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

The need for non-destructive testing/structural health monitoring (SHM) is becoming increasingly important for gas turbine manufacturers. Incipient cracks have to be detected before catastrophic events occur. With respect to condition-based maintenance, the complex and expensive parts should be used as long as their performance or integrity is not compromised. In this study, the main failure modes of turbines are reported. In particular, we focus on the turbine blades, turbine vanes and the transition ducts of the combustion chambers. The existing monitoring techniques for these components, with their own particular advantages and disadvantages, are summarised in this review. In addition to the vibrational approach, tip timing technology is the most used technique for blade monitoring. Several sensor types are appropriate for the extreme conditions in a gas turbine, but besides tip timing, other technologies are also very promising for future NDT/SHM applications. For static parts, like turbine vanes and the transition ducts of the combustion chambers, different monitoring possibilities are identified and discussed.

A Review of NDT/Structural Health Monitoring Techniques for Hot Gas Components in Gas Turbines

https://hal-centralesupelec.archives-ouvertes.fr/hal-02125263/document

Blade vibration study by spectral analysis of tip-timing signals with OMP algorithm

Blade tip timing (BTT) methods have been increasingly implemented for blade health monitoring (BHM). However, there are two drawbacks of current signal analysis methods preventing them from applying to online monitoring: first, current online monitoring requires the manual judgment of the resonance region, which is time-consuming. Second, existing BTT resonance signal analysis methods are not suitable for online monitoring. The spectral-analysis-based method presents spectral aliasing, while the computational complexity of the sparse-based method is usually high. In this article, we propose an adaptive online BHM method that includes two steps: automatic resonance region recognition and parameters identification in resonance area. For the former step, we demonstrate different methods for synchronous and asynchronous resonances, use the cross correlation to judge the occurrence of synchronous vibration, and use the linear estimation to determine the appearance of asynchronous vibration. For the latter step, an iterative adaptive least-squares periodogram is adopted for its tradeoff between spectral aliasing and computational complexity. The effectiveness of the above steps is first verified using different simulation data separately. Then, the laboratory data are used to test the effectiveness of the whole method. Finally, the online monitoring function of the proposed method is verified by the engineering data with both synchronous and asynchronous resonances.

An Adaptive Online Blade Health Monitoring Method: From Raw Data to Parameters Identification

With the ultimate goal of rotating machinery diagnosis using Instantaneous Angular Speed (IAS) and Time of Arrival (TOA) signals, this paper provides the theoretical background of non-stationary processes existing in the aero-engines and their monitoring using atypical encoders (e.g. fans, compressors and turbine blades cooperating with the induction sensors, AC and DC generators). The model of TOA signal including aperiodic, periodic and stochastics components has been described. The classical and expert approach to monitoring of operational and structural health parameters (CM, NDT, SHM) of aircraft and its power transmission system has been also described. Finally, the experience of the Tip Timing method used in the Armed Forces of the Republic of Poland is presented. The possibility of structural health monitoring and active controlling of the material fatigue by the aero-engine user through interference in the fuel system adjustment quality has been confirmed. Phase portraits have been used to analyze TOA components in transient state of the engine. Diagnostic criteria and expert algorithms have been verified during active and passive experiments.

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Advances in Condition Monitoring of Machinery in Non-stationary Operations

Blade resonance parameter identification based on tip-timing method without the once-per revolution sensor

Blade tip timing is an effective method for blade vibration measurements in turbomachinery. This method is increasing in popularity because it is non-intrusive and has several advantages over the conventional strain gauge method. Different kinds of sensors have been developed for blade tip timing, including optical, eddy current and capacitance sensors. However, these sensors are unsuitable in environments with contaminants or high temperatures. Microwave sensors offer a promising potential solution to overcome these limitations. In this article, a microwave sensor-based blade tip timing measurement system is proposed. A patch antenna probe is used to transmit and receive the microwave signals. The signal model and process method is analyzed. Zero intermediate frequency structure is employed to maintain timing accuracy and dynamic performance, and the received signal can also be used to measure tip clearance. The timing method uses the rising and falling edges of the signal and an auto-gain control circuit to reduce the effect of tip clearance change. To validate the accuracy of the system, it is compared experimentally with a fiber optic tip timing system. The results show that the microwave tip timing system achieves good accuracy.

https://www.mdpi.com/1424-8220/17/5/1097/pdf

A Blade Tip Timing Method Based on a Microwave Sensor

The invention discloses a tip clearance measurement method based on all-fiber tip timing. The method comprises the following steps: converting measurement on length measurement in a triangle method into measurement on a tip timing signal; adopting two fiber bundle type timing sensors, and enabling emission fibers in the timing sensors to emit two beams of auto-collimation emergent light with different wavelengths; enabling receiving fibers in the timing sensors to receive moment signals when leaves approach and leave a measurement region; monitoring the rotating speed of a rotor in real time by a rotating speed synchronization sensor; performing high-speed signal acquisition and circuit module processing on all the sensor signals, and reversely calculating a distance between the end face of each sensor and each leaf tip by an upper computer through a math model. According to the tip clearance measurement method, a clearance value is ingeniously converted into a tip timing signal relevant to the clearance value, so that a measurement system is irrelative to most environmental factors such as the leaf and electromagnetic interference, and the interference resistance and the clearance measurement precision of the system are improved.

Tip clearance measurement method based on all-fiber tip timing

Blade vibration measurement based on the blade tip-timing method has become an industry-standard procedure. Fiber bundle sensors are widely used for tip-timing measurement. However, the variation of clearance between the sensor and the blade will bring a tip-timing error to fiber bundle sensors due to the change in signal amplitude. This article presents methods based on software and hardware to reduce the error caused by the tip clearance change. The software method utilizes both the rising and falling edges of the tip-timing signal to determine the blade arrival time, and a calibration process suitable for asymmetric tip-timing signals is presented. The hardware method uses an automatic gain control circuit to stabilize the signal amplitude. Experiments are conducted and the results prove that both methods can effectively reduce the impact of tip clearance variation on the blade tip-timing and improve the accuracy of measurements.

Method to improve the blade tip-timing accuracy of fiber bundle sensor under varying tip clearance

The invention relates to the technical field of on-line measurement of blade vibration parameters. In order to realize blade synchronous vibration parameter identification based on the least square principle under the condition of not adopting a speed synchronization sensor, the invention adopts a technical scheme that a method for realizing blade synchronous vibration parameter identification comprises the following steps: first, mounting blade tip timing sensors on the tops of a plurality of blades, and sequentially numbering the blade tip timing sensors as #0, #1 and #2; second, calculating the blade vibration displacement difference between the displacement of the blades when the blades arrive at other different sensors and the displacement of the blades when the blades arrive at the #0 sensor according to the speed and the sensor mounting angle; and third, under the condition that the Campbell diagram is known before measurement, using the blade vibration displacement difference measured by the multiple sensors, the sensor mounting angle and a set of unknown quantities related to the blade vibration parameters to form a hyperstatic binary linear equation set. The method of the invention is mainly applied to on-line measurement of blade vibration parameters.

Zhang Jilong

Papers

Blade resonance parameter identification based on tip-timing method without the once-per revolution sensor

A Blade Tip Timing Method Based on a Microwave Sensor

Tip clearance measurement method based on all-fiber tip timing

Method to improve the blade tip-timing accuracy of fiber bundle sensor under varying tip clearance

Method for realizing blade synchronous vibration parameter identification