfoil three-dimensional simulation verification.

In step S1, the operating condition parameters include a blade rotation speed n (rpm), and a pulling force, an inflow speed V, and an inflow angle α at the rotation speed;

and the selection reference wing section is an wing section which meets the working condition use condition or is close to the working condition use condition and is selected from a wing section library.

In step S2, the base airfoil is parameterized by the PARSEC method, and the upper and lower surfaces of the airfoil are described using a weighted linear combination fit of polynomials to obtain the base airfoil.

In step S3, the basic airfoil profile is optimized by a genetic algorithm, including the following sub-steps:

s31, encoding and group initializing;

s32, selecting operation, cross operation and mutation operation;

and S33, detecting and evaluating the individual fitness to obtain the ideal airfoil profile.

And S34, optimizing the ideal airfoil profile to obtain the optimal airfoil profile.

Further, in step S31, the encoding is to encode the obtained curve expression of the basic airfoil, the population initialization includes setting a population scale, a variable string length, an evolution algebra, a cross probability and a variation probability, preferably, the population scale is 10 to 200, the variable string length is 11, and the evolution algebra is 100 to 200;

preferably, the optimization objective function is the airfoil lift-drag ratio y:

wherein alpha is airfoil angle of attack, T is airfoil tension, D is airfoil resistance, C_LIs the coefficient of airfoil lift, C_dIs the airfoil drag coefficient. 6. The method of claim 4, wherein the rotor blade is a rotor blade of a multi-rotor drone,

in step S32, a selection operation, a crossover operation, and a mutation operation are applied to the population to obtain a next generation population.

Wherein a selection operator of the selection operation selects for optimal reservation:

the operator or the cross probability of the cross operation is 0.5-0.9;

the operator mutation probability of the mutation operation is 0.1-0.3;

in a preferred embodiment, in step S33, the fitness function is set to:

wherein y is airfoil lift-drag ratio, y₀The lift-drag ratio of the original airfoil shape is obtained.

Further, in step S34, the chord length of the ideal airfoil profile is again varied by the genetic algorithm to generate a new airfoil profile library, and the variable of the genetic algorithm is the chord length c of the airfoil profile, and the aerodynamic data of the airfoil profile is encoded.

According to the invention, said aerodynamic data are obtained by integrating the phyllo-elements along the development of the wing profile.

In a preferred embodiment, the optimization in the genetic algorithm takes the blade force effect as an optimization objective function, and the blade force effect can be expressed as:

wherein eta is the force effect of the blades, and omega is the rotating speed of the blades.

The invention has the advantages that:

(1) the working parameters of the blades under different working conditions are used as input, the blades can be optimally designed according to different working conditions, and the method is wider in applicability compared with the traditional blade design method;

(2) through twice optimization, a primary optimized airfoil profile library and a secondary optimized airfoil profile library are respectively generated, and the optimization dimension is higher;

(3) the genetic algorithm and the phyllotactic momentum method are adopted to carry out the metamorphosis optimization on the airfoil profile, the optimization efficiency is high, and the optimized airfoil profile is good in effect.

Drawings

Fig. 1 shows a schematic flow diagram of a multi-rotor drone blade optimization design method according to a preferred embodiment of the invention;

FIG. 2 illustrates the embodiment of the PARSEC parameter in the airfoil according to a preferred embodiment of the present invention;

FIG. 3 shows a schematic diagram of a genetic algorithm for a multi-rotor drone blade optimization design method according to a preferred embodiment of the invention;

FIG. 4 shows a comparison of the airfoil results of the PARSEC fit in example 1 according to the present invention with the original NACA6412 airfoil;

FIG. 5 shows the PARSEC fitting airfoil to the original NACA6412 airfoil error in example 1 according to the present invention;

FIG. 6 shows the ideal airfoil results in embodiment 1 according to the present invention;

FIG. 7 shows the ideal airfoil results in embodiment 1 according to the present invention;

FIG. 8 shows the result of the pneumatic simulation in the hovering state of the blade according to embodiment 1 of the present invention;

FIG. 9 is a schematic diagram of an embodiment 1 of the present invention for illustrating the production of the best airfoil profile;

FIG. 10 shows the aerodynamic performance comparison results of the wind tunnel test of the best airfoil blade and the reference paddle according to example 1 of the present invention.

Detailed Description

The invention is explained in more detail below with reference to the figures and examples. The features and advantages of the present invention will become more apparent from the description.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

According to the optimal design method for the blades of the multi-rotor unmanned aerial vehicle, as shown in fig. 1, the method comprises the following steps:

s1, determining working condition parameters and selecting a reference wing profile;

s2, parameterizing the reference airfoil profile to obtain a basic airfoil profile;

s3, optimizing the basic airfoil profile to obtain the optimal airfoil profile;

and S4, carrying out optimal airfoil three-dimensional simulation verification.

In step S1, the operating condition parameters are operating state parameters of the blade to be designed under the condition directly related to the action thereof, including the rotating speed n (rpm) of the blade, and the pulling force, the incoming flow speed V and the incoming flow angle α at the rotating speed.

The selection reference airfoil is an airfoil which meets working condition use conditions or is close to the working condition use conditions and is selected from designed airfoils, preferably an airfoil library, such as a profilei airfoil database, an NACA airfoil database and the like.

In the present invention, the selection manner of the reference airfoil profile is not particularly limited, and those skilled in the art can select the reference airfoil profile according to experience or actual use requirements.

The airfoil profile is used as the section shape of the blade, the geometric shape of the airfoil profile has important influence on the performance of the whole blade part and even the whole aircraft, and the basic airfoil profile is directly applied to the unmanned aerial vehicle and is difficult to obtain a higher performance target, so that the basic airfoil profile needs to be optimized.

In step S2, the parameterization of the reference airfoil is performed by a PARSEC method, which is a typical airfoil parameterization method with a certain number of parameters and is widely used in the parameterization of the blade.

The base airfoil profile is described by the PARSEC method by parameters including airfoil leading edge radius R_LEMaximum height X of airfoil suction surface_upMaximum height position Z of airfoil suction surface_upAirfoil suction surface curvature Z _ XX_upMaximum height X of airfoil pressure surface_loMaximum height position Z of airfoil pressure surface_loAirfoil pressure surface curvature Z _ XX_loX of the abscissa of the upper trailing edge of the airfoil_te,upHorizontal coordinate X of lower trailing edge of airfoil profile_te,loAirfoil trailing edge thickness dZ _ Te, airfoil trailing edge position Z _ Te, airfoil upper trailing edge angle α _ Te, airfoil lower trailing edge angle β _ Te, as shown in fig. 2.

Further, in the present invention, the upper and lower surfaces of the airfoil are described by means of fitting, preferably by weighted linear combination of polynomials, as shown in equation one, to obtain a base airfoil:

wherein, Y_u、Y_lThe X is the control point which is the abscissa of the airfoil along the chord direction, and can be selected on the airfoil according to the requirement, and theoretically, the more the control points are, the higher the fitting precision is.

a_n、b_nFor polynomial coefficients, the upper surface is solved by:

the polynomial coefficient of the PARSEC parameter equation can be obtained through the formula II, namely, the coordinate of each point of the airfoil on the upper surface can be obtained by substituting the formula I for the constraint condition of the control point.

Likewise, the lower surface is solved by:

and (3) solving a polynomial coefficient of a PARSEC parameter equation through the formula III, and substituting the polynomial coefficient into the formula I to obtain the coordinates of each point of the lower surface airfoil.

After the fitting is finished, taking the square difference of the original airfoil longitudinal coordinate corresponding to the control point and the fitting longitudinal coordinate result as a fitting result evaluation index, and if the mean square difference of the original airfoil longitudinal coordinate and the fitting longitudinal coordinate result is less than 2 multiplied by 10^-3The fit is considered good if the mean square error of the two is greater than 2 × 10^-3Then the fitting is performed again.

In step S3, the base airfoil is optimized by a genetic algorithm.

The genetic algorithm refers to a calculation model for simulating Darwinian natural selection and a genetic mechanism, the main idea is derived from the natural law of biological genetics and survival of a suitable person, and the genetic algorithm belongs to a random search algorithm with survival and detection.

Further, the step S3 includes the following sub-steps:

s31, encoding and group initializing;

s32, selecting operation, cross operation and mutation operation;

and S33, detecting and evaluating the individual fitness to obtain the ideal airfoil profile.

And S34, optimizing the ideal airfoil profile to obtain the optimal airfoil profile.

In step S31, the encoding means that the obtained curve expression of the basic airfoil profile is encoded, and since the genetic algorithm cannot directly process the parameters of the problem space, the problem to be solved must be represented as a chromosome or an individual of the genetic space by encoding, that is, the encoding process is to map the phenotype (curve expression of the basic airfoil profile) to the genotype. In step S31, the encoding method is the same as the conventional encoding method, and thus is not described again.

In the genetic algorithm, in order to ensure the unconstrained property of an initial value, individuals in an initial population are completely randomly generated, and before generation, the population needs to be initialized, wherein the initialization comprises the setting of the population scale, the length of a variable character string, the evolution algebra, the cross probability and the variation probability.

The population scale refers to the total number of individuals in any generation, is set manually, the larger the population scale is, the more possible a global solution can be found, but the running time is also relatively longer, and the value is taken from 10 to 200 in the invention;

the length of the variable character string needs to be set according to a specific case, and in the present invention, the length of the variable character string is preferably 11, corresponding to the parameter PARSEC.

The evolution algebra needs to be determined according to the actual convergence condition, generally speaking, the larger the evolution algebra is, the more stable the calculation result is, but the corresponding calculation time is also increased, and the calculation time is 100-200 in the invention.

Optimizing an objective function as an airfoil lift-drag ratio y:

wherein alpha is an airfoil angle of attack, and can be selected by a person skilled in the art according to the specific working conditions of the blade according to experience; t is the wing tension, D is the wing resistance, C_LIs the coefficient of airfoil lift, C_dIs the airfoil coefficient of drag, C_L、C_dMay be obtained by aerodynamic simulation software, such as Fluent calculations.

In step S32, a selection operation, a crossover operation, and a mutation operation are applied to the population to obtain a next generation population.

The selection operator of the selection operation is the optimal reservation selection, the optimal reservation selection is a selection strategy commonly used in the selection operator, and the selection strategy is also called as a championship selection algorithm, namely, the individual structure with the highest fitness in each generation of population is selected to be completely copied to the next generation of population, and the final result obtained when the genetic algorithm is terminated can be ensured to be the individual with the highest fitness appearing in the past generation.

The cross probability of the cross operation is used for judging whether the two individuals carry out cross operation, and in the invention, the cross probability is set to be 0.5-0.9, so that the efficiency of forming a new individual by crossing is ensured.

The mutation probability of the mutation operation is set to be 0.1-0.3, so that a small number of individuals are allowed to have mutation conditions, the local optimal solution is avoided, and the operation convergence is ensured.

In step S33, individual fitness detection and evaluation is performed on the next generation population, that is, the probability that an individual with higher fitness inherits into the next generation is higher, and the individual fitness needs to be determined according to the designed fitness function.

In the genetic algorithm, the design of the fitness function is determined by combining the requirement of solving the problem, and in the invention, the fitness function is set as follows:

wherein y is airfoil lift dragRatio, y₀For the lift-drag ratio of the original airfoil shape, in the fitness function, the smaller the value of S is, the larger the lift-drag ratio of the airfoil shape is proved to be. The method has the advantages that the improvement of the airfoil lift-drag ratio is the optimization target of the design method, so that the function is used as a fitness function, the selection is visual, and the good consistency of the selection process and the optimization target is kept.

When the fitness of a certain airfoil is evaluated, if S does not meet the numerical constraint condition, the airfoil is abandoned; if so, retained in the generation and used as a sample for selection in the generation.

And when all individuals in a certain generation do not meet the evaluation condition, repeating the step S32, and performing once selection operation, cross operation and mutation operation again, namely performing once evolution again until the evaluation condition is reached.

And when the group meets the evaluation condition, outputting the group, and thus obtaining a primary optimized airfoil profile library.

Further, simulating each wing section in the primary optimization wing section library, and screening out the optimal wing section as an ideal wing section.

Preferably, the optimal airfoil profile is determined by taking an airfoil lift-drag ratio as a considered parameter, and the airfoil profile with the largest lift-drag is selected as the optimal airfoil profile.

In a preferred embodiment, the simulation is performed using ICEM and Fluent under the ANSYS platform.

In step S34, each section setting angle and chord length of the ideal airfoil profile is designed by combining the phyllotactic momentum method.

The phyllotactic momentum method is that when airflow flows through the wing profile, the airflow speeds on the upper and lower wing surfaces are different, the flow speed of the upper wing surface is high, and the airflow static pressure is reduced; the lower airfoil velocity is low and the static airflow pressure rises.

Specifically, the differential formalism using the method of the momentum of the phylline is used to analyze the aerodynamic force dF acting on a phylline of length dr in the spanwise direction of the blade:

wherein dA isMaximum projected area of the leaf element, omega is wind speed relative to the leaf element, rho is air density, C is airfoil chord length, C_rAnd dr is the length of the phyllanthus.

And (3) integrating the phyllotaxis along the airfoil extension by utilizing an integral form of a phyllotaxis momentum method to obtain the aerodynamic data of the blade:

wherein, T is airfoil lift, D is airfoil resistance, and M is airfoil moment of torsion. C_LIs the coefficient of airfoil lift, C_dIs the airfoil coefficient of drag, C_MThe three are obtained by Fluent simulation software, and R represents the radius of a propeller, for example, the radius of the propeller of a 17-inch blade is 21.6 cm.

And (3) carrying out variation on the chord length of the ideal airfoil profile by utilizing the genetic algorithm again to generate a new airfoil profile library, wherein the variable of the genetic algorithm at this time is the chord length c of the airfoil profile, the aerodynamic data of the airfoil profile is encoded, the cross probability is 0.5-0.9, preferably 0.7, and the variation probability is 0.1-0.5, preferably 0.3.

The force effect of the blade is taken as an optimization objective function in the genetic algorithm, the force effect is the lift force which can be improved by 1w of electric quantity consumed by the blade, and the higher the force effect of the blade is, the better the dynamic performance is proved, and the power performance can be expressed as follows:

wherein eta is the force effect of the blades, and omega is the rotating speed of the blades.

In the genetic algorithm, the optimization target is directly used as a fitness function, and the target with the highest effect in each generation is used as the initial individual of the next generation for crossing and variation, so that the consistency of the optimization design idea is maintained.

In step S4, the obtained optimal blade is simulated by software to verify whether it meets the design target, and if not, steps S1 to S3 are repeated.

Preferably, the optimal airfoil profile is simulated by three types of software, namely Geometry, Meshing and Fluent under an ANSYS platform.

Examples

Example 1

Optimize certain many rotor unmanned aerial vehicle paddle, this unmanned aerial vehicle operating condition is mainly with hovering, and its operating condition parameter is: the incoming flow speed is 10m/s, the incoming flow angle is 0 degrees, and the tension generated by the paddle under the rotating speed of 5500rpm is not lower than 3.5 kg.

The NACA6412 airfoil was selected as the base airfoil and the NACA6412 airfoil was parameterized by the PARSEC method, the results of which are shown in the table below.

Watch 1

The polynomial weighted linear combination is adopted to describe the upper surface and the lower surface of the airfoil profile, the result is shown in fig. 4, it can be seen from the graph that the obtained description curve is basically and completely overlapped with the original NACA6412 airfoil profile, the covariance of each fitting point ordinate and the original airfoil profile ordinate is taken as a fitting error judgment index, the fitting error is shown in fig. 5, it can be seen that the fitting errors are all controlled within one thousandth (generally, the fitting error is within two thousandth, the fitting result is considered to be good), and the fitting effect is good.

And optimally designing the airfoil profile by utilizing a mathematical simulation program of a genetic algorithm and a phyllotoxin momentum method, wherein the population scale is set to be 50, the evolution algebra is 100, the cross probability is set to be 0.7, and the variation probability is 0.3. Optimizing an objective function as an airfoil lift-drag ratio y:

wherein alpha is a wingThe angle of attack is shaped, in this example, in order to make the simulation calculation cover all possible working conditions of the blade, the value range of alpha is set as [ -20 degrees, 20 degrees °]The step size is 1 °. C_L、C_dThe coefficient of lift and the coefficient of resistance under the organism system are obtained by Fluent simulation calculation, T is airfoil tension, and D is airfoil resistance.

The fitness function is:

the method comprises the steps of determining and obtaining an ideal airfoil profile by taking an airfoil profile lift-drag ratio as a considered parameter after optimization through a genetic algorithm, selecting ICEM software under an ANSYS platform to establish a calculation domain and divide a grid for the ideal airfoil profile, carrying out aerodynamic simulation on the airfoil profile by using Fluent software, and generating the optimal airfoil profile lift-drag ratio which is obviously superior to that of the original NACA6412 airfoil profile in the airfoil profile library as shown in a result of FIG. 6. The optimal airfoils in the airfoil library are shown in FIG. 7.

Optimizing each section installation angle and chord length by utilizing a phyllotactic momentum theory to obtain the optimal airfoil profile, wherein the results of each section installation angle and chord length are shown in the following table:

watch two

And performing simulation verification on the paddle by using Geometry software, Meshing software and Fluent software under an ANSYS platform, wherein the Geometry software is used for establishing a calculation domain of the paddle, the Meshing software is used for performing grid division on the calculation domain of the paddle, the Fluent software is used for performing aerodynamic simulation on the paddle, and the result of the aerodynamic simulation is shown in figure 8 in the hovering state of the paddle.

The obtained optimum airfoil profile processing production object is subjected to wind tunnel test to test the performance of the blade as shown in fig. 9, and is compared with the wind tunnel test aerodynamic performance of a reference blade (17-inch commercial blade), and the result is shown in fig. 10, and the force efficiency of the optimally designed blade under unit tension is about 13% higher than that of the reference blade in the hovering state.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", and the like indicate orientations or positional relationships based on operational states of the present invention, and are only used for convenience of description and simplification of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise specifically stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the connection may be direct or indirect via an intermediate medium, and may be a communication between the two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The present invention has been described above in connection with preferred embodiments, but these embodiments are merely exemplary and merely illustrative. On the basis of the above, the invention can be subjected to various substitutions and modifications, and the substitutions and the modifications are all within the protection scope of the invention.