Calculation method for rotation flutter damping of tilt rotorcraft

Abstract

The invention belongs to the field of dynamics of high-speed rotor aircrafts, and particularly relates to a method for calculating rotation flutter damping of a tilt rotorcraft. The method comprises the following steps: acquiring a full-aircraft modal shape and modal frequency of the tilt-rotor helicopter; screening out a mode which can be excited by a load transmitted by a rotor wing from a full-machine mode vibration mode of the tilt rotor wing helicopter; extracting modal displacement vectors and angular displacement vectors of the centers of the left and right pairs of rotor hubs in respective modals from the modals excited by the loads transmitted by the rotors, and converting the modal displacement vectors and the angular displacement vectors to a fuselage coordinate system; a rotor dynamics simulation model is established in CAMRAD, and the modal displacement vector and the angular displacement vector which are converted to the fuselage coordinate system are used for replacing the fuselage modal; a fuselage horizontal tail and a wing aerodynamic force output interface are respectively connected with the centers of a left propeller hub and a right propeller hub by using a CAMRAD CORE command.

Description

Technical Field

[0001] The invention belongs to the field of dynamics of high-speed rotorcraft, and in particular relates to a method for calculating the rotation flutter damping of a tiltrotor aircraft. Background Art

[0002] At present, the flutter stability calculation of rotorcraft is mostly implemented by using the commonly used CAMRAD software in the industry. This software has excellent performance in calculating the flutter stability of the rotor itself, but does not add the function of calculating the gyration flutter stability for the tilt-rotor configuration. Therefore, when evaluating the flutter stability of a tilt-rotor helicopter, the rotor is usually evaluated by using CAMRAD software first, and then the gyration flutter stability is evaluated by a self-programmed program. The latter consumes a lot of manpower and time, and is limited by the programmer's level, so the accuracy of the analysis cannot be guaranteed. Summary of the invention

[0003] Purpose of the invention: To provide a method for calculating the gyro flutter damping of a tilt-rotor helicopter based on CAMRAD software, which can establish a whole-machine calculation model of the tilt-rotor helicopter in CAMRAD and simultaneously calculate the rotor flutter stability and gyro flutter stability of the tilt-rotor helicopter.

[0004] Technical solution:

[0005] A method for calculating the rotation flutter damping of a tiltrotor aircraft is provided, comprising:

[0006] Obtain the full-machine modal vibration shape and modal frequency of the tilt-rotor helicopter;

[0007] Select the modes that can be excited by the loads transmitted by the rotor from the full-machine modal vibration shapes of the tilt-rotor helicopter;

[0008] Extract the modal displacement vectors and angular displacement vectors of the centers of the left and right rotor hubs in their respective modes from the modes that can be excited by the loads transmitted by the rotor, and transform the modal displacement vectors and angular displacement vectors into the fuselage coordinate system;

[0009] A rotor dynamics simulation model was established in CAMRAD, and the fuselage modes were replaced by the modal displacement vectors and angular displacement vectors converted to the fuselage coordinate system.

[0010] Use the CAMRAD CORE command to connect the fuselage horizontal tail and wing aerodynamic force output interfaces to the left and right propeller hub centers respectively.

[0011] Furthermore, the method further comprises:

[0012] Use CFD software to calculate the aerodynamic coefficients of the tiltrotor wing, and fill the calculated aerodynamic coefficients into the interpolation table of the fuselage, horizontal tail and wing aerodynamic coefficients of the CAMRAD software;

[0013] Run the flutter solution module of CAMRAD software to calculate the rotation flutter damping coefficient of the tilt-rotor helicopter.

[0014] Furthermore, the modes that can be excited by the load transmitted by the rotor include 6 modes, namely, the first-order symmetric flapping mode, the first-order symmetric swing mode, the first-order symmetric torsional mode, the first-order antisymmetric flapping mode, the first-order antisymmetric swing mode and the first-order antisymmetric torsional mode.

[0015] Furthermore, the modal displacement vectors and angular displacement vectors of the centers of the left and right rotor hubs in their respective modes are extracted from the modes that can be excited by the loads transmitted by the rotors, and the modal displacement vectors and angular displacement vectors are converted to the fuselage coordinate system, including:

[0016] The center displacement vector and angular displacement vector of the left hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the fuselage No. 1 geometric feature point, respectively. Then, the center displacement vector and angular displacement vector of the right hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the fuselage No. 2 geometric feature point, respectively. In this way, the center modes of the left and right rotor hubs replace the original fuselage modes of CAMRAD.

[0017] Furthermore, the modal vibration shape and modal frequency of the whole machine are obtained by modal analysis using finite element software or through modal testing.

[0018] Furthermore, if the modal vibration shape and modal frequency of the whole aircraft are obtained by modal analysis using finite element software, the whole aircraft model established by the finite element software must have a central rigid body for simulating the fuselage and two beam components for simulating the wings.

[0019] Furthermore, each beam component is composed of no less than 10 Beam188 beam units, and a concentrated mass equal to the total mass of the rotor nacelle should be added to the outermost end of each beam component.

[0020] Beneficial effects:

[0021] The method can solve the problem that CAMRAD cannot calculate the rotation flutter damping of a tilt-rotor helicopter. By using the method described in the present invention, a method can be established in the CAMRAD software that can simultaneously take into account the effects of the rotor-wing structure coupling and the wing aerodynamic damping on the rotation flutter stability, thereby accurately calculating the rotation flutter damping of the tilt-rotor helicopter. Compared with the method of calculating the rotation flutter damping of a tilt-rotor helicopter by a self-programmed program, the method described in the present invention can greatly reduce the manpower consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Set up a plot for the tiltrotor helicopter mode shapes and modal frequencies.

[0023] Figure 2 This is the file format of the interpolation table of wing aerodynamic coefficients. DETAILED DESCRIPTION

[0024] A method for calculating the rotation flutter damping of a tilt-rotor helicopter based on CAMRAD software is provided, the method comprising:

[0025] 1) Use finite element software to perform modal analysis or obtain the modal vibration shape and modal frequency of the tilt-rotor helicopter through modal testing;

[0026] 2) Manually identify the modal vibration modes of the tilt-rotor helicopter, and select the first-order symmetric flapping mode, the first-order symmetric swing mode, the first-order symmetric torsion mode, the first-order antisymmetric flapping mode, the first-order antisymmetric swing mode and the first-order antisymmetric torsion mode;

[0027] 3) Extract the displacement vector and angular displacement vector of the left and right rotor hub centers in the selected 6th-order mode, transform the vector to the fuselage coordinate system and replace the original fuselage mode of CAMRAD with these vectors;

[0028] The center displacement vector and angular displacement vector of the left propeller hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the geometric feature point No. 1 of the fuselage, respectively. Then, the center displacement vector and angular displacement vector of the right propeller hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the geometric feature point No. 2 of the fuselage, respectively. In this way, the center modes of the left and right rotor hubs replace the original fuselage modes of CAMRAD.

[0029] 4) Use the CAMRAD CORE command to connect the fuselage horizontal tail and fuselage center aerodynamic output interfaces to the left and right propeller hub centers respectively;

[0030] Use the CAMRAD CORE command to change the component geometric feature point that the No. 7 connection point of the "AIRFRME" component depends on to the No. 6 component geometric feature point, and change the collection points of the No. 27 to No. 32 sensors of the "AIRFRME" component to the No. 6 component geometric feature point, so that the fuselage horizontal tail aerodynamic collection point output interface is connected to the center of the left propeller hub.

[0031] Use the CAMRAD CORE command to change the component geometric feature point that the No. 5 connection point of the "AIRFRME" component depends on to the No. 8 component geometric feature point, and change the collection points of the No. 33 to No. 38 sensors of the "AIRFRME" component to the No. 8 component geometric feature point, so that the output interface of the fuselage center aerodynamic collection point is connected to the center of the left propeller hub.

[0032] 5) Use CFD software to calculate the aerodynamic coefficients of the tiltrotor wing, and fill the calculated aerodynamic coefficients into the CAMRAD software horizontal tail and wing aerodynamic coefficient interpolation table;

[0033] 6) Run the CAMRAD software flutter solution module to calculate the tilt-rotor helicopter's rotation flutter damping coefficient.

[0034] The key points of the present invention are as follows: using finite element software to perform whole-machine analysis on a tilt-rotor helicopter to obtain modal vibration shapes and modal frequencies; using the first-order symmetric mode and the first-order antisymmetric mode of the wing to replace the fuselage mode in the CAMRAD software, so that these modes can be excited by the load transmitted by the rotor, thereby being able to calculate and simulate the gyration flutter phenomenon generated by the coupling of these modes with the rotor motion; using the CAMRAD CORE command to connect the fuselage aerodynamic output interface with the left and right hub centers, thereby being able to take into account the influence of the wing aerodynamic damping on the gyration flutter stability.

[0035] Example 1

[0036] This embodiment provides a method for calculating the rotation flutter damping of a tilt-rotor helicopter based on CAMRAD software, which solves the problem that the rotation flutter damping of a tilt-rotor helicopter cannot be calculated using CAMRAD. Specifically, the method includes the following steps:

[0037] Step 1: Establish a tilt-rotor twin-rotor whole machine analysis model in CAMRAD software, and perform whole machine structure modeling based on the surveying and mapping results of the analysis object. Set the left and right hub center positions, rotor tilt angle, whole machine center position, and fuselage aerodynamic force collection point positions in sequence. Taking this embodiment as an example, the following settings are made: FSRTR = 6.8, BLRTR = 5, WLRTR = 4, ATILT = 2*0, FSCG = 6,

[0038] WLCG=1.734, BLCG=-0.005, FSWB=6.5, BLWB=-3.6, WLWB=2.186;

[0039] Step 2: In the finite element software, according to the design parameters of the analysis object, establish the finite element model of the whole aircraft, and call the modal analysis module to calculate the modal vibration shape and modal frequency of the analysis object, and extract the first-order wing symmetric mode and the first-order wing antisymmetric mode from the results;

[0040] Step 3: According to the modal analysis results, set the modal number NMODE=6 in the CAMRAD software, and fill in the modal vibration shape and modal frequency extracted in step 2 respectively. Taking this embodiment as an example, the following is performed: Figure 1 Settings in;

[0041] Step 4: According to the surveying and mapping results of the simulated object, set the rotor parameters in the CAMRAD software. Taking this embodiment as an example, the following settings are made: RADIUS=4, NBLADE=3, SIGMA=0.07, ROTATE=-1, VTIPN=195.5, gimbal=1, kgmbl=8621CONFIG=1, CONTRL=2, CONE=2.5, ZUS=-0.025;

[0042] Step 5: Use the CAMRAD CORE command to connect the fuselage aerodynamic output interface to the center of the left propeller hub, and connect the tail aerodynamic output interface to the center of the right propeller hub. Taking this embodiment as an example, the following settings are made: CNXLOC(7)=6, CNXLOC(6)=7, IDENTQ(27)=6*6, CNXLOC(8)=5, CNXLOC(5)=8, IDENTQ(33)=6*5;

[0043] Step 6: Perform a wind test on the wing of the simulation object to obtain the characteristics of the wing aerodynamic coefficient changing with the angle of attack. This step can also be replaced by CFD simulation;

[0044] Step 7: Edit the characteristics of the wing aerodynamic coefficient changing with the angle of attack into an interpolation table file (.tab), and replace the fuselage aerodynamic file and the horizontal tail aerodynamic file in the CAMRAD calculation file with their file names and storage paths, such as Figure 2 As shown;

[0045] Step 8: Run the CAMRAD flutter calculation module and wait for the calculation to complete to obtain the rotational flutter damping coefficient of the simulated object.

[0046] In summary, the present invention proposes a method for calculating the rotation flutter damping of a tilt-rotor helicopter based on CAMRAD software. The present invention integrates the wing mode into the fuselage module, replaces the fuselage aerodynamic tab file with the characteristics of the wing aerodynamic force changing with the angle of attack, and connects the wing aerodynamic force to the hub center point through the CAMRAD CORE command, so that the structural coupling of the wing and the rotor, as well as the influence of the wing aerodynamic damping on the rotation flutter stability can be taken into account during the simulation process, so as to achieve the purpose of accurately calculating the rotation flutter damping of the tilt-rotor helicopter using CAMRAD software.

Claims

1. A method for calculating the rotation flutter damping of a tiltrotor aircraft, characterized in that: include: Obtain the full-machine modal vibration shape and modal frequency of the tilt-rotor helicopter; Select the modes that can be excited by the loads transmitted by the rotor from the full-machine modal vibration shapes of the tilt-rotor helicopter; Extract the modal displacement vectors and angular displacement vectors of the centers of the left and right rotor hubs in their respective modes from the modes that can be excited by the loads transmitted by the rotor, and transform the modal displacement vectors and angular displacement vectors into the fuselage coordinate system; A rotor dynamics simulation model was established in CAMRAD, and the fuselage modes were replaced by the modal displacement vectors and angular displacement vectors converted to the fuselage coordinate system. Use the CAMRAD CORE command to connect the fuselage horizontal tail and wing aerodynamic force output interfaces to the left and right propeller hub centers respectively.

2. The method according to claim 1, characterized in that The method further comprises: Use CFD software to calculate the aerodynamic coefficients of the tiltrotor wing, and fill the calculated aerodynamic coefficients into the interpolation table of the fuselage, horizontal tail and wing aerodynamic coefficients of the CAMRAD software; Run the flutter solution module of CAMRAD software to calculate the rotation flutter damping coefficient of the tilt-rotor helicopter.

3. The method according to claim 1, characterized in that The modes that can be excited by the load transmitted by the rotor include 6 modes, namely the first-order symmetric flapping mode, the first-order symmetric swing mode, the first-order symmetric torsional mode, the first-order antisymmetric flapping mode, the first-order antisymmetric swing mode and the first-order antisymmetric torsional mode.

4. The method according to claim 3, characterized in that Extract the modal displacement vectors and angular displacement vectors of the left and right rotor hub centers in their respective modes from the modes that can be excited by the loads transmitted by the rotor, and transform the modal displacement vectors and angular displacement vectors to the fuselage coordinate system, including: The center displacement vector and angular displacement vector of the left hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the fuselage No. 1 geometric feature point, respectively. Then, the center displacement vector and angular displacement vector of the right hub in the fuselage coordinate system are input into the CAMRAD software as the displacement modal parameters and angular displacement modal parameters of the fuselage No. 2 geometric feature point, respectively. In this way, the center modes of the left and right rotor hubs replace the original fuselage modes of CAMRAD.

5. The method according to claim 1, characterized in that The modal vibration shape and modal frequency of the whole machine are obtained by modal analysis using finite element software or through modal testing.

6. The method according to claim 5, characterized in that If the modal vibration shape and modal frequency of the whole aircraft are obtained by modal analysis using finite element software, the whole aircraft model established by the finite element software must have a central rigid body for simulating the fuselage and two beam components for simulating the wings.

7. The method according to claim 6, characterized in that Each beam component is composed of no less than 10 Beam188 beam units, and a concentrated mass equal to the total mass of the rotor nacelle should be added to the outermost end of each beam component.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

Images