RU2374615C1 - Method of diagnosing turbomachine impeller vibration - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: in compliance with this invention, during blades aeroelastic vibrations, signal coming from radial clearance pickup is registered to be converted into frequency spectrum. Frequency and magnitudes of two spectral components symmetrically spaced from blade repetition frequency and spectral component located at the same distance from origin of coordinates are compared. Comparison results are used to judge upon availability and type of vibrations, while amplitude difference allows judging upon variation in turbomachine impeller variation amplitude.

EFFECT: higher quality of diagnostics.

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Description

The invention relates to power engineering and can be widely used in the strength and aerodynamic refinement of axial turbines and compressors, as well as in the creation of diagnostic systems for turbomachines in aviation and power engineering.

A known method for diagnosing vibrations of the blades of the impeller of an axial turbomachine, based on the discrete-phase method, which allows to determine the deformation state of each blade of the impeller of the turbomachine [1]. The essence of the method consists in measuring the time intervals between the pulses of the root and peripheral sensors, comparing them with the geometric position of a particular blade in the wheel at certain points in time and the corresponding interpretation of the obtained values.

The disadvantage of this method is the need to install root sensors in the internal path of the turbomachine. In addition, this method does not allow to determine the direction of the deformation waves traveling along the wheel and the numbers of the diametrical forms of vibrations along which the vibrations of the blades are realized.

Closest to the invention is a method for diagnosing oscillations of the impeller of a turbomachine, which consists in registering a signal of a flow pulsation sensor, converting the signal into a frequency spectrum, recording the repetition frequency of the blades and comparing the magnitude of the two components of the spectrum symmetrically equally spaced from the repetition frequency of the blades and judging by the results of this comparison the direction of the deformation waves traveling along the wheel and the change in the amplitude of the oscillations of the blades [2].

The disadvantage of this method is its narrow functionality. The method allows to determine only the response of the flow to the vibrations of the blades in the form of traveling deformation waves. In this case, the flow pulsations caused by the vibrations of the blades, which are also realized as traveling deformation waves, are usually subject to reflection and superposition phenomena in a turbomachine, as a result of which their amplitudes can be distorted and lead to an incorrect judgment about the direction of the traveling deformation wave and the amplitudes of the vibrations of the blades. Therefore, the known diagnostic method gives reliable results only under certain conditions, when the observed components of the spectrum of the pulsations of the gas flow are not subject to the phenomena of reflection and superposition. In addition, in a turbomachine, as a rule, there are acoustic disturbances that make it difficult to search for diagnostic spectral components.

An object of the invention is to increase the reliability of diagnosing traveling waves of deformations that occur in the wheel during vibrations of the blades, as well as the amplitudes of the vibrations of the blades based on measuring the radial clearance between the blades and the stator of the impeller of the turbomachine.

The technical result is achieved in the inventive method for diagnosing oscillations of the blades of the impeller of a turbomachine, which consists in registering a signal of a sensor for measuring the gap between the rotor blades and the stator of the turbomachine, wherein the registered signal of the sensor for measuring the gap is converted into the frequency spectrum, the repetition frequencies of the blades are recorded, and two signals are observed in the signal spectrum the components of the spectrum symmetrically equally spaced from the blade repetition frequency and the spectrum component spaced at the same distance from acala coordinate spectrum are compared with each other in the development of vibrations of the magnitude of said spectral components and the results of observation and comparison of the judged direction of traveling movement of wheel deformation waves and to change the amplitude of oscillation of the impeller of the turbomachine.

The inventive method for diagnosing oscillations of the impeller of a turbomachine differs from the prototype in that it is not the magnitude of the spectral components in the flow pulsations that compare the oscillations of the blades, but the magnitudes of the spectral components in the signals of the radial clearance measurement sensor, characterizing the oscillations of the blades with deformation waves running along the wheel, and according to the results of comparison, they judge the direction of movement of these waves.

The influence of the listed distinguishing features on the achieved technical result is confirmed by the results of experiments.

In the process of experimental studies conducted on aircraft engine compressors, we observed two components f ₂ and f ₃ of the signal spectrum from the gap measurement sensor, symmetrically equidistant from the blade repetition frequency Nf _p , and another spectral component f ₁ located at the same distance from the beginning spectrum coordinates. It was found that with flutter the spectral component f ₂ located to the left of the blades repetition frequency Nf _p is smaller in magnitude than the spectral component f ₃ located to the right of it, and at the same distance from the coordinate origin, another spectral component is present in the spectrum component f ₁ . The specific values of the frequencies and amplitudes of the listed spectral components during flutter were as follows:

Frequency Hz f ₁ f ₂ f ₃ Nf _p 565.4 2966.8 4097.6 3522,2 Amplitudes, V 0,099 0.326 0.346 1,043

Figure 1 shows the signal spectrum of the gap sensor in the absence of oscillations of the blades.

Figure 2 shows the signal spectrum of the gap sensor during oscillations with the direction of motion of the deformation wave traveling along the wheel corresponding to flutter.

Figure 3 shows the signal spectrum of the gap sensor during oscillations with the direction of motion of the deformation wave traveling along the wheel, corresponding to the presence of oscillations from a rotating stall.

Figure 4 schematically shows a working view of a device that implements the inventive method.

A method for diagnosing oscillations of the impeller of a turbomachine is as follows.

When the turbomachine is operating, the rotor of which rotates with a frequency f _p , the signal from the radial clearance measurement sensor is fed through an amplifier to the input of the recorder-analyzer, Fig. 4.

In the absence of aeroelastic vibrations in the signal spectrum on the screen of the recorder-analyzer, only the repetition rate of the blades is observed, equal to

Nf _p , (Fig. 1), where N is the number of blades in the wheel, f _p is the rotor speed.

At the time of the occurrence of aeroelastic vibrations, FIGS. 2, 3, deformation waves traveling along the wheel occur, generating phase-modulated traveling waves in the signal of the radial clearance sensor. In this case, in the spectrum of the signal of the gap sensor for each form of vibration of the wheel, along which flutter or oscillations from a rotating stall is realized, two spectral components with frequencies f ₂ and f ₃ are observed, while

f ₂ = Nf _p -f _d , where f _d = f _l ± zf _p ; z is the number of waves of deformation of the wheel; f _l - the oscillation frequency of the blades,

and f ₃ = Nf _p + f _d symmetrically equally spaced from the repetition frequency of the blades Nf _p at a distance f _d and the spectral component f ₁ = f _d located at the same distance from the origin.

If the direction of the deformation waves traveling along the wheel corresponds to a rotating stall, then at the beginning practically the same level of spectral components with frequencies f ₂ and f ₃ will be observed. As the amplitude of the oscillations of the blades increases, the spectral component with a frequency f ₂ will overtake the spectral component with a frequency f ₃ (Fig. 3), and comparing them with each other will enable the observer to confidently judge that the direction of movement of the deformation waves running along the wheel is opposite to the direction of rotation wheels, which corresponds to the case of vibrations of the blades from a rotating stall.

In the case when the direction of the deformation waves traveling along the wheel corresponds to flutter, that is, the direction of the deformation waves coincides with the direction of rotation of the wheel, then the components in the spectrum with frequencies f ₂ and f ₃ behave differently as the oscillations develop. As the amplitude of the oscillations of the blades increases, the spectral component with a frequency f ₃ will begin to noticeably overtake the component with a frequency f ₂ , Fig. 2, and a comparison of their values among themselves will make it possible to judge the presence of a flutter of the blades.

The spectral component with a frequency of f ₁ = f _d = f _l ± zf _p in both cases will increase with increasing amplitude of the oscillations of the blades.

Thus, by simply detecting in the signal from the radial gap measurement sensor three spectral components with frequencies f ₁ , f ₂ and f ₃ , interconnected by known relations, we can make an unambiguous conclusion about the occurrence of aeroelastic vibrations with deformation waves running along the wheel, about the direction of movement these waves and therefore determine the type of developing oscillations.

A change in the difference in the values of the components of the spectrum at frequencies f ₂ and f ₃ , as well as a change in the magnitude of the spectral component at a frequency f _1, makes it possible to judge the change in the amplitude of vibrations of the wheel blades at a given time in comparison with the amplitude at the time of aeroelastic vibrations.

Information sources

1. Zablotsky I.E., Korostelev Yu.A., Shipov R.A. Non-contact measurements of vibrations of turbomachine blades. M., Mechanical Engineering, 1977, pp. 23-27.

2. RF patent No. 2111469, G01M 15/00, F01D 25/04, 04/11/1997, "Method for the diagnosis of oscillations of the impeller of a turbomachine."

Claims (1)

A method for diagnosing oscillations of the impeller of a turbomachine, comprising registering a signal of a sensor measuring the gap between the rotor blades and the stator of the turbomachine, characterized in that the recorded sensor signal is converted into the frequency spectrum, the repetition frequencies of the blades are recorded, and two symmetrically equally spaced apart from the repetition frequency of the blades are observed in the signal spectrum components of the spectrum, and the spectrum component that is at the same distance from the origin of the spectrum coordinates is compared with each other in the process of fluctuations in the magnitude of the indicated spectrum components and from the results of observation and comparison judge the direction of motion of the deformation waves traveling along the wheel and the change in the amplitude of the oscillations of the impeller of the turbomachine.

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