A free rolling test method for a dynamically similar scaled model

Abstract

A kind of power similar scale model free roll test method, belong to wind tunnel test technical field.For solving the problem of accurately evaluating the motion characteristics of real aircraft by using scale model.The present application includes calculating the maximum moment of inertia of scale model according to the moment of inertia of real aircraft, flight height, flight Mach number, designing and processing scale model;Build scale model moment of inertia test system;Using forced vibration method, by inputting fixed amplitude equal frequency sine vibration to scale model, measure the actual roll moment of inertia of scale model;Calculate wind tunnel total pressure;Carry out free roll test of scale model dynamic similarity simulation, release the roll degree of freedom of model, obtain the relationship between roll angle and time, select each wave crest and adjacent wave trough in the obtained angle curve, record the roll angle value and time of wave crest, the roll angle value and time of wave trough, calculate the maximum dimensionless roll angular velocity, for evaluating the non-command roll motion characteristics of aircraft.

Description

Technical Field

[0001] This invention belongs to the field of wind tunnel testing technology, specifically relating to a method for free roll test of a scaled-down model with similar dynamics. Background Technology

[0002] When an aircraft flies at high subsonic speeds and at medium angles of attack, the asymmetrical separation of airflow over the surfaces of the left and right wings will cause asymmetry in the aerodynamic forces of the left and right wings, making the aircraft prone to uncommanded roll motion. This phenomenon limits the flight envelope of the aircraft and affects flight quality. The severity of uncommanded roll motion should be accurately predicted and assessed during the aircraft design phase.

[0003] Uncommanded roll motion includes motion forms such as wing descent and wing rocking, which are pure roll motions of the aircraft around its body axis. The most direct method is to use a scaled-down model in a wind tunnel to conduct free roll tests with the roll degree of freedom released to obtain the motion trajectory under aerodynamic excitation, and to evaluate the severity of uncommanded motion by solving for the dimensionless roll angular velocity.

[0004] When conducting free roll tests using a scaled-down model, dynamic similarity conditions must be met to ensure that motion parameters such as angle, angular velocity, and angular acceleration are similar to those of the actual aircraft. Based on flow and motion similarity relationships, it can be concluded that in addition to satisfying geometric shape, Mach number, and attitude angle similarity, the scaled-down model also needs to satisfy Strouhal number similarity, meaning the roll inertia must satisfy the following relationship:

[0005]

[0006] in, To scale down the model, For the roll inertia of a full-size aircraft, The moment of inertia of the scaled-down test model during rolling. The incoming flow density for a full-size aircraft under flight conditions. Let be the incoming air density of the scaled-down test model in the wind tunnel. Under normal pressure conditions during wind tunnel testing, the air density is typically slightly higher than the air density at the actual flight altitude of the aircraft. For a scaled-down model, if the density and volume are the same as the actual model, the ratio of the moment of inertia of the scaled-down model to that of the actual aircraft is . Slightly scaling up the model's rolling moment of inertia would satisfy the Strouhal number similarity requirement. However, in reality, because real aircraft are primarily made of aluminum and have a hollow interior, while the experimental model is mainly made of steel with limited internal hollowing, the experimental model cannot be modeled according to the actual aircraft's design. When scaled proportionally, its moment of inertia is much greater than that of a real aircraft. This makes it impossible for similarity relationships to be established.

[0007] Therefore, it is necessary to invent a dynamically similar free roll test method to solve the problem that the motion parameters obtained when using scaled-down model tests in high-speed wind tunnels are similar to those of real aircraft. Summary of the Invention

[0008] The problem this invention aims to solve is that in wind tunnel tests for non-command roll motion evaluation, a scaled-down model can be used to accurately evaluate the motion characteristics of a real aircraft. This invention proposes a method for free roll testing using a scaled-down model with similar dynamics.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for a scaled-down model with similar dynamics to undergo free roll test includes the following steps:

[0011] S1. Calculate the maximum moment of inertia of the scaled-down model based on the actual aircraft's moment of inertia, flight altitude, and flight Mach number, and design and manufacture the scaled-down model.

[0012] S2. For the scaled-down model obtained in step S1, build a test system for the moment of inertia of the scaled-down model;

[0013] S3. Using the forced vibration method, the actual rolling moment of inertia of the scaled-down model is measured by inputting sinusoidal vibrations of fixed amplitude and frequency into the scaled-down model.

[0014] S4. Calculate the total wind tunnel pressure based on the actual rolling moment of inertia obtained in step S2;

[0015] S5. Based on the total wind tunnel pressure obtained in step S3, conduct a free roll test of the scaled-down model dynamic similarity simulation under the target Mach number, angle of attack, and total pressure conditions. Release the roll degree of freedom of the model, obtain the relationship between the roll angle and time, select each peak and adjacent trough in the obtained angle curve, record the roll angle value and time of the peak and the roll angle value and time of the trough, and calculate the maximum dimensionless roll angular velocity to evaluate the non-commanded roll motion characteristics of the aircraft.

[0016] Furthermore, the scaled-down model moment of inertia test system in step S2 includes a scaled-down model, a force balance, an angle measuring balance, a support rod, a motion conversion mechanism, and a drive motor connected in sequence.

[0017] Furthermore, the specific implementation method of step S3 is to use the forced vibration method to perform sinusoidal oscillations of fixed amplitude and frequency on the scaled-down model under windless conditions on the ground, and to measure the rolling torque using a force balance. An angle measuring balance is used to measure the roll angle history of the scaled-down model, and then the actual roll moment of inertia of the scaled-down model is calculated. The expression is:

[0018]

[0019]

[0020]

[0021] in, The rolling torque is measured by the force balance. The magnitude of the rolling torque measured by the force balance; The roll angle history of a scaled-down model under sinusoidal vibration; This represents the roll angle amplitude of a scaled-down model under sinusoidal vibration. Let be the angular acceleration of the model under sinusoidal vibration. The frequency of sinusoidal vibration is... This represents the actual rolling moment of inertia of the scaled-down model.

[0022] Furthermore, the expression for calculating the total wind tunnel pressure in step S4 is as follows:

[0023]

[0024] in, For the total pressure of the wind tunnel, For the total temperature of the wind tunnel, The scaling factor is the model scaling factor. The incoming flow density of a full-size aircraft at its flight altitude. For wind tunnel testing Mach number; The gas constant is For wind tunnel testing Mach number, This refers to the rolling moment of inertia of a full-size aircraft.

[0025] Furthermore, the specific implementation method of step S5 includes the following steps:

[0026] S5.1. A free roll test of a scaled-down model under wind load conditions was conducted. An angle encoder acquired the roll angle history of the model. Each peak and its adjacent trough were selected from the obtained angle curve. The roll angle value and time corresponding to the i-th peak were recorded. Roll angle value and time of trough ;

[0027] S5.2. Calculate the dimensionless roll velocity, and then filter for the maximum dimensionless roll velocity. The expression is:

[0028]

[0029]

[0030] in, Let be the dimensionless roll angular velocity corresponding to the i-th wave crest. The maximum dimensionless roll velocity; This is the lateral reference length for the scaled-down model; denoted as the incoming flow velocity under wind tunnel test conditions; max is the maximum value function; and m is the total number of wave crests.

[0031] The beneficial effects of this invention are:

[0032] This invention discloses a method for conducting free roll tests on a scaled-down model with dynamic similarity. Aiming to meet the dynamic similarity conditions that the scaled-down model must satisfy, it achieves dynamic similarity simulation by rationally designing the roll inertia of the scaled-down model and increasing the total wind tunnel pressure. This ensures that the motion parameters of the scaled-down model are similar to those of the actual aircraft, enabling accurate evaluation of the uncommanded roll motion characteristics of the actual aircraft. This invention provides inertia constraints during the scaled-down model design phase and accurately measures the actual inertia on the ground using forced vibration to ensure compliance with requirements. Simultaneously, it obtains accurate wind tunnel test conditions, avoiding deviations caused by theoretical data and improving the accuracy of motion parameter prediction in the free roll test of the scaled-down model. The motion parameter measurement results of this invention can quickly and accurately evaluate the uncommanded roll motion characteristics of the actual aircraft, establish a correlation between ground and space, predict the probability and severity of problems during aircraft flight, improve safety, and save costs. Attached Figure Description

[0033] Figure 1 This is a flowchart of a dynamically similar scaled-down model free roll test method according to the present invention;

[0034] Figure 2 This is a schematic diagram of the scaled-down model moment of inertia test system of the present invention;

[0035] Figure 3 This is a schematic diagram of the free roll test mechanism for the scaled-down model dynamic similarity simulation in step S5 of the present invention;

[0036] Figure 4 This is a schematic diagram illustrating the dimensionless angular velocity calculation of the present invention;

[0037] In the figure, 1 is a scaled-down model, 2 is a force balance, 3 is an angle measuring balance, 4 is a support rod, 5 is a motion conversion mechanism, 6 is a drive motor, 7 is a tail support rod, 8 is a combined bearing one, 9 is a combined bearing two, 10 is a pitch angle measuring sensor, and 11 is a roll angle measuring sensor. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0039] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0040] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 4 Detailed explanation is as follows:

[0041] Example 1:

[0042] A method for a scaled-down model with similar dynamics to undergo free roll test includes the following steps:

[0043] S1. Calculate the maximum moment of inertia of the scaled-down model based on the actual aircraft's moment of inertia, flight altitude, and flight Mach number, and design and manufacture the scaled-down model.

[0044] S2. For the scaled-down model obtained in step S1, build a test system for the moment of inertia of the scaled-down model;

[0045] Furthermore, the scaled-down model moment of inertia test system in step S2 includes a scaled-down model, a force balance, an angle measuring balance, a support rod, a motion conversion mechanism, and a drive motor connected in sequence.

[0046] S3. Using the forced vibration method, the actual rolling moment of inertia of the scaled-down model is measured by inputting sinusoidal vibrations of fixed amplitude and frequency into the scaled-down model.

[0047] Furthermore, the specific implementation method of step S3 is to use the forced vibration method to perform sinusoidal oscillations of fixed amplitude and frequency on the scaled-down model under windless conditions on the ground, and to measure the rolling torque using a force balance. An angle measuring balance is used to measure the roll angle history of the scaled-down model, and then the actual roll moment of inertia of the scaled-down model is calculated. The expression is:

[0048]

[0049]

[0050]

[0051] in, The rolling torque is measured by the force balance. The magnitude of the rolling torque measured by the force balance; The roll angle history of a scaled-down model under sinusoidal vibration; This represents the roll angle amplitude of a scaled-down model under sinusoidal vibration. Let be the angular acceleration of the model under sinusoidal vibration. The frequency of sinusoidal vibration is... This represents the actual rolling moment of inertia of the scaled-down model.

[0052] S4. Calculate the total wind tunnel pressure based on the actual rolling moment of inertia obtained in step S2;

[0053] Furthermore, the expression for calculating the total wind tunnel pressure in step S4 is as follows:

[0054]

[0055] in, For the total pressure of the wind tunnel, For the total temperature of the wind tunnel, The scaling factor is the model scaling factor. The incoming flow density of a full-size aircraft at its flight altitude. For wind tunnel testing Mach number; The gas constant is For wind tunnel testing Mach number, This refers to the rolling moment of inertia of a full-size aircraft.

[0056] S5. Based on the total wind tunnel pressure obtained in step S3, conduct a free roll test of the scaled-down model dynamic similarity simulation under the target Mach number, angle of attack, and total pressure conditions. Release the roll degree of freedom of the model, obtain the relationship between the roll angle and time, select each peak and adjacent trough in the obtained angle curve, record the roll angle value and time of the peak and the roll angle value and time of the trough, and calculate the maximum dimensionless roll angular velocity to evaluate the non-commanded roll motion characteristics of the aircraft.

[0057] Furthermore, the specific implementation method of step S5 includes the following steps:

[0058] S5.1. A free roll test of a scaled-down model under wind load conditions was conducted. An angle encoder acquired the roll angle history of the model. Each peak and its adjacent trough were selected from the obtained angle curve. The roll angle value and time corresponding to the i-th peak were recorded. Roll angle value and time of trough ;

[0059] S5.2. Calculate the dimensionless roll velocity, and then filter for the maximum dimensionless roll velocity. The expression is:

[0060]

[0061]

[0062] in, Let be the dimensionless roll angular velocity corresponding to the i-th wave crest. The maximum dimensionless roll velocity; This is the lateral reference length for the scaled-down model; denoted as the incoming flow velocity under wind tunnel test conditions; max is the maximum value function; and m is the total number of wave crests.

[0063] This embodiment describes a dynamic similarity-based scaled-down model free roll test method for evaluating the non-commanded roll motion characteristics of a high-subsonic wind tunnel aircraft. By limiting the roll inertia of the scaled-down model and increasing the total wind tunnel pressure to improve the incoming flow density, dynamic similarity simulation is achieved, ensuring that the motion history of the scaled-down model is consistent with that of the real aircraft. This test method was invented to address the issue of obtaining motion parameters similar to those of a real aircraft when using a scaled-down model in a high-speed wind tunnel. Through reasonable design of the roll inertia of the scaled-down model and the use of increased total wind tunnel pressure, dynamic similarity simulation is achieved, ensuring that the motion parameters of the scaled-down model are similar to those of the real aircraft, and accurately evaluating the non-commanded roll motion characteristics of the real aircraft. By providing roll inertia constraints during the scaled-down model design stage, the actual roll inertia can be accurately measured on the ground using the forced vibration method to ensure that the requirements are met. Simultaneously, accurate wind tunnel test conditions can be obtained, avoiding deviations caused by using theoretical data and improving the accuracy of motion parameter prediction in the scaled-down model free roll test. The motion parameter measurement results of the scaled-down model in this embodiment can quickly and accurately assess the non-commanded roll motion characteristics of a real aircraft, establish a correlation between ground and space, predict the probability and severity of problems that may occur during aircraft flight, improve safety, and save costs. It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0064] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for a scaled-down model with dynamic similarity to undergo free roll test, characterized in that, Includes the following steps: S1. Calculate the maximum moment of inertia of the scaled-down model based on the actual aircraft's moment of inertia, flight altitude, and flight Mach number, and design and manufacture the scaled-down model. S2. For the scaled-down model obtained in step S1, build a test system for the moment of inertia of the scaled-down model; S3. Using the forced vibration method, the actual rolling moment of inertia of the scaled-down model is measured by inputting sinusoidal vibrations of fixed amplitude and frequency into the scaled-down model. S4. Calculate the total wind tunnel pressure based on the actual rolling moment of inertia obtained in step S2; S5. Based on the total wind tunnel pressure obtained in step S3, conduct a free roll test of the scaled-down model dynamic similarity simulation under the target Mach number, angle of attack, and total pressure conditions. Release the roll degree of freedom of the model, obtain the relationship between the roll angle and time, select each peak and adjacent trough in the obtained angle curve, record the roll angle value and time of the peak and the roll angle value and time of the trough, and calculate the maximum dimensionless roll angular velocity to evaluate the non-commanded roll motion characteristics of the aircraft.

2. The method for free roll test of a scaled-down model with dynamic similarity according to claim 1, characterized in that, The scaled-down model moment of inertia test system in step S2 includes a scaled-down model, a force balance, an angle measuring balance, a support rod, a motion conversion mechanism, and a drive motor connected in sequence.

3. A method for a dynamically similar scaled-down model free roll test according to claim 1 or 2, characterized in that, The specific implementation method of step S3 is as follows: under windless conditions on the ground, the scaled-down model is subjected to sinusoidal oscillations of fixed amplitude and frequency using the forced vibration method, and the rolling torque is measured by a force balance. An angle measuring balance is used to measure the roll angle history of the scaled-down model, and then the actual roll moment of inertia of the scaled-down model is calculated. The expression is: in, The rolling torque is measured by the force balance. The magnitude of the rolling torque measured by the force balance; The roll angle history of a scaled-down model under sinusoidal vibration; This represents the roll angle amplitude of a scaled-down model under sinusoidal vibration. Let be the angular acceleration of the model under sinusoidal vibration. The frequency of sinusoidal vibration is... This represents the actual rolling moment of inertia of the scaled-down model.

4. The method for free roll test of a scaled-down model with dynamic similarity according to claim 3, characterized in that, The expression for calculating the total wind tunnel pressure in step S4 is: in, For the total pressure of the wind tunnel, For the total temperature of the wind tunnel, The scaling factor is the model scaling factor. The incoming flow density of a full-size aircraft at its flight altitude. The gas constant is For wind tunnel testing Mach number, This refers to the rolling moment of inertia of a full-size aircraft.

5. The method for a scaled-down model with dynamic similarity to undergo free roll test according to claim 4, characterized in that, The specific implementation method of step S5 includes the following steps: S5.

1. A free roll test of a scaled-down model under wind load conditions was conducted. An angle encoder acquired the roll angle history of the model. Each peak and its adjacent trough were selected from the obtained angle curve. The roll angle value and time corresponding to the i-th peak were recorded. Roll angle value and time of trough ; S5.

2. Calculate the dimensionless roll velocity, and then filter for the maximum dimensionless roll velocity. The expression is: in, Let be the dimensionless roll angular velocity corresponding to the i-th wave crest. The maximum dimensionless roll velocity; This is the lateral reference length for the scaled-down model; denoted as the incoming flow velocity under wind tunnel test conditions; max is the maximum value function; and m is the total number of wave crests.

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