Step-durability vibration test method and aero-engine test system

Abstract

The application discloses a kind of ladder endurance vibration test method and aero-engine test system, determine the phase distribution of most adverse unbalance;Step vibration test, according to the unbalance distribution, precast rotor unbalance, carry out ladder endurance test;Speed dwell test;The selection of installed vibration sensor position;Determine the maximum allowable vibration value of engine.First, determine the phase distribution of most adverse unbalance, the determination of most adverse unbalance state fully considers the influence of rotor vibration mode, then the method of ladder endurance test and speed dwell test is combined, the anti-vibration capability of engine and each component under different vibration states is systematically verified, the examination is more sufficient, the selection of installed vibration sensor position changes the situation of traditional dependence on experience, the most sensitive sensor position to each order vibration of rotor can be selected, the effectiveness of vibration monitoring is improved, the determination of maximum allowable vibration value is directly related to the vibration level of actual examination and verification, and the reliability is strong.

Description

Technical Field

[0001] This invention relates to the field of aero-engine testing technology, and in particular, to a method for step-wise sustained vibration testing. Furthermore, this invention also relates to an aero-engine testing system incorporating the aforementioned step-wise sustained vibration testing method. Background Technology

[0002] As the core power unit of an aircraft, the structural integrity and operational reliability of an aero-engine gas turbine engine directly affect flight safety. During engine operation, the high-speed rotation of the rotor system inevitably generates mechanical vibration. When the vibration level exceeds a certain limit, it may lead to serious consequences such as high-cycle fatigue fracture of blades, bearing damage, accessory failure, and pipeline leakage. Therefore, conducting thorough vibration testing on the engine is an indispensable part of the airworthiness verification process for aero-engines.

[0003] According to the relevant requirements of CCAR-33-R2, the "Airworthiness Regulations for Aircraft Engines," engines must undergo vibration testing under extreme unbalance conditions during the development phase to verify their structural integrity and reliability under the most demanding operating conditions. However, the existing "vibration scanning + speed dwell" assessment method has many shortcomings.

[0004] Specifically, the main drawbacks of existing technologies include: First, traditional vibration testing methods typically involve vibration scanning across the entire operating speed range to identify critical speeds with significant vibration responses, followed by a period of time at those speeds for verification. While this method can identify obvious resonance peaks, it often requires separate environmental vibration tests for accessory systems and external piping systems. Because laboratory-scale environmental vibration tables cannot fully simulate the complex vibration spectrum, temperature field, pressure field, and multi-source excitation coupling effects of a real engine operating environment, vibration testing of accessories and piping is insufficient, posing safety hazards.

[0005] Second, regarding the determination of the worst-case imbalance state, most existing technologies only consider the critical speed within 100% of the operating speed range, and the phase distribution of the imbalance lacks a scientific basis for selection. In reality, the mode shape of the rotor at the operating speed may be closer to the mode shape characteristics of the previous or next critical speed. Considering only the 100% operating speed range will lead to an underestimation of the worst-case vibration state.

[0006] Third, the selection of vibration sensor locations has long relied on engineering experience, lacking a systematic quantitative analysis method. Vibration sensors installed in different locations have significantly different sensitivities to different orders of rotor vibration. Improper selection may result in monitored vibration values ​​that fail to accurately reflect the actual vibration state inside the rotor, thus affecting the effectiveness of vibration over-limit protection.

[0007] Fourth, the determination of the maximum permissible vibration value of the engine also relies heavily on empirical values ​​or the instantaneous maximum value of the maximum imbalance test, which lacks a direct correlation with the fatigue life under that vibration value. This results in the vibration limit value being set either too conservatively (affecting engine performance) or at risk (vibration exceeding the limit without triggering protection). Summary of the Invention

[0008] This invention provides a stepped sustained vibration test method and an aero-engine test system to solve a series of technical problems in the prior art, such as insufficient assessment of the vibration resistance of aero-engines, difficulty in assessing accessory pipelines following the engine, unscientific determination of the worst imbalance state, and reliance on experience for the location of installed sensors and allowable vibration values.

[0009] According to one aspect of the present invention, a stepped sustained vibration test method is provided, applied to an aero-engine, comprising the following: S1. Determine the phase distribution of the worst imbalance; S2. Step vibration test: Based on the unbalanced distribution of the pre-fabricated rotor unbalance, a step-by-step endurance test is carried out. S3. Rotational speed dwell test; S4. Selection of the installation location for the vibration sensor; S5. Determine the maximum permissible vibration value for the engine.

[0010] As a further improvement to the above technical solution, step S1 includes: Determine all critical speeds and their corresponding mode shapes within 130% of the engine rotor system's operating speed. Based on the principles of force balance and torque balance, distribute the limit imbalance to each wheel disk. Select the distribution where the imbalance phase is consistent with the mode shape direction as the phase distribution of the worst imbalance. Determine the worst imbalance state corresponding to the first two mode shapes with the largest vibration response, denoted as worst imbalance 1 and worst imbalance 2.

[0011] As a further improvement to the above technical solution, step S1 includes: When determining the worst-case unbalance phase distribution, the vibration response at the bearing at each critical speed is calculated using the finite element method. The vibration response at the first and third critical speeds satisfies the equation... No component testing is required at this time, where, and The vibration velocity responses at the first and second bearings are respectively shown at the first-order critical speed. and The vibration velocity responses at bearings 1 and 2 are respectively measured at the third critical speed. If these conditions are not met, rotor component tests are required to determine the worst order of imbalance.

[0012] As a further improvement to the above technical solution, step S2 includes: The engine was subjected to step vibration tests under the worst imbalance 1 and worst imbalance 2 conditions, respectively.

[0013] As a further improvement to the above technical solution, step S2 includes: Set the rotation speed interval for each step, and pause at each rotation speed step. The stress alternation cycle has a total duration of N hours, and N and k satisfy the following relationship: ; In the formula, Let represent the i-th operating speed value, and m represent the number of stops at m steps.

[0014] As a further improvement to the above technical solution, step S3 includes: Select the peak speeds of vibration measuring points on the engine body, all accessories, and external pipelines, and remain at each peak speed for at least [time value missing]. In a secondary stress alternating cycle, for different worst-case imbalance states, if the peak vibration amplitude of the later state is less than the corresponding amplitude of the previous state, then the peak rotational speed of the later state is exempt from dwell.

[0015] As a further improvement to the above technical solution, step S4 includes: Based on the vibration response data at each critical speed in the stepped endurance test, the sum of vibration amplitude of each candidate vibration sensor is calculated, and the sensor with the largest sum is selected as the installed vibration sensor. The formula for calculating the sum of vibration amplitudes of candidate vibration sensors is as follows: , This represents the sum of the vibration amplitudes of sensor number a. The value represents the vibration component amplitude of sensor a at the first critical speed of the rotor. The superscripts 1, 2, and 3 indicate the first, second, and third critical speeds, respectively.

[0016] As a further improvement to the above technical solution, step S5 includes: The maximum allowable vibration value of the sensor is determined by multiplying the maximum vibration amplitude measured by the installation vibration sensor during the entire stepped endurance test as a benchmark and a safety margin factor.

[0017] As a further improvement to the above technical solution, the test method further includes: For dual-rotor or multi-rotor engines, the worst imbalance state of each rotor is determined, and all combinations of imbalance states are listed. Step-by-step endurance tests and speed dwell tests are carried out under each combination state.

[0018] According to another aspect of the present invention, an aero-engine testing system is also provided, which includes the above-described stepped sustained vibration testing method.

[0019] The present invention has the following beneficial effects: This test method first determines the phase distribution of the worst imbalance, and the determination of the worst imbalance state fully considers the influence of rotor vibration mode. Then, it adopts a combination of stepped endurance test and speed dwell test to systematically verify the vibration resistance of the engine and its components under different vibration states. The assessment is more comprehensive. The selection of the installation vibration sensor position changes the traditional reliance on experience and can select the sensor position most sensitive to each order of rotor vibration, improving the effectiveness of vibration monitoring. The determination of the allowable maximum vibration value is directly related to the vibration level verified in the actual test. Its scientificity and reliability are significantly better than the experience value method.

[0020] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a first-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of a second-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of a third-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 4 This is a flowchart of the test method of a preferred embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0023] Figure 1 This is a schematic diagram of a first-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of a second-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of a third-order vibration mode of a rotor according to a preferred embodiment of the present invention; Figure 4 This is a flowchart of the test method of a preferred embodiment of the present invention.

[0024] refer to Figure 4 The stepped sustained vibration test method of this embodiment includes the following: S1. Determine the phase distribution of the worst imbalance; S2. Step vibration test: Based on the unbalanced distribution of the pre-fabricated rotor unbalance, a step-by-step endurance test is carried out. S3. Rotational speed dwell test; S4. Selection of the installation location for the vibration sensor; S5. Determine the maximum permissible vibration value for the engine.

[0025] Understandably, this test method first determines the phase distribution of the worst imbalance, and the determination of the worst imbalance state fully considers the influence of rotor vibration mode. Then, it adopts a combination of stepped endurance test and speed dwell test to systematically verify the vibration resistance of the engine and its components under different vibration states. The assessment is more comprehensive. The selection of the installation vibration sensor position changes the traditional reliance on experience and can select the sensor position most sensitive to each order of rotor vibration, improving the effectiveness of vibration monitoring. The determination of the allowable maximum vibration value is directly related to the vibration level verified in the actual test. Its scientificity and reliability are significantly better than the experience value method.

[0026] In some preferred embodiments, step S1 includes: Determine all critical speeds and their corresponding mode shapes within 130% of the engine rotor system's operating speed. Based on the principles of force balance and torque balance, distribute the limit imbalance to each wheel disk. Select the distribution where the imbalance phase is consistent with the mode shape direction as the phase distribution of the worst imbalance. Determine the worst imbalance state corresponding to the first two mode shapes with the largest vibration response, denoted as worst imbalance 1 and worst imbalance 2. Specifically, according to regulations, engine vibration tests must be conducted under extreme imbalance conditions to verify the structural integrity and operational reliability of the engine under the most stringent conditions. Extreme imbalance refers to the maximum possible imbalance caused by blade wear, disc machining errors, assembly deviations, residual imbalance of rotor dynamic balance, and other factors within the specified service life of the engine. First, based on the principles of force balance and torque balance, the extreme imbalance is distributed to each disc of the rotor system. Based on the critical speed within the operating speed range and the most recent critical speed exceeding the operating speed by up to 30%, one or two of the worst imbalance phase distributions are selected according to the mode shape of the rotor system. The "worst unbalanced phase distribution" refers to a situation where, in a certain mode shape, the phase direction of the unbalance is consistent with the vibration direction of that mode shape, thus maximizing the excitation of that mode shape and producing the most intense vibration response. This physical principle can be understood from the perspective of structural dynamics: when the direction of the excitation force is consistent with the direction of the structure's natural mode shape, the modal participation coefficient is maximized, and the resonance response reaches its peak. The critical speed within the operating speed range obviously needs to be given special consideration. Through extensive theoretical analysis and experimental research, it has been found that when the rotor operates at its operating speed, its actual mode shape is often closer to the mode shape characteristics of the previous or next critical speed, rather than just the critical mode shape within the operating speed range. In other words, even if a certain critical speed is higher than the operating speed, its mode shape characteristics may still appear within the operating speed range and affect the vibration behavior of the rotor. Based on this important finding, the scope of consideration was expanded to all critical speeds within 130% of the operating speed. That is, the selection of 130% was not arbitrary, but a reasonable threshold derived from a large amount of engineering practice and theoretical calculation. Statistical analysis and experimental verification show that for a typical aero-engine rotor, the mode shape corresponding to the critical speed outside 130% of the operating speed has decayed to an extremely low level within the operating speed range, and its impact on the rotor vibration response can be ignored. The setting of this threshold ensures the sufficiency of the assessment and avoids unnecessary experimental workload.

[0027] In some preferred embodiments, step S1 includes: When determining the worst-case unbalance phase distribution, the vibration response at the bearing at each critical speed is calculated using the finite element method. The vibration response at the first and third critical speeds satisfies the equation... No component testing is required at this time, where, and The vibration velocity responses at the first and second bearings are respectively shown at the first-order critical speed. and The vibration velocity responses at bearings 1 and 2 are respectively measured at the third critical speed. If these conditions are not met, rotor component tests are required to determine the order of the worst imbalance. In one specific embodiment, reference is made to Figure 1 The first-order mode shape shown demonstrates that at the first critical speed, the rotor system primarily exhibits rigid body motion modes, with each disk oscillating in the same direction and having essentially the same phase. At this point, if the phases of the unbalances of each disk are also arranged in the same direction, the first-order mode shape will be violently excited, resulting in a significant vibration response at the bearing. (Reference) Figure 2 The demonstrated second-order vibration mode, at the second-order critical speed, exhibits a bending vibration mode, with the disks above the centerline moving in opposite directions to the disks below the centerline, forming a node. At this point, the worst-case unbalance phase distribution should result in the unbalance of the disks above the centerline being out of phase with the unbalance of the disks below the centerline, thereby maximizing the excitation of second-order bending vibration; (Reference) Figure 3 The demonstrated third-order vibration mode is more complex, exhibiting an S-shaped bend at two nodes. The corresponding worst-case unbalance phase distribution should cause the unbalance vectors of the disk assemblies in different vibration directions to be out of phase. For a turboshaft engine rotor in this example, there are three critical speeds within its operating speed range (including up to 130% of the operating speed), correspondingly presenting three different possibilities for worst-case unbalance distributions. To determine which one or two worst-case unbalance distributions will be used for subsequent experiments, quantitative calculations are performed using the finite element analysis method. S11. Using the actual imbalance distributed in each wheel as boundary conditions, establish a dynamic model of the rotor system in commercial finite element software; the finite element model should include the main components such as wheel, shaft, blade, and support bearing, and accurately reflect their mass distribution, stiffness characteristics and damping characteristics; the support stiffness of the bearing can be estimated by experimental determination or empirical formula. S12. Calculate the vibration response of the rotor at the first three critical speeds; the vibration response can be calculated using the modal superposition method or the direct integration method, with a focus on the response amplitude of the vibration sensors located at the bearing positions; typically, two mutually perpendicular vibration sensors are arranged at each bearing to measure the vibration velocity or vibration displacement in the horizontal and vertical directions, respectively. S13. Compare the vibration response amplitudes of the bearing positions at each critical speed; select the worst unbalance distributions corresponding to the two vibration modes with the largest vibration responses for subsequent step-by-step endurance tests; for example, if the design calculation results show that the vibration response at the second critical speed is greater than that at the first critical speed, and the vibration response at the first critical speed is greater than that at the third critical speed, i.e., the response order is v2 > v1 > v3, then select the unbalance distributions corresponding to the second and first vibration modes as the worst unbalance states. S14. When the vibration response values ​​are not significantly different, i.e., when the first-order and third-order critical speed responses are basically close, further correction and verification are required through rotor component testing; that is, when the relationship is satisfied... If the ratio of the first-order to the third-order vibration response at the two bearings is approximately equal, it indicates that the vibration transmission characteristics excited by the first-order and third-order modes in the rotor system are consistent. Therefore, component testing is unnecessary, and the unbalance distribution of the second-order and first-order modes can be directly selected. Conversely, if the ratio of the vibration response at the two bearings is significantly different, it indicates that the transmission paths of the first-order and third-order modes through the rotor system are different. In this case, rotor component testing is required to determine, through actual measurement, which unbalance distribution corresponding to the critical speed should be selected as the worst-case scenario. Ultimately, two worst-case unbalance scenarios are determined: worst-case unbalance 1 and worst-case unbalance 2, corresponding to the unbalance distributions of the two modes with the largest vibration responses, respectively. These two scenarios will be used in subsequent stepped endurance tests.

[0028] In some preferred embodiments, step S2 includes: The engine was subjected to step vibration tests under the worst imbalance 1 and worst imbalance 2 conditions, respectively.

[0029] Understandably, in step S2, the pre-production of the unbalance is usually achieved by the material removal method, that is, removing a certain mass of material at a specific angular position of the wheel to generate the required unbalance vector; the location and depth of the material removal need to be precisely designed based on the density of the material, the structural strength requirements of the wheel, and the feasibility of processing; and quantitative calculation is performed using the finite element analysis method. Specifically, after determining the worst-case imbalance state, the rotor imbalance is pre-fabricated according to two methods: worst-case imbalance 1 and worst-case imbalance 2, and step-by-step endurance tests are conducted for each. The tests under the two states are independent of each other; that is, after completing all the test items under one state, the rotor is removed, the other imbalance is pre-fabricated, and the test is conducted again. The speed range of the step-by-step endurance test is all the speeds at which the engine can stably remain under actual operating conditions. For aero-engines, this typically starts from idle speed and goes up to the speed corresponding to maximum takeoff power, including typical operating conditions such as cruise speed and maximum continuous speed. Furthermore, step S2 includes: Set the rotation speed interval for each step, and pause at each rotation speed step. The stress alternation cycle has a total duration of N hours, and N and k satisfy the following relationship: In the formula, This represents the i-th operating speed value, and m represents the m steps at which the vehicle stops. Specifically, the speed interval between each step is 120 rpm. This interval value was determined based on extensive engineering practice; it is sufficiently refined to capture the characteristics of vibration peaks without making the number of steps excessive. At each speed step, the engine needs to undergo a certain number of stress alternation cycles. Each time the engine rotates, the components within the rotor system (especially the blades) undergo one stress alternation cycle; therefore, the number of cycles directly determines the amount of fatigue damage accumulated at that speed, leading to excessively long test times. Tests show that a 120 rpm interval is sufficient to distinguish resonance peaks within the half-power bandwidth. The same number of stress alternation cycles at each speed step is denoted as... This is different from the fixed number of loops commonly used in existing technologies (such as 1). The number of cycles differs from the previous method, but the purpose of using the same number of cycles is to ensure a relatively balanced contribution of vibration damage at each speed step, avoiding insufficient exposure of vibration hazards at a certain speed due to excessively short dwell times. More importantly, a formula for controlling the overall test time is proposed to ensure that engines in different speed ranges can be fully tested. The relationship between the overall test time N (usually taken as 100 hours) and the number of cycles k at each speed step is shown in the formula. It is determined that for engines with a narrow speed range (such as small turboshaft engines), their operating speed range may only be 10,000 rpm to 50,000 rpm. If a fixed k value is used, the total test time may be much less than 100 hours, which is not sufficient for the assessment. The k value is adjusted by formula so that the total test time reaches exactly 100 hours, ensuring that all engines undergo vibration assessment for the same duration. Conversely, for engines with a wide speed range, the k value is automatically adjusted according to the formula to avoid the test exceeding the reasonable time range.

[0030] In some preferred embodiments, step S3 includes: Select the peak speeds of vibration measuring points on the engine body, all accessories, and external pipelines, and remain at each peak speed for at least [time value missing]. Secondary stress alternating cycle, in which for different worst unbalanced states, if the peak vibration amplitude of the later state is less than the corresponding amplitude of the previous state, then the peak rotational speed of the later state is exempt from dwell. Specifically, during the stepped endurance test or a single vibration scan test, the readings of all vibration sensors on the engine are recorded. The vibration measurement points to be monitored include, but are not limited to: engine body vibration sensors such as bearing housing vibration sensors, casing vibration sensors, and shaft strain gauges; vibration acceleration of mounting brackets for accessories such as fuel pumps, oil pumps, generators, and starters; and vibration strain or acceleration of external pipelines such as fuel lines, oil lines, bleed air lines, and return lines. The vibration response amplitude of each measurement point at different speeds is recorded, forming a "speed-vibration amplitude" curve. The peak speed is extracted from each curve. For engine body measurement points, there may be multiple peak speeds, each corresponding to a certain critical speed or local resonance point. For accessory and pipeline measurement points, the peak speed is usually related to the rotor's critical speed, but may differ due to the local modes of the mounting structure. The peak speeds of all measurement points are merged and deduplicated to obtain a set of target speeds to be used for dwell. Dwell tests are performed sequentially at each target speed under the worst imbalance 1 and worst imbalance 2 conditions. The dwell test requires the engine to operate stably at that speed, accumulating... Secondary stress alternating cycles; for tests under different worst-case imbalance states, a simplification principle can be adopted. If the worst-case imbalance state 1 is tested first, and when the worst-case imbalance state 2 test is conducted, if the peak vibration amplitude at a certain target rotational speed is less than the peak amplitude at the same measuring point under the worst-case imbalance state 1, then that peak rotational speed does not need to be stopped. This simplification principle is based on the following logic: it has been verified under more severe vibration conditions. In the next cycle, the requirements will be met under relatively smooth vibration conditions, and no further verification is needed. The order of the speed dwell test can be flexibly arranged according to the test conditions; all dwell times under the worst imbalance 1 condition can be completed first and then the state can be switched, or the two states can be alternated. The important thing is to ensure that each target speed (under each imbalance state) is fully tested.

[0031] In some preferred embodiments, step S4 includes: Based on the vibration response data at each critical speed in the stepped endurance test, the sum of vibration amplitude of each candidate vibration sensor is calculated, and the sensor with the largest sum is selected as the installed vibration sensor. The formula for calculating the sum of vibration amplitudes of candidate vibration sensors is as follows: , This represents the sum of the vibration amplitudes of sensor number a. This represents the vibration component amplitude of sensor a at the first critical speed of the rotor; the superscripts 1, 2, and 3 indicate the first, second, and third critical speeds, respectively. It should be noted that in this test method, such as the stepped endurance test and the speed dwell test, multiple vibration sensors are installed on the engine to obtain comprehensive vibration data. However, in actual flight testing, due to limitations in the number of channels and installation space of the aircraft monitoring system, typically only 1 to 3 vibration sensors can be retained for real-time flight monitoring. Therefore, considering the selection of the sensor location most sensitive to the critical vibration response of each order of the rotor, for the candidate sensor location a, the sum of its vibration amplitude is defined as... The method involves summing the vibration responses of each candidate sensor at each critical speed and along each major vibration transmission path, and the sensor with the largest sum is the one that best reflects the rotor vibration.

[0032] Furthermore, for multi-rotor engines (such as dual-rotor turbofan engines, which include low-pressure and high-pressure rotors), the selection of vibration sensor locations needs to comprehensively consider the vibration contributions of both rotors. In this case, the sum of the vibration responses of each sensor to the low-pressure rotor and the sum of the vibration responses to the high-pressure rotor can be calculated separately. Finally, a sensor that is sensitive to both rotors can be selected, or two sensors can be selected as monitoring sensors for the low-pressure and high-pressure rotors respectively. This method is based on actual experimental data rather than empirical judgment, and can quantitatively evaluate the sensitivity of each candidate location. The results are objective and repeatable. Moreover, this method is deeply integrated with stepped endurance testing, and all input data comes from the same set of tests, exhibiting good consistency.

[0033] In some preferred embodiments, step S5 includes: The maximum allowable vibration value of the sensor is determined by multiplying the maximum vibration amplitude measured by the installation vibration sensor during the entire stepped endurance test by a safety margin factor. Specifically, after determining the location of the installed sensor, the next step is to set the maximum allowable vibration value of the sensor, i.e., the vibration over-limit protection trigger threshold. In the existing technology, the maximum allowable vibration value is usually set based on engineering experience, or based on the instantaneous maximum value measured in the maximum imbalance test multiplied by an empirical coefficient. This approach has two problems: First, the accuracy of the empirical value is limited by the engineer's accumulated experience, and there are large differences between different engine models; second, the instantaneous maximum value may only be a short-term peak at a certain speed, which does not mean that it is safe to operate at that vibration level for a long time. In this preferred embodiment, the determination of the allowable maximum vibration value is directly related to the stepped endurance test and the speed dwell test. Specifically, based on the selected sensor 'a', during the entire stepped endurance test, the vibration amplitude of the sensor at all speed steps is recorded, and the maximum value is recorded as 'a'. Since the stepped endurance test covers all speed steps within the operating speed range, and the k value was calculated according to the method of this invention so that the total test time reaches 100 hours, therefore... This refers to the vibration level after long-term testing under actual operating conditions; more importantly, in subsequent speed dwell tests, the vibration amplitude at each peak speed is usually greater than or equal to the non-peak speed, while the vibration at the peak speed is... This was verified in the subsequent cycle of residence tests. If If the vibration occurs precisely at a certain peak rotational speed, then the vibration level has passed the test. Fatigue verification in the next cycle; if When it occurs at non-peak speeds, its amplitude is smaller than that at peak speeds, and it has undergone at least 100 hours of testing, ensuring its safety. Based on this, the formula for calculating the allowable maximum vibration value is set as follows: , This represents the maximum permissible vibration value for sensor number a. The maximum vibration amplitude measured by sensor A throughout the entire step-by-step endurance test; different vibration sensors can be set with different allowable maximum vibration values ​​based on their location and function in the engine.

[0034] In some preferred embodiments, the test method further includes: For dual-rotor or multi-rotor engines, the worst imbalance state of each rotor is determined, and all combinations of imbalance states are listed. Step-by-step endurance tests and speed dwell tests are carried out under each combination state.

[0035] Understandably, for multi-rotor engines, such as dual-rotor or tri-rotor turbofan engines, the stepped endurance test method needs to be expanded accordingly. This embodiment takes the most common dual-rotor engine as an example. A dual-rotor engine includes a low-pressure rotor (usually a fan and a low-pressure turbine) and a high-pressure rotor (a high-pressure compressor and a high-pressure turbine). The two rotors have different speeds, typically with the low-pressure rotor having a lower speed and the high-pressure rotor having a higher speed. The worst-case imbalance state of the two rotors needs to be considered separately. First, the worst-case imbalance distribution of the low-pressure rotor and the high-pressure rotor are determined separately. Second, stepped endurance tests are carried out under various imbalance combinations. After the stepped endurance test under each combination, a speed dwell test is performed, and the subsequent test methods are completed.

[0036] On the other hand, a preferred embodiment of the present invention also provides an aero-engine test system that applies the above-mentioned stepped sustained vibration test method. The test system includes a test bench, sensors, etc.

[0037] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A stepped sustained vibration test method, applied to aero-engines, characterized in that, Includes the following: S1. Determine the phase distribution of the worst imbalance; determine all critical speeds and corresponding mode shapes of the engine rotor system within 130% operating speed, distribute the limit imbalance to each wheel disk according to the principles of force balance and moment balance, and select the distribution where the imbalance phase and mode shape direction are consistent as the phase distribution of the worst imbalance. Determine the worst imbalance state corresponding to the first two mode shapes with the largest vibration response, denoted as worst imbalance 1 and worst imbalance 2; when determining the phase distribution of the worst imbalance, the vibration response at the bearing at each critical speed is calculated using the finite element method. When the vibration response at the first critical speed and the third critical speed satisfies the equation... No component testing is required at this time, where, and The vibration velocity responses at the first and second bearings are respectively shown at the first-order critical speed. and The vibration velocity responses at bearings 1 and 2 are respectively measured at the third critical speed. If these conditions are not met, rotor component tests are required to determine the order of the worst imbalance. S2. Step vibration test: Based on the unbalanced distribution, the rotor unbalance is pre-fabricated, and a step-by-step endurance test is carried out. The engine is subjected to step vibration test under the worst unbalanced state 1 and the worst unbalanced state 2 respectively. S3. Speed ​​dwell test: For different worst imbalance states, if the peak vibration amplitude of the later state is less than the corresponding amplitude of the previous state, then the peak speed of the later state is exempt from dwell. S4. Selection of installation vibration sensor location; Based on the vibration response data at each critical speed in the stepped endurance test, calculate the sum of vibration amplitude of each candidate vibration sensor, and select the sensor with the largest sum as the installation vibration sensor; The formula for calculating the sum of vibration amplitudes of candidate vibration sensors is as follows: , This represents the sum of the vibration amplitudes of sensor number a. This represents the vibration component amplitude of sensor a at the first critical speed of the rotor; the superscripts 1, 2, and 3 indicate the first, second, and third critical speeds, respectively. S5. Determine the maximum permissible vibration value of the engine; based on the maximum vibration amplitude measured by the installed vibration sensor during the entire stepped endurance test, multiply by a safety margin factor to determine the maximum permissible vibration value of the sensor.

2. The stepped sustained vibration test method according to claim 1, characterized in that, Step S2 includes: Set the rotation speed interval for each step, and pause at each rotation speed step. The stress alternation cycle has a total duration of N hours, and N and k satisfy the following relationship: ; In the formula, Let represent the i-th operating speed value, and m represent the number of stops at m steps.

3. The stepped sustained vibration test method according to claim 1, characterized in that, Step S3 includes: Select the peak speeds of vibration measuring points on the engine body, all accessories, and external pipelines, and remain at each peak speed for at least [time value missing]. Secondary stress alternation cycle.

4. The stepped sustained vibration test method according to claim 1, characterized in that, The test method also includes: For dual-rotor or multi-rotor engines, the worst imbalance state of each rotor is determined, and all combinations of imbalance states are listed. Step-by-step endurance tests and speed dwell tests are carried out under each combination state.

5. An aero-engine testing system, characterized in that, The step-by-step sustained vibration test method as described in any one of claims 1-4 is used, wherein the test system includes a test bench and a vibration sensor.

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