Airfoil scale model for low-speed flutter wind tunnel test and design method

Abstract

According to the airfoil scale model for the low-speed flutter wind tunnel test and the design method, through simplification of an airfoil and cooperation of a skeleton and a dimensional box section, the model design difficulty is reduced and the processing period and cost are reduced on the premise of ensuring that the model meets a similarity criterion; by using the beam unit and the concentrated mass unit, the rigidity characteristic and the mass characteristic of the structure are decoupled and simulated, and the calculation accuracy is improved.

Description

Technical Field

[0001] This invention belongs to the field of flutter wind tunnel testing technology, specifically relating to a scaled-down airfoil model and design method for low-speed flutter wind tunnel testing. Background Technology

[0002] Flutter is an aeroelastic dynamic instability phenomenon caused by the coupling of elastic structural dynamics and unsteady aerodynamic forces. Since flutter often leads to the failure of a structural system in a very short time, the development of all aircraft requires structural flutter characteristic analysis, optimization, and experimental verification to ensure flight safety. Wind tunnel testing, as an important verification method for aeroelastic design, is used to study structural flutter characteristics, obtain flutter boundaries, and verify the calculation accuracy of theoretical methods. However, due to limitations such as actual structural dimensions and wind tunnel capabilities, scaled-down model flutter wind tunnel tests that meet similarity requirements are necessary.

[0003] Aircraft typically employ wing surfaces with high lift-to-drag ratios as their primary lifting surfaces, and their trailing edges usually feature multiple controllable aerodynamic surfaces. These control surfaces deflect according to servo commands, altering the aerodynamic force distribution to accurately control the aircraft's attitude. Control surface flutter is a typical and complex problem in aircraft structural flutter. During the design and development phases, low-speed flutter wind tunnel tests of scaled-down models of wing structures with trailing-edge control surfaces are planned and conducted to study the characteristics of multi-modal coupled flutter, the influence of key parameters on flutter characteristics, and other factors, supporting the optimization and closure of the overall and structural design.

[0004] The actual airfoil structure has internal structural components such as main beams, stringers, webs, and stiffeners. The stiffness-to-mass ratio of each component is relatively large. Due to the requirement of large-scale scaling, the design of a scaled-down airfoil model that simultaneously meets the requirements of shape simulation, stiffness simulation, and inertia simulation is extremely difficult, and there may even be no available materials or processes to produce the model. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for designing scaled-down airfoil models for low-speed flutter wind tunnel testing. This invention solves the problems existing in the prior art.

[0006] The technical solution of this invention:

[0007] According to the first aspect, a method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing is provided, comprising the following steps:

[0008] The first step is to establish a detailed dynamic finite element model based on the actual three-dimensional structural model, and to correct the key stiffness parameters of the model based on the main order modal data obtained from the ground modal test, so as to complete the flutter characteristic analysis of the wing structure.

[0009] The second step is to determine the similarity ratio between the scaled-down model and the actual airfoil structure: based on the external dimensions of the airfoil structure and the effective dimensions of the wind tunnel test section, determine the size ratio K. L Based on the critical flutter velocity of the wing structure and the wind tunnel blowing speed, the velocity ratio K is determined. υ The density ratio K is determined based on the atmospheric density corresponding to the actual flight altitude and the wind tunnel inflow density. ρ The mass ratio K is derived from the three basic similarity ratios. m =K ρ K L 3 Frequency ratio K f =K υ / K L ;

[0010] The third step is to reduce the wing structure model proportionally according to the determined similarity ratio to obtain the scaled-down detailed structure, and then calculate the modal characteristics and flutter characteristics of the scaled-down detailed structure.

[0011] The fourth step is to compare the main modal characteristics and flutter analysis results of the scaled-down detailed structure obtained in the third step with the main modal characteristics and flutter analysis results of the airfoil structure obtained in the first step to ensure that the modal frequencies of the scaled-down detailed structure and the actual airfoil meet the frequency ratio and the flutter critical velocity meets the velocity ratio.

[0012] Step 5, Constructing the initial scaled-down model: The method for constructing the initial scaled-down model includes the following steps:

[0013] S5.1 The main load-bearing frame and the outer peripheral frame of the wing surface are retained in the scaled-down detailed structure, while the auxiliary supports with low cross-sectional stiffness are removed. The retained frame divides the initial scaled-down model into multiple blocks.

[0014] S5.2 replaces the retained skeleton with rectangular cross-section beam elements of equivalent stiffness, and assigns elastic modulus and Poisson's ratio to the beam elements based on the selected material properties, with the material density set to 0 kg / m³. 3 ;

[0015] S5.3 Extract the mass characteristic data of each block of the scaled detailed structure of the airfoil, including mass, center of mass and moment of inertia, simulate it with lumped mass elements, and bind it to the nodes of the adjacent beam elements through rigid connection elements;

[0016] S5.4 The scaled-down detailed structural outline is the same as the scaled-down model outline.

[0017] The sixth step is to calculate the main modal parameters of the initial scaled-down model, take the moment of inertia of the beam element section for sensitivity analysis and parameter optimization, and ensure that the main modal frequency errors and modal confidence criterion values ​​of the initial scaled-down model and the scaled-down detailed structure of the airfoil meet the requirements.

[0018] Step 7: Based on the optimized beam element moment of inertia, reconstruct the cross-sectional dimensions of the model beam element, assign the beam element the real material density property, distribute the beam element mass evenly to the adjacent block regions, and calculate the remaining mass characteristic data of each block region based on the mass characteristic data of each block of the detailed structure of the scaled-down flange.

[0019] Step 8: Using the intersection of beam elements as the center, divide the scaled-down model shape. Design V-shaped box segments according to each division. The V-shaped box segments retain four sides, have internal reinforcing ribs, and open top and bottom surfaces.

[0020] Based on the remaining mass characteristics data of the segmented areas, the position, shape and mass of the V-shaped box segments are designed. Taking the beam intersection position or the middle position of the near intersection point of the beam model as the center, the V-shaped box segments are symmetrically fixed around the beam model. Skins are set on the top and bottom of the V-shaped box segments to achieve the integrity of the model's outer surface.

[0021] Furthermore, the beam unit size should be as small as possible, and each block should be divided into at least 5 beam units on each side.

[0022] Furthermore, the main modal data includes modal frequencies and mode shapes.

[0023] Furthermore, the criteria for the main modal parameters to meet the requirements in the sixth step are: the main modal frequency error is less than 5%, and the mode shape MAC value is higher than 0.9.

[0024] Furthermore, the main frame and the outer peripheral frame of the wing surface are obtained by machining a single sheet of aluminum alloy metal, and the shaped box segment is obtained by additive manufacturing technology using resin materials.

[0025] According to the second aspect, a scaled-down airfoil model for low-speed flutter wind tunnel testing is provided, comprising a skeleton, a sculpted box segment, and a skin. The skeleton includes a main load-bearing skeleton and an outer peripheral airfoil skeleton, which divides the scaled-down model into several sections. The skeleton is replaced by several beam elements, and adjacent beam elements are bound together by rigid connection elements to form a beam model. The sculpted box segment retains four sides, has internal reinforcing ribs, and has open top and bottom surfaces. It is symmetrically fixed around the beam model with the beam intersection or the middle of the nearest intersection point as the center. The top and bottom of the sculpted box segment are covered with skin to achieve the integrity of the model's outer surface.

[0026] The beneficial effects of this invention compared to the prior art are as follows:

[0027] (1) By simplifying the wing surface, the present invention uses beam elements to form a skeleton and cooperates with the dimensional box segment, thereby reducing the difficulty of model design and reducing the processing cycle and cost while ensuring that the model meets the similarity criteria.

[0028] (2) This invention improves the accuracy of calculation by using beam elements and partitions close to beam elements as concentrated mass elements, thereby decoupling the simulation of structural stiffness and mass characteristics. Attached Figure Description

[0029] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0030] Figure 1 A schematic diagram of the steps of a scaled-down airfoil model design method for low-speed flutter wind tunnel testing provided by an embodiment of the present invention is shown.

[0031] Figure 2 A schematic diagram of the installation of a V-shaped box segment according to an embodiment of the present invention is shown. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0035] like Figure 1 As shown, according to an embodiment of the present invention, a method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing is provided according to a first aspect, comprising the following steps:

[0036] The first step is to establish a detailed dynamic finite element model based on the actual three-dimensional structural model, and to correct the key stiffness parameters of the model based on the main order modal data obtained from the ground modal test, so as to complete the flutter characteristic analysis of the wing structure.

[0037] The second step is to determine the similarity ratio between the scaled-down model and the actual airfoil structure: based on the external dimensions of the airfoil structure and the effective dimensions of the wind tunnel test section, determine the size ratio K. L Based on the critical flutter velocity of the wing structure and the wind tunnel blowing speed, the velocity ratio K is determined. υ The density ratio K is determined based on the atmospheric density corresponding to the actual flight altitude and the wind tunnel inflow density. ρ The mass ratio K is derived from the three basic similarity ratios. m =K ρ K L 3 Frequency ratio K f =K υ / K L ;

[0038] The third step is to reduce the wing structure model proportionally according to the determined similarity ratio to obtain the scaled-down detailed structure, and then calculate the modal characteristics and flutter characteristics of the scaled-down detailed structure.

[0039] The fourth step is to compare the main modal characteristics and flutter analysis results of the scaled-down detailed structure obtained in the third step with the main modal characteristics and flutter analysis results of the airfoil structure obtained in the first step to ensure that the modal frequencies of the scaled-down detailed structure and the actual airfoil meet the frequency ratio and the flutter critical velocity meets the velocity ratio.

[0040] Step 5, Constructing the initial scaled-down model: The method for constructing the initial scaled-down model includes the following steps:

[0041] S5.1 The main load-bearing frame and the outer peripheral frame of the wing surface are retained in the scaled-down detailed structure, while the auxiliary supports with low cross-sectional stiffness are removed. The retained frame divides the initial scaled-down model into multiple blocks.

[0042] S5.2 replaces the retained skeleton with rectangular cross-section beam elements of equivalent stiffness, and assigns elastic modulus and Poisson's ratio to the beam elements based on the selected material properties, with the material density set to 0 kg / m³. 3 ;

[0043] S5.3 Extract the mass characteristic data of each block of the scaled detailed structure of the airfoil, including mass, center of mass and moment of inertia, simulate it with lumped mass elements, and bind it to the nodes of the adjacent beam elements through rigid connection elements;

[0044] S5.4 The scaled-down detailed structural outline is the same as the scaled-down model outline.

[0045] The sixth step is to calculate the main modal parameters of the initial scaled-down model, take the moment of inertia of the beam element section for sensitivity analysis and parameter optimization, and ensure that the main modal frequency errors and modal confidence criterion values ​​of the initial scaled-down model and the scaled-down detailed structure of the airfoil meet the requirements.

[0046] Step 7: Based on the optimized beam element moment of inertia, reconstruct the cross-sectional dimensions of the model beam element, assign the beam element the real material density property, distribute the beam element mass evenly to the adjacent block regions, and calculate the remaining mass characteristic data of each block region based on the mass characteristic data of each block of the detailed structure of the scaled-down flange.

[0047] Step 8: Using the intersection of beam elements as the center, divide the scaled-down model shape. Design V-shaped box segments according to each division. The V-shaped box segments retain four sides, have internal reinforcing ribs, and open top and bottom surfaces.

[0048] Based on the remaining mass characteristics data of the segmented areas, the position, shape and mass of the V-shaped box segments are designed. Taking the beam intersection position or the middle position of the near intersection point of the beam model as the center, the V-shaped box segments are symmetrically fixed around the beam model. Skins are set on the top and bottom of the V-shaped box segments to achieve the integrity of the model's outer surface.

[0049] In a further embodiment, the beam element size should be as small as possible, and each block should be divided into at least 5 beam elements on each side.

[0050] In a further embodiment, the primary modal data includes modal frequencies and mode shapes.

[0051] In a further embodiment, the criteria for the main modal parameters to meet the requirements in step six are: the main modal frequency error is less than 5% and the mode shape MAC value is higher than 0.9.

[0052] In one further embodiment, the main frame and the outer peripheral frame of the wing are obtained by machining a single sheet of aluminum alloy, while the shaped box segment is obtained by additive manufacturing technology using resin materials.

[0053] According to the second aspect, a scaled-down airfoil model for low-speed flutter wind tunnel testing is provided, comprising a skeleton, a sculpted box segment, and a skin. The skeleton includes a main load-bearing skeleton and an outer peripheral airfoil skeleton, which divides the scaled-down model into several sections. The skeleton is replaced by several beam elements, and adjacent beam elements are bound together by rigid connection elements to form a beam model. The sculpted box segment retains four sides, has internal reinforcing ribs, and has open top and bottom surfaces. It is symmetrically fixed around the beam model with the beam intersection or the middle of the nearest intersection point as the center. The top and bottom of the sculpted box segment are covered with skin to achieve the integrity of the model's outer surface.

[0054] To gain a better understanding of the airfoil scaled-down model design method for low-speed flutter wind tunnel testing provided by this invention, a detailed description is provided below with reference to specific examples and accompanying drawings.

[0055] This invention proposes a method for designing scaled-down airfoil models for low-speed flutter wind tunnel testing, the method comprising:

[0056] The first step is the analysis of the airfoil structure's modal and flutter characteristics. A detailed dynamic finite element model is established based on the actual three-dimensional structural model. The key stiffness parameters of the model are corrected based on the main modal data (modal frequencies and mode shapes) obtained from ground modal tests, thus completing the flutter characteristic analysis of the airfoil structure.

[0057] The second step is to determine the similarity ratio. First, determine the basic similarity ratio value. Based on the external dimensions of the airfoil structure and the cross-sectional dimensions of the wind tunnel test section, determine the size ratio K. L The velocity ratio K is determined based on the flutter critical velocity of the wing structure and the wind tunnel wind speed (generally, the median wind speed is taken). υ The density ratio K is determined based on the atmospheric density corresponding to the actual flight altitude and the wind tunnel inflow density. ρ (The density ratio for low-speed wind tunnel tests is taken as 1, i.e., K) ρ =1). The mass ratio K is derived from the three basic similarity ratios. m =K ρ K L 3 Frequency ratio K f =K υ / K L wait.

[0058] The third step involves modal and flutter characteristic analysis of the scaled-down airfoil structure (which is a simplified structure scaled down from the detailed structure according to the size ratio, not a scaled-down model. The scaled-down model is a simplified structure that meets the similarity ratio requirement). The airfoil structure model is scaled down proportionally according to the size ratio to obtain the main modal characteristics and flutter characteristics of the scaled-down structure. The modal frequencies and flutter critical velocities of each order are verified to meet the similarity ratio requirements. The scaled-down structure serves as the object of flutter wind tunnel testing.

[0059] The fourth step is to construct a scaled-down model baseline for the flutter test. Based on the main beams and ribs of the scaled-down airfoil structure, a simplified beam model is constructed. First, auxiliary supports with low cross-sectional stiffness are removed, retaining the main load-bearing frame with high stiffness and large span, as well as the outer perimeter frame of the airfoil. The simplified frame is replaced by rectangular cross-section beam elements with equivalent stiffness. Beams along the chord and spanwise directions divide the airfoil structure into multiple blocks. The beam element size should be as small as possible (generally, it is recommended that each block be divided into at least 5 beam elements on each side), and an elastic modulus and Poisson's ratio (based on the selected material properties) are assigned, while the density is set to 0 kg / m³. 3 Mass characteristic data (mass, center of mass, moment of inertia) of each segment of the scaled-down airfoil structure are extracted, simulated using lumped mass elements, and rigidly connected to adjacent beam element nodes. This approach effectively solves the decoupling problem between model stiffness and mass, with model stiffness and mass provided by massless beam elements and stiffnessless mass elements, respectively.

[0060] The fifth step is to optimize the parameters of the scaled-down model for the flutter test. The main modal parameters of the scaled-down airfoil structure are used as the correction targets. Specific optimization targets include the relative error of the modal frequencies and the mode shape MAC value (modal confidence criterion, used to evaluate the correlation between two modes). Sensitivity analysis and parameter optimization are performed on the moment of inertia of the beam element sections to ensure that the optimized target parameters meet the requirements (generally, the error of the main modal frequencies should be less than 5%, and the mode shape MAC value should be higher than 0.9).

[0061] Step 6: Reconstruct the scaled-down flutter test model. Based on the optimized beam section moment of inertia parameters, reconstruct the beam element section dimensions and assign material density properties. Distribute the beam element mass evenly to adjacent sub-regions and calculate the mass characteristic data of each sub-region of the beam model. Based on the sub-regional mass characteristic data of the scaled-down airfoil structure, obtain the residual mass characteristic data of each sub-region.

[0062] Step 7: Detailed Design of the Flutter Test Scale-Down Model. Based on the structural form of "skeleton + dimensional box segment," a detailed design of the scale-down model is conducted. The skeleton, i.e., the reconstructed beam model, is recommended to be made of aluminum alloy with a high stiffness-to-mass ratio and mature processing technology, and machined from a single sheet of metal. The dimensional box segment is recommended to be made of low-density, low-cost resin material, and processed using additive manufacturing technology. Using the beam model (beam units form the beam model, and the skeleton is the specific structure simulated by the beam model) as the center, the scale-down shape of the flange is divided. The detailed structure of the box segment is designed according to each division. The box segment retains four sides, internal stiffeners, and open top and bottom surfaces to ensure sufficient dimensional stiffness while also accommodating on-site operations such as model installation, sensor placement, and component replacement. Through reasonable allocation and optimization, the mass characteristics of the box segment are ensured to be consistent with the remaining mass characteristics of the corresponding segmented areas, and the center of mass is located in the middle of the internal stiffeners. Each box segment is bonded to the skeleton by ribs at the center of gravity. After assembly, cotton paper is laid on the top and bottom surfaces of each box segment and glue is applied to achieve the integrity of the model's outer surface. Figure 2 This illustrates the installation process of a single shaped box segment.

[0063] This invention has been successfully applied to the design of a large-scale scaled-down model for low-speed flutter wind tunnel testing of an airfoil with trailing edge control surfaces. Based on a detailed scaled-down airfoil structural model reduced to its original size, an equivalent stiffness simplified beam model is constructed using the internal main load-bearing structure and the outer peripheral skeleton. By providing stiffness and mass respectively through massless beam elements and stiffnessless mass elements, the design factors of the model's stiffness and mass characteristics are effectively decoupled. The skeleton is integrally formed from a single sheet of aluminum alloy, reducing the complexity of component assembly and maximizing the consistency between the finished model and the design state. The three-dimensional shape of the scaled-down airfoil structure is divided into mesh segments, and a detailed resin dimensional box segment structure is designed and processed using additive manufacturing technology. This achieves high fidelity to the complex three-dimensional shape of the airfoil, effectively reducing the processing cycle and cost, and facilitating on-site installation and adjustment.

[0064] Using the method of this patent, a scaled-down model of a wing with trailing edge control surfaces for low-speed flutter wind tunnel testing with a size ratio of 3:1 was designed. The analysis results of the first four main modes had an error of less than 4.6% compared with the experimental data. The model successfully completed 40 low-speed wind tunnel tests. The analysis results of the flutter critical speed had an error of 7.6% compared with the experimental data.

[0065] This invention can be widely applied in the design of scaled-down models for low-speed flutter wind tunnel tests of wing structures such as fixed wings and control surfaces.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing, characterized in that, Includes the following steps: The first step is to establish a detailed dynamic finite element model based on the actual three-dimensional structural model, and to correct the key stiffness parameters of the model based on the main order modal data obtained from the ground modal test, so as to complete the flutter characteristic analysis of the wing structure. The second step is to determine the similarity ratio between the scaled-down model and the actual airfoil structure: based on the external dimensions of the airfoil structure and the effective dimensions of the wind tunnel test section, determine the size ratio K. L Based on the critical flutter velocity of the wing structure and the wind tunnel blowing speed, the velocity ratio K is determined. υ The density ratio K is determined based on the atmospheric density corresponding to the actual flight altitude and the wind tunnel inflow density. ρ The mass ratio K is derived from the three basic similarity ratios. m =K ρ K L 3 Frequency ratio K f =K υ / K L ; The third step is to reduce the wing structure model proportionally according to the determined similarity ratio to obtain the scaled-down detailed structure, and then calculate the modal characteristics and flutter characteristics of the scaled-down detailed structure. The fourth step is to compare the main modal characteristics and flutter analysis results of the scaled-down detailed structure obtained in the third step with the main modal characteristics and flutter analysis results of the airfoil structure obtained in the first step to ensure that the modal frequencies of the scaled-down detailed structure and the actual airfoil meet the frequency ratio and the flutter critical velocity meets the velocity ratio. Step 5, Constructing the initial scaled-down model: The method for constructing the initial scaled-down model includes the following steps: S5.1 The main load-bearing frame and the outer peripheral frame of the wing surface are retained in the scaled-down detailed structure, while the auxiliary supports with low cross-sectional stiffness are removed. The retained frame divides the initial scaled-down model into multiple blocks. S5.2 replaces the retained skeleton with rectangular cross-section beam elements of equivalent stiffness, and assigns elastic modulus and Poisson's ratio to the beam elements based on the selected material properties, with the material density set to 0 kg / m³. 3 ; S5.3 Extract the mass characteristic data of each block of the scaled detailed structure of the airfoil, including mass, center of mass and moment of inertia, simulate it with lumped mass elements, and bind it to the nodes of the adjacent beam elements through rigid connection elements; S5.4 The scaled-down detailed structural outline is the same as the scaled-down model outline. The sixth step is to calculate the main modal parameters of the initial scaled-down model, take the moment of inertia of the beam element section for sensitivity analysis and parameter optimization, and ensure that the main modal frequency errors and modal confidence criterion values ​​of the initial scaled-down model and the scaled-down detailed structure of the airfoil meet the requirements. Step 7: Based on the optimized beam element moment of inertia, reconstruct the cross-sectional dimensions of the model beam element, assign the beam element the real material density property, distribute the beam element mass evenly to the adjacent block regions, and calculate the remaining mass characteristic data of each block region based on the mass characteristic data of each block of the detailed structure of the scaled-down flange. Step 8: Using the intersection of beam elements as the center, divide the scaled-down model shape. Design V-shaped box segments according to each division. The V-shaped box segments retain four sides, have internal reinforcing ribs, and open top and bottom surfaces. Based on the remaining mass characteristics data of the segmented areas, the position, shape and mass of the V-shaped box segments are designed. Taking the beam intersection position or the middle position of the near intersection point of the beam model as the center, the V-shaped box segments are symmetrically fixed around the beam model. Skins are set on the top and bottom of the V-shaped box segments to achieve the integrity of the model's outer surface.

2. The method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing according to claim 1, characterized in that, The beam element size should be as small as possible, and each block should be divided into at least 5 beam elements on one side.

3. The method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing according to claim 2, characterized in that, The main modal data include modal frequencies and mode shapes.

4. The method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing according to claim 3, characterized in that, The criteria for the main modal parameters in the sixth step are: the main modal frequency error is less than 5% and the mode shape MAC value is higher than 0.

9.

5. The method for designing a scaled-down airfoil model for low-speed flutter wind tunnel testing according to claim 4, characterized in that, The main frame and the outer peripheral frame of the wing surface are obtained by machining a whole sheet of aluminum alloy metal, and the shaped box segment is obtained by additive manufacturing technology using resin material.

6. The scaled-down airfoil model obtained by the airfoil scaled-down model design method for low-speed flutter wind tunnel testing according to any one of claims 1-5, characterized in that, The model includes a skeleton, three-dimensional box segments, and a skin. The skeleton comprises a main load-bearing skeleton and an outer peripheral skeleton for the wing surfaces. The skeleton divides the scaled-down model into several sections. The skeleton is replaced by several beam elements, and adjacent beam elements are bound together by rigid connection elements to form a beam model. The three-dimensional box segments retain four sides, have internal reinforcing ribs, and open top and bottom surfaces. They are symmetrically fixed around the beam model with the beam intersection or the middle of the nearest intersection point as the center. Skins are provided on the top and bottom of the three-dimensional box segments to achieve the integrity of the model's external surface.

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