A comprehensive review on blade tip timing-based health monitoring: status and future

Rotating blade vibration measurements are very important for any turbomachinery research and development program. The blade tip timing (BTT) technique uses the time of arrival (ToA) of the blade tip passing the casing mounted probes to give the blade vibration. As a non-contact technique, BTT is necessary for rotating blade vibration measurements. The higher accuracy of amplitude and vibration frequency identification has been pursued since the development of BTT. An improved circumferential Fourier fit (ICFF) method is proposed. In this method, the ToA is not only dependent on the rotating speed and monitoring position, but also on blade vibration. Compared with the traditional circumferential Fourier fit (TCFF) method, this improvement is more consistent with reality. A 12-blade assembly simulator and experimental data were used to evaluate the ICFF performance. The simulated results showed that the ICFF performance is comparable to TCFF in terms of EO identification, except the lower PSR or more number probes that have a more negative effect on ICFF. Besides, the accuracy of amplitude identification is higher for ICFF than TCFF on all test conditions. Meanwhile, the higher accuracy of the reconstruction of ICFF was further verified in all measurement resonance analysis.

https://www.mdpi.com/2076-3417/10/11/3675/pdf

An Improved Circumferential Fourier Fit (CFF) Method for Blade Tip Timing Measurements

Complex blade responses such as a rotating stall or simultaneous resonances are common in modern engines and their observation can be a challenge even for state-of-the-art tip-timing systems and trained operators. This paper analyses forced vibrations of axial compressor blades, measured during the bench tests of the SO-3 turbojet. In relation to earlier studies conducted in Poland with a small number of sensors, a multichannel tip-timing system let us observe simultaneous responses or higher-order modes. To find possible symptoms of a failure, blade responses in a healthy and unhealthy engine configuration with an inlet blocker were studied. The used analysis methods covered all-blade spectrum and the circumferential fitting of blade deflections to the harmonic oscillator model. The Pearson coefficient of correlation between the measured and predicted tip deflection is calculated to evaluate fitting results. It helps to avoid common operator mistakes and misinterpreting the results. The proposed modal solver can track the vibration frequency and adjust the engine order on the fly. That way, synchronous and asynchronous vibrations are observed and analysed together with an extended variant of least squares. This approach saves a lot of work related to configuring the conventional tip-timing solver.

https://www.mdpi.com/1424-8220/20/1/68/pdf

Non-Contact Measurement of Blade Vibration in an Axial Compressor.

Non-contact full-field dynamic strain reconstruction of rotating blades under multi-mode vibration

Assessment of rotor blades stationarity condition based on differences in phase shifts

Reconstruction of blade tip-timing signals based on the MUSIC algorithm

It is important to obtain accurate dynamic vibrations of steam turbine blades for safe operation. Strain gauge (SG) measurements cannot fully obtain vibrations of all blades and nodal diameter (ND) details. The blade tip timing (BTT) technique could resolve this problem because it has the advantage of measuring all blades' vibrations. This article proposed an improved BTT technique for measuring synchronous vibrations of shrouded blades in a steam turbine based on fiber optical sensors with lenses. The newly developed sensor was equipped with a Plano-convex lens, and the optical path was specifically designed to collimate the beam within a large working distance from 4 to 19 mm and improve the measuring accuracy. A method to search the spectra of all peak vibration amplitudes of all the blades was proposed to obtain the ND details of synchronous vibration. Experimental results validated the efficiency and accuracy of the proposed methods and sensors. Comparison results of BTT measurements with SG measurements showed that the relative errors of normalized frequency and strain were small and acceptable.

Synchronous Vibration Measurements for Shrouded Blades Based on Fiber Optical Sensors with Lenses in a Steam Turbine

The present invention relates to the field of rotation mechanical device moving blade fault detections. A moving blade crack sample database is established, blade vibration information is obtained through a vibration measurement experiment to determine whether the blade generates cracks or not and achieve online quantitative diagnosis for the blade crack length and the position information. In theinvention, the moving blade crack online diagnostic method comprises the following steps of: performing modeling for a complete blade; further, performing vibration feature and vibration modal analysis for blade models with different crack positions and cracks with different depth to obtain a relation of blade inherent frequencies in different vibration types and the crack depths and the crack positions; and further, analyzing the relation of the blade inherent frequencies in different vibration types and the crack depths and the crack positions, and taking the analyzed and obtained relationof the blade inherent frequencies and the crack depths and the crack positions as a blade crack fault samples for storage to establish a blade crack sample database. The moving blade crack online diagnostic method is mainly applied to the blade fault detection occasions.

Moving blade crack online diagnostic method

Tip-timing technology has been widely used to monitor blade vibration of the aeroengine. In the off-line analysis of tip-timing signals, it is key and a prerequisite in blade fault diagnosis to locate the vibration event accurately. It is the most common method used to locate abnormal vibration based on the correlation of tip-timing data in adjacent revolutions. However, the data in the adjacent revolutions only include little vibration information, which results in the location performance being susceptible to noise. This paper located the vibration event using the area of the ellipse calculated based on the two-parameter plot. The relationship between the area of the fitted ellipse and the blade vibration parameters was derived for the first time in this paper. The feasibility of the method was verified using the tip-timing data of the low-pressure fan of an aeroengine. The results showed that the method can locate both synchronous resonance and rotating stall accurately. Its performance in anti-noise interference was far superior to the correlation coefficient methods due to enough information provided by multi-revolutions rather than only two revolutions. The work in this paper is of great significance for the realization of automatic processing of tip-timing signals.

The location method of blade vibration events based on the tip-timing signal

The invention belongs to the field of communication, and provides an amplitude/frequency/time coding and short-time Fourier transform decoding method and device so as to improve communication speed and antijamming capability. According to the adopted technical scheme, the amplitude/frequency/time coding and short-time Fourier transform decoding device comprises a coding part and a decoding part. The coding part comprises an amplitude coder, a frequency coder, a time coder, a time interval coder and a transmitter. The decoding part comprises a receiver, a short-time Fourier transformer, a time interval decoder, a time decoder, a frequency decoder and an amplitude decoder. Finally, a decoding output result is transmitted to a data receiver. The amplitude/frequency/time coding and short-time Fourier transform decoding method and device are mainly applied in the design manufacturing occasions of communication equipment.

Cheng Zhonghai

Papers

Reconstruction of blade tip-timing signals based on the MUSIC algorithm

Synchronous Vibration Measurements for Shrouded Blades Based on Fiber Optical Sensors with Lenses in a Steam Turbine

Moving blade crack online diagnostic method

The location method of blade vibration events based on the tip-timing signal

Amplitude/frequency/time coding and short-time Fourier transform decoding method and device