Design method for high cycle fatigue test of aviation turbojet and turbofan engines

Abstract

The present invention provides a high-cycle fatigue test design method for aviation turbojet and turbofan engines, including: determining the blade frequency sweep number measurement standard, test design reference level, and speed steps; according to the blade high-cycle fatigue cycle number requirements, the test design reference level is used to calculate the theoretical total operation time of each speed step and the theoretical total operation time of the entire test run; decomposing the theoretical total operation time of each speed step, determining the operation time of each speed step in each test run and rounding it up to obtain the total operation time required for the entire test run; comparing the total operation time required for the entire test run with the theoretical total operation time of the entire test run, if the increased time does not exceed the set threshold, continuing the design steps, otherwise re-rounding; arranging each speed step and the corresponding engine operation time according to a rule to obtain a high-cycle fatigue test run program. The present invention has the advantages of simple test design process, sufficient assessment, short test cycle, good economic benefits, etc.

Description

Technical Field

[0001] The invention relates to the technical field of aviation gas turbine engine whole machine testing, and in particular to a high cycle fatigue test design method for aviation turbojet and turbofan engines. Background Art

[0002] High-cycle fatigue damage of parts such as blades is a typical damage mode of aviation gas turbine engines. In order to obtain good engine performance, aircraft engine blade parts are generally designed to be as thin and light as possible, and the surface is relatively complex. However, high performance and high reliability are contradictory. The airflow flowing through the engine will excite the blades to produce vibrations with low stress levels but high frequencies. If the blade vibration frequency caused by the excitation coincides with or is close to the blade natural frequency, it will cause blade resonance. At this time, the blade vibration stress will increase significantly. Under high-frequency vibration conditions, the possibility of blade damage increases. This is a typical blade high-cycle fatigue damage mechanism. For axial compressors or turbines with a large number of stages, it is basically impossible to avoid the resonant frequency of each stage of blades within the entire operating speed range. Vibration reduction measures must be taken or the excitation frequency of the excitation source must be adjusted to minimize the possibility of high-cycle fatigue damage to the blades. For the designed compressor or turbine, or the entire aviation gas turbine engine, on the basis of design analysis, it is also necessary to pass necessary high-cycle fatigue tests to test the engine's ability to resist high-cycle fatigue damage.

[0003] The current high-cycle fatigue test design method, especially the high-cycle fatigue test method for the complete aircraft gas turbine engine, is not mature and complete. Therefore, it is necessary to propose a high-cycle fatigue test design method for the complete aircraft turbojet and turbofan engine with a small diameter and a high rotation speed. Summary of the invention

[0004] In view of this, an embodiment of the present application provides a high-cycle fatigue test design method for aviation turbojet and turbofan engines. This test design method is a high-cycle fatigue test design method for aviation turbojet and turbofan engines with small diameter and high rotation speed. It has the advantages of simple test design process, sufficient assessment, short test cycle and good economic benefits.

[0005] The embodiment of the present application provides the following technical solution: a method for designing a high-cycle fatigue test for an aviation turbojet and turbofan engine, comprising the following steps:

[0006] S101. Determine the blade frequency sweeping number measurement standard and test design reference level;

[0007] S102. Determine the speed steps for test program design at equal speed intervals within the engine operating speed range;

[0008] S103, according to the total number of high-cycle fatigue cycles of the blades, and based on the test design reference level, calculate the theoretical total time the engine needs to run at each speed step and the theoretical total time required for the entire test run;

[0009] S104, decomposing the theoretical total time required for the engine to run at each speed step, and determining the number of test runs and the running time of each speed step in each test run;

[0010] S105, rounding the operation time of each speed step in each test run to obtain the single test run operation time and the total operation time required for the entire test run;

[0011] S106, comparing the total operation time required for the entire test run after rounding in S105 with the theoretical total operation time required for the entire test run obtained in S103, if the added time does not exceed the set threshold, continue with the design step of S107, otherwise return to S105 to round again;

[0012] S107, arranging each speed step and the corresponding engine running time according to a rule to obtain a high cycle fatigue test program.

[0013] According to an implementation of an embodiment of the present invention, when determining the measurement standard of the number of frequency sweeps of the blades: the measurement standard of the number of frequency sweeps of the working blades is: when the working blades of each stage rotate through one preceding stage rectifying blade, it is recorded that the corresponding working blade experiences one "frequency sweep", and when the engine rotor rotates one circle, the number of "frequency sweeps" experienced by each working blade is equal to the number of upstream rectifying blades;

[0014] The measurement standard for the frequency sweep times of the rectifying blades is: when one front-stage working blade rotates past the downstream rectifying blade, it is recorded as one "frequency sweep" experienced by the downstream rectifying blade. When the rotor rotates one circle, the number of "frequency sweeps" experienced by each downstream rectifying blade is equal to the number of front-stage working blades.

[0015] According to an implementation manner of an embodiment of the present invention, the total requirement for the number of high-cycle fatigue cycles of the blade includes that the number of "sweeping frequencies" of non-ferrous metal parts of titanium alloy is not less than 3X10^7 times, and the number of "sweeping frequencies" of steel parts is not less than 10^7 times.

[0016] According to an implementation of an embodiment of the present invention, a method for determining the selection of the experimental design reference level is: selecting the level with the least frequency sweep times when the inner rotor of the compressor rotates one circle as the design reference level.

[0017] According to an implementation of the embodiment of the present invention, the high cycle fatigue test program includes a step operation curve that increases from a minimum speed to a maximum speed and then decreases to a minimum speed.

[0018] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least: the high-cycle fatigue test design method of the embodiment of the present invention can be extended to the high-pressure compressor, medium-pressure compressor, turbine of medium and large bypass ratio turbofan engines, compressor, turbine of turboshaft engines, compressor, turbine of turbopropeller fan engines and other components, and high-cycle fatigue test assessment is carried out in the whole machine state. The use of this test method to carry out high-cycle fatigue tests on corresponding types of engines has the advantages of simple test design process, sufficient assessment, short test cycle, good economic benefits, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic flow chart of a high cycle fatigue test design method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0022] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments, and the technical scheme of the present invention will be clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] like Figure 1 As shown, a high cycle fatigue test design method for an aviation turbojet and turbofan engine according to an embodiment of the present invention comprises the following steps:

[0024] S101. Determine the blade frequency sweeping number measurement standard and test design reference level;

[0025] 1. Determine the measurement standard for the number of blade "sweeps": During the operation of the engine, the airflow flowing out of each stage of the rectifying blade ring forms a fixed, circumferentially periodically changing annular flow field under the isolation effect of the rectifying blades. Each working blade after the rectifying blade of this stage is "swept" once when rotating through each changing cycle of this annular flow field. Therefore, when a working blade rotates through one upstream rectifying blade, it is recorded as one "sweep" experienced by the working blade. When the rotor rotates one circle, the number of "sweeps" experienced by each working blade is equal to the number of upstream rectifying blades. Correspondingly, when a previous stage working blade rotates through the downstream rectifying blade, it is recorded as one "sweep" experienced by the downstream rectifying blade. When the rotor rotates one circle, the number of "sweeps" experienced by each downstream rectifying blade is equal to the number of previous stage working blades.

[0026] 2. Determine the total number of "sweep frequency" requirements: The total number of "sweep frequency" is equal to the high-cycle fatigue cycle requirements of the blade being tested. For the whole machine high-cycle fatigue test, it is recommended to determine the blade high-cycle fatigue cycle requirements according to GJB 241-1987 "General Specifications for Aviation Turbojet and Turbofan Engines", that is, non-ferrous metal (including titanium alloy) parts are not less than 3X10^7 times, steel parts are not less than 10^7 times, and for titanium alloy parts specified in GJB241A-2010 "General Specifications for Aviation Turbojet and Turbofan Engines", it is not less than 10^9 times. It is recommended to conduct research from the perspective of high-cycle fatigue performance of titanium alloy materials, and not to conduct assessment in the whole machine high-cycle fatigue test;

[0027] Among them, the basic principle of the "sweep frequency method" high-cycle fatigue test design method is as follows: when the engine is working normally, the blades are in a high-frequency, low-stress vibration state, and the blade vibration stress is very small, which is not enough to cause high-cycle fatigue damage. When the blades are working in a resonant state, the vibration stress will increase significantly. If the vibration reduction measures taken are unreasonable, it will cause high-cycle fatigue damage to the blades. The "sweep frequency method" assumes that the blades are in a resonant state at each speed within the working speed range. Through the whole machine test, each stage of the blades undergoes a sufficient number of high-cycle fatigue stress cycles at each working speed to check whether there is an operating speed at which the vibration stress is large enough to cause high-cycle fatigue damage to the blades. If the whole machine high-cycle fatigue test assessment shows that there is no such speed, then the structural design of the blades at all levels is considered reasonable.

[0028] 3. Determine the experimental design reference level: select the level with the least number of "sweep frequencies" when the compressor rotor rotates one circle as the design reference level.

[0029] Specifically: Generally speaking, along the upstream to downstream of the fan or compressor air flow channel, the number of blades at each stage gradually increases, the blade vibration frequency increases, and the material used for the blades gradually transitions from non-ferrous metals to steel (or high-temperature alloys). Turbine blades usually use high-temperature alloys. Therefore, generally speaking, the stage upstream of the fan or compressor takes the longest time to reach the required number of high-cycle fatigue cycles, and the stage upstream of the air flow channel is selected as the design reference stage for the high-cycle fatigue test.

[0030] S102. Determine the speed steps for test program design at equal speed intervals within the engine operating speed range;

[0031] In specific implementation, within the stable operating speed range designed for the engine, the speed steps are determined at equal speed intervals of about 1%;

[0032] S103, according to the total number of high-cycle fatigue cycles of the blades, and based on the test design reference level, calculate the theoretical total time the engine needs to run at each speed step, and the theoretical total time required for the entire test run;

[0033] In specific implementation, according to the total number of frequency sweeps and the test design reference level, the total operation time of each speed step is calculated, and the total operation time of all speed steps is calculated. This total operation time is the theoretical total time required for the high cycle fatigue test;

[0034] S104, decomposing the theoretical total time required for the engine to run at each speed step, and determining the number of test runs and the running time of each speed step in each test run;

[0035] In specific implementation, combined with the characteristics of engine use restrictions, the total operation time of each speed step is decomposed to determine the number of test runs required, the theoretical time of a single test run, and the engine operation time at each speed step in a single test run;

[0036] S105, rounding the operation time of each speed step in each test run to obtain the single test run operation time and the total operation time required for the entire test run;

[0037] In specific implementation, in order to facilitate operation and not reduce or increase the program time too much, the operation time of each speed step is rounded to obtain the single test operation time and the total test operation time;

[0038] S106, comparing the total operation time required for the entire test run after rounding in S105 with the theoretical total operation time required for the entire test run obtained in S103, if the added time does not exceed the set threshold, continue with the design step of S107, otherwise return to S105 to round again;

[0039] S107, arranging each speed step and the corresponding engine running time according to a rule to obtain a high cycle fatigue test program.

[0040] In specific implementation, each speed step and the corresponding operation time are arranged in a manner of increasing from the minimum speed to the maximum speed and then decreasing to the minimum speed, so as to obtain a step operation test program for high-cycle fatigue test of the whole machine.

[0041] The high-cycle fatigue test design method for aviation turbojet and turbofan engines in the embodiment of the present invention adopts a sweep frequency method, which is suitable for the high-cycle fatigue resistance assessment of blades at various levels of turbojet and turbofan engines with small rotor diameters and high rotation speeds. The high-cycle fatigue resistance assessment of blades at various levels of intermediate-pressure compressors, high-pressure compressors, and turbines of medium and large bypass ratio turbofan engines, and blades at various levels of compressors and turbines of turboshaft engines and turbopropeller engines can also be tested with reference to this method.

[0042] The use of this test method to conduct high-cycle fatigue tests on the corresponding type of engine has the advantages of simple test design process, sufficient assessment, short test cycle and good economic benefits.

[0043] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for designing high cycle fatigue tests for aviation turbojet and turbofan engines, characterized in that: The following steps are involved: S101. Determine the blade frequency sweep frequency measurement standard and the test program design benchmark level; S102, within the engine operating speed range, determining speed steps for test run program design at equal speed intervals; S103, according to the total number of high-cycle fatigue cycles of the blades, and based on the test design reference level, calculate the theoretical total time the engine needs to run at each speed step and the theoretical total time required for the entire test run; S104, decomposing the theoretical total time required for the engine to run at each speed step, and determining the number of test runs and the running time of each speed step in each test run; S105, rounding the operation time of each speed step in each test run to obtain the single test run operation time and the total operation time required for the entire test run; S106, comparing the total operation time required for the entire test run after rounding in S105 with the theoretical total operation time required for the entire test run obtained in S103, if the added time does not exceed the set threshold, continue with the design step of S107, otherwise return to S105 to round again; S107, arranging each speed step and the corresponding engine running time according to a rule to obtain a high cycle fatigue test program; When determining the measurement standard of the number of frequency sweeps of the blades: the measurement standard of the number of frequency sweeps of the working blades is: when the working blades of each stage rotate through one preceding stage rectifying blade, it is recorded that the corresponding working blade experiences one frequency sweep, and when the engine rotor rotates one circle, the number of frequency sweeps experienced by each working blade is equal to the number of upstream rectifying blades; The measurement standard for the frequency sweep times of the rectifying blades is: one preceding working blade rotates past the downstream rectifying blade, which is counted as one frequency sweep experienced by the downstream rectifying blade. When the rotor rotates one circle, the frequency sweep times experienced by each downstream rectifying blade is equal to the number of preceding working blades.

2. The method for designing high cycle fatigue tests for aviation turbojet and turbofan engines according to claim 1, characterized in that: The total requirement for the number of high-cycle fatigue cycles of the blades includes that the frequency sweeping times of non-ferrous metal parts of titanium alloy shall be no less than 3X10^7 times, and the frequency sweeping times of steel parts shall be no less than 10^7 times.

3. The high cycle fatigue test design method for aviation turbojet and turbofan engines according to claim 1, characterized in that: The method for selecting the design reference level of the test run procedure is: select the level with the least frequency sweep times when the compressor rotor rotates one circle as the design reference level.

4. The method for designing high cycle fatigue tests for aviation turbojet and turbofan engines according to claim 1, characterized in that: The high cycle fatigue test program includes a step operation curve that increases from a minimum speed to a maximum speed and then decreases to a minimum speed.

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