Rotorcraft whirl flutter ground test system and test method

Abstract

The present application belongs to the technical field of rotorcraft flutter test, and discloses a rotorcraft spiral flutter ground test system and a test method. The rotorcraft spiral flutter ground test system comprises a hardware part and a software part. The hardware part comprises a rotor test piece, a support system, a force loading device, a vibration signal sensor, a force sensor, a vibration signal acquisition card, an industrial control computer, a force signal output card, a power amplifier and a force sensor signal acquisition card. The software part of the rotorcraft spiral flutter ground test system comprises a rotor force and torque calculation program and a multiple-input multiple-output force control program running on the industrial control computer. The method can retain all the dynamic characteristics of the aircraft structure, is not limited by the size of the wind tunnel test section, does not need to scale the aircraft structure, has low cost, short cycle, can be quickly deployed and ground test completed.

Description

Technical Field

[0001] This invention belongs to the field of rotorcraft flutter testing technology, specifically relating to a rotorcraft helical flutter ground testing system and testing method. Background Technology

[0002] Whirl flutter is an aeroelastic divergence phenomenon commonly encountered in fixed-wing propeller aircraft, tiltrotor aircraft, and other similar aircraft. It involves the aeroelastic divergence of pitch and yaw coupled precession motions of the engine nacelle under specific rotational and flight speed conditions, resulting from the interaction of aerodynamic forces, elastic restoring forces, and inertial forces on a flexibly mounted engine nacelle and rotor system. This phenomenon can cause structural instability and damage, seriously threatening flight safety. Currently, whirl flutter is difficult to predict accurately through theoretical modeling and simulation analysis; therefore, testing is a crucial technical means for studying whirl flutter. Wind tunnel testing is a traditional method for whirl flutter testing; however, due to the limitations of wind tunnel size, full-scale testing of rotorcraft is not possible, necessitating scaled-down similarity. Scaled-down similarity inevitably ignores the dynamic characteristics and nonlinear factors of the actual aircraft, retaining only a few structural dynamic features of interest. Furthermore, wind tunnel test results need to be extrapolated to the scale of the actual aircraft, making it impossible to directly obtain the flutter boundary of the real aircraft. Moreover, the dynamic scaling similarity law of rotorcraft is quite complex, and so far no engineering-usable dynamic scaling similarity law of rotorcraft has been established; in addition, wind tunnel testing has a long cycle and high cost, and large-scale wind tunnel testing consumes huge amounts of manpower and economic resources. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a ground-based test method for propeller flutter, conducted on a full-size, real rotorcraft. Without a wind tunnel, it utilizes ground-based sensing equipment, force loading devices, and industrial control equipment to physically simulate rotor aerodynamic forces on the structure. This achieves the coupled interaction between rotor aerodynamic forces and the aircraft on the ground, realizing the propeller flutter phenomenon. This is a semi-physical, semi-simulation testing method.

[0004] A ground test system for rotor flutter of a rotorcraft, comprising hardware and software components.

[0005] Figure 1 The hardware components of the rotorcraft spiral flutter ground test system include a rotor test piece 1, a support system 2, a force loading device 3, a vibration signal sensor 4, a force sensor 5, a vibration signal acquisition card 7, an industrial control computer 8, a force signal output card 10, a power amplifier 11, and a force sensor signal acquisition card 14.

[0006] Figure 2The rotor test piece 1 includes a wing 101, a nacelle 102, a rotor hub 103, rotor blades 104, and a power output shaft 105. The root of the wing 101 is fixed to the support system 2, and the nacelle 102 is located at the tip of the wing 101. A power system or transmission system is installed inside the nacelle 102. The power output shaft 105 is fixed to the nacelle 102, and its front end is connected to the rotor hub 103. The rotor hub 103 is further connected to three rotor blades 104, which are responsible for transmitting torque from the power output shaft 105 to the rotor blades 104.

[0007] Figure 2 In the process, a local coordinate system OXYZ is constructed for rotor test piece 1, where the origin O is fixed at the center of the hub 103 and located at the intersection of the axis of the power output shaft 105 and the rotor disk plane of the rotor blade 104. When viewed from the tail of the nacelle 102 toward the position of the hub 103 at the head of the nacelle 102, the X-axis is forward and coincides with the axis of the power output shaft 105; the Y-axis is perpendicular to the X-axis and points horizontally to the right; the Z-axis is perpendicular to the OXY plane and points vertically downward.

[0008] Figure 1 In the middle, the force loading device 3 is placed along the OY axis and OZ axis respectively, and the applied excitation force and torque act on point O.

[0009] The force sensor 5 is located at the top of the force loading device 3 and collects the force sensor signal 13 applied by the force loading device 3 at point O.

[0010] The vibration signal sensor 4 is arranged along the OY and OZ axes to collect the vibration signal 6 at point O along the OY and OZ axes.

[0011] The vibration signal 6 is acquired by the vibration signal acquisition card 7;

[0012] The force output signal 12 of the force loading device 3 is output through the force signal output card 10, and the power is amplified by the power amplifier 11.

[0013] The force sensor signal 13 is acquired by the force sensor signal acquisition card 14;

[0014] The closed-loop signal transmission process of the rotor flutter ground test system is as follows: the vibration signal 6 acquired by the vibration signal acquisition card 7 is recorded by the industrial control computer 8. The industrial control computer 8 calculates the force acting on the center point O of the rotor hub 103 based on the vibration signal 6 and the pre-programmed rotor force and torque calculation program. The industrial control computer 8 outputs the force control signal 9 to the power amplifier 11 through the force signal output card 10. The power amplifier 11 outputs the amplified force output signal 12 to the force loading device 3, driving the force loading device 3 to load the rotor test piece 1. At the same time, the force sensor 5 acquires the force applied by the force loading device 3 and feeds it back to the industrial control computer 8 through the force sensor signal acquisition card 14. The industrial control computer 8 performs closed-loop feedback control on the force applied by the force loading device 3 based on the feedback force signal and the pre-programmed multi-input multi-output force control program, so as to achieve precise loading of rotor aerodynamic force and torque, and finally realize the reproduction of the rotor flutter phenomenon on the ground.

[0015] The software component of the rotorcraft spiral flutter ground test system includes rotor force and torque calculation programs and multi-input multi-output force control programs running on the industrial control computer 8.

[0016] The rapid calculation program for rotor force and torque quickly calculates the force and torque acting on rotor hub point O based on the vibration signal 6. The rotor aerodynamic force and gyroscopic torque are calculated using the formulas given in the literature (Rodden, W.; Rose, T. Propeller / nacelle whirl flutter addition to MSC / Nastran. In Proceedings of the 1989 MSC World User's Conference, Anaheim, CA, USA, 26–27 January 1989), as follows:

[0017] (1)

[0018] (2)

[0019] Equation (1) is the formula for calculating rotor aerodynamic forces, where, These are the forces exerted by the rotor on point O of the rotor hub along the OY and OZ directions, respectively. It is the torque acting on point O of the rotor hub in the OY and OZ directions. S is the area of ​​the rotor blade disk 104, and D is the diameter of the rotor blade disk 104. The displacements of point O along the Z and Y directions, and the angular displacements around the Y and Z axes, respectively. These are the linear velocities of point O along the Z and Y directions, and the angular velocities around the Y and Z axes, respectively. V is the incoming flow pressure, and V is the incoming flow velocity.

[0020] This is the aerodynamic derivative of the propeller, calculated using the following formula:

[0021] (3)

[0022] According to symmetry,

[0023] (4)

[0024] In formula (3) For the leaf integral, see the reference for the specific form (Rodden, W.; Rose, T. Propeller / nacelle whirl flutter addition to MSC / Nastran. In Proceedings of the 1989 MSC World User's Conference, Anaheim, CA, USA, 26–27 January 1989).

[0025] Equation (2) is the formula for calculating the torque of a rotor gyroscope. It is the additional torque about the OY and OZ axes caused by the gyroscopic effect, where It is the moment of inertia of the rotating body consisting of rotor blade 104 and power output shaft 105 along the OX direction. It's the rotational speed.

[0026] Combining equations (1) and (2), and separating the velocity and damping terms, we obtain the additional stiffness and additional damping terms caused by the rotation of rotor blade 104, as shown below.

[0027] (5)

[0028] (6)

[0029] Among them, the two formulas above show and These are the additional stiffness and damping matrices caused by the propeller's rotational motion, respectively, which can be calculated for each combination of incoming flow velocity V and air density ρ. Typically, a series of incoming flow velocities are given. and air density Combine them, and then calculate the current experimental state using linear interpolation. and matrix.

[0030] The feedback control program of the force loading device 3 adopts a multi-input multi-output control method. The input information includes: the displacement of the hub O point along the OY and OZ directions, and the rotation angles around the OY and OZ axes.

[0031] A ground test method for rotor flutter of a rotary-wing aircraft, comprising the following steps:

[0032] Step 1: Construct the hardware components of the rotorcraft spiral flutter ground test system;

[0033] Step 2: Build the software part of the rotorcraft spiral flutter ground test system; the software running on the industrial control computer 8 includes two parts: the first part is the rotor force and torque calculation program, and the second part is the multi-input multi-output force control program.

[0034] Step 2.1, Rapid calculation program for rotor force and torque: The input is the vibration signal 6 recorded by the industrial control computer 8 at the origin O of the local coordinate system of the rotor test piece 1, and the output is the equivalent force and torque acting on point O. The calculation process is shown in Formulas 1-7.

[0035] Step 2.2, the multi-input multi-output force control program, whose input is the force actually applied by the force loading device 3 as measured by the force sensor 5, and whose output is the force control signal 9; first, a dynamic model of the controlled object composed of the power amplifier 11 and the force loading device 3 is established, and the transmission relationship of the controlled object is established by using the reverse identification method; then, according to the multi-input multi-output modern control theory, the control law of the power amplifier 11 and the force loading device 3 is established;

[0036] Step 3: Ground test of rotor flutter;

[0037] Step 3.1: Turn on the industrial control computer 8 and check all acquisition and output channels to ensure they are working properly;

[0038] Step 3.2: Set the rotor speed Ω, set the air density ρ, and change the incoming flow velocity V to apply a disturbance to the rotor hub 103. Observe whether the rotor test piece 1 exhibits constant amplitude or divergent motion.

[0039] Step 3.3: If rotor test piece 1 undergoes constant amplitude or critical divergent motion, then the incoming flow velocity V at this time is the helical flutter velocity V at the current rotor speed Ω and air density ρ. FL If the vibration of rotor test piece 1 converges, then continue to increase the incoming flow velocity V and repeat step 3.2 until the flutter critical velocity V is found. FL ;

[0040] Step 3.4: Set the new rotor speed Ω and air density ρ, repeat step 3.2, and find the spiral flutter boundary velocity V for the next state. FL ;

[0041] Step 3.5: Change other structural parameters of rotor test piece 1, including structural support stiffness, mass distribution, and moment of inertia, and repeat step 3.2 to study the effect of different structural parameters on the V-shaped boundary velocity of helical flutter. FL Influence patterns;

[0042] Step 3.6: After the test has completed all combinations of rotor speed, air density, incoming flow velocity, and other structural parameters, the ground spiral flutter test of the current test model is considered complete, and the ground spiral flutter test ends.

[0043] The beneficial effects of this invention are as follows: This invention solves the problem of conducting helical flutter tests on real rotorcraft of original size. It employs ground-based physical sensing, loading, and measurement and control equipment to collect structural vibration signals in real time, and generates aerodynamic loads based on these signals. The physical equipment is then used to load the real aircraft structure, achieving a technological breakthrough in helical flutter testing without relying on a wind tunnel. This method preserves all the dynamic characteristics of the aircraft structure, is not limited by the size of the wind tunnel test section, does not require scaled-down similarity to the aircraft structure, and is lower in cost and shorter in cycle time, allowing for rapid deployment and completion of ground tests.

[0044] This invention is applicable not only to tiltrotor aircraft, but also to ground-based spiral flutter tests of fixed-wing propeller aircraft. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a ground test system for rotor flutter of a rotary-wing aircraft.

[0046] Figure 2 This is a schematic diagram of a ground test specimen for a rotary-wing aircraft.

[0047] Figure 3 This is a simulation diagram of a ground test system for rotor flutter of a rotary-wing aircraft.

[0048] Figure 4 This is a simulation result of a ground test of helical flutter with an incoming flow velocity of V1=100m / s;

[0049] Figure 5 The figure shows the simulation results of a ground test of helical flutter with an incoming flow velocity of V2=114.06m / s.

[0050] Figure 6 This is a simulation result of a ground test of helical flutter with an incoming flow velocity of V3=150m / s.

[0051] Figure 7This is the VG plot of the frequency domain helical flutter calculation results;

[0052] Figure 8 This is the Vf plot of the frequency domain helical flutter calculation results;

[0053] In the diagram: 1. Rotor test piece, 2. Support system, 3. Force loading device, 4. Vibration sensor, 5. Force sensor, 6. Vibration signal, 7. Vibration signal acquisition card, 8. Industrial computer, 9. Force control signal, 10. Force signal output card, 11. Power amplifier, 12. Force output signal, 13. Force sensor signal, 14. Force sensor signal acquisition card, 101. Wing, 102. Nacelle, 103. Rotor hub, 104. Rotor blade, 105. Power output shaft, S1. Rotor test piece simulation model, S2. Virtual vibration signal, S3. Rotor force / torque fast solver, S4. Multi-input multi-output force controller, S5. Virtual force loading device, S6. Virtual force signal, S7. Disturbance signal, S8. Rotor hub point displacement signal. Detailed Implementation

[0054] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0055] To verify the effectiveness of the invented rotorcraft propeller flutter ground test system and test method, targeting Figure 1 The rotorcraft spiral flutter ground test system shown is used to build a simulation model, such as... Figure 3 As shown, a virtual experiment was conducted.

[0056] The specific steps are as follows:

[0057] Step 1: Build the virtual hardware for the rotor flutter ground test system.

[0058] The rotor test specimen 1 was replaced by a finite element model. The first four modal frequencies of the finite element model are shown in Table 1, and the mass-normalized modal displacements of the hub point (O point) in the finite element model are shown in Table 2.

[0059] The first and third order modes, which have the highest correlation with helical flutter, were selected to participate in the construction of the rotor test specimen simulation model S1. Mass-normalized modes were used to construct the generalized mass, generalized stiffness, and generalized damping matrices, with the damping ratio set to 0.0. Based on the structural dynamic response equations, the rotor test specimen simulation model was constructed, as follows: Figure 3 As shown.

[0060] Rotor structural parameters include: disk radius propeller disk area Moment of inertia about axis OX =86.940 (kg·m) 2 ).

[0061] Step 2: Build the ground test system software for rotor flutter.

[0062] The rapid calculation program for rotor force and torque running on the industrial control computer (8) includes rotor aerodynamic force calculation (Formula 1) and rotor gyro torque calculation (Formula 2). The air density is set to ρ = 1.225 kg / m³. 3 The rotational speed Ω = 370 RPM, and the rotor gyro torque can be calculated according to equation (2). In addition, the rotor aerodynamic derivatives in the range of incoming flow velocity 0~200 m / s are shown in Table 3. Substitute the results in Table 3 into equations (5)-(6) and calculate using linear interpolation. and matrix.

[0063] In addition, there is a multi-input multi-output force control program running on the industrial control computer (8). Based on the virtual force loading device S5 of the controlled object, a multi-input multi-output force controller S4 is established, such as... Figure 3 As shown.

[0064] Step 3: Conduct ground simulation test of rotor propeller flutter.

[0065] like Figure 3 As shown, the rotor speed is set to Ω = 370 RPM and the air density is set to ρ = 1.225 kg / m³. 3 Simulation was performed by changing the incoming flow velocity V.

[0066] Step 3.1: Set the incoming flow velocity V1 = 100 m / s and conduct a virtual ground test simulation. Figure 4 This is a simulation result diagram of a ground test of helical flutter with an incoming flow velocity of V1=100m / s. These represent the linear and angular displacements of point O on the propeller hub along the OZ and OY axes, respectively. The simulation results show that the curves converge, indicating that V1 has not reached the critical velocity V for helical flutter. FL .

[0067] Step 3.2: Set the incoming flow velocity V2 = 114.06 m / s and conduct a virtual ground test simulation. Figure 5 This is a simulation result of a ground test of helical flutter with an incoming flow velocity V2 = 114.06 m / s. The simulation curve shows constant-amplitude oscillations, indicating that V2 is the critical velocity V for helical flutter in this system. FL .from Figure 5 It can be seen that the displacements z and y in the OZ and OY directions have more obvious responses, while the angular displacement... The response amplitude is relatively small.

[0068] Step 3.3: Set the incoming flow velocity V2 = 150 m / s and conduct a virtual ground test simulation. Figure 6This is a simulation result of a ground test of helical flutter with an incoming flow velocity V3 = 150 m / s. The simulation curve shows divergent oscillations, indicating that V3 exceeds the critical velocity V of the helical flutter. FL The system exhibited spiral flutter divergence.

[0069] Table 4 summarizes the simulation results of the helical flutter ground test system. To verify the correctness of the virtual simulation results of the helical flutter ground test system, the frequency domain helical flutter calculation results (vg and vf plots) of the system are given, as shown below. Figure 7 and Figure 8 As shown in the figure. From the frequency domain results curve, it can be seen that the boundary velocity of the helical flutter in this example is between 113 and 115 m / s, and the flutter frequency is 2.2379 Hz. Compared with the results in Table 4, the errors in flutter velocity and flutter frequency are both less than 1%, which proves the effectiveness of the system and method.

[0070] Table 1. Frequency of the first 4 modes

[0071]

[0072] Table 2. Mass-normalized modal displacements (point O)

[0073]

[0074] Table 3 Rotor aerodynamic coefficients

[0075]

[0076]

[0077]

[0078]

[0079] Table 4 Simulation results of the ground test system for helical flutter at a rotational speed Ω=370RPM

[0080] .

Claims

1. A rotary wing aircraft whirl flutter ground test system, characterized by, The rotorcraft spiral flutter ground test system includes hardware and software components; The hardware components include rotor test piece (1), support system (2), force loading device (3), vibration signal sensor (4), force sensor (5), vibration signal acquisition card (7), industrial control computer (8), force signal output card (10), power amplifier (11) and force sensor signal acquisition card (14). The rotor test piece (1) is fixed on the support system (2); The force loading device (3) is placed along the OY axis and OZ axis respectively, and the applied excitation force and torque act on point O; The force sensor (5) is located at the top of the force loading device (3) and collects the force sensor signal (13) applied by the force loading device (3) at point O. Vibration signal sensor (4) is arranged along the OY and OZ axes to collect vibration signals (6) at point O along the OY and OZ axes. The vibration signal (6) is acquired by the vibration signal acquisition card (7); The force output signal (12) of the force loading device (3) is output through the force signal output card (10) and the power is amplified by the power amplifier (11); Force sensor signal (13) is acquired by force sensor signal acquisition card (14); The software component includes a rotor force and torque calculation program and a multi-input multi-output force control program running on an industrial control computer (8); The characteristic feature is that the closed-loop signal transmission process of the rotor flutter ground test system is as follows: the vibration signal (6) collected by the vibration signal acquisition card (7) is recorded by the industrial control computer (8); the industrial control computer (8) calculates the force acting on the center point O of the rotor hub (103) based on the vibration signal (6) and the pre-programmed rotor force and torque calculation program; the industrial control computer (8) outputs the force control signal (9) to the power amplifier (11) through the force signal output card (10); the power amplifier (11) outputs the amplified force output signal (12) to the power amplifier. Force loading device (3) drives the force loading device (3) to load the rotor test piece (1); at the same time, force sensor (5) collects the force applied by the force loading device (3) and feeds it back to the industrial control computer (8) via force sensor signal acquisition card (14). The industrial control computer (8) performs closed-loop feedback control on the force applied by the force loading device (3) according to the feedback force signal and the pre-programmed multi-input multi-output force control program, so as to realize the precise loading of rotor aerodynamic force and torque, and finally realize the reproduction of the rotor flutter phenomenon of rotor test piece (1) on the ground.

2. The rotorcraft shaker ground test system of claim 1, wherein, The rotor test piece (1) includes a wing (101), a nacelle (102), a rotor hub (103), rotor blades (104), and a power output shaft (105). The root of the wing (101) is fixed to the support system (2), and the nacelle (102) is located at the tip of the wing (101). The nacelle (102) is equipped with a power system or transmission system. The power output shaft (105) is fixed on the nacelle (102), and its front end is connected to the rotor hub (103). The rotor hub (103) is further connected to three rotor blades (104) and is responsible for transmitting torque from the power output shaft (105) to the rotor blades (104).

3. The rotorcraft shaker ground test system of Claim 2, wherein, Construct a local coordinate system OXYZ for the rotor test piece (1), where the origin O is fixed at the center of the hub (103) and located at the intersection of the axis of the power output shaft (105) and the rotor blade (104) disk plane; when viewed from the tail of the nacelle (102) towards the position of the hub (103) at the head of the nacelle (102), the X-axis is forward and coincides with the axis of the power output shaft (105); the Y-axis is perpendicular to the X-axis and is horizontal to the right; the Z-axis is perpendicular to the OXY plane and is vertically downward.

4. The rotorcraft shaker ground test system of Claim 3, wherein, The rotor force and torque calculation program calculates the rotor aerodynamic force and rotor gyro torque that are fed back to the origin O of the coordinate system on the rotor hub (103) based on the vibration signal (6) of the origin O on the rotor hub (103).

5. The rotorcraft spiral flutter ground test system according to claim 4, characterized in that, The feedback control program of the force loading device (3) adopts a multi-input multi-output control method; the input information is: the displacement of the origin O on the propeller hub (103) along the OY and OZ directions, and the rotation angle around the OY and OZ axes.

6. A method for conducting a ground test of rotorcraft propeller flutter using the rotorcraft propeller flutter ground test system according to any one of claims 1-5, characterized in that, The steps are as follows: Step 1: Construct the hardware components of the rotorcraft spiral flutter ground test system; Step 2: Build the software part of the rotorcraft spiral flutter ground test system; The software running on the industrial control computer (8) includes two parts: the first part is the rotor force and torque calculation program, and the second part is the multi-input multi-output force control program; Step 2.1, Rapid calculation program for rotor force and torque: The input is the vibration signal (6) at the origin O of the local coordinate system of the rotor test piece (1) collected and recorded by the industrial control computer (8), and the output is the equivalent force and torque acting on point O. The calculation process is shown in formulas (1)-(7). Step 2.2, Multi-input Multi-output force control program, whose input is the force actually applied by the force loading device (3) measured by the force sensor (5), and whose output is the force control signal (9); First, establish the dynamic model of the controlled object composed of the power amplifier (11) and the force loading device (3), and establish the transmission relationship of the controlled object by using the reverse identification method; then, according to the multi-input multi-output modern control theory, establish the control law of the power amplifier (11) and the force loading device (3) link; Step 3: Ground test of rotor flutter; Step 3.1: Turn on the industrial control computer (8) and check all acquisition and output channels to ensure they are working properly; Step 3.2: Set the rotor speed Ω, set the air density ρ, and change the incoming flow velocity V to apply a disturbance to the rotor hub (103). Observe whether the rotor test piece (1) exhibits constant amplitude or divergent motion. Step 3.3, if the rotor test piece (1) has a constant amplitude or critical divergent motion, then the flow velocity V at this time is the helical flutter speed V under the current rotor speed Ω and air density ρ FL ; if the vibration of the rotor test piece (1) converges, then continue to increase the flow velocity V, repeat step 3.2, until the flutter critical speed V FL is found Step 3.4, set new rotor speed Ω and air density p, repeat step 3.2 to find the next state's whirl flutter boundary speed V FL ; Step 3.5, change other structural parameters of the rotor test piece (1), including structural support stiffness, mass distribution and moment of inertia, repeat step 3.2, study the influence of different structural parameters on the V FL influence law; Step 3.6: After the test has completed all combinations of rotor speed, air density, incoming flow velocity, and other structural parameters, the ground spiral flutter test of the current test model is considered complete, and the ground spiral flutter test ends.

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