A method for designing a rigid-flexible coupling aeroelastic scaled model of a high-aspect-ratio flying wing layout aircraft

Abstract

The application discloses a large-aspect-ratio flying wing layout aircraft rigid-elastic coupling aeroelastic scaling model design method. The method is based on the rigid-elastic coupling aeroelastic equation, the key parameters to be matched are determined through dimensionless, including inertia ratio, reduced frequency and Froude number, and length, speed and density are used as basic scales to derive target scaling parameters such as mass / inertia, structural stiffness and modal frequency. When the flow similarity is difficult to meet, the iterative optimization strategy of lift and moment coefficient error minimization is introduced, and the speed ratio and mass / inertia scaling constraints are coupled into the structural arrangement variable optimization to realize the coordination of static / dynamic aeroelastic compatibility. The model design adopts the spar-pod structure system of'stiffness beam + external shape', and the mass / inertia and modal matching are completed by adjusting the beam section and counterweight, and the flutter critical speed, frequency and shape are used as the similarity verification indexes. The method can be used for early evaluation and verification of large-aspect-ratio flying wing aeroelastic phenomena.

Description

Technical Field

[0001] This invention relates to the fields of aircraft design, vibration, and aerodynamics, specifically to a method for designing a scaled-down aeroelastic model of a high aspect ratio flying wing aircraft under the condition of coupling between rigid body modes and low-order elastic modes. It is particularly suitable for scaled-down verification of rigid-elastic coupling instability phenomena such as flutter of body degrees of freedom. Background Technology

[0002] High-aspect-ratio flying wing aircraft exhibit high structural flexibility and relatively small pitch inertia. Short-period pitch modes are prone to coupling with low-order bending modes under aerodynamic forces, inducing flutter within the flight envelope. To reduce the risks and costs of full-scale testing, scaled-down model tests are often necessary. However, traditional flutter scaling methods tend to focus on matching natural modal frequencies and modal effective mass, making it difficult to simultaneously account for the significant inertial coupling and static aeroelastic effects in flying wing configurations. To achieve aeroelastic responses consistent with full-scale models, a set of key dimensionless parameters (such as inertia ratio, scaling frequency, and Froude number) needs to be matched. Furthermore, a coordinated similarity and iterative optimization method for rigid-elastic coupling in flying wings is proposed.

[0003] Therefore, there is an urgent need for a scaled-down model design method that can be implemented in engineering, can be achieved through structural layout and counterweight adjustment, and can be verified in a closed loop by observable experimental indicators. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a scaled-down rigid-elastic coupled aeroelastic model. Even when flow similarity is difficult to fully satisfy, the scaled-down model can still ensure consistency or acceptable consistency with the original model in key rigid-elastic coupling mechanisms and flutter boundaries (velocity / frequency / morphology) through coordinated similarity criteria and iterative optimization.

[0005] To achieve the above objectives, the present invention employs the following steps:

[0006] Step 1: Determine the scaled-down object and target phenomenon

[0007] The original model was selected as the scaled-down benchmark, and the dominant coupling mechanism and target phenomenon to be reproduced were identified (such as the critical trend of rigid-elastic coupling caused by the coupling of longitudinal short-period pitch mode and symmetrical first-order bending mode).

[0008] Step 2: Establish a set of key dimensionless parameters for scaled-down similarity

[0009] The linearized aeroelastic equations of motion are made dimensionless, and the set of dimensionless parameters that must be matched to the scaled-down model is determined to include at least the following: inertia ratio, scaling frequency, Froude number, etc., to ensure consistent dynamic response at scaled-down scales.

[0010] Step 3: Select the basic scale and derive the target scaling parameters

[0011] Length, velocity, and air density are selected as the basic scale to derive the relationships between target parameters such as mass ratio, inertia ratio, stiffness ratio, and modal frequency ratio, which are used to form design constraints and indicators for scaled-down models.

[0012] Step 4: Static aeroelastic constraints and flow dissimilarity handling

[0013] When Mach number / flow similarity is difficult to satisfy, static aeroelastic similarity, such as dimensionless deformation similarity, is transformed into a multidisciplinary design optimization problem. By adjusting the local geometric and structural characteristics, the scaled-down model can achieve equivalent similarity in terms of total load and deflection.

[0014] Step 5: Selecting the scaling factor for rigid-elastic coupling coordinated similarity and iterative optimization.

[0015] A multi-step iterative strategy is constructed that takes into account both static and dynamic aeroelasticity and includes inertial characteristic constraints: First, the candidate ranges for scale ratio and velocity ratio are determined based on classical flutter scaling; then, structural layout variables are optimized with the goal of minimizing the error of lift / moment coefficients at multiple cross-sections and angles of attack, while incorporating velocity ratio and mass / inertia similarity constraints; if the structure is not feasible, the scale ratio / velocity ratio is adjusted back and iterated until engineering feasibility is met; finally, a combination of scaling factors that satisfy coordination and similarity is output.

[0016] Step 6: Overall and Structural Design of the Scaled-Down Verification Machine

[0017] Based on scaling parameters and engineering constraints, similarity in shape and center of gravity ratio is determined, with priority given to ensuring similarity in mass / moment of inertia and consistency in the dominant coupled modal frequency relationships, resulting in a manufacturable structural scheme. The principles of scaling design based on similarity laws and using observable measurements such as flutter velocity and frequency as final verification indicators are presented. Examples of key scaling parameters (such as flutter velocity, span, center of gravity position, and modal frequencies) for both the original and scaled-down verification machines are also provided.

[0018] Step 7: Achieving mass / inertia and stiffness matching

[0019] A spar-pod structural design system of "load-bearing beam + external formwork" was adopted to establish the design scheme of the scaled-down model prototype. The metal beam provides the overall stiffness of the aircraft, while the external formwork simulates the aerodynamic shape of the original reference model. This approach has the following advantages: using a single beam facilitates adjustment of the wing stiffness to ensure it meets the scaling requirements and controls the flutter velocity range; the external formwork only provides the aerodynamic shape and is connected to the beam at a single point, contributing little to the aircraft's stiffness, which can be ignored during modeling to simplify the model; furthermore, the external formwork can be manufactured using innovative methods such as 3D printing, shortening processing time, ensuring lightweight design, and improving experimental safety and repairability. Throughout the finite element modeling process, the mass, moment of inertia, and stiffness can be approximated to target values ​​by adding or removing mass points, adjusting their position / mass, and modifying beam cross-sectional dimensions.

[0020] Step 8: Model verification and experimental validation closed loop

[0021] A simplified finite element model was established, and key modal frequencies and mode shapes were obtained through free-free boundary modal analysis. Ground vibration tests were conducted for calibration to verify the consistency between the finite element model and the actual object. By combining aeroelastic prediction and field flight tests, flutter critical velocity, frequency and morphology were identified and compared with scaled-down predictions to complete the similarity verification closed loop.

[0022] Compared with existing technologies, this invention has at least the following advantages: It focuses on matching key dimensionless parameters, avoiding stiff-elastic coupling distortion caused by relying solely on "modal frequency / effective mass matching." Addressing the influence of flow dissimilarity and static aeroelasticity, it introduces an implementable multidisciplinary optimization and iteration strategy to achieve coordinated similarity that considers both static and dynamic aeroelasticity. It provides an adjustable engineering implementation path, enabling rapid matching of mass / inertia and stiffness through cross-sections and counterweights, thus reducing experimental risks. It constructs a closed-loop verification process of "design-analysis-experiment" using observable measurements such as flutter critical velocity / frequency / morphology, improving the credibility of scaled-down models. Attached Figure Description

[0023] Figure 1 This is a flowchart of the scaled-down model design method;

[0024] Figure 2 This is a schematic diagram of multidisciplinary optimization of a scaled-down flight test model;

[0025] Figure 3 This is a schematic diagram of the scaled-down verification machine;

[0026] Figure 4 This is a schematic diagram of the "spar-pod" structure of the wing;

[0027] Figure 5 This is a schematic diagram of the external pod structure scheme;

[0028] Figure 6 This is a schematic diagram of a spar beam used to provide stiffness;

[0029] Figure 7 This is a schematic diagram of the scaled-down model of the rudder surface structure. Detailed Implementation

[0030] To illustrate the technical features of the present invention, specific embodiments are described in further detail with reference to the accompanying drawings and examples. The following embodiments are used to illustrate the present invention but are not intended to limit its scope.

[0031] like Figure 1 The diagram shown is a block diagram of the scaling method of the present invention. Based on the dimensionless parameters required for flow similarity and geometric similarity, the relevant parameters affecting the scaling are derived by combining the rigid-elastic coupling aeroelastic motion equation. By satisfying these parameters, the scaling model achieves coordinated similarity between flight mechanics and aeroelasticity.

[0032] like Figure 2 The diagram shown is a scaled-down optimization design of the present invention. First, the scaled-down model needs to satisfy basic aeroelastic similarity. When further considering flow similarity, "static aeroelastic equivalent similarity" is required, using the lift coefficient, pitching moment coefficient, and corresponding deflection / torsional response of the original aircraft under the stated working condition as a benchmark. Under the premise of satisfying manufacturing and strength constraints, the optimization problem is solved, and the combination of design variables for static aeroelastic equivalent similarity is output. At the same time, velocity ratio and mass / inertia similarity constraints are added. An iterative strategy is used to determine the scale ratio and velocity ratio. If the structure is not feasible, the scale ratio / velocity ratio is adjusted back and iterated until engineering feasibility is satisfied. Finally, the combination of scaled-down factors that satisfy the coordination similarity is output.

[0033] like Figure 3 This is a scaled-down structural design diagram of the aircraft. The fuselage adopts a modular design, making manufacturing more convenient and faster. After manufacturing, it is connected to the internal frame via bolts or other detachable methods, improving maintenance convenience. The entire wing adopts a spar-pod design, consisting of a main sparsity that provides wing stiffness and multiple external aerodynamic sections. The sparsity and the external aerodynamic sections only make tight contact with each other at the bolt holes, minimizing the impact of the aerodynamic sections on the stiffness of the sparsity.

[0034] Figure 4 This is a schematic diagram of a single wing. Small gaps are set between the various aerodynamic shapes on the outside to prevent the shape blocks from squeezing each other and affecting the rigidity of the entire wing due to bending deformation caused by aerodynamic loads during flight.

[0035] Figure 5This is a side view of the external aerodynamic shape, with two protruding blocks inside. A spar passes between the two parts and is then bolted through to tightly connect them. The outer protrusion is the control surface connection point. Aligning the circular holes on the control surface with these holes and passing them through a pivot allows the control surface to rotate.

[0036] Figure 6 This is a schematic diagram of a wing beam that bears the load. The wing beam has through holes for connecting to external pods, and the ideal stiffness conditions can be obtained by adjusting the cross-sectional shape of the wing beam.

[0037] Figure 7 The diagram below shows the corresponding control surface. In this model design, the span of one control surface includes two pods. The length of the control surface should not be too long, otherwise the lateral bending stiffness of the control surface may affect the stiffness of the wing during flight.

[0038] The following is a detailed description of the implementation method:

[0039] Based on steps 2 and 3, key dimensionless parameters need to be matched, and indices such as flutter velocity, mass, center of gravity position, and target modal frequency of the scaled-down verification machine are derived. A comparison of key parameters between the scaled-down verification machine and the original verification machine (such as span, flutter velocity, and symmetrical bend frequency) is provided. According to step 4, when the scaled-down verification machine cannot simultaneously meet flow similarity conditions such as Mach number or Reynolds number within the test speed range, a "static aeroelastic equivalent similarity" strategy is adopted to select multiple representative working conditions (at least including multiple profiles, multiple angles of attack, or multiple load levels). The lift coefficient, pitching moment coefficient, and corresponding deflection / torsional response of the original verification machine under the stated working conditions are used as benchmarks. Under the premise of satisfying manufacturing and strength constraints, the optimization problem is solved, and the combination of design variables for static aeroelastic equivalent similarity is output. Based on the results of step 4, aerodynamic aeroelastic similarity and rigid-elastic coupling constraints are further introduced. An iterative strategy is used to determine the scale ratio and velocity ratio, and the closed-loop correction of structural parameters is completed.

[0040] Based on the spar-pod structure determined in steps 6 and 7, a single-point bolt connection is used between the beam and the external shape to minimize the stiffness influence of the external shape. The beam section parameterization and counterweight / equipment layout achieve the target matching of mass and rotational inertia, and the calibration is completed through free boundary modal analysis and ground vibration test. The method of matching mass / inertia and stiffness by adding or removing mass points, adjusting their positions, and modifying the carbon fiber beam section is given.

[0041] Based on step 8, aeroelastic analysis and field flight tests were conducted. During the gradual increase in speed, flutter criticality was identified and characteristic quantities such as frequency were extracted as final similarity test indicators. An example of the extraction method and results of flutter speed and frequency of the prototype aircraft is given.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for designing a scaled-down model of a rigid-elastic coupled aeroelastic configuration aircraft with a high aspect ratio flying wing, characterized in that, The method is as follows: Step 1: Determine the aeroelastic coupling phenomenon between the original machine and the target to be reproduced; Step 2: Establish the set of key dimensionless parameters for scaled-down similarity: Dimensionlessize the aeroelastic motion equations to obtain the set of key dimensionless parameters that the scaled-down model needs to match; Step 3: Select the basic scale and derive the target scaling parameters: Select length, speed and air density as the basic scale, and derive the target scaling parameters for mass, moment of inertia, structural stiffness and modal frequency; Step 4: Static aeroelastic constraints and flow dissimilarity handling: When flow similarity is difficult to meet, the static aeroelastic similarity requirements are transformed into an optimization problem. By adjusting the structural layout variables, the error of lift and moment coefficient of multi-section and multi-angle of attack is minimized, and the velocity ratio and mass / inertia similarity constraints are introduced. Step 5: Selecting the scaling factor for rigid-elastic coupling coordinated similarity and iterative optimization; Step 6: Overall and structural design of the scaled-down verification machine; Step 7: Achieve mass / inertia and stiffness matching; Step 8: Closed loop of model verification and experimental validation.

2. The design method for a scaled-down model of a rigid-elastic coupled aeroelastic system for a high aspect ratio flying wing aircraft according to claim 1, characterized in that, Step 5 is as follows: Construct a multi-step iterative strategy that takes into account both static and dynamic aeroelasticity and includes inertial characteristic constraints: First, determine the candidate ranges for scale ratio and velocity ratio based on the classical flutter scaling; then, optimize the structural layout variables with the goal of minimizing the error of lift / moment coefficients in multiple profiles and angles of attack, while adding velocity ratio and mass / inertia similarity constraints. If the structure is not feasible, backtrack and adjust the scale ratio / speed ratio and iterate until engineering feasibility is met; the final output satisfies the combination of scaling factors that are compatible and similar.

3. The design method for a scaled-down model of a high aspect ratio flying wing aircraft with rigid-elastic coupling according to claim 1, characterized in that, Step 6 is as follows: Based on the scaling parameters and engineering constraints, determine the similarity in shape and center of gravity ratio, and prioritize ensuring the similarity in mass / moment of inertia and the consistency of the dominant coupled mode frequency relationship to form a manufacturable structural scheme.

4. The method for designing a scaled-down model of a rigid-elastic coupled aeroelastic system for a high aspect ratio flying wing aircraft according to claim 1, characterized in that, Step 7 is as follows: The design scheme of the scaled-down model prototype is established by adopting the load-bearing beam frame and the external dimensional spar-pod structural design system. The metal beam frame is used to provide the rigidity of the whole machine, and the external dimensional shape is used to simulate the aerodynamic shape of the original reference base.

5. The method for designing a scaled-down model of a high aspect ratio flying wing aircraft with rigid-elastic coupling according to claim 1, characterized in that, In step 2, the set of key dimensionless parameters includes at least two of the following: inertia ratio, reduction frequency, and Froude number. By matching the dimensionless parameters, the scaled-down model is made to maintain consistency with the aeroelastic dynamic response of the original model.

6. The method for designing a scaled-down model of a rigid-elastic coupled aeroelastic system for a high aspect ratio flying wing aircraft according to claim 1, characterized in that, In step 3, at least two of the mass ratio, frequency ratio, stiffness ratio, and dynamic pressure ratio are derived from the basic scale and used as design constraints for the scaled-down model.

7. The method for designing a scaled-down model of a high aspect ratio flying wing aircraft with rigid-elastic coupling according to claim 1, characterized in that, Step 4 employs a feasibility multidisciplinary optimization framework to minimize the error in lift and moment coefficients under multiple angles of attack conditions, in order to approximate the static aeroelastic equivalent similarity under dissimilar flow conditions.

8. The method for designing a scaled-down model of a high aspect ratio flying wing aircraft with rigid-elastic coupling according to claim 1, characterized in that, Steps 4 and 5 employ a multi-step iterative strategy. When the structure becomes unfeasible, the candidate ranges for the scale ratio and velocity ratio are adjusted and re-optimized until the requirements for engineering feasibility and coordination similarity are met.

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