A rotary flutter wind tunnel test system and method with powered rotors

Abstract

A wind tunnel testing system and method for a powered rotor-driven flutter system, belonging to the field of wind tunnel testing technology, addresses the problems associated with relying on airflow to drive rotor rotation in testing. The system includes a test model and a protection system. The test model comprises a semi-modular wing and a nacelle connected to the right end of the semi-modular wing. The semi-modular wing is fixed to the wall panel of the test section. A motor tray is located inside the nacelle, and a drive motor is mounted on the motor tray. The output shaft of the drive motor is connected to the rotor shaft, and the rotor is fitted onto the front end of the rotor shaft. A counterweight is located at the rear end of the motor tray. The protection system applies a vertical upward traction to the counterweight through one protective rope and a vertical downward traction through another protective rope. This invention applies a horizontal rightward traction to the counterweight through the excitation rope, which can promptly break through the critical state, thereby preventing the test model from suddenly experiencing flutter in a certain state and causing damage to the test model.

Description

Technical Field

[0001] This invention belongs to the field of wind tunnel testing technology, and particularly relates to a rotating flutter wind tunnel testing system and method with a powered rotor. Background Technology

[0002] A tiltrotor aircraft is a type of aircraft that cleverly combines the advantages of helicopters and fixed-wing aircraft by installing integrally tiltable engine nacelles at the wingtips. During vertical takeoff and landing and hovering, the nacelles tilt upwards to provide lift; during forward cruise, the nacelles tilt forward to a horizontal position, with the rotor providing thrust and the wings providing lift, thus achieving high speeds and long ranges far exceeding those of traditional helicopters. This design gives tiltrotor aircraft unique deployment flexibility and speed advantages in military transport, search and rescue, and other fields, thus holding enormous development potential in both military and civilian sectors.

[0003] Due to their unique tiltrotor nacelle structure, tiltrotor aircraft are highly susceptible to gyroscopic flutter. Gyroscopic flutter is a specific type of aeroelastic instability, manifesting as a self-excited instability caused by the coupling of the aerodynamic forces generated by the rotor with the inherent vibration modes of the relatively flexible nacelle support structure during flight. The massive rotor system, mounted at the slender wingtip, generates significant flapping torque when its rotation produces strong thrust and, due to disturbances, flaps. This torque acts on the relatively flexible nacelle support structure through the rotation axis, forcing the rotor nacelle to undergo gyroscopic vibration. Simultaneously, the nacelle's gyroscopic vibration, in turn, alters the nacelle-rotor attitude, severely disrupting the angle between the rotor disk and the airflow. This disruption further amplifies the initial flapping motion of the rotor, resulting in self-excited, divergent gyroscopic flutter. At certain tilt angles and medium-to-high speeds, gyroscopic flutter can severely threaten the flight safety of tiltrotor aircraft, potentially leading to catastrophic structural damage in a very short time.

[0004] Currently, domestic research on gyroscopic flutter in tiltrotor aircraft mainly focuses on wind tunnel testing and numerical simulation. However, due to the strong nonlinearity of gyroscopic flutter, numerical simulation is difficult to accurately simulate, making wind tunnel testing a more powerful method for studying this phenomenon. Existing wind tunnel tests on rotor gyroscopic flutter are typically unpowered tests, relying mainly on airflow to drive rotor rotation. This method has several shortcomings: 1. Because rotor speed is related to wind speed, it is impossible to obtain flutter wind speeds at different speeds; 2. If the rotor rotation excitation frequency couples with a certain modal frequency of the model, resonance will occur. It is difficult to avoid the resonance speed range by adjusting the wind speed, and it is easy to misjudge the flutter wind speed; 3. Due to inertia, when gyroscopic flutter occurs, it is impossible to quickly stop the rotor rotation, failing to effectively protect the model and thus putting the test in a dangerous state. If the rotor or model is damaged, it will affect the test progress. Summary of the Invention

[0005] The purpose of this invention is to provide a powered rotor-driven flutter wind tunnel testing system and method to solve the technical problems associated with relying on airflow to drive rotor rotation for testing. The technical solution adopted by this invention is as follows:

[0006] A wind tunnel testing system for a powered rotor flutter includes a test model, a motor control system, a protection system, and a data acquisition and monitoring system. The test model includes a semi-mode wing and a nacelle connected to the right end of the semi-mode wing. The left end of the semi-mode wing is fixed to the left wall of the test section. A motor tray is provided inside the nacelle, and a drive motor is mounted on the motor tray. The output shaft of the drive motor is connected to the rear end of the rotor shaft through a flange. The front end of the rotor shaft extends forward out of the nacelle, and the rotor is sleeved on the front end of the rotor shaft.

[0007] The motor control system includes a control cabinet and a water-cooled cabinet. The drive motor is electrically connected to the control cabinet, the water-cooled cavity of the drive motor is connected to the water-cooled cabinet, and the water-cooled cabinet establishes a data connection with the control cabinet.

[0008] The rear end of the motor tray is equipped with a counterweight bar. The protection system applies a vertical upward traction to the counterweight bar through a protection rope, a vertical downward traction to the counterweight bar through another protection rope, and a horizontal rightward traction to the counterweight bar through an excitation rope.

[0009] The data acquisition and monitoring system includes a data acquisition host, strain gauges, pitch acceleration sensors, and yaw acceleration sensors. The data acquisition host is equipped with data acquisition and monitoring software. The strain gauges are attached to the root of the semi-mode wing. The pitch acceleration sensors are located at the front end of the motor tray, and the yaw acceleration sensors are located on the left or right side of the motor tray. The data from the strain gauges, pitch acceleration sensors, and yaw acceleration sensors are uploaded to the data acquisition host via a data acquisition card and read and stored by the data acquisition and monitoring software.

[0010] Furthermore, the semi-mold wing is provided with wiring channels. The control cabinet and the water-cooled cabinet are both located outside the test section. The power line between the drive motor and the control cabinet passes through one of the wiring channels through the semi-mold wing and is led out of the test section through the wiring hole on the left wall panel. The coolant pipe between the drive motor and the water-cooled cabinet passes through the semi-mold wing through another wiring channel and is led out of the test section through the wiring hole on the left wall panel.

[0011] Furthermore, the protective system also includes pulleys and protective handles. Pulleys are provided on both the upper and lower walls of the test section. The two pulleys are respectively located directly above and below the counterweight rod. One end of each of the two protective ropes is connected to the protective handle fixed outside the test section, and the other end of each of the two protective ropes passes around the two pulleys and is connected to the counterweight rod.

[0012] Furthermore, the protection system also includes an excitation handle, which is mounted on the right wall of the test section, and the counterweight bar is connected to the excitation handle via an excitation rope.

[0013] Furthermore, the root of the semi-modular wing is fixed to the side wall of the test section via an L-shaped adapter.

[0014] Furthermore, it also includes a fairing fuselage, which is mounted at the connection between the semi-engineered wing and the test section.

[0015] This invention also provides a method for testing rotary flutter wind tunnels with powered rotors, based on the aforementioned rotary flutter wind tunnel testing system with powered rotors, comprising the following steps:

[0016] Step 1: Use a dynamic balancing machine to adjust the dynamic balance of the rotor to ensure that the vibration value of the rotor is below 0.2 ips, so as to avoid excessive excitation to the test model when the rotor rotates;

[0017] Step 2: Conduct ground modal tests to determine the modal frequencies of the half-mode wing and nacelle. Based on the modal frequencies of the half-mode wing and nacelle, determine the range of the test rotor speed n. Ensure that the test speed frequencies n / 60, 2n / 60, and 3n / 60 do not coincide with the modes of the test model, thus avoiding excessive excitation to the test model due to rotor rotation.

[0018] If a certain modal frequency of the semi-mode wing and nacelle cannot be avoided from the rotor's rotational speed frequency, a rotational speed restriction zone is set to prevent the rotor speed from remaining within this zone. The range of the rotational speed restriction zone is ±15% of the corresponding modal frequency, meaning that n / 60, 2n / 60, and 3n / 60 are all outside 0.85f. i ~1.15f i Within the range, f i Let i represent the modal frequencies of the experimental model, where i is the corresponding modal order.

[0019] Step 3: Determine the parameters of the drive motor based on the range of the test speed n. First, determine the maximum test speed n based on the range of the test speed n. max Then, find n according to the rotor speed table. max The corresponding theoretical wind speed V L The theoretical wind speed V L Increase the current wind speed by 20%, then determine the current wind speed as 1.2V according to the windmill speed reference table. L The corresponding rotational speed n 1.2max The engineering estimation formula for the aerodynamic torque of the rotor is as follows:

[0020] (1)

[0021] In the formula, C Q This is the torque coefficient, which is obtained experimentally or determined based on empirical data from similar rotors;

[0022] A is the rotor disk area, in meters (m²). 2 ;

[0023] ω is the angular velocity of the rotor, measured in rad / s;

[0024] ρ is the air density, with units of kg / m³. 3 ;

[0025] R is the radius of the rotor, in meters (m).

[0026] The area A of the propeller disk is calculated using the following formula:

[0027] (2)

[0028] Angular velocity ω is calculated using the following formula:

[0029] (3)

[0030] Combining equations (1) to (3), we get:

[0031] (4)

[0032] The maximum speed of the drive motor is taken as twice the maximum speed used in the test. The minimum power P of the drive motor is calculated according to the following formula:

[0033] (5)

[0034] The selection of drive motors is based on the principle that the maximum torque of the drive motor is greater than or equal to Q and the rated power is greater than or equal to P. The drive motor with the largest rated current is given priority to improve the adjustment capability of the drive motor.

[0035] Step 4: Conduct flow display tests. Use the smoke flow method to determine the influence area of ​​the separated flow after the rotor rotates, observe the generation and natural development process of the rotor tip vortex, and observe the process of the tip vortex attaching and spreading on the surface of the half-mode wing. Determine the maximum area of ​​influence of the separated flow by changing the collective pitch of the rotor, preliminarily determine the test conditions for flutter, and use the collective pitch when the area of ​​influence of the separated flow is the maximum as the reference collective pitch to conduct a rotary flutter test.

[0036] Step 5: Confirm that the test system is operating normally. Conduct a rotary flutter wind tunnel test using the reference collective distance determined in Step 4. First, start the drive motor at a speed of 30 rpm to 80 rpm and start the wind tunnel with a wind speed of 10 m / s to 15 m / s. Then, increase the speed of the drive motor to the test set speed n0. Then, gradually increase the wind speed according to the preset wind speed step. When the wind speed is close to the flutter wind speed calculated in theory, adjust the wind speed step to 0.5 m / s to 1 m / s.

[0037] Step Six: When the wind speed stabilizes, collect data for 15 seconds using the strain gauges, pitch acceleration sensor, and yaw acceleration sensor. Process the collected data using the subcritical response analysis method. The processing procedure is as follows:

[0038] Assume the acquired test system response signal can be represented in discrete-time form as follows:

[0039] (6)

[0040] In the formula, k is the number of samplings, k = 1, 2, ..., N, z i For the system response poles, M is twice the number of modes in the experimental system. ω is the sampling period. i With ξ i Let be the natural frequency and damping ratio of the i-th mode of the test system, respectively; the Hankel matrix Y constructed from the response signal y(k) is as follows:

[0041] (7)

[0042] In the formula, L is the matrix bundle parameter, taking values ​​between N / 3 and N / 2. Assuming Y is an m×n matrix, performing singular value decomposition on matrix Y yields:

[0043] Y=UXV T (8)

[0044] In the formula, U is an m×m unitary matrix, X is an m×n diagonal matrix, and V T It is the conjugate transpose of V, and is an n×n unitary matrix;

[0045] The first M dominant right singular vectors of the unitary matrix V are used to form an (L+1)×M dimensional matrix V1. Deleting the last row of V1 yields an L×M dimensional matrix V. a Meanwhile, deleting the first row of elements from V1 yields an L×M dimensional matrix V. b This results in the following two (N+L)×L dimensional matrices:

[0046] (9)

[0047] Use Y a and Y b The constructed matrix bundle is as follows:

[0048] (10)

[0049] The poles of the signal z i That is, the generalized eigenvalues ​​of equation (10), which can be transformed into solving the matrix G=Y. a +Y b Eigenvalues, where matrix Y a + It is the pseudo-inverse of a matrix, and matrix G has M non-zero eigenvalues ​​λ. i (i=1, 2, ..., M), after solving for the eigenvalues ​​of matrix G, the corresponding coefficient matrix α of the characteristic equation can be obtained. i Thus, the natural frequency ω is obtained. i With damping ratio ξ i When the wind speed is stable, the damping ratio ξ is obtained by processing the last five collected data points. i Then, based on the damping ratio ξ i Plot a scatter plot of wind speed-damping ratio, perform curve fitting, and extrapolate to obtain the wind speed corresponding to the damping ratio being zero, which is the estimated flutter wind speed.

[0050] Step 7: When the wind speed approaches and stabilizes near the estimated flutter wind speed, manually pull the excitation handle while observing the state of the test model and the time and frequency domain data of the data monitoring software. The first peak in the frequency domain data is the excitation frequency of the rotor. When the test model produces vibrations that stop decaying, or when the amplitude of the time domain data shows obvious divergence, or when the frequency domain data shows a second peak that does not decrease, it is determined that the test model is experiencing rotational flutter.

[0051] Step 8: If the test model experiences flutter, tighten the protective handle and reduce the speed of the drive motor to a stop. To prevent excessive deceleration from causing current overshoot, the drive motor can be reduced to 50 rpm before stopping. Simultaneously, the wind tunnel should be shut down. Then, extract the flutter test data and plot the rotor flutter amplitude-frequency characteristic curve. Calculate the current rotor rotation excitation frequency using n0 / 60. When the rotation excitation frequency equals one peak value in the amplitude-frequency characteristic curve, the other peak value is the rotor flutter frequency. If the wind speed V... S If the flutter speed exceeds the calculated flutter speed by 20%, it is assumed that no rotational flutter will occur at a speed of 50 rpm. If the temperature of the drive motor reaches the set threshold, the test is stopped. If the temperature of the drive motor is within the safe range, the speed can be increased to the next test speed n0, and the speed can be increased according to the preset speed step. Steps six and seven are repeated to measure the flutter speed of the test model at each speed under the current collective distance and to plot the speed-flutter speed envelope.

[0052] Furthermore, during the process of increasing the wind speed, observe the current and drive motor temperature feedback on the control cabinet. If the drive motor current reaches the maximum current and the drive motor temperature rise rate reaches 5° / s, it indicates that the rotor speed is too different from the windmill speed under the current wind speed condition. In this case, first increase the current set speed by 5%, then increase the wind speed, and observe whether the drive motor current and temperature have a decreasing trend. If the temperature decreases, continue the test according to step seven, and at the same time observe whether the test model exhibits the gyroscopic flutter described in step seven. If gyroscopic flutter occurs, the test ends; if gyroscopic flutter does not occur, it is determined that gyroscopic flutter will not occur at this speed. Observe the drive motor temperature again. If the drive motor temperature reaches the set threshold, the test stops. If the drive motor temperature is within the safe range, increase the speed to the next test speed n1 and continue the test.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] This invention selects the drive motor based on the rotor's rotational speed range, ensuring sufficient power and torque. Precise speed control of the drive motor allows for the acquisition of flutter speeds at different rotational speeds with the same collective pitch, enabling the plotting of rotational speed-flutter speed envelopes. This provides data reference for the design and operation of related aircraft types. Furthermore, during testing, the drive motor can provide high torque to the rotor, quickly escaping the flutter state and protecting the test model from damage caused by prolonged vibration. By pre-setting the rotational speed range using modal test data from the test model, it effectively avoids prolonged resonance or misjudgments of flutter caused by resonance. This invention utilizes smoke flow testing to preliminarily determine the basic test conditions, effectively reducing the total number of test runs and thus saving testing costs. This invention utilizes subcritical response analysis to process collected experimental data, obtaining the vibration frequency and damping ratio of the test model during wind blowing, and predicting the flutter wind speed, thereby assisting in determining whether the model has reached the critical state of rotational flutter. An excitation rope is used to excite the test model when the wind speed approaches the predicted flutter wind speed, causing it to undergo rotational flutter. This allows for timely breakthrough of the critical state, bringing the test model into the rotational flutter state, thus preventing damage to the test model caused by sudden rotational flutter in a certain state. This makes the rotational flutter test safer and more controllable, ensuring the safety of the test model during the test process, avoiding the need for repair after damage, improving test efficiency, and saving costs. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0056] Figure 2 This is a schematic diagram of the connection structure between the protection system and the test model;

[0057] Figure 3 This is a flowchart of the parameter selection process for the drive motor;

[0058] Figure 4 This is a flowchart of the method of the present invention;

[0059] Figure 5 This is a curve showing the predicted flutter speed of the rotor.

[0060] Figure 6 It is the amplitude-frequency characteristic curve of the rotor's flutter point.

[0061] In the diagram, 1-test section, 2-rectifier fuselage, 3-half-mode wing, 4-rotor, 5-rotor shaft, 6-flange, 7-drive motor, 8-motor tray, 9-nacelle, 10-counterweight bar, 11-control cabinet, 12-water-cooled cabinet, 13-protective rope, 14-pulley, 15-excitation rope, 16-excitation handle, 17-protective handle, 18-L-type adapter. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0063] The connections mentioned in this invention are divided into fixed connections and detachable connections. Fixed connections, also known as non-detachable connections, include but are not limited to conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include but are not limited to conventional disassembly methods such as bolted connections, snap-fit ​​connections, pin connections, and hinged connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can be found to achieve this function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for fixed connections, and a bolted connection can be chosen for detachable connections.

[0064] The present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0065] Example 1: As Figures 1-5As shown, a wind tunnel test system for a powered rotor flutter includes a test model, a motor control system, a protection system, and a data acquisition and monitoring system. The test model includes a semi-mode wing 3 and a nacelle 9 connected to the right end of the semi-mode wing 3. The left end of the semi-mode wing 3 is fixed to the left wall of the test section 1. A motor tray 8 is provided inside the nacelle 9. A drive motor 7 is installed on the motor tray 8. The output shaft of the drive motor 7 is connected to the rear end of the rotor shaft 5 through a flange 6. The front end of the rotor shaft 5 extends forward out of the nacelle 9, and the rotor 4 is sleeved on the front end of the rotor shaft 5.

[0066] The motor control system includes a control cabinet 11 and a water-cooled cabinet 12. The drive motor 7 is electrically connected to the control cabinet 11, the water-cooled cavity of the drive motor 7 is connected to the water-cooled cabinet 12, and the water-cooled cabinet 12 establishes a data connection with the control cabinet 11.

[0067] The rear end of the motor tray 8 is provided with a counterweight rod 10. The protection system applies a vertical upward traction to the counterweight rod 10 through a protection rope 13, applies a vertical downward traction to the counterweight rod 10 through another protection rope 13, and applies a horizontal rightward traction to the counterweight rod 10 through an excitation rope 15.

[0068] The data acquisition and monitoring system includes a data acquisition host, strain gauges, pitch acceleration sensors, and yaw acceleration sensors. The data acquisition host is equipped with data acquisition and monitoring software. The strain gauges are attached to the root of the semi-mode wing 3 to monitor the bending and twisting of the semi-mode wing 3. The pitch acceleration sensor is located at the front end of the motor tray 8, and the yaw acceleration sensor is located on the left or right side of the motor tray 8 to monitor the vibration of the nacelle 9 in the pitch and yaw directions. The data from the strain gauges, pitch acceleration sensors, and yaw acceleration sensors are uploaded to the data acquisition host via a data acquisition card and read and stored by the data acquisition and monitoring software.

[0069] The semi-mold wing 3 is provided with wiring channels. The control cabinet 11 and the water-cooled cabinet 12 are both located outside the test section 1. The power line between the drive motor 7 and the control cabinet 11 passes through the semi-mold wing 3 through one of the wiring channels and is led out of the test section 1 through the wiring hole on the left wall panel. The coolant pipe between the drive motor 7 and the water-cooled cabinet 12 passes through the semi-mold wing 3 through another wiring channel and is led out of the test section 1 through the wiring hole on the left wall panel.

[0070] The protective system also includes pulleys 14 and protective handles 17. Pulleys 14 are provided on both the upper and lower walls of the test section 1. The two pulleys 14 are respectively located directly above and below the counterweight rod 10. One end of each of the two protective ropes 13 is connected to the protective handle 17 fixed outside the test section 1. The other end of each of the two protective ropes 13 passes around the two pulleys 14 and is connected to the counterweight rod 10.

[0071] The protection system also includes an excitation handle 16, which is set on the right wall of the test section 1. The counterweight rod 10 is connected to the excitation handle 16 via an excitation rope 15.

[0072] The root of the semi-modular wing 3 is fixed to the side wall of the test section 1 via an L-shaped adapter 18.

[0073] It also includes a rectifier fuselage 2, which is mounted on the connection between the semi-mode wing 3 and the test section 1.

[0074] Example 2: Figures 1-6 As shown, a method for testing rotary flutter wind tunnels with powered rotors, based on the rotary flutter wind tunnel testing system with powered rotors described in Example 1, includes the following steps:

[0075] Step 1: Use a dynamic balancing machine to adjust the dynamic balance of rotor 4 to ensure that the vibration value of rotor 4 is below 0.2ips, so as to avoid excessive excitation to the test model when rotor 4 rotates;

[0076] Step 2: Conduct ground modal tests to determine the modal frequencies of the half-mode wing 3 and nacelle 9. Based on the modal frequencies of the half-mode wing 3 and nacelle 9, determine the range of the test rotational speed n of the rotor 4. Ensure that the rotational speed frequencies n / 60, second harmonic 2n / 60, and third harmonic 3n / 60 used in the test do not coincide with the modes of the test model, so as to avoid excessive excitation to the test model due to the rotation of the rotor 4.

[0077] If a certain modal frequency of the semi-mode wing 3 and nacelle 9 cannot be avoided from the rotational speed frequency of the rotor 4, a rotational speed restriction zone is set to prevent the rotor 4's rotational speed from remaining within the restriction zone. The range of the rotational speed restriction zone is ±15% of the corresponding modal frequency, that is, n / 60, 2n / 60, and 3n / 60 are all not above 0.85f. i ~1.15f i Within the range, f i Let i represent the modal frequencies of the experimental model, where i is the corresponding modal order.

[0078] Step 3: Determine the parameters of the drive motor 7 based on the range of the test speed n. First, determine the maximum test speed n based on the range of the test speed n. max Then, find n according to the wind turbine speed reference table for rotor 4. max The corresponding theoretical wind speed V L The theoretical wind speed V L Increase the current wind speed by 20%, then determine the current wind speed as 1.2V according to the windmill speed reference table. L The corresponding rotational speed n 1.2max The aerodynamic torque estimation formula for rotor 4 is as follows:

[0079] (1)

[0080] In the formula, C Q This is the torque coefficient, which is obtained experimentally or determined based on empirical data from similar rotors;

[0081] A represents the rotor disk area of ​​rotor 4, in meters (m²). 2 ;

[0082] ω is the angular velocity of rotor 4, in rad / s;

[0083] ρ is the air density, with units of kg / m³. 3 ;

[0084] R is the radius of rotor 4, in meters;

[0085] The area A of the propeller disk is calculated using the following formula:

[0086] (2)

[0087] Angular velocity ω is calculated using the following formula:

[0088] (3)

[0089] Combining equations (1) to (3), we get:

[0090] (4)

[0091] The maximum speed of drive motor 7 is taken as twice the maximum speed used in the experiment. The minimum power P of drive motor 7 is calculated according to the following formula:

[0092] (5)

[0093] The principle is to select drive motor 7 based on the maximum torque being greater than or equal to Q and the rated power being greater than or equal to P, and to prioritize drive motor 7 with the largest rated current in order to improve the adjustment capability of drive motor 7.

[0094] Step 4: Begin wind tunnel testing. First, conduct flow display tests. Use the smoke flow method to determine the influence area of ​​the separated flow after the rotor 4 rotates. Observe the generation and natural development process of the tip vortex of the rotor 4, and observe the process of the tip vortex attaching and spreading on the surface of the half-mode wing 3. Determine the maximum area of ​​influence of the separated flow by changing the collective pitch of the rotor 4, and preliminarily determine the test conditions for flutter. Use the collective pitch when the area of ​​influence of the separated flow is the maximum as the reference collective pitch to conduct a rotational flutter test.

[0095] Step 5: Confirm that the test system is operating normally. Conduct a rotary flutter wind tunnel test using the reference collective distance determined in Step 4. First, start the drive motor 7 at a speed of 30 rpm to 80 rpm and start the wind tunnel at a wind speed of 10 m / s to 15 m / s. Then, increase the speed of the drive motor 7 to the test set speed n0. Then, gradually increase the wind speed according to the preset wind speed step. When the wind speed is close to the flutter wind speed calculated theoretically, adjust the wind speed step to 0.5 m / s to 1 m / s.

[0096] Step Six: When the wind speed stabilizes, collect data for 15 seconds using the strain gauges, pitch acceleration sensor, and yaw acceleration sensor. Process the collected data using the subcritical response analysis method. The processing procedure is as follows:

[0097] Assume the acquired test system response signal can be represented in discrete-time form as follows:

[0098] (6)

[0099] In the formula, k is the number of samplings, k = 1, 2, ..., N, z i For the system response poles, M is twice the number of modes in the experimental system. ω is the sampling period. i With ξ i Let be the natural frequency and damping ratio of the i-th mode of the test system, respectively; the Hankel matrix Y constructed from the response signal y(k) is as follows:

[0100] (7)

[0101] In the formula, L is the matrix bundle parameter, taking values ​​between N / 3 and N / 2. Assuming Y is an m×n matrix, performing singular value decomposition on matrix Y yields:

[0102] Y=UXV T (8)

[0103] In the formula, U is an m×m unitary matrix, X is an m×n diagonal matrix, and V T It is the conjugate transpose of V, and is an n×n unitary matrix;

[0104] The first M dominant right singular vectors of the unitary matrix V are used to form an (L+1)×M dimensional matrix V1. Deleting the last row of V1 yields an L×M dimensional matrix V. a Meanwhile, deleting the first row of elements from V1 yields an L×M dimensional matrix V. b This results in the following two (N+L) ×L dimensional matrices:

[0105] (9)

[0106] Use Y a and Y b The constructed matrix bundle is as follows:

[0107] (10)

[0108] The poles of the signal z i That is, the generalized eigenvalues ​​of equation (10), which can be transformed into solving the matrix G=Y. a +Y b Eigenvalues, where matrix Y a + It is the pseudo-inverse of a matrix, and matrix G has M non-zero eigenvalues ​​λ. i (i=1, 2, ..., M), after solving for the eigenvalues ​​of matrix G, the corresponding coefficient matrix α of the characteristic equation can be obtained. i Thus, the natural frequency ω is obtained. i With damping ratio ξ i When the wind speed is stable, the damping ratio ξ is obtained by processing the last five collected data points. i Then, based on the damping ratio ξ i Plot a scatter plot of wind speed versus damping ratio, perform curve fitting, and extrapolate to obtain the wind speed corresponding to a damping ratio of zero, which is the estimated flutter wind speed. Figure 5 As shown;

[0109] Step 7: When the wind speed approaches and stabilizes near the estimated flutter wind speed, manually pull the excitation handle 16 and observe the state of the test model and the time and frequency domain data of the data monitoring software. The first peak in the frequency domain data is the excitation frequency of the rotor 4. When the test model produces a vibration that stops decaying, or the amplitude of the time domain data shows obvious divergence, or the frequency domain data shows a second peak that does not decrease, it is determined that the test model is experiencing rotational flutter.

[0110] Step 8: If the test model experiences flutter, tighten the protective handle 17 and reduce the speed of the drive motor 7 to a stop. To prevent excessive deceleration from causing current overshoot, the drive motor 7 can be reduced to 50 rpm before stopping. Simultaneously, the wind tunnel should be stopped. Then, extract the flutter test data and plot the rotor flutter amplitude-frequency characteristic curve. Calculate the current rotor 4 rotation excitation frequency using n0 / 60. When the rotation excitation frequency equals one peak value in the amplitude-frequency characteristic curve, the other peak value is the rotor 4 rotation flutter frequency. If the wind speed V... SIf the flutter wind speed exceeds the numerically calculated value by 20%, it is assumed that no rotational flutter will occur at a speed of 50 rpm. If the temperature of the drive motor 7 reaches the set threshold, the test is stopped. If the temperature of the drive motor 7 is within the safe range, the speed can be increased to the next test speed n0, and the wind speed can be increased according to the preset wind speed step. Steps six and seven are repeated to measure the flutter wind speed of the test model at each speed under the current collective distance and to plot the speed-flutter wind speed envelope.

[0111] During the process of increasing the wind speed, observe the current on the control cabinet 11 and the temperature feedback of the drive motor 7. If the current of the drive motor 7 reaches the maximum current and the temperature rise rate of the drive motor 7 reaches 5° / s, it indicates that the rotation speed of the rotor 4 is too different from the windmill rotation speed under the current wind speed. Then, first increase the current set speed by 5%, then increase the wind speed, and observe whether the current and temperature of the drive motor 7 have a decreasing trend. If the temperature decreases, continue to conduct the test according to step seven. At the same time, observe whether the test model exhibits the gyroscopic flutter described in step seven. If gyroscopic flutter occurs, the test ends. If gyroscopic flutter does not occur, it is determined that gyroscopic flutter will not occur at this speed. Observe the temperature of the drive motor 7 again. If the temperature of the drive motor 7 reaches the set threshold, the test stops. If the temperature of the drive motor 7 is within the safe range, increase the speed to the next test speed n1 and continue the test.

[0112] This invention selects the drive motor 7 based on the rotor 4's rotational speed range, ensuring sufficient power and torque. Precise speed control of the drive motor 7 allows for the acquisition of flutter speeds at different rotational speeds with the same collective pitch, enabling the plotting of rotational speed-flutter speed envelopes. This provides data reference for the design and operation of related aircraft types. Furthermore, during testing, the drive motor 7 can provide high torque to the rotor 4, quickly escaping the flutter state and protecting the test model from damage caused by prolonged vibration. By pre-setting the rotational speed range using modal test data from the test model, it effectively avoids prolonged resonance or misjudgments of flutter caused by resonance. This invention utilizes smoke flow testing to preliminarily determine the basic test conditions, effectively reducing the total number of test runs and thus saving testing costs. This invention utilizes subcritical response analysis to process collected experimental data, obtaining the vibration frequency and damping ratio of the test model during wind blowing, and predicting the flutter wind speed, thereby assisting in determining whether the model has reached the critical state of rotational flutter. An excitation rope 15 is used to excite the test model when the wind speed approaches the predicted flutter wind speed, causing it to undergo rotational flutter. This allows the critical state to be broken in time, enabling the test model to enter the rotational flutter state. This avoids sudden rotational flutter in a certain state that could damage the test model, making the rotational flutter test safer and more controllable, ensuring the safety of the test model during the test, avoiding damage and subsequent repair, improving test efficiency, and saving costs.

[0113] The above embodiments are merely illustrative examples of the present invention and do not limit its scope of protection. Those skilled in the art can make partial changes to them, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A rotary flutter wind tunnel testing system with a powered rotor, characterized in that: It includes a test model, a motor control system, a protection system and a data acquisition and monitoring system; the test model includes a half-model wing (3) and a nacelle (9) connected to the right end of the half-model wing (3), the left end of the half-model wing (3) is fixed to the left wall of the test section (1), a motor tray (8) is provided in the nacelle (9), a drive motor (7) is installed on the motor tray (8), the output shaft of the drive motor (7) is connected to the rear end of the rotor shaft (5) through a flange (6), the front end of the rotor shaft (5) extends forward out of the nacelle (9), and the rotor (4) is sleeved on the front end of the rotor shaft (5); The motor control system includes a control cabinet (11) and a water-cooled cabinet (12). The drive motor (7) is electrically connected to the control cabinet (11), the water-cooled cavity of the drive motor (7) is connected to the water-cooled cabinet (12), and the water-cooled cabinet (12) establishes a data connection with the control cabinet (11). The rear end of the motor tray (8) is provided with a counterweight rod (10). The protection system applies vertical upward traction to the counterweight rod (10) through a protection rope (13), applies vertical downward traction to the counterweight rod (10) through another protection rope (13), and applies horizontal rightward traction to the counterweight rod (10) through an excitation rope (15). The data acquisition and monitoring system includes a data acquisition host, strain gauges, pitch acceleration sensors, and yaw acceleration sensors. The data acquisition host is equipped with data acquisition and monitoring software. The strain gauges are attached to the root of the semi-mode wing (3). The pitch acceleration sensors are located at the front end of the motor tray (8). The yaw acceleration sensors are located on the left or right side of the motor tray (8). The data from the strain gauges, pitch acceleration sensors, and yaw acceleration sensors are uploaded to the data acquisition host via a data acquisition card and read and stored by the data acquisition and monitoring software.

2. The rotary flutter wind tunnel testing system with a powered rotor according to claim 1, characterized in that: The semi-mold wing (3) is provided with wiring channels. The control cabinet (11) and the water-cooled cabinet (12) are both located outside the test section (1). The power line between the drive motor (7) and the control cabinet (11) passes through the semi-mold wing (3) through one of the wiring channels and is led out of the test section (1) through the wiring hole on the left wall panel. The coolant pipe between the drive motor (7) and the water-cooled cabinet (12) passes through the semi-mold wing (3) through another wiring channel and is led out of the test section (1) through the wiring hole on the left wall panel.

3. The rotary flutter wind tunnel testing system with a powered rotor according to claim 1, characterized in that: The protective system also includes pulleys (14) and protective handles (17). The upper and lower walls of the test section (1) are equipped with pulleys (14). The two pulleys (14) are respectively located directly above and below the counterweight rod (10). One end of the two protective ropes (13) is connected to the protective handle (17) fixed outside the test section (1). The other end of the two protective ropes (13) passes around the two pulleys (14) and is connected to the counterweight rod (10).

4. The rotary flutter wind tunnel testing system with a powered rotor according to claim 3, characterized in that: The protection system also includes an excitation handle (16), which is set on the right wall of the test section (1), and the counterweight rod (10) is connected to the excitation handle (16) through the excitation rope (15).

5. The rotary flutter wind tunnel testing system with a powered rotor according to claim 1, characterized in that: The root of the semi-modular wing (3) is fixed to the side wall of the test section (1) via an L-shaped adapter (18).

6. The rotary flutter wind tunnel testing system with a powered rotor according to claim 5, characterized in that: It also includes a rectifier fuselage (2), which is mounted on the connection between the semi-mode wing (3) and the test section (1).

7. A method for testing rotary flutter wind tunnels with powered rotors, implemented using the rotary flutter wind tunnel testing system with powered rotors as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Use a dynamic balancing machine to adjust the dynamic balance of the rotor (4) to ensure that the vibration value of the rotor (4) is below 0.2ips, so as to avoid excessive excitation to the test model when the rotor (4) rotates; Step 2: Conduct ground modal tests to determine the modal frequencies of the half-mode wing (3) and nacelle (9). Based on the modal frequencies of the half-mode wing (3) and nacelle (9), determine the range of the test rotational speed n of the rotor (4). Ensure that the rotational speed frequencies n / 60, second harmonic 2n / 60, and third harmonic 3n / 60 used in the test do not coincide with the modal frequencies of the test model, so as to avoid excessive excitation to the test model due to the rotation of the rotor (4). If a certain modal frequency of the semi-mode wing (3) and nacelle (9) cannot be avoided from the rotational speed frequency of the rotor (4), a rotational speed restriction zone is set to prevent the rotor (4) speed from remaining within the restriction zone. The range of the rotational speed restriction zone is ±15% of the corresponding modal frequency, that is, n / 60, 2n / 60, and 3n / 60 are all not above 0.85f. i ~1.15f i Within the range, f i Let i represent the modal frequencies of the experimental model, where i is the corresponding modal order. Step 3: Determine the parameters of the drive motor (7) according to the range of the test speed n. First, determine the maximum test speed n based on the range of the test speed n. max Then, find n according to the wind turbine speed reference table of rotor (4). max The corresponding theoretical wind speed V L The theoretical wind speed V L Increase the current wind speed by 20%, then determine the current wind speed as 1.2V according to the windmill speed reference table. L The corresponding rotational speed n 1.2max The aerodynamic torque estimation formula for rotor (4) is as follows: ； (1) In the formula, C Q This is the torque coefficient, which is obtained experimentally or determined based on empirical data from similar rotors; A is the rotor disk area of ​​rotor (4), in m². 2 ; ω is the angular velocity of the rotor (4), in rad / s; ρ is the air density, with units of kg / m³. 3 ; R is the radius of the rotor (4), in meters; The area A of the propeller disk is calculated using the following formula: ；(2) Angular velocity ω is calculated using the following formula: ；(3) Combining equations (1) to (3), we get: ； (4) The maximum speed of the drive motor (7) is taken as twice the maximum speed used in the experiment. The minimum power P of the drive motor (7) is calculated according to the following formula: ； (5) The principle is to select the drive motor (7) with the maximum torque greater than or equal to Q and the rated power greater than or equal to P, and to prioritize the drive motor (7) with the largest rated current in order to improve the adjustment capability of the drive motor (7); Step 4: Conduct flow display test, use the smoke flow method to determine the influence area of ​​the separated flow after the rotor (4) rotates, observe the generation and natural development process of the rotor tip vortex of the rotor (4), and observe the process of the tip vortex attaching and spreading on the surface of the half-mode wing (3). By changing the collective pitch of the rotor (4), determine the maximum area of ​​the separated flow influence, preliminarily determine the test conditions for flutter, and take the collective pitch when the separated flow influence area is the maximum as the reference collective pitch to conduct a rotary flutter test; Step 5: Confirm that the test system is operating normally, and conduct a rotary flutter wind tunnel test based on the reference total distance determined in Step 4. First, start the drive motor (7) at a speed of 30 rpm to 80 rpm, and make the wind tunnel start with a wind speed of 10 m / s to 15 m / s. Then, increase the speed of the drive motor (7) to the test set speed n0, and then gradually increase the wind speed according to the preset wind speed step. When the wind speed is close to the flutter wind speed calculated theoretically, adjust the wind speed step to 0.5 m / s to 1 m / s. Step Six: When the wind speed stabilizes, collect data for 15 seconds using the strain gauges, pitch acceleration sensor, and yaw acceleration sensor. Process the collected data using the subcritical response analysis method. The processing procedure is as follows: Assume the acquired test system response signal can be represented in discrete-time form as follows: ； (6) In the formula, k is the number of samplings, k = 1, 2, ..., N, z i For the system response poles, M is twice the number of modes in the experimental system. ω is the sampling period. i With ξ i Let be the natural frequency and damping ratio of the i-th mode of the test system, respectively; the Hankel matrix Y constructed from the response signal y(k) is as follows: ；(7) In the formula, L is the matrix bundle parameter, taking values ​​between N / 3 and N / 2. Assuming Y is an m×n matrix, performing singular value decomposition on matrix Y yields: Y=UXV T ; (8) In the formula, U is an m×m unitary matrix, X is an m×n diagonal matrix, and V T It is the conjugate transpose of V, and is an n×n unitary matrix; The first M dominant right singular vectors in the unitary matrix V are used to construct an (L+1)×M dimensional matrix V1. Deleting the last row of V1 yields an L... An M-dimensional matrix V a At the same time, deleting the first row of elements in V1 yields an L. An M-dimensional matrix V b Thus, we obtain the following two (N+L) results. An L-dimensional matrix: ； (9) Use Y a and Y b The constructed matrix bundle is as follows: Y a -λY b ;(10) The poles of the signal z i That is, the generalized eigenvalues ​​of equation (10), which can be transformed into solving the matrix G=Y. a + Y b Eigenvalues, where matrix Y a + It is the pseudo-inverse of a matrix, and matrix G has M non-zero eigenvalues ​​λ. i For i = 1, 2, ..., M, after solving for the eigenvalues ​​of matrix G, the corresponding coefficient matrix α of the characteristic equation can be obtained. i Thus, the natural frequency ω is obtained. i With damping ratio ξ i When the wind speed is stable, the damping ratio ξ is obtained by processing the last five collected data points. i Then, based on the damping ratio ξ i Plot a scatter plot of wind speed-damping ratio, perform curve fitting, and extrapolate to obtain the wind speed corresponding to the damping ratio being zero, which is the estimated flutter wind speed. Step 7: When the wind speed is close to the estimated flutter wind speed and stabilizes, manually pull the excitation handle (16) and observe the state of the test model and the time and frequency domain data of the data monitoring software. The first peak in the frequency domain data is the excitation frequency of the rotor (4). When the test model produces a vibration that stops decaying, or the time domain data shows obvious amplitude divergence, or the frequency domain data shows a second peak that does not decrease, it is judged that the test model is experiencing rotational flutter. Step 8: If the test model experiences flutter, tighten the protective handle (17) and reduce the speed of the drive motor (7) to a stop. To prevent excessive speed reduction from causing current overshoot, the drive motor (7) can be reduced to 50 rpm and then stopped. At the same time, the wind tunnel should be stopped. Then, extract the flutter test data and plot the rotor flutter amplitude-frequency characteristic curve. The current rotor (4) rotation excitation frequency is calculated by n0 / 60. When the rotation excitation frequency is equal to one peak of the amplitude-frequency characteristic curve, the other peak is the rotor (4) rotation flutter frequency. If the wind speed V S If the flutter wind speed exceeds the numerically calculated value by 20%, it is assumed that no rotational flutter will occur at a speed of 50 rpm. If the temperature of the drive motor (7) reaches the set threshold, the test is stopped. If the temperature of the drive motor (7) is within the safe range, the speed can be increased to the next test speed n0, and the wind speed can be increased according to the preset wind speed step. Steps six and seven are repeated to measure the flutter wind speed of the test model at each speed under the current collective distance and draw the speed-flutter wind speed envelope.

8. The wind tunnel testing method for a powered rotor flutter according to claim 7, characterized in that: During the process of increasing the wind speed, observe the current on the control cabinet (11) and the temperature feedback of the drive motor (7). If the current of the drive motor (7) reaches the maximum current and the temperature rise rate of the drive motor (7) reaches 5° / s, it indicates that the rotation speed of the rotor (4) is too different from the windmill speed under the current wind speed. Then, increase the current set speed by 5% and then increase the wind speed. Observe whether the current and temperature of the drive motor (7) have a downward trend. If the temperature drops, continue to conduct the test according to step seven. At the same time, observe whether the test model has the situation of rotational flutter described in step seven. If rotational flutter occurs, the test ends. If rotational flutter does not occur, it is determined that rotational flutter will not occur at this speed. Observe the temperature of the drive motor (7) again. If the temperature of the drive motor (7) reaches the set threshold, the test stops. If the temperature of the drive motor (7) is in the safe range, increase the speed to the next test speed n1 and continue the test.

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