Method for determining a module to be balanced in a turbomachine and method for servicing the turbomachine
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MTU AERO ENGINES GMBH
- Filing Date
- 2026-01-28
- Publication Date
- 2026-08-06
Smart Images
Figure DE2026100106_06082026_PF_FP_ABST
Abstract
Description
[0001] Method for determining a module to be balanced in a turbomachine and method for maintaining the turbomachine
[0002] Description
[0003] The invention relates to a method for determining a module requiring balancing in a turbomachine with an impermissible imbalance, for which vibrations are detected by means of at least one vibration sensor of the turbomachine as a function of an operating frequency during operation of the turbomachine. The invention also relates to a method for maintaining the turbomachine.
[0004] CN 11 04 57861 B shows a visual diagnostic platform and a design method for an aircraft propulsion turbine.
[0005] EP 4071 453 Al discloses methods for identifying an imbalance of rotors of a turbomachine based on a vibration of the motor.
[0006] US patent 7400943 B2 discloses methods and a system for analyzing imbalance conditions in a turbomachine. This involves the use of artificial intelligence or a machine learning algorithm.
[0007] The invention is based on the objective of determining a module or component to be balanced in a turbomachine.
[0008] The problem is solved by the independent claim procedure. Advantageous embodiments of the invention are described by the dependent claims, the following description, and the figures.
[0009] A turbomachine is a heat engine, particularly a gas turbine, through which a working fluid such as air flows. Work is generated by burning a fuel, for example, with the working fluid, to drive a generator for electricity production. Viewed in the direction of the working fluid flow, the turbomachine has an inlet for the working fluid, a compressor (which may have several stages) for compressing the working fluid before the combustion chamber, the combustion chamber (where energy or power is supplied to the working fluid, for example, by burning fuel), and a turbine driven by the working fluid exiting the combustion chamber. Analogous to the compressor, the turbine can have one or more stages.The turbine and compressor, or their respective stages, can be connected to each other via one or more shafts of the turbomachine. Rotor blades or rotor blade assemblies are arranged on each shaft. When the turbomachine is in operation, these blades are rigidly connected to their respective shafts and rotate around an axis of rotation defined by the shaft. The rotor blade assemblies are generally rotationally symmetrical around the shaft or axis of rotation and exhibit a symmetrical mass distribution in the radial direction perpendicular to, or relative to, the axis of rotation. Thus, when the turbomachine is in operation or the shaft is rotating, the centrifugal forces acting on the shaft cancel each other out in the radial direction. For example, a homogeneous mass distribution within a ring segment of the rotor blade assembly around the axis of rotation can achieve this.If the mass distribution of at least one of the impeller blade assemblies is not symmetrical or homogeneous, the shaft assembly with its one or more impeller blade assemblies will exhibit an imbalance. Additionally or alternatively, the shaft itself can also generate or exhibit an imbalance, for example, in flange connections. When the turbomachine is operated, i.e., when the shaft rotates, a resulting centrifugal force acts on the shaft in the radial direction, and the natural frequencies of the shaft and / or the turbomachine as a whole can change compared to a balanced state. More than just the change in one or more natural frequencies, an imbalance can alter the amplitudes of vibrations, especially vibrations with specific natural frequencies.This can manifest as a greater deflection of the vibration sensor, i.e., its measured values, compared to one or more smaller imbalances. If the damping of the components involved in the oscillation of the turbomachine is neglected, the natural frequencies of a system or the turbomachine coincide with the system's resonance frequencies. These resonance frequencies depend, among other things, on the mass distribution, stiffness, and geometry of the oscillating system, such as the turbomachine. A natural mode of an oscillating system, corresponding to a natural frequency, describes a characteristic way in which a system oscillates when excited at its associated natural frequency. With further excitation of the system at the natural or resonance frequency, the amplitude of the oscillation can increase until the system fails in what is known as "resonance catastrophe."The compressor and the turbine, or their respective stages, are also referred to as so-called "modules".
[0010] Turbomachinery typically incorporates at least one vibration sensor, which measures vibration at its location within the machine. Vibration is defined as the speed at which a given position within the turbomachine moves, for example, the position of the vibration sensor. The vibration is expressed, for instance, in millimeters per second and can represent the amplitude of the oscillating system, such as the turbomachine, at that position. The vibration during operation of the turbomachine can be measured, and exceeding a predetermined vibration threshold can indicate the presence of an impermissible imbalance. In the event of such a suspected or confirmed imbalance, all modules of the turbomachine must be removed, tested for imbalance, and balanced if necessary, which is detrimental to the machine's performance.
[0011] According to the invention, a method for determining a module requiring balancing in a turbomachine with an impermissible imbalance is proposed, wherein vibrations are detected by means of at least one vibration sensor of the turbomachine as a function of an operating frequency during operation of the turbomachine. The operating frequency during operation of the turbomachine is understood to be, in particular, the rotational speed of one or more shafts. The vibrations are thus detected together with the operating frequency or the rotational speed of one or more shafts. The turbomachine can comprise one or more vibration sensors, but the method is described below only with respect to one vibration sensor of the turbomachine.If a detected vibration exceeds a predetermined threshold, the detected vibrations, assigned to their respective frequencies or the operating frequency at which they occurred, are compared with a predetermined, characteristic vibration pattern. This pattern describes the frequency-dependent vibration behavior of the turbomachine under impermissible imbalance in one of the modules. The detected vibrations can be recorded across the entire frequency range occurring during turbomachine operation or within predetermined frequency ranges, for example, a frequency range corresponding to start-up or steady-state operation of the turbomachine. Correspondingly, the characteristic vibration pattern should exhibit vibration values, at least partially, within the same frequency ranges or at the same operating frequencies.Each characteristic vibration pattern can describe the vibration behavior of the turbomachine under an impermissible imbalance in only one module or shaft, which may also be encompassed by the modules. In particular, it is provided that a characteristic vibration pattern is available for the imbalance of each module. The one or more characteristic vibration patterns can be generated by, for example, imposing a predetermined, impermissible imbalance on one module or shaft of the turbomachine at a time on a test rig or test bench, for example, by adding weights to the impeller blade rims, and recording the vibrations over the specified frequency ranges.If the detected vibrations or vibration pattern correspond at least partially and / or within a predetermined frequency range to the characteristic vibration pattern(s), the imbalance can be attributed to the module whose imbalance generated the respective characteristic vibration pattern. In other words, the module with the impermissible imbalance is determined based on the result of comparing the detected vibrations with the at least one characteristic vibration pattern. This allows for a particularly advantageous and cost-effective balancing of the turbomachine. It is not necessary to remove and individually test all modules of the turbomachine, but only the module or shaft for which an imbalance is indicated or determined.
[0012] The invention also includes further developments that result in additional advantages.
[0013] A further development of the method provides that the at least one characteristic vibration pattern, relative to the position of the at least one vibration sensor in the turbomachine, is determined by means of a numerical computational model. This is achieved by imposing a predetermined, impermissible imbalance on only one module at a time and calculating the vibration behavior of the turbomachine over a predefined operating frequency range. In other words, the characteristic vibration pattern is not determined by actually operating the turbomachine with an impermissible imbalance in a given module, but rather by means of a numerical computational model that describes or represents the vibration behavior or dynamics of the turbomachine. This offers the advantage that generating the one or more characteristic vibration patterns is particularly cost-effective.The numerical model can, for example, be a so-called "finite element model" of the turbomachine. To enable a particularly accurate comparison of the characteristic vibration patterns with the measured vibrations, the vibrations—that is, the oscillations of the turbomachine—are evaluated or calculated at the same position in the model where the at least one vibration sensor is located in the actual turbomachine. The specified operating frequency range can encompass all frequencies or rotational speeds occurring during the operation of the turbomachine, or only those frequency ranges in which the vibration sensor detects vibrations in the actual turbomachine.To calculate vibration behavior in a particularly realistic way using the computational model, the same mass and stiffness distribution of the engine, consisting of rotors or impeller blade assemblies and the casing together with the guide vanes, is stored in the computational model. Additionally, mounting points, suspension points, or bearings of the turbomachine during operation can be included or modeled in the numerical computational model.
[0014] In particular, it is provided that the turbomachine has two shafts, wherein the high-pressure compressor and the high-pressure turbine can be connected to each other as modules via a first shaft of the high-pressure system, which can also be referred to as stages of the compressor and the turbine, and the low-pressure compressor can be connected to the low-pressure turbine by means of a second shaft of the low-pressure system.
[0015] Vibration refers in particular to the first order of the oscillation velocity of the respective system or of the respective first or second wave, whereby the vibrations caused by the waves can be filtered out from the total vibrations detected by the sensor(s) arranged in the turbomachine by means of a filter when the turbomachine is operated.
[0016] A further development of the method involves calculating an initial vibration pattern across the operating frequency range with a predetermined, impermissible imbalance of the modules. Within this initial vibration pattern, at least two characteristic frequency responses of the turbomachine are determined, at least one of which differs from the frequency response of the at least one characteristic vibration pattern. The module to be balanced is then determined by comparing the measured vibrations with this at least one frequency response. Here, the frequency response is understood to be the vibration associated with an operating frequency or rotational speed.A characteristic frequency response can be observed if, at its associated excitation or operating frequency, such as rotational speed, a particularly high vibration or vibration amplitude occurs, for example, compared to the vibrations or frequency responses at different excitation frequencies. The frequencies or frequency ranges in which a characteristic frequency response occurs should not overlap. A characteristic frequency response can be identified, for example, by a particularly high vibration value when the vibration is plotted against the operating frequency, for both measured and calculated vibration values. For the initial vibration pattern, a predefined, permissible imbalance can be assigned to each module in the computational model.The permissible imbalance can be specified by having the same value as that permitted for the modules on the actual turbomachine, for example, after balancing. This value can be, for example, 1 gmm (1 gram times millimeter), where the millimeters refer to the radius away from the axis of rotation of the respective shaft. In particular, it is stipulated that the at least two characteristic frequency responses are natural modes or modes of the turbomachine, i.e., they occur at an excitation or rotational speed of the turbomachine that corresponds to a natural frequency of the turbomachine.At least one of the at least two characteristic frequency responses should, for example, deviate in its amplitude, vibration intensity, or vibration from the frequency response or mode of the at least one characteristic vibration pattern (at the same excitation frequency), for example, by 10 to 150 percent relative to the respective frequency response in the initial vibration pattern. For example, a first frequency response in the characteristic vibration pattern can be increased to the described extent compared to the frequency response or first mode at the same excitation frequency in the initial vibration pattern. If, for example, the impermissible imbalance is imposed on the compressor or a compressor stage in this vibration pattern, the first frequency response can also be called the compressor mode; if a second frequency response is increased or altered by imposing the impermissible imbalance on the turbine, it can be called the turbine mode.If the recorded vibrations, or the vibration pattern measured on the actual turbomachine, reveal an increased compressor or turbine mode compared to the initial vibration pattern, the impermissible and / or dominant imbalance can be located in the compressor or turbine. This offers the advantage of particularly efficient and rapid identification of the module requiring balancing. The operating frequency range in which the initial vibration pattern is determined can encompass all frequencies occurring or permissible during turbomachine operation, or only sub-ranges or partial frequency ranges thereof.
[0017] A further development of the method provides that an initial ratio between two of the at least two characteristic frequency responses of the initial vibration pattern and a measurement ratio of the same frequency responses in the recorded vibrations are determined, and the module to be balanced is determined by comparing these at least two ratios. In other words, the vibrations or amplitudes of the at least two characteristic frequency responses of the recorded vibration pattern are not to be compared absolutely with the corresponding values in the initial vibration pattern, but rather the ratio or quotient of the vibration values of two of the at least two characteristic frequency responses is to be compared.Depending on environmental conditions such as the density of the working medium (e.g., air density) and / or the degree or severity of the imbalance, vibration values can be particularly elevated in modes or characteristic frequency responses that do not indicate an imbalance in the module where the actual, impermissible imbalance is present. In other words, the recorded vibration pattern may exhibit overall elevated vibration values, giving the initial impression that several modules are imbalanced. However, it has been recognized that the relationship between two characteristic frequency responses changes significantly less than absolute vibration values. This offers the advantage of identifying the module requiring balancing with exceptional accuracy.
[0018] A further development of the method involves multiplying the initial ratio by a correction factor before comparing it to the measured ratio. It has been observed that the characteristic frequency responses can change relative to each other to varying degrees depending on environmental or operating conditions of the actual turbomachine. Additionally or alternatively, manufacturing variations between two turbomachines can have an influence, even if an impermissible imbalance is present in only one module of the turbomachine. Relevant environmental conditions here can include the temperature, density, and / or humidity of the working medium.For example, the correction factor can be determined depending on the temperature difference between the temperature assumed in the computational model for calculating the initial vibration pattern and the temperature at which the vibrations were recorded in the actual engine. If, for instance, the temperature at which the vibrations were recorded is significantly higher than the temperature assumed for the initial vibration pattern, the initial ratio can be increased using the correction factor in order to advantageously determine the module to be balanced despite the changed environmental conditions.
[0019] A further development of the method involves assigning the at least two characteristic frequency responses to each of at least two different steady-state operating conditions of the turbomachine. These steady-state operating conditions correspond to excitation frequencies, rotational speeds, or operating frequencies at which the turbomachine operates for a particularly long period. In the case of a gas turbine for power generation, a first steady-state operating condition can correspond to a rotational speed when the turbomachine is operating at full load, and a second steady-state operating condition to a rotational speed at partial load, where the rotational speed may be lower than at full load.It is intended that the recorded vibrations, which represent a value profile over time, are averaged over an operating frequency or operating frequency range for evaluation or comparison, for example, with a characteristic vibration pattern, using the arithmetic mean. To obtain a particularly meaningful or accurate vibration mean value for the characteristic frequency responses despite potential measurement errors of the vibration sensor, tachometer, or operating frequency meter, it is especially advantageous if the turbomachine is operated for extended periods at the corresponding frequencies or operating frequencies. Furthermore, the steady-state operating conditions are advantageously characterized by the fact that the operating frequency changes very little when the turbomachine is operated in such a steady state.To illustrate, it is disadvantageous, for example, if a characteristic frequency response exists at a rotational speed that is only traversed for a relatively short time when the turbomachine is switched on and ramped up to a steady operating state.
[0020] A further development of the method involves validating the numerical model with recorded vibration data from the turbomachine, specifying the permissible unbalance of each module. This offers the advantage that the numerical model can represent the turbomachine's vibration behavior, as depicted by the initial vibration pattern, with exceptional realism, allowing for highly accurate determination of the module to be balanced. For this purpose, the modules can be measured and weighed with greater precision than would be possible with conventional balancing, and the vibration data can be recorded on a test rig. The numerical model can be adjusted until the calculated and measured initial vibration patterns match with sufficient accuracy, for example, with regard to the characteristic frequency responses.
[0021] A further development of the procedure envisages the ability to identify not only the module with the dominant imbalance, but also the stage that generates this dominant imbalance, for example, the disc equipped with blades or blade rings. This more detailed information allows for optimization of the workload during module repair, for example, by providing only the necessary materials or personnel.
[0022] A further development of the method specifies that the turbomachine is an aircraft propulsion turbine and / or that the method is at least partially computer-implemented. In other words, the turbomachine is a turbine for propelling aircraft, and the method is executed on a computing device such as a microcontroller and / or a processor and / or a control unit. In particular, it is specified that the turbine has at least one compressor. The steady-state operating conditions in this case are, for example, takeoff and cruise flight.
[0023] The numerical model can be implemented as a whole-engine model, i.e., a three-dimensional model of the turbomachine. The position for which or at which the vibrations are calculated preferably corresponds to the finite element node, which represents the position of the actual sensor. Using this three-dimensional numerical model, which maps the three-dimensional geometry of the turbomachine, the modes or frequency responses of the turbomachine can be determined particularly advantageously. These modes are attributable to a natural mode of the compressor or a compressor stage and / or the turbine or a turbine stage. For this purpose, the model can, for example, consider a deformation of the end of a shaft on which the compressor or turbine is located. This allows for the selection of particularly informative characteristic frequency responses.
[0024] The initial vibration pattern and / or the initial ratio can be determined for any type or model of turbomachine by recording the vibrations with a vibration sensor after commissioning the turbomachine. From the factory or after balancing, the turbomachine exhibits only the permissible imbalance. The measured vibrations allow the numerical model to be validated without having to operate each turbomachine on a test bench before commissioning and record the vibrations during that process.
[0025] The invention further comprises a method for maintaining a turbomachine comprising balancing a module of the turbomachine, wherein the module is or was determined as one to be balanced in the manner described according to the invention.
[0026] FIG. 1 shows an initial vibration pattern over the operating frequency range with a predetermined, permissible imbalance of the modules of a shaft of a turbomachine;
[0027] FIG. 2 shows a characteristic vibration pattern for a given, impermissible imbalance in the compressor, in particular on a shaft of the turbomachine over the operating frequency range;
[0028] FIG. 3 shows a characteristic vibration pattern for a given, impermissible imbalance in a turbine and / or on its shaft of the turbomachine over the operating frequency range; and
[0029] FIG. 4 shows a schematic, partially transparent representation of a numerical computational model of the turbomachine with two shafts and their respective deformation under a given impermissible compressor imbalance.
[0030] FIG. 1 shows an initial vibration pattern 13 over an operating frequency range with a predetermined, permissible imbalance of the modules, in particular a shaft, of a turbomachine. In FIG. 1, a vibration 10, for example in millimeters per second [mm / s], is plotted against an operating frequency 11 of the turbomachine. A characteristic of the initial vibration pattern 13 is that all modules, in particular a shaft, of the turbomachine have a permissible imbalance or a maximum permissible imbalance, for example of 1 gmm. The initial vibration pattern can be calculated using a numerical model 22 or detected or measured during operation of the turbomachine, for example on a test bench, using a vibration sensor arranged in the turbomachine. The operating frequency 11 in Hertz or revolutions per minute is plotted along the x-axis, and the rotational speed of a shaft of the turbomachine, designed as an axial turbine, is represented.In FIGS. 1 to 3, operating range limits 12 are shown, representing a minimum and a maximum rotational speed of the shaft. The local maxima shown in FIGS. 1 to 3 during the vibration can represent frequency responses, modes, or eigenmodes of the turbomachine. In FIG. 1, such frequency responses 19 can be seen at rotational speeds of 60, 90, and 120 Hz. Characteristic frequency responses can be selected if they can be significantly altered by an eigenmode or imbalance of a module of the turbomachine, starting from the initial vibration pattern 13. At least two characteristic frequency responses 19 must be determined. For this purpose, the initial vibration pattern 13 can be compared with a characteristic vibration pattern for an impermissible, predetermined imbalance in one of the modules of the turbomachine. Additionally, for verification, or alternatively, the frequency response shown in FIG.The numerical calculation model shown in Figure 4 can be used to check whether the natural mode or a respective local maximum of the vibration 10 is due to a comparatively particularly pronounced natural mode of the respective module, for example, a deformation of a shaft end on which the respective module is arranged. Figure 2 shows a characteristic vibration pattern for a given, impermissible compressor imbalance, for example, in one stage of the compressor. Compared with Figure 1, the vibrations of the modes at approximately 60 Hz, 90 Hz, and 120 Hz are more pronounced in Figure 2. A comparison of Figures 1 and 2 alone, for example, does not allow for the identification of a unique compressor mode 20 that could indicate an impermissible imbalance in the compressor. All three possible modes are increased compared to Figure 1. By comparing Figure 2 with Figure 1, the vibrations of the modes at approximately 60 Hz, 90 Hz, and 120 Hz are more pronounced.Figure 3, which depicts a characteristic vibration pattern for a given, impermissible turbine imbalance, shows that the frequency response 19 at 60 Hz increases more sharply with an impermissible compressor imbalance than with an impermissible turbine imbalance. However, the frequency response 19 at 120 Hz increases significantly more with the impermissible turbine imbalance than with the impermissible compressor imbalance, compared to the initial vibration pattern 13. Additionally or alternatively, the computational model can be used to simulate operation of the turbomachine at 60 Hz in order to, for example, check the deformation of the shaft end of the first shaft, which, as shown in FIG. 4, indicates that this shaft end exhibits the greatest deformation as a result of the calculated impermissible compressor imbalance. Thus, the frequency response 19 at 60 Hz can be identified as compressor mode 20.It is not necessarily the case that a compressor imbalance will exhibit the greatest deformation at the shaft end on which the compressor or a compressor stage is located. On the contrary, depending on the shaft's bearing point, a compressor imbalance can, for example, significantly increase the imbalance at the end of the same shaft where the turbine or a turbine stage is located. Using the computational model and / or a comparison of FIGS. 1 to FIGS. 3, the frequency response 19 at 120 Hz can be selected as turbine mode 21. FIGS. 1 to FIGS. 3 show three steady-state operating conditions 16, 17, 18, characterized by their respective operating frequencies or shaft speeds. A first operating condition 16 at 60 Hz can represent the "taxi" operating condition, which could refer to the aircraft taxiing on the runway.The steady-state operating condition at 120 Hz can indicate cruise mode, and the third operating condition 18 can indicate operation of the turbomachine during takeoff. If, during an aircraft flight, vibration in the actual aircraft engine turbine (i.e., turbomachine) is detected by at least one vibration sensor, a predefined vibration threshold may be exceeded within a specified operating frequency range or in absolute terms. This can indicate an imbalance in one of the engine or turbomachine modules. To determine in which module the impermissible imbalance is present, it is particularly precise to calculate the ratio of the measured vibrations of two eigenmodes of the at least two characteristic frequency responses 19 (here compressor mode 20 and turbine mode 21) to each other and the ratio of these frequency responses of the initial vibration pattern 13.In the initial vibration pattern 13 shown in FIG. 1, the compressor mode can exhibit a vibration of 3 mm / s at 60 Hz and the turbine mode 21 a vibration of 10 mm / s at 120 Hz. The initial ratio can be the quotient of the vibration of the turbine mode 21 and the compressor mode 20, thus amounting to 10 / 3 in this case. In FIG. 2, with an impermissible imbalance of the compressor, despite the increase in the frequency responses 19, the corresponding ratio of vibration of the turbine mode 21 to the vibration of the compressor mode 20 can be reduced to 20 / 10, i.e., to 2. In FIG. 3, with the impermissible turbine imbalance, the corresponding ratio can increase to 25 / 5, i.e., to 5. By comparing the respective ratios of the recorded vibrations, for example in the flight-recorded vibrations 10, it is possible to determine in which module the impermissible imbalance is present.In this example, the ratio of turbine mode vibrations to compressor mode vibrations is smaller with impermissible compressor imbalance than in the initial vibration pattern, and the ratio of these frequency responses is larger with impermissible turbine imbalance than the initial ratio in the initial vibration pattern. With an impermissible modulus -1 imbalance, or first modulus imbalance, a first modulus of a shaft and / or a module of a first shaft may exhibit an imbalance. With an impermissible modulus 2 imbalance, or second modulus imbalance, a second modulus of a shaft and / or a module of a second shaft may exhibit an imbalance.
[0031] Additionally, the initial ratio can be multiplied by a correction factor to account for environmental conditions such as the temperature of the working fluid in the turbomachine. To compare the ratio of recorded or actually measured vibration values of turbine mode 21 to compressor mode 20 with the initial ratio, the initial ratio can be multiplied by the sum of 1 plus the correction factor before the comparison to check whether a dominant imbalance exists in the turbine (the ratio must be greater than the initial ratio for this to be the case): VB ratio > (1+x) VBratio, init. When checking whether the dominant imbalance is in the compressor, the measured ratio of the vibration of turbine mode 21 to the vibration of compressor mode 20 can be compared with the initial ratio multiplied by the difference between 1 and the correction factor (the measured vibration ratio should be smaller than the weighted initial ratio as described if the dominant imbalance is in the compressor): VBratio < (1-x) VBratio, init.
[0032] Overall, the examples show how a method for determining a modulus to be balanced in a turbomachine can be implemented. Reference list:
[0033] 10 Vibration
[0034] 11 Operating frequency
[0035] 12 Operating area boundary
[0036] 13 Initial vibration patterns
[0037] 14 characteristic vibration patterns for impermissible compressor imbalance 15 characteristic vibration patterns for impermissible turbine imbalance 16 first steady-state operating condition
[0038] 17 second steady-state operating condition
[0039] 18 third steady-state operating condition
[0040] 19 F frequency response
[0041] 20 compressor modes
[0042] 21 Turbine mode
[0043] 22 Computational model
[0044] 23 first wave
[0045] 24 second wave
Claims
Patent claims 1. Method for determining a module to be balanced in a turbomachine with an impermissible imbalance, wherein • vibrations (10) are detected by means of at least one vibration sensor of the turbomachine as a function of an operating frequency during the operation of the turbomachine and • if a predetermined vibration threshold value of the detected vibrations is exceeded, these are compared with at least one predetermined, characteristic vibration pattern (14,15) which describes a frequency-dependent vibration behavior of the turbomachine in the event of impermissible imbalance in one of the modules and • the module with the impermissible imbalance is determined depending on a result of the comparison.
2. Method according to claim 1, wherein the at least one characteristic vibration pattern (14, 15) with respect to a position of the at least one vibration sensor in the turbomachine is determined by means of a numerical calculation model by imposing a predetermined, impermissible imbalance on only one module at a time and calculating the vibration behavior of the turbomachine over a predetermined operating frequency range.
3. Method according to claim 2, wherein an initial vibration pattern (13) is calculated over the operating frequency range with a predetermined, permissible imbalance of the modules and at least two characteristic frequency responses (19) of the turbomachine are determined in this initial vibration pattern (13), at least one of which is different from the same frequency response (19) of the at least one characteristic vibration pattern (14, 15) and the module to be balanced is determined by comparing the measured vibrations (10) with this at least one frequency response (19).
4. The method of claim 3, wherein an initial ratio of two of the at least two characteristic frequency responses (14, 15) of the initial vibration pattern (13) to each other and a measurement ratio of the same frequency responses (19) in the detected vibrations (10) is determined, and the module to be balanced is determined by comparing these at least two ratios to each other.
5. The method of claim 4, wherein the initial ratio is multiplied by a correction factor before comparison with the measurement ratio.
6. Method according to one of claims 3 to 5, wherein the at least two characteristic frequency responses (19) are each assigned to one of at least two different steady-state operating conditions (16, 17, 18) of the turbomachine.
7. Method according to one of claims 3 to 6, wherein the numerical calculation model is validated with recorded vibration data of the turbomachine with a predetermined, permissible imbalance of each module.
8. A method according to any of the preceding claims, wherein the turbomachine is an aircraft propulsion turbine and / or wherein the method is at least partially computer-implemented.
9. A method for maintaining a turbomachine comprising balancing a module of the turbomachine, wherein the module was determined using a method according to one of the preceding claims.
10. Method according to one of the preceding claims, wherein the dominant imbalance was determined at the stage level of a module of the turbomachine.