Rotor Blade Vibration Measurement on Aero Gas Turbine Engines
01 Jan 2021-pp 263-273
TL;DR: In this article, a non-contact measurement technique using blade tip timing was used to capture vibratory signatures of all the blades of the rotor stage of a low pressure compressors and low pressure turbines of a developmental gas turbine engine.
Abstract: Rotor blade vibration in turbomachinery has been a major cause of failure due to HCF, often resulting in catastrophic damage. The primary aeromechanical design concerns are blade flutter and forced vibration that need to be quantified. The severity of blade vibratory response is almost impossible to predict using theoretical tools as it depends on the strength of excitation. Hence in order to evaluate the HCF characteristics of rotating blades, aero industry depends on measurements for actual vibratory response during engine tests. Various methods are used for measurement of rotor blade vibration. Conventionally strain gauges are extensively used for characterizing vibratory signatures of rotating blades. However, the strain gauges have their own limitations posed by operating temperatures and high-end technology is required to transmit signal from rotating components. Hence only a few blades in a rotor can be instrumented resulting in limited data capture. This paper presents a non-contact type of measurement technique using blade tip timing to capture vibratory signatures of all the blades of the rotor stage. This method is used to characterize monitor rotor blade vibrations of Low-Pressure Compressor and Low-Pressure Turbine of a developmental gas turbine engine. It has provided valuable data with respect to incipient damages, preventing catastrophic failure.
Citations
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TL;DR: In this article , three lattice-based turbine blades were designed and manufactured via additive manufacturing by replacing the internal volume of solid blades with octet truss unit cells of variable strut thickness.
Abstract: This paper aims to investigate the utilization of octet truss lattice structures in gas turbine blades to achieve weight reduction and improvement in vibration characteristics, which are desired for turbine blades to improve the efficiency and load capacity of turbines. A solid blade model using NACA 23012 airfoil was designed as reference. Three lattice-based blades were designed and manufactured via additive manufacturing by replacing the internal volume of solid blades with octet truss unit cells of variable strut thickness. Experimental and numerical vibration analyses were performed on the blades to establish their suitability for potential use in turbine blades. A maximum weight reduction of 24.91% was achieved. The natural frequencies of lattice blades were higher than those of solid blades. A stress reduction up to 38.6% and deformation reduction of up to 21.5% compared with solid blades were also observed. Both experimental and numerical results showed good agreement with a maximum difference of 3.94% in natural frequencies. Therefore, apart from being lightweight, octet-truss-lattice-based blades have excellent vibration characteristics and low stress levels, thereby making these blades ideal for enhancing the efficiency and durability of gas turbines.
8 citations
TL;DR: In this article, the area of the ellipse calculated based on the two-parameter plot was derived for the first time in order to locate the vibration event using the area.
Abstract: 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.
4 citations
TL;DR: In this article , the authors investigated a unique way for identifying, measuring, and validating flutter signature by assessing wall static pressure pulsations produced during blade tip transit across a casing mounted high bandwidth sensor.
Abstract: Abstract Flutter, an aeroelastic blade vibration phenomena, experienced by the fan of an developmental aero gas turbine engine, result in blade failure. Hence, suitable flutter detection instrumentation is required during engine testing. Flutter signature capture from revolving blades is a challenging task that necessitates either a complicated strain gauge-based rotating instrumentation or a noncontact tip timing system. Authors investigated a unique way for identifying, measuring, and validating flutter signature by assessing wall static pressure pulsations produced during blade tip transit across a casing mounted high bandwidth sensor during this research. The authors devised a mathematical model to explain signal spectrum components that feature both amplitude and angle modulation properties at the same time. The theory was tested using first-stage fan rotor blades that were fluttering in the first flexural mode (1F) and forming the second nodal diameter (2ND). The approach’s estimated blade deflection was compared to measurements taken using a traditional tip timing method up to 7 mm and determined to be within 1% inaccuracy. This research provides a low-cost, easy alternative technique for measuring flutter during engine development testing.
1 citations
04 Aug 2022
06 Jan 2022
TL;DR: In this article , the authors investigated changes in dynamic behavior of turbine blades for the detection of defects, with focus on substrate cracks and TBC spallation as they relate to vibration modes 1 to 6.
Abstract: The reliability of critical aircraft components continues to shift towards onboard monitoring to optimize maintenance scheduling, economy efficiency and safety. Therefore, the present study investigates changes in dynamic behavior of turbine blades for the detection of defects, with focus on substrate cracks and TBC spallation as they relate to vibration modes 1 to 6. Two‐dimensional and three-dimensional finite element simulation is used. The results indicate that TBC spallation reduces natural frequencies due to the ensuing hot spot and overall increase in temperature, leading to drops in blade stiffness and strength. Cracks cause even larger frequency shifts due to local plastic deformation at the crack that changes the energy dissipation behavior. Mode 1 vibration shows the largest shifts in natural frequencies that best correlate to the size of defects and their position. As such, it may be most appropriate for the early assessment of the severity and location of defects.
References
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TL;DR: In this article, the authors present an in-depth study of blade vibration problems that seriously impact development of advanced gas turbine configurations, and they conclude that structural integrity of power plants is the dominant factor that influences the quality, reliability, and marketability of the product.
Abstract: This paper presents an in-depth study of blade vibration problems that seriously impact development of advanced gas turbine configurations. The motivation for this study arises from the author's conviction that structural integrity of power plants is the dominant factor that influences the quality, reliability, and marketability of the product. Implications of this study in the context of potential R&D challenges and opportunities of interest to industry, governments, and academia are discussed.
313 citations
TL;DR: In turbine engine development, rotor blade vibration measurements are made to ensure the blades are sufficiently durable in later service as mentioned in this paper, using a number of probes installed in the engine casing to sense the points in time at which the rotor are passing the probes.
Abstract: In turbine engine development, rotor blade vibration measurements are made to ensure the blades are sufficiently durable in later service. These measurements are conventionally taken using strain gauges or the frequency modulated grid. In recent years, a noncontact method of blade vibration measurement has become an increasingly accepted, low-cost alternative technique. This method uses a number of probes installed in the engine casing to sense the points in time at which the blades are passing the probes. When analysed, these blade passing times yield data on blade vibrations. This paper briefly describes the configuration of such a measurement system and the operating principle of two different probe types. An extended explanation is then provided of the various analysis methods in use at MTU. The methods are described by means of the essential equations and elucidated using comprehensive compressor test data.
134 citations
TL;DR: In this article, a comparative survey of tip timing analysis methods for the interpretation of vibration data measured at turbomachinery rotor blade tip using optical laser probes is presented. But the performance of the various techniques is investigated by using both actual assembly measurements and simulated response data.
Abstract: This paper aims at providing a comparative survey of current analysis methods for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration that they attempt to identify, namely, asynchronous and synchronous with respect to rotor speed. The performance of the various techniques is investigated by using both actual assembly measurements and simulated response data. In the latter case, synchronous vibration data are obtained via a multidegree-of-freedom numerical simulator that includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms, and the characteristics of the optical probe. When using experimental data, the results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing industry standard, tip-timing analysis techniques are found to exhibit a number of inherent limitations and suggestions were made to address these deficiencies, A detailed tip-timing case study for a steam turbine rotor is presented in some detail, and other potential application areas are explored. Of particular note is the introduction of a new indirect analysis method for identifying the characteristics of synchronous vibration modes using measurements from two probes. Finally, new avenues for future analysis methods and further developments in tip-timing systems are also discussed.
112 citations
02 Jun 1997
TL;DR: In this paper, the performance of the analysis methods currently used for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes is evaluated and compared with those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning.
Abstract: This paper aims at evaluating the performance of the analysis methods currently used for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration which they can identify, namely asynchronous and synchronous with respect to rotor speed. Both actual assembly measurements and simulated response data are used during the investigation. In the latter case, synchronous vibration data are obtained via a multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe. The results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing industry-standard tip-timing analysis techniques are found to exhibit a number of inherent limitations and suggestions were made to address these deficiencies. A detailed tip-timing case study for a steam turbine rotor is presented in some detail and other potential application areas are explored. Finally, future analysis methods and possible future developments in tip-timing systems are discussed.Copyright © 1997 by ASME
28 citations
10 Mar 2001
TL;DR: In this article, the authors compared simulation results to experimental data obtained during seeded fault tests and found that the forced resonant response of a blade is seldom dominated by the blade's uncoupled dynamics.
Abstract: Damage in rotor blades, including cracks, tend to shift the blades' resonant frequencies. Blade resonances have thus been envisioned as a damage indicator. This paper studies issues that arise in blade resonance identification using Non-contacting Stress Monitoring Systems (NSMS) when blade resonances have slight variation (mistuning) and are dynamically coupled. The study compares simulation results to experimental data obtained during seeded fault tests. The main findings are as follows: 1) The forced resonant response of a blade is seldom dominated by the blade's uncoupled dynamics. Changes due to damage in one blade are thus often reflected in the responses of many blades. 2) To reliably identify damage by looking at one individual response at a time, the shift in resonant frequency resulting from damage must be larger than the frequency redistribution due to blade-to-blade coupling (e.g. 1%-2%). Only for uncoupled blades can smaller shifts in resonance frequency be reliably detected. 3) For finer damage identification (e.g. less than 1%), a global identification method utilizing all blade responses at once must be use to determine blade dynamics and coupling. This can be attempted with an NSMS system, which senses every blade response.
24 citations