CN110543694A - vibration calculation method for auxiliary suspension pull rod of aircraft engine - Google Patents
vibration calculation method for auxiliary suspension pull rod of aircraft engine Download PDFInfo
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Abstract
The invention discloses a vibration calculation method for an auxiliary suspension pull rod of an aero-engine, which comprises the following steps: establishing and simplifying a three-dimensional model of an engine, and reserving a main bearing part; inputting conditions such as environment, finite element boundary conditions and the like; correcting the mass of the three-dimensional model according to the theoretical mass of the engine and inputting an external load; step four, calculating to obtain a vibration conclusion; by the aid of the method for calculating vibration of the auxiliary suspension pull rod of the aircraft engine, models of the engine and the pull rod assembly body can be built, the resonant frequency and the vibration mode of the assembly body can be calculated, and data support is provided for complete machine vibration troubleshooting.
Description
Technical Field
The invention belongs to the technical field of test runs of an aero-engine bench, and particularly relates to a method for calculating vibration finite elements of auxiliary suspension pull rods of the bench test.
background
the aero-engine is installed on the special stand for ground test run. The engine is fixed on the rack through three fulcrums of two fronts and one back, wherein the two fronts are the main mounting section of the engine, and thrust generated by the engine is transmitted to the airplane or the rack through the main mounting section. The 'one rear' is an auxiliary hanger of the engine and is mainly used for fine adjustment of the pitching installation posture of the engine and bearing part of the load of the engine. During engine test run, vibration sensors are usually arranged at three pivot positions, and most of vibration overproof signals come from the vibration sensors at the rear hanging part.
Most of engine vibration is caused by unbalance of rotor components, if the vibration of the whole engine before delivery exceeds standard, the rotor components need to be disassembled and re-balanced and then loaded on a loader for test run, and millions of yuan of aviation kerosene is consumed in the process. However, the vibration amplitude of the whole engine can be effectively reduced by changing the rigidity of the auxiliary hanging pull rod. And the vibration signal detected by the sensor arranged at the tie rod is not caused entirely by the rotor component imbalance, and may also be caused by engine casing resonance. The traditional method can only solve the problem of overlarge vibration by rebalancing the rotor part, but due to the structural design characteristics of the rotor part of the engine, the method cannot completely eliminate the fault of overlarge vibration.
disclosure of Invention
The purpose of the invention is as follows: the invention provides a vibration calculation method for an auxiliary suspension pull rod of an aircraft engine, which can accurately calculate the natural frequency and the vibration mode of a pull rod and an engine assembly body and provide data support for troubleshooting of the vibration of the whole machine.
The technical scheme is as follows: the invention discloses a vibration calculation method for an auxiliary suspension pull rod of an aircraft engine, which comprises the following steps of: establishing and simplifying a three-dimensional model of an engine, and reserving a main bearing part; inputting conditions such as environment, finite element boundary conditions and the like; correcting the mass of the three-dimensional model according to the theoretical mass of the engine and inputting an external load; and step four, calculating to obtain a vibration conclusion.
Further, the step three of correcting the quality of the three-dimensional model according to the theoretical quality of the engine specifically comprises the following steps: a. according to the structure diagram of the engine, applying the mass of the accessory casing, the central transmission, the vector nozzle/tail nozzle, the exhaust tail cone and other components on the corresponding mounting surfaces of the three-dimensional model of the engine by concentrated mass points; b. the mass of the rotor component and other accessories is added on a main bearing component of the three-dimensional engine model by concentrated mass points; c. and replacing the huge external pipeline by a plurality of concentrated masses by adopting a distributed concentrated mass method for the mass of the rest pipeline, and adding the concentrated masses to the three-dimensional model of the engine.
further, step a of the third step is specifically: applying components such as an accessory casing, a central transmission, a vector nozzle/tail nozzle, an exhaust tail cone and the like as concentrated masses to corresponding mounting sections, correcting the mass of the three-dimensional model established in the step one into the theoretical mass of the additional components, and enabling the mass center of the concentrated mass to be the same as the actual mass center of the additional components.
Further, step b of step three is specifically: and taking the rotor component and other accessories as concentrated masses, correcting the mass of the main force bearing component established in the step one, correcting the mass of the three-dimensional model established in the step one into the theoretical mass of the additional component, and enabling the mass center of the concentrated masses to be the same as the actual mass center of the component.
further, step c of the third step is specifically: according to the layout of the engine pipelines, the mass points are distributed on the outer surface of the whole engine model according to different densities, the mass points at the parts with dense pipelines are distributed densely, and the mass value of each mass point is the total mass of the total pipelines divided by the number of the mass points.
further, the conditions input in the second step include material properties, coordinate systems, temperature fields and boundary conditions of each component.
further, the external loads input in the third step include pneumatic loads and rotor component loads.
Further, the step four of calculating the vibration conclusion specifically includes the following steps: a. checking errors of the total mass of the finite element calculation and the theoretical mass of the engine; b. carrying out stress analysis; c. carrying out modal analysis; d. and carrying out finite element and test comparison to obtain an evaluation result.
The beneficial technical effects are as follows: according to the method for calculating the vibration of the auxiliary suspension pull rod of the aircraft engine, an engine and pull rod assembly model is established, the resonant frequency and the vibration mode of an assembly are calculated, and data support is provided for troubleshooting of the vibration of the whole machine.
Drawings
FIG. 1 is a simplified three-dimensional model of an engine according to an embodiment of the present invention;
The system comprises a fan front casing, a fan intermediate casing, a fan outer casing, a mixer, a booster nozzle casing, a high-pressure compressor casing, a combustor casing and a turbine support, wherein the fan front casing, the fan intermediate casing, the fan outer casing, the booster nozzle casing, the mixer, the booster nozzle casing, the high-pressure compressor casing, the combustor casing and the turbine support are arranged in a 1-mode.
Detailed Description
This section is an embodiment of the present invention to help understand the purpose and concept of the present invention.
1. Establishing a three-dimensional model for the vibration calculation of the whole machine as shown in figure 1: the method comprises the steps of establishing main force bearing parts of the engine, such as a fan front casing 1, a fan casing 2, an intermediate casing 3, an outer culvert casing 4, a mixer 5, a thrust augmentation nozzle casing 6, a high-pressure compressor casing 7, a combustion chamber casing 8, a turbine support 9 and the like. Assembling the auxiliary hanging pull rod 10 to a three-dimensional model of the whole machine, and establishing the same three-dimensional model as the engine test run;
2. Setting material properties for each part: the material properties at least comprise density, elastic modulus, Poisson's ratio, thermal expansion coefficient and the like;
3. Establishing a coordinate system: the axis of the engine is taken as an X axis, and the forward direction is positive. The right side of the forward heading of the engine is a positive Y axis. The Z axis is determined by a right hand rule;
4. application of a temperature field: applying a temperature field according to each section temperature value in an engine air system calculation report provided by an upstream department;
5. Applying a boundary condition: the boundary conditions imposed by the finite element calculations are the same as for the actual engine installation. In general, only the rotational freedom degree of the engine around the Y axis is reserved after the engine is mainly installed and saved, and the freedom degree is restrained by an auxiliary hanger; (2-5 finite element boundary conditions)
6. applying a pneumatic load: and applying pneumatic load on the corresponding section according to an engine pneumatic axial force and torque calculation report provided by an upstream department. The pneumatic load comprises the pneumatic axial force and torque to which all the stator and rotor components are subjected; (6, 9 external load)
7. and (3) correcting the quality of the whole machine: the model established in the step 1 only comprises main bearing parts of the engine, rotor parts and other accessories are not considered, and the mass of the parts which are not considered accounts for about two thirds of the total mass of the engine. Performing mass correction on the main force bearing part established in the step 1 in a mass concentration mode, correcting the mass established in the step 1 into actual theoretical mass, and requiring that the corrected part mass center is the same as the actual mass center of the engine (2); and (3) applying components such as an accessory casing, a central transmission, a vector nozzle/tail nozzle, an exhaust tail cone and the like as concentrated masses to the corresponding mounting section, correcting the masses established in the step (1) into actual theoretical masses, and requiring that the concentrated mass centroid is the same as the actual mass centroid of the component. The culvert pipeline is applied to a corresponding position in a distributed and concentrated mass mode according to the actual distribution condition of the culvert pipeline on the engine, and the specific steps are shown in step 8;
8. Distributed centralized mass application: step 1 and step 7 establish most of the mass of the engine;
9. rotor component load application: at present, most of the aero-engines are of a double-rotor structure, and rotors are generally simplified into simple supporting beams or cantilever beams for stress calculation. And respectively carrying out stress analysis on the fan rotor, the low-pressure turbine rotor and the high-pressure rotor to obtain the reaction force at the rotor supporting position. Applying a reaction force to the corresponding position of the model established in the step 1;
10. And (4) checking: the relative error between the mass center of the finite element calculation model and the actually measured mass center of the engine is less than 10mm in the three directions of XYZ;
11. And (3) stress analysis: and in the stage state, applying inertia overload of one time in the + Z direction. Dividing grids to complete stress analysis;
12. And (3) modal analysis: applying the stress obtained in the step (11) to modal analysis, and calculating the natural frequency and the vibration mode of the whole machine under prestress;
13. finite element and test comparison: and evaluating the vibration at the pull rod by combining the vibration measurement result of the auxiliary hanging part during the test run of the whole machine.
The working principle of the invention is as follows: and establishing an engine and pull rod assembly model in the stand state of the aero-engine. The model comprises main bearing parts of the engine, and the mass of the rest parts is applied in a mass point concentration mode. Firstly, calculating the stress of a part in a trial run state of the engine, and applying the stress to modal calculation to obtain the resonance frequency and the vibration mode of the whole machine. And comparing the resonance frequency and the vibration mode with the test result to verify whether the vibration at the auxiliary pull rod is caused by resonance of a casing around the sensor.
another embodiment of the present invention is as follows.
1. and (3) establishing a complete machine vibration calculation three-dimensional model according to the steps 1-3 in the previous embodiment, and setting material properties, boundary conditions and grid sizes. The mesh size is 30mm and the total number of nodes is 4315138. The connection surface between each component is set as 'binding';
2. Pneumatic and temperature loads were applied according to steps 4-6 of the "embodiment";
3. the quality correction is divided into three parts: the method comprises the following steps of correcting the mass of a bearing casing of the engine, correcting the centralized mass of main parts and correcting the distributed centralized mass of external pipelines.
3.1, correcting the quality of the engine bearing case: in the specific implementation mode, an assembly body of a main bearing frame of the engine is built in the step 1, but parts mounted on the bearing frame are not considered. For example, the finite element calculated mass of the bearing case in the fan case 2 is 35kg, and the total mass of the actual fan case assembly is 72 kg. In the embodiment, 3 concentrated masses are adopted for correction, and the corrected mass center is the same as the mass center of the fan casing in a 72kg state. The quality correction methods of other casings are the same;
3.2, main component centralized quality correction: the influence of the central transmission gear assembly, the accessory casing and the tail nozzle on the calculation result of the vibration of the pull rod is small, 1 concentrated mass can be adopted for simulation, and the mass center of the concentrated mass is the same as the actual mass center;
3.3, correcting the distributed centralized quality of the external pipelines: taking the engine accessory casing as an example, the external pipelines of the engine are uniformly distributed on the circumferential direction of the fan casing 2, and the external pipelines are distributed on the intermediate casing 3, the bypass casing 4 and the mixer 5 only in the + Z direction. Therefore, the fan casing 2 adopts 2 rows of 16 circumferentially uniformly distributed quality simulation external pipelines, the intermediate casing 3, the bypass casing 4 and the mixer 5 adopt 5 rows of 25 uniformly distributed quality simulation external pipelines at the lower part of the engine (+ Z direction), and all distributed concentrated qualities are tightly attached to corresponding casing components.
4. the analysis was performed according to "steps 9-12 of the previous example, and all resonance points and modes were obtained for the engine and tie rod assembly in the range of 50Hz to 250 Hz.
5. Finite element calculation and rack measured data comparative analysis: when a certain engine rack is tested, vibration detection in XYZ directions of a main mounting joint is normal, the vibration value in Y direction at the left auxiliary hanging part along the heading is 38mm/s and is close to 40mm/s required by the regulation, and parking inspection is needed. Finite element calculation finds that a plurality of resonance points of a casing and a tail nozzle exist in the working frequency range of the engine, and the condition of the resonance of a pull rod exists under low frequency. The vibration of the whole finite element machine visually presents the vibration state of the auxiliary hanger in the engine test process, provides more alternative fault sources for vibration troubleshooting, and provides technical support for subsequent vibration troubleshooting.
Claims (8)
1. The method for calculating the vibration of the auxiliary hanging pull rod of the aircraft engine is characterized by comprising the following steps of:
establishing and simplifying a three-dimensional model of an engine, and reserving a main bearing part;
Inputting conditions such as environment, finite element boundary conditions and the like;
Correcting the mass of the three-dimensional model according to the theoretical mass of the engine and inputting an external load;
And step four, calculating to obtain a vibration conclusion.
2. The vibration calculation method for the auxiliary hanging pull rod of the aero-engine according to claim 1, wherein the step three of correcting the mass of the three-dimensional model according to the theoretical mass of the engine specifically comprises the following steps:
a. According to the structure diagram of the engine, applying the mass of the accessory casing, the central transmission, the vector nozzle/tail nozzle, the exhaust tail cone and other components on the corresponding mounting surfaces of the three-dimensional model of the engine by concentrated mass points;
b. the mass of the rotor component and other accessories is added on a main bearing component of the three-dimensional engine model by concentrated mass points;
c. and replacing the huge external pipeline by a plurality of concentrated masses by adopting a distributed concentrated mass method for the mass of the rest pipeline, and adding the concentrated masses to the three-dimensional model of the engine.
3. The vibration calculation method for the auxiliary suspension pull rod of the aero-engine according to claim 2, wherein the step a in the step three specifically comprises the following steps: applying components such as an accessory casing, a central transmission, a vector nozzle/tail nozzle, an exhaust tail cone and the like as concentrated masses to corresponding mounting sections, correcting the mass of the three-dimensional model established in the step one into the theoretical mass of the additional components, and enabling the mass center of the concentrated mass to be the same as the actual mass center of the additional components.
4. the vibration calculation method for the auxiliary suspension pull rod of the aero-engine according to claim 2, wherein the step b in the step three specifically comprises the following steps: and taking the rotor component and other accessories as concentrated masses, correcting the mass of the main force bearing component established in the step one, correcting the mass of the three-dimensional model established in the step one into the theoretical mass of the additional component, and enabling the mass center of the concentrated masses to be the same as the actual mass center of the component.
5. the vibration calculation method for the auxiliary suspension pull rod of the aero-engine according to claim 2, wherein the step c of the step three comprises the following specific steps: according to the layout of the engine pipelines, the mass points are distributed on the outer surface of the whole engine model according to different densities, the mass points at the parts with dense pipelines are distributed densely, and the mass value of each mass point is the total mass of the total pipelines divided by the number of the mass points.
6. The method for calculating the vibration of the auxiliary suspension pull rod of the aircraft engine according to claim 1, wherein the input conditions in the second step comprise material properties, a coordinate system, a temperature field and boundary conditions of each component.
7. The method for calculating vibration of an auxiliary suspension rod of an aircraft engine according to claim 1, wherein the external loads input in the third step comprise pneumatic loads and rotor component loads.
8. The vibration calculation method for the auxiliary suspension pull rod of the aircraft engine according to claim 1, wherein the step four of calculating the vibration conclusion specifically comprises the following steps:
a. checking errors of the total mass of the finite element calculation and the theoretical mass of the engine;
b. Carrying out stress analysis;
c. carrying out modal analysis;
d. And carrying out finite element and test comparison to obtain an evaluation result.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113530707A (en) * | 2021-08-16 | 2021-10-22 | 中国航发贵阳发动机设计研究所 | Spray pipe heat insulation layer structure and installation method |
| CN114510798A (en) * | 2022-01-25 | 2022-05-17 | 中国航发沈阳发动机研究所 | Pneumatic axial force error-proofing analysis method for aircraft engine |
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