Blade Vibration

One of the undesirable phenomena in turbomachinery is linked to the contact between rotating and stationary parts, which is more likely to occur when clearance is minimized in order to improve aerodynamic efficiency. These mechanical characteristics favor energy exchanges between the two structures, and this in turn may lead to high dynamic excitations of the impeller and stator or even to unstable vibrations. Lot of numerical studies have been conducted in order to derive a better understanding of the dynamic behavior taking place during blade-to-casing contact. However, the influence of other physical phenomena, such as wear and heating, remain poorly understood. A recent experimental study shows that the dynamic behavior of structures is significantly influenced by both wear and thermal expansion. The focus of this paper therefore is show some effects associated with friction and wear. The numerical study reported in this paper is based on a simplified finite element model of a r...

The exploitation of different unsteady quantity measurements for identifying various blade faults is examined in this paper. Measurements of sound emission, casing vibration, shaft displacement and unsteady inner wall pressure are considered. It is demonstrated that particular measurements are sensitive to specific faults. The suitability of measuring each of the above physical quantities for tracing the existence of each kind of fault is discussed. The advantage of combining different measurements originates from the possibility of extending the fault repertory covered when only one particular quantity is considered. The data analysis techniques employed range from conventional signal processing to the derivation of acoustic images of the engine outer surface. Relative features of each technique, as to their effectiveness and level of intrusivity, are discussed.

A methodology for the design of automated diagnostic systems for Gas Turbines is presented. The first stage of the proposed methodology consists in an initial selection of instruments and measuring positions on the engine, based on a basic knowledge of the engine itself and previous experience, as well as modelling capabilities of the phenomena happening in it. It is followed by a stage of "learning" experiments. One purpose of these experiments is to provide measurement data, on which a final selection of instruments will be based. The instruments most suitable for the fault cases of interest are selected, according to the diagnostic potential they offer. Another purpose is to develop procedures of automated fault diagnosis. The necessary background information for the later exploitation of the system is also established. The applicability of the entire methodology is demonstrated for the case of designing a blade fault diagnostic system for an Industrial Gas Turbine.

Blade tip timing (BTT) vibration measurement is a promising on-line blade monitoring method, but various uncertainties bring great challenge in engineering applications. Most existing works are based on the assumption of constant rotating speeds. However, rotating speed is hardly fixed under variable conditions. In this case, these uncertainties always become more serious. To deal with this problem, this paper proposes to investigate BTT measurement derivations in angular domain, instead of time domain. Firstly, this paper systematically analyzes the effects of variable rotating speed, static angle errors and translational blade motions on the accuracy of BTT vibration measurement. Then the corresponding calibration methods are presented by only using times of arrival (TOAs). In the end, Matlab/Simulink simulations are done to validate the proposed method under linear and quadratic variations of rotating speeds. The results demonstrate that BTT measurement deviation under low rotating speeds is more than those under high rotating speeds and BTT measurement deviation due to static angle errors is independent of rotating speeds. And the proposed TOAs-based calibration method can reduce BTT measurement deviation greatly under variable rotating speeds, compared with traditional methods. BTT measurement deviation due to static angle errors can be calibrated by using low rotating speeds and those due to translational blade motions are difficult to be calibrated under variable rotating speeds. Thus simulation results indicate great potential of the proposed method for practical applications of the BTT method. INDEX TERMS Blade tip-timing, variable rotating speed, measurement uncertainty, angular sampling, vibration calibration.

Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.

Blade faults and blade failures are ranked among the most frequent causes of failures in turbomachinery. This paper provides a review on the condition monitoring techniques and the most suitable signal analysis methods to detect and diagnose the health condition of blades in turbomachinery. In this paper, blade faults are categorised into five types in accordance with their nature and characteristics, namely, blade rubbing, blade fatigue failure, blade deformations (twisting, creeping, corrosion, and erosion), blade fouling, and loose blade. Reviews on characteristics and the specific diagnostic methods to detect each type of blade faults are also presented. This paper also aims to provide a reference in selecting the most suitable approaches to monitor the health condition of blades in turbomachinery.

Wind turbine blades operate in a harsh environment causing them to always be susceptible to damage. Variable wind loading, debris impact, and thermal gradient, among other factors, can cause damage to the blades. Detection of blade damage at early stages can prevent massive cost associated with turbine down-time and blade replacement. In this work, a vibration-based method is presented to detect damage at early stages. The presented method takes advantage of the effect of crack on modal parameters of the blades vibration. Finite element model (FEA) is constructed for both healthy and damage blade to study that effect. Power spectral density (PSD) plots of the blade's vibration before and after damage are compared and the changes in the resonant modal amplitudes frequencies are identified. To minimize the number accelerometers needed to monitor the health of the blade and without compromising the accuracy of damage predictions, ordinary kriging method is used to predict cracks in the blade's structure. Kriging uses modal parameter data, experimental or otherwise, to estimate damage location on the blade. It creates a map of damage predictions throughout the region use measurements from far less sensors than common techniques. Damage characteristics estimates using the proposed method showed damage attributes predictions with accuracy greater than 93 %. Simulation is used to validate the proposed method and the results are discussed.

This paper studies the detection of twisted blade in a multi stages rotor system. Experimental study was undertaken to simulate twisted blade conditions in a three stages rotor system. The feasibility of vibration analysis as the technique to detect twisted blade based on the rotor operating frequency and its blade passing frequency was investigated in this study. Experimental results show that twisted blade can be easily detected by looking into the pattern of the vibration spectrum and its individual peaks.

This paper presents an analysis of nonsynchronous rotor blade vibrations in the last stage of an LP steam turbine at various condenser pressures. The nonlinear least squares Levenberg–Marquardt method is used in a tip-timing analysis to determine nonsynchronous multimode rotor blade vibrations, which is a novelty. This is done with two sensors in the casing and a once-per-revolution sensor. The accuracy of the nonlinear least squares Levenberg–Marquardt multimode method is compared with the one-mode linear method. The algorithm is verified by comparing it with one-mode tip-timing methods for synchronous and nonsynchronous vibrations. The analysis shows that the rotor blades vibrate simultaneously with two modes in non-nominal conditions, which is also a novelty. The rotor frequencies are unchanged, although the blade vibration amplitudes vary, depending on the pressure in the condenser. Flutter does not appear in the last stage for the various condenser pressures and powers that wer...

Non-contact measurement of gas turbine blade vibrations has made significant progress over recent years; however, there still exist some limitations in the current techniques available. Specifically with blade tip timing (BTT) methods, some of the limitations are: the requirement of a large number of sensors for each engine stage, difficulties in dealing with multiple excitation frequencies, and sensors being located in the gas path. An alternative technique is examined here, utilising the unsteady casing wall pressure, which has the potential to rectify some of these limitations. Analytical simulation of the internal casing wall pressure is derived, for the situation with rotor blades undergoing forced vibration. The amplitude of the blade forced vibrations is then reconstructed from the simulated unsteady casing wall pressure, with results showing the robustness of the method to sensor location, measurement noise and a limited number of sensors.

Non-contact measurement of gas turbine rotor blade vibration is a non-trivial task, with no method available which achieves this aim without some significant drawbacks. This paper presents a truly non-contact method to estimate rotor blade natural frequencies from casing vibration measurements at a single engine operating speed. An analytical model is derived to simulate the internal casing pressure in a turbine engine including the effects of blade vibration on this pressure signal. It is shown that the internal pressure inside a turbine contains measureable information about the rotor blade natural frequencies and in-turn the casing vibration response also contains this information. The results presented herein show the residual, pressure and casing vibration, spectrum can be used to determine the rotor blade natural frequencies with validation provided for the analytical model by experimental measurements on a simplified test rig. A simulated blade fault in one of the rotor blades is introduced with successful estimation of the simulated faulty blade natural frequency.

This paper presents a summary of a recent research program, focusing on a new method of non-contact gas turbine blade vibration measurement using casing pressure and vibration signals. Currently the dominant method of non-contact measurement of turbine blade vibrations employs the use of a number of proximity probes located around the engine periphery measuring the blade tip (arrival) time (BTT). Despite the increasing ability of this method there still exist some limitations, viz: the requirement of a large number of sensors ...

The non-intrusive measurement of blade condition within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is obviously the ambition of most techniques, with a number of methods proposed, investigated and employed for such measurement. The current dominant method uses proximity probes to measure blade arrival time for subsequent processing. It has been recently proposed ...

Non-contact measurement of gas turbine blade vibrations has made significant progress over recent years; however, there still exist some limitations in the current techniques available. Specifically with blade tip timing (BTT) methods, some of the limitations are: the requirement of a large number of sensors for each engine stage, difficulties in dealing with multiple excitation frequencies, and sensors being located in the gas path. An alternative technique is examined here, utilising the unsteady casing wall pressure, which has the potential to rectify some of these limitations. Analytical simulation of the internal casing wall pressure is derived, for the situation with rotor blades undergoing forced vibration. The amplitude of the blade forced vibrations is then reconstructed from the simulated unsteady casing wall pressure, with results showing the robustness of the method to sensor location, measurement noise and a limited number of sensors.

This study presents the numerical fluid-structure interaction (FSI) modelling of a vibrating turbine blade using the commercial software ANSYS-12.1. The study has two major aims: (i) discussion of the current state of the art of modelling FSI in gas turbine engines and (ii) development of a "tuned" one-way FSI model of a vibrating turbine blade to investigate the correlation between the pressure at the turbine casing surface and the vibrating blade motion. Firstly, the feasibility of the complete FSI coupled twoway, three-dimensional modelling of a turbine blade undergoing vibration using current commercial software is discussed. Various modelling simplifications, which reduce the full coupling between the fluid and structural domains, are then presented. The oneway FSI model of the vibrating turbine blade is introduced, which has the computational efficiency of a moving boundary CFD model. This one-way FSI model includes the corrected motion of the vibrating turbine blade under given engine flow conditions. This one-way FSI model is used to interrogate the pressure around a vibrating gas turbine blade. The results obtained show that the pressure distribution at the casing surface does not differ significantly, in its general form, from the pressure at the vibrating rotor blade tip.

Non-contact measurement of gas turbine rotor blade vibration is a non-trivial task, with no method available which achieves this aim without some significant draw-backs. This paper presents a truly non-contact method to estimate rotor blade natural frequencies from casing vibration measurements at a single engine operating speed. An analytical model is derived to simulate the internal casing pressure in a turbine engine including the effects of blade vibration on this pressure signal. It is shown that the internal pressure inside a turbine contains measureable information about the rotor blade natural frequencies and in-turn the casing vibration response also contains this information. The results presented herein show the residual, pressure and casing vibration, spectrum can be used to determine the rotor blade natural frequencies with validation provided for the analytical model by experimental measurements on a simplified test rig. A simulated blade fault in one of the rotor blades is introduced with successful estimation of the simulated faulty blade natural frequency.

This paper presents a summary of a recent research program, focusing on a new method of non-contact gas turbine blade vibration measurement using casing pressure and vibration signals. Currently the dominant method of non-contact measurement of turbine blade vibrations employs the use of a number of proximity probes located around the engine periphery measuring the blade tip (arrival) time (BTT). Despite the increasing ability of this method there still exist some limitations, viz: the requirement of a large number of sensors ...

The non-intrusive measurement of blade condition within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is obviously the ambition of most techniques, with a number of methods proposed, investigated and employed for such measurement. The current dominant method uses proximity probes to measure blade arrival time for subsequent processing. It has been recently proposed ...

Condition monitoring of blades within gas turbines has been and will continue to be of importance in all areas of their use. Non-intrusive measurement of blade condition is the ambition of most techniques, with many methods proposed, investigated and employed for such measurement, with the current dominant method using proximity probes to measure blade arrival time for subsequent monitoring. It is proposed however that the measurement of the casing vibration, due to the aerodynamic-structural interaction within a gas turbine, ...

Abstract: The non-intrusive measurement of the condition of blades within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is the ambition of most techniques. The current dominant method uses proximity probes to measure blade arrival time for subsequent monitoring. It has recently been proposed however, that measurement of the turbine casing vibration response could provide a ...

Abstract: Non-intrusive measurement of blade condition within gas turbines is of major interest within all areas of their use. It is proposed that the measurement of the casing vibration, due to the aerodynamic-structural interaction within the turbine, could provide a means of blade condition monitoring and modal parameter estimation. In order to understand the complex relationship between blade vibrations and casing response, an analytical model of the casing and simulated pressure signal associated with the rotor ...

Non-contact measurement of gas turbine blade vibrations has made significant progress over recent years; however, there still exist some limitations in the current techniques available. Specifically with blade tip timing (BTT) methods, some of the limitations are: the requirement of a large number of sensors for each engine stage, difficulties in dealing with multiple excitation frequencies, and sensors being located in the gas path. An alternative technique is examined here, utilising the unsteady casing wall pressure, which has the potential to rectify some of these limitations. Analytical simulation of the internal casing wall pressure is derived, for the situation with rotor blades undergoing forced vibration. The amplitude of the blade forced vibrations is then reconstructed from the simulated unsteady casing wall pressure, with results showing the robustness of the method to sensor location, measurement noise and a limited number of sensors.

This paper studies the diagnosis of twisted blade in a multi stages rotor system using adapted wavelet transform and casing vibration. The common detection method (FFT) is effective only if sever blade faults occurred while the minor faults usually remain undetected. Wavelet analysis as alternative technique is still unable to fulfill the fault detection and diagnosis accurately due to its inadequate time-frequency resolution. In this paper, wavelet is adapted and its time-frequency is improved. Experimental study was undertaken to simulate multi stages rotor system. Results showed that the adapted wavelet analysis is effective in twisted blade diagnosis compared to the conventional one.

Non-intrusive measurement of blade condition within gas turbines is of major interest within all areas of their use. It is proposed that the measurement of the casing vibration, due to the aerodynamic-structural interaction within the turbine, could provide a means of blade condition monitoring and modal parameter estimation. In order to understand the complex relationship between blade vibrations and casing response, an analytical model of the casing and simulated pressure signal associated with the rotor blades is presented. A mathematical formulation is undertaken of the internal pressure signal due to both the rotating bladed disk as well as individual blade vibrations and the solution of the casing response is formulated. Excitation by the stator blades and their contribution to the casing response is also investigated. Some verification of the presented analytical model is provided by comparison with Finite Element Analysis results for various rotor rotational speeds.

When it comes to measuring blade-tip clearance or blade-tip timing in turbines, reflective intensity-modulated optical fiber sensors overcome several traditional limitations of capacitive, inductive or discharging probe sensors. This paper presents the signals and results corresponding to the third stage of a multistage turbine rig, obtained from a transonic wind-tunnel test. The probe is based on a trifurcated bundle of optical fibers that is mounted on the turbine casing. To eliminate the influence of light source intensity variations and blade surface reflectivity, the sensing principle is based on the quotient of the voltages obtained from the two receiving bundle legs. A discrepancy lower than 3% with respect to a commercial sensor was observed in tip clearance measurements. Regarding tip timing measurements, the travel wave spectrum was obtained, which provides the average vibration amplitude for all blades at a particular nodal diameter. With this approach, both blade-tip timing and tip clearance measurements can be carried out simultaneously. The results obtained on the test turbine rig demonstrate the suitability and reliability of the type of sensor used, and suggest the possibility of performing these measurements in real turbines under real working conditions.

A procedure for the derivation of signatures for faults in the blades of a gas turbine is presented here. A variety of blade faults,corresponding to changes in the angle or spacing of one or more blades, are examined. A ?uid dynamic simulation model is used to derive the unsteady pressure signals sensed by a stationary transducer for the cases of faulty blades. The blade fault signatures are derived by processing these signals using Fourier techniques. The features of blade fault signatures are studied. Finally, the possibilities they o§er for the discrimination and identi?cation of di§erent possible blade faults are also examined.

Blade faults and blade failures are ranked among the most frequent causes of failures in turbomachinery. This paper provides a review on the condition monitoring techniques and the most suitable signal analysis methods to detect and diagnose the health condition of blades in turbomachinery. In this paper, blade faults are categorised into five types in accordance with their nature and characteristics, namely, blade rubbing, blade fatigue failure, blade deformations (twisting, creeping, corrosion, and erosion), blade fouling, and loose blade. Reviews on characteristics and the specific diagnostic methods to detect each type of blade faults are also presented. This paper also aims to provide a reference in selecting the most suitable approaches to monitor the health condition of blades in turbomachinery.

Non-contact measurement of gas turbine blade vibrations has made significant progress over recent years; however, there still exist some limitations in the current techniques available. Specifically with blade tip timing (BTT) methods, some of the limitations are: the requirement of a large number of sensors for each engine stage, difficulties in dealing with multiple excitation frequencies, and sensors being located in the gas path. An alternative technique is examined here, utilising the unsteady casing wall pressure, which has the potential to rectify some of these limitations. Analytical simulation of the internal casing wall pressure is derived, for the situation with rotor blades undergoing forced vibration. The amplitude of the blade forced vibrations is then reconstructed from the simulated unsteady casing wall pressure, with results showing the robustness of the method to sensor location, measurement noise and a limited number of sensors.

A recent research program has identified the possibility of using the analysis of casing wall pressures in the direct measurement of gas turbine rotor blade vibration amplitudes. Currently the dominant method of non-contact measurement of gas turbine blade vibrations employs the use of a number of proximity probes located around the engine periphery measuring the blade tip (arrival) time (BTT). Despite the increasing ability of this method there still exist some limitations, viz: the requirement of a large number of sensors for each engine stage, sensitivity to sensor location, difficulties in dealing with multiple excitation frequencies and sensors being located in the gas path. Analytical modelling of the casing wall pressures and reconstruction of rotor blade vibration amplitudes from the analysis of these simulated pressure signals has shown significant improvement over current non-contact rotor blade vibration measurement limitations by requiring only a limited number of sensors and providing robust rotor blade vibration amplitude estimates in the presence of simulated measurement noise. However, this modelling was conducted with some fundamental assumptions about the casing wall pressures being made. One of these assumptions presumed that during blade motion the pressure profile around the rotor blades follows the blade’s motion while it oscillates around its equilibrium position. This assumption is investigated in this paper through the numerical modelling of the fully coupled two-way rotor blade motion and fluid pressure interaction.

Condition monitoring of blades within gas turbines has been and will continue to be of importance in all areas of their use, for maintenance and reliability purposes. Non-intrusive measurement of blade condition is the ambition of most techniques for this endeavour, with a number of methods proposed, investigated and employed for such measurement, with the current dominant method using proximity probes to measure blade arrival time for subsequent processing. It is proposed, however, that the measurement of the casing vibration, due to the aerodynamic-structural interaction within a gas turbine, could provide a means of blade condition monitoring and modal parameter estimation, without requiring perforation of the casing. An analytical model of a gas turbine casing and simulated pressure signal associated with the rotating blades, individual blade vibrations and transfer of stator blade vibrations has been developed in order to understand the complex relationship between casing response and the most important excitation forces. Due to the force interaction being through a fluid medium, a certain degree of randomness is introduced into the excitations, and the viability of this inherent randomness as a useful aid for separation of the contributing excitation forces from the system response is explored.

Condition monitoring of blades within gas turbines has been and will continue to be of importance in all areas of their use. Non-intrusive measurement of blade condition is the ambition of most techniques, with many methods proposed, investigated and employed for such measurement, with the current dominant method using proximity probes to measure blade arrival time for subsequent monitoring. It is proposed however that the measurement of the casing vibration, due to the aerodynamic-structural interaction within a gas turbine, could provide a means of blade condition monitoring and modal parameter estimation. An analytical model has been developed of the response of a gas turbine casing to what is believed to be the dominant forces acting on it, viz: (i) the moving pressure waveform around each blade throughout its motion and (ii) the forces (and moments) applied through the stationary stator blades, to understand the form of the casing response. A simulated blade fault has then been added to the model to represent a damaged blade, of arbitrary form, by reducing the stiffness of one blade. The change in the contribution to the casing response measurements due to this simulated fault is explored.

The non-intrusive measurement of blade condition within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is obviously the ambition of most techniques, with a number of methods proposed, investigated and employed for such measurement. The current dominant method uses proximity probes to measure blade arrival time for subsequent processing. It has been recently proposed however, that measurement of the turbine casing vibration response could provide a means of blade condition monitoring. The casing vibration is believed to be excited pre-dominantly by (i) the moving pressure waveform around each blade throughout its motion and (ii) the moments applied by the stationary stator blades. Any changes to the pressure profile around the rotating blades, due to their vibration, will therefore in turn affect these excitation forces. Previous work has introduced an analytical model of a gas turbine casing, and simulated pressure signal associated with the rotating blades. The model has been extended in this paper to more closely represent a commercial gas turbine with experimental verification being presented for various aspects of the analytical modelling procedure.