A tiltrotor aircraft turn flutter damping calculation method

Abstract

The present application belongs to the field of rotorcraft dynamics, and particularly relates to a method for calculating the turn flutter damping of a tiltrotor aircraft. The method comprises: obtaining the full-aircraft modal shape and modal frequency of the tiltrotor helicopter; selecting the modes excited by the load transmitted by the rotors from the full-aircraft modal shape of the tiltrotor helicopter; extracting the modal displacement vector and the angular displacement vector of the hub center of the left and right rotors in the respective modes from the modes excited by the load transmitted by the rotors, and converting the modal displacement vector and the angular displacement vector to the body coordinate system; establishing a rotor dynamics simulation model in CAMRAD, and replacing the body modal with the modal displacement vector and the angular displacement vector converted to the body coordinate system; and connecting the body tail and the wing aerodynamic force output interface to the left and right hub centers respectively by using the CAMRAD CORE command.

Description

Technical Field

[0001] This invention belongs to the field of rotorcraft dynamics, specifically relating to a method for calculating the flutter damping of a tiltrotor aircraft. Background Technology

[0002] Currently, flutter stability calculations for rotorcraft are mostly performed using the industry-standard CAMRAD software. While this software excels at calculating the flutter stability of the rotor itself, it lacks a function for calculating gyroscopic flutter stability for tiltrotor configurations. Therefore, when assessing the flutter stability of tiltrotor helicopters, the usual approach is to first evaluate the rotor flutter stability using CAMRAD software, and then perform a gyroscopic flutter stability assessment using a custom-written program. The latter is extremely time-consuming and labor-intensive, and its accuracy is limited by the programmer's skill level. Summary of the Invention

[0003] Objective of the invention: To provide a method for calculating the gyroscopic flutter damping of tiltrotor helicopters based on CAMRAD software, which can establish a whole-aircraft calculation model of tiltrotor helicopters in CAMRAD, and simultaneously solve the rotor flutter stability and gyroscopic flutter stability of tiltrotor helicopters.

[0004] Technical solution:

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

[0006] Obtain the full-aircraft mode shapes and modal frequencies of a tiltrotor helicopter;

[0007] The modes that can be excited by the load transmitted by the rotor are selected from the full-aircraft mode vibration modes of the tiltrotor helicopter;

[0008] Extract the modal displacement vector and angular displacement vector of the center of the left and right rotor hubs in their respective modes from the modes excited by the loads transmitted by the rotor, and transform the modal displacement vector and angular displacement vector to the fuselage coordinate system;

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

[0010] Use the CAMRAD CORE command to connect the fuselage horizontal stabilizer and wing aerodynamic output interfaces to the centers of the left and right rotor hubs, respectively.

[0011] Furthermore, the method also includes:

[0012] The aerodynamic coefficients of the tiltrotor wing were calculated using CFD software, and the calculated aerodynamic coefficients were entered into the fuselage, horizontal stabilizer and wing aerodynamic coefficient interpolation table in the CAMRAD software.

[0013] The flutter damping coefficient of the tiltrotor helicopter was calculated by running the flutter solution module of the CAMRAD software.

[0014] Furthermore, the modes excited by the load transmitted by the rotor include six modes, namely the first-order symmetric flapping mode, the first-order symmetric oscillation mode, the first-order symmetric torsional mode, the first-order antisymmetric flapping mode, the first-order antisymmetric oscillation mode, and the first-order antisymmetric torsional mode.

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

[0016] The displacement vector and angular displacement vector of the left rotor hub center in the fuselage coordinate system are used as the displacement mode parameters and angular displacement mode parameters of the first geometric feature point of the fuselage, respectively, and then the displacement vector and angular displacement vector of the right rotor hub center in the fuselage coordinate system are used as the displacement mode parameters and angular displacement mode parameters of the second geometric feature point of the fuselage, respectively, and then input into the CAMRAD software. In this way, the center modes of the left and right rotor hubs replace the original fuselage modes in CAMRAD.

[0017] Furthermore, the mode shapes and modal frequencies of the entire machine are obtained through modal analysis using finite element software or through modal testing.

[0018] Furthermore, if the mode shapes and modal frequencies of the entire aircraft are obtained through modal analysis using finite element software, the full aircraft model established by the finite element software must have a central rigid body to simulate the fuselage and two beam components to simulate the wings.

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

[0020] Beneficial effects:

[0021] This method solves the problem that CAMRAD cannot calculate the flutter damping of tiltrotor helicopters. Using the method described in this invention, a system can be established in CAMRAD software that simultaneously considers the effects of rotor-wing structural coupling and wing aerodynamic damping on flutter stability, thereby enabling accurate calculation of the flutter damping of tiltrotor helicopters. Compared to methods that require custom programming to calculate the flutter damping of tiltrotor helicopters, the method described in this invention significantly reduces manpower requirements. Attached Figure Description

[0022] Figure 1 A diagram showing the mode shapes and modal frequencies of a tiltrotor helicopter.

[0023] Figure 2 This is a file format diagram of the interpolation table for wing aerodynamic coefficients. Detailed Implementation

[0024] A method for calculating the sway flutter damping of a tiltrotor helicopter based on CAMRAD software is provided, the method comprising:

[0025] 1) Use finite element software to perform modal analysis or conduct modal tests to obtain the full-aircraft mode shapes and modal frequencies of the tiltrotor helicopter;

[0026] 2) Manually identify the mode shapes of the entire tiltrotor helicopter and select the first-order symmetrical flapping mode, the first-order symmetrical oscillation mode, the first-order symmetrical torsional mode, the first-order antisymmetric flapping mode, the first-order antisymmetric oscillation mode, and the first-order antisymmetric torsional mode.

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

[0028] The displacement vector and angular displacement vector of the left rotor hub center in the fuselage coordinate system are input into the CAMRAD software as the displacement mode parameters and angular displacement mode parameters of the first geometric feature point of the fuselage, respectively. Then, the displacement vector and angular displacement vector of the right rotor hub center in the fuselage coordinate system are input into the CAMRAD software as the displacement mode parameters and angular displacement mode parameters of the second geometric feature point of the fuselage, respectively. This achieves the replacement of the original fuselage modes in CAMRAD with the center modes of the left and right rotor hubs.

[0029] 4) Use the CAMRAD CORE command to connect the fuselage horizontal stabilizer and the fuselage center aerodynamic output interface to the centers of the left and right propeller hubs respectively;

[0030] Using the CAMRAD CORE command, change the component geometric feature point on which the 7th connection point of the "AIRFRME" component depends to the 6th component geometric feature point, and change the acquisition points of sensors 27 to 32 of the "AIRFRME" component to the 6th component geometric feature point, thus connecting the fuselage horizontal stabilizer aerodynamic acquisition point output interface to the center of the left propeller hub.

[0031] Using the CAMRAD CORE command, change the component geometric feature point on which the 5th connection point of the "AIRFRME" component depends to the 8th component geometric feature point, and change the acquisition points of sensors 33 to 38 of the "AIRFRME" component to the 8th component geometric feature point, thus connecting the output interface of the fuselage center aerodynamic acquisition point 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 stabilizer and wing aerodynamic coefficient interpolation table;

[0033] 6) Run the flutter solver module of the CAMRAD software to calculate the flutter damping coefficient of the tiltrotor helicopter.

[0034] Key points of this invention: Finite element analysis software is used to perform whole-machine analysis on a tiltrotor helicopter to obtain mode shapes and modal frequencies; the fuselage modes in the CAMRAD software are replaced with first-order symmetric and first-order antisymmetric wing modes, allowing these modes to be excited by the loads transmitted by the rotor, thus enabling the calculation and simulation of the rotational flutter phenomenon generated by the coupling of these modes with rotor motion; the CAMRAD CORE command is used to connect the fuselage aerodynamic output interface to the center of the left and right rotor hubs, thus allowing the influence of wing aerodynamic damping on the stability of rotational flutter to be taken into account.

[0035] Example 1

[0036] This embodiment provides a method for calculating the flutter damping of tiltrotor helicopters based on CAMRAD software, solving the problem that the flutter damping of tiltrotor helicopters cannot be calculated using CAMRAD. Specifically, it includes the following steps:

[0037] Step 1: Establish a tiltrotor twin-rotor whole-aircraft analysis model in CAMRAD software. Based on the survey results of the analysis object, perform whole-aircraft structural modeling. Sequentially set the center positions of the left and right rotor hubs, rotor tilt angle, overall aircraft center position, and fuselage aerodynamic data acquisition point positions. Taking this embodiment as an example, the settings are as follows: 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, establish a full-aircraft finite element model based on the design parameters of the object being analyzed, and call the modal analysis module to calculate the mode shapes and modal frequencies of the object being analyzed. Extract the first-order wing symmetric mode and the first-order wing antisymmetric mode from the results.

[0040] Step 3: Based on the modal analysis results, set the number of modes NMODE = 6 in the CAMRAD software, and fill in the mode shapes and modal frequencies extracted in Step 2. Taking this embodiment as an example, the following steps are performed: Figure 1 Settings in;

[0041] Step 4: Based on the 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=8621, CONFIG=1, CONTRL=2, CONE=2.5, ZUS=-0.025;

[0042] Step 5: Using the CAMRAD CORE command, connect the fuselage aerodynamic output interface to the center of the left propeller hub and the horizontal stabilizer 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: Conduct a wind test on the simulated airfoil to obtain the characteristics of the airfoil's aerodynamic coefficient as a function of angle of attack. This step can also be replaced by CFD simulation.

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

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

[0046] In summary, this invention proposes a method for calculating the flutter damping of tiltrotor helicopters based on CAMRAD software. This invention integrates wing modes into the fuselage module, replaces the fuselage aerodynamic tab file with the wing aerodynamic characteristics as a function of angle of attack, and connects the wing aerodynamics to the rotor hub center point using the CAMRAD CORE command. Therefore, it can account for the wing-rotor structural coupling and the influence of wing aerodynamic damping on flutter stability during simulation, achieving the goal of accurately calculating the flutter damping of tiltrotor helicopters using CAMRAD software.

Claims

1. A method for calculating the flutter damping of a tiltrotor aircraft, characterized in that, include: Obtain the full-aircraft mode shapes and modal frequencies of a tiltrotor helicopter; The modes that can be excited by the load transmitted by the rotor are selected from the full-aircraft mode vibration modes of the tiltrotor helicopter; Extract the modal displacement vector and angular displacement vector of the center of the left and right rotor hubs in their respective modes from the modes excited by the loads transmitted by the rotor, and transform the modal displacement vector and angular displacement vector to the fuselage coordinate system; A rotor dynamics simulation model was established in CAMRAD, and the fuselage modes were replaced by modal displacement vectors and angular displacement vectors transformed to the fuselage coordinate system. The method further includes using the CAMRAD CORE command to connect the fuselage horizontal stabilizer and the wing aerodynamic output interface to the centers of the left and right rotor hubs, respectively; The aerodynamic coefficients of the tiltrotor wing were calculated using CFD software, and the calculated aerodynamic coefficients were entered into the fuselage, horizontal stabilizer and wing aerodynamic coefficient interpolation table in the CAMRAD software. The flutter damping coefficient of the tilt rotor helicopter was calculated by running the flutter solver module of the CAMRAD software. The modes excited by the load transmitted by the rotor include six modes, namely the first-order symmetric flapping mode, the first-order symmetric oscillation mode, the first-order symmetric torsional mode, the first-order antisymmetric flapping mode, the first-order antisymmetric oscillation mode, and the first-order antisymmetric torsional mode.

2. The method according to claim 1, 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 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 displacement vector and angular displacement vector of the left rotor hub center in the fuselage coordinate system are used as the displacement mode parameters and angular displacement mode parameters of the first geometric feature point of the fuselage, respectively, and then the displacement vector and angular displacement vector of the right rotor hub center in the fuselage coordinate system are used as the displacement mode parameters and angular displacement mode parameters of the second geometric feature point of the fuselage, respectively, and then input into the CAMRAD software. In this way, the center modes of the left and right rotor hubs replace the original fuselage modes in CAMRAD.

3. The method according to claim 1, characterized in that, The mode shapes and modal frequencies of the entire machine are obtained by modal analysis using finite element software or by modal testing.

4. The method according to claim 3, characterized in that, If the mode shapes and modal frequencies of the entire aircraft are obtained by modal analysis using finite element software, the full aircraft model established by the finite element software must have a central rigid body to simulate the fuselage and two beam components to simulate the wings.

5. The method according to claim 4, characterized in that, Each beam component consists of no fewer than 10 Beam188 beam units, and the outermost end of each beam component should have a concentrated mass equal to the total mass of the rotor nacelle.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-5.

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