Blade Fracture Research Articles

Study on the Influence of Volute Throat Jet on Excitation Vibration Alleviation of Radial Turbine Blade

Abstract Turbine blade fracture, resulting from high-cycle fatigue (HCF), is the most commonly observed failure mode of turbochargers. In a vaneless turbine, the radial turbine blade is susceptible to HCF under excessive aerodynamic excitation due to the flow field distortion caused by the volute tongue. The present study explores a technique to mitigate blade excitation by reducing pressure disturbance in the volute tongue area. The gas with higher pressure in the inlet section of the volute is transferred to the low-static pressure area upstream of the volute tongue through a throat jet hole. The usage of high-pressure gas improved the homogeneity of the flow field near the volute tongue. The study investigates the mitigation of high-pressure gas jet on turbine blade excitation, the impact of jet hole geometry on the suppression effect of the blade vibration, and the effect of high-pressure jet on turbine performance using numerical simulation of unsteady flow fields. The results indicate that the jet flow has a substantial impact on dampening the blade vibrations. The harmonic pressure amplitude at the monitor point located within the high blade vibration amplitude region is reduced by up to 56%. Generalized pressure analysis reveals that the aerodynamic excitation of the turbine blades is significantly reduced. Experimental evidence verifies the effectiveness of the jet hole scheme in reducing blade vibration. Moreover, the jet hole has a negligible effect on turbine efficiency. However, there is a degree of increased stress in the volute tongue with a jet hole which needs to be evaluated in engineering applications.

Case report: a case of single-sided shoulder blade fracture resulting from an electrical shock

Case report: a case of single-sided shoulder blade fracture resulting from an electrical shock

Unexpected Laryngoscope Blade Fracture at the Base during Laryngoscopy

Unexpected Laryngoscope Blade Fracture at the Base during Laryngoscopy

A Numerical Method for the Dynamics Analysis of Blade Fracture Faults in Wind Turbines Using Geometrically Exact Beam Theory and Its Validation

In pursuit of China’s goals for carbon peak and carbon neutrality, wind turbines are continually evolving to achieve a lower levelized cost of energy. The primary technological focus in the wind power industry is on large-scale, lightweight designs for entire turbines to enhance cost competitiveness. However, this advancement has led to an increased risk of blade fractures under extreme operating conditions. This paper addresses this challenging issue by using geometrically exact beam theory to develop a nonlinear simulation model for long, flexible blades. The model accounts for sudden changes in blade properties at the moment of failure, covering both the extensive motions and deformations of the fractured blade. The validation of the proposed model is carried out by comparing the results from power production cases with bladed simulations and further validating the simulations of blade fracture load cases against measurement data. The methodologies and findings presented in this study offer valuable insights for diagnosing faults in wind turbines.

Failure analysis of large and complex engine blades based on experimental research

On a certain day in December 2022, a GE90 engine equipped by an airline experienced a surge during flight. Ground inspection revealed broken blades of the 9-stage high-pressure compressor. To identify the cause of its fracture failure, the macroscopic fracture surface was first analyzed. Obvious fatigue crack propagation characteristics were found at the blade cross-section. Small pits formed by the impact were observed at the crack source location, indicating that the blade was first formed into a circular arc-shaped impact wound after being impacted by an external object. In the subsequent service process, under continuous vibration, fatigue cracks are formed at the impact point as the crack source and gradually propagate, ultimately leading to blade fracture and failure. To further explore the source of foreign objects causing impact damage, the surface scanning method using energy spectrum analysis was used. An enriched region of C element was found near the impact point. However, due to the lack of conditions for the formation of C combustion products at the compressor location, it can be considered that the foreign object may have come from external sources.

Fault diagnosis of horizontal centrifugal pump orifice ring wear and blade fracture based on complete ensemble empirical mode decomposition with adaptive noise-singular value decomposition algorithm

Horizontal centrifugal pump orifice ring wear and blade fracture failure will not only affect the hydraulic performance but also affect the safety and stability of the whole unit. In this paper, the horizontal centrifugal pump orifice ring wear and blade fracture failure are studied, and carry out condition monitoring and fault identification through the vibration signal under the failure. Combined with the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise and Singular Value Decomposition algorithm of adaptive noise, a vibration feature extraction method of horizontal centrifugal pump based on intrinsic mode singular value is proposed. Through the BP neural network, based on the time domain, frequency domain, wavelet packet-AR spectrum, and intrinsic mode singular value characteristics of single-point and double-point vibration, the identification model is constructed and the identification effect is compared. The research shows that the vibration feature recognition effect of CEEMDAN-SVD decomposition is verified based on BP neural network model, and the BP neural network is improved by Particle Swarm Optimization to further improve the recognition effect and speed, which provides the diagnosis model for the design of subsequent diagnosis system.

The influence of blade fracture on the internal flow characteristics and rotor system of horizontal centrifugal pumps

The blade fracture of horizontal centrifugal pump will not only affect the hydraulic performance of the pump, but also affect the safety and stability of the whole unit. In this paper, for horizontal centrifugal pumps, five single-blade fracture schemes are designed and numerical simulations are carried out under different operating conditions. The results show that with the increase of fracture size, the influence on the hydraulic characteristics of the pump shows a decreasing trend, and it will also affect the turbulent kinetic energy distribution near the impeller inlet, so that the internal flow becomes complex and the flow loss increases. The radial force on the impeller changes periodically, and its magnitude shows a nonlinear decreasing change with the increase of the fracture size. The pressure pulsation analysis of several monitoring points in the worm shell shows that as the fracture size increases, the amplitude of the lobe frequency slowly rises, and the shaft frequency, which is second only to the lobe frequency, becomes higher and higher and begins to dominate. A study of the rotor system shows that the maximum deformation of the impeller occurs at the edge of the impeller cover and the maximum equivalent stress occurs at the blade exit; blade fracture causes a significant reduction in the latter third-order intrinsic frequency.

Failure Analysis of High-Pressure Turbine Blades in Steam Power Plants

This paper describes the failure of high-pressure steam turbine blades. During the Serious Inspection, it was discovered that the ninth-stage high-pressure turbine blade had failed. The causes of blade failure are examined via visual inspection and destructive testing. The failure mechanism of the blades was determined by conducting mechanical properties testing, metallographic inspection, and energy spectrum analysis. The mechanical properties of the leaf and root blade specimens were within the range of blade steel for steam turbines according to the Chinese National Standard (GB/T 8732-2004), but the chemical composition was not identical. This is consistent with the root blade fracture pattern where the hardness value plotted from the test results is the lowest at the root blade location, which is the primary cause of fissure propagation.

Study on Fracture Mechanism of Low-Pressure Blades of Steam Turbines in Power Plants

With the continuous improvement of steam turbine design technology and production level, steam turbine blade fracture accidents have dropped significantly, and blade fracture accidents are no longer the main reason for the forced shutdown of thermal power generation units. Due to the bad working conditions of turbine blades, blade designers still need help to accurately analyze their dynamic stress and evaluate their high cycle fatigue life. Up to now, blade fracture accidents still occur frequently. In this paper, a comprehensive analysis is made of the causes of the fracture of the low-pressure 16th stage blade of a 25 MW steam turbine in a thermal power plant. The fracture property of turbine moving blades is that small corrosion pits are formed first, and then the fatigue propagation fracture occurs. The main cause of corrosion is poor steam quality.

Fatigue fracture failure analysis of 12Cr12Mo steam turbine blade

Turbine blade is one of the key components in thermal power plant, and its premature failure is a common accident. The fourth blade of the low-pressure turbine unit in a power plant broke, resulting in the unplanned shutdown of the turbine unit. Through different analysis methods, the failure cause of the steam turbine blade was determined. The macro morphology of the fracture was observed by optical light microscope (OLM), and the micro characteristics of the fracture were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The mechanical properties of the failed blade were analyzed by room temperature tensile test and Charpy impact test. The results indicated that the root cause of blade fracture was the decrease of fatigue strength and rupture strength caused by high δ-ferrite content. Consistency between crack propagation direction and banded δ-ferrite direction further promotes crack initiation and prolongation. Eventually leading to fatigue fracture of the blade. According to the test and analysis results, some recommendations to prevent the early failure of steam turbine blades are put forward.

CFD simulation analysis of aerodynamic characteristics of large wind turbine unit under accident condition

In this paper, according to different locations of blade fracture accidents, it is divided into three fractures: blade root fracture, leaf middle fracture and blade tip fracture. Assuming that the blade fracture accident due to aging is operated at the rated wind speed and rated speed, CFD simulation is carried out to analyze the wind rotation field, aerodynamic load and blade surface streamline characteristics of NREL 5MW wind turbine with different fracture positions. This paper also assumes that under the condition of a strong typhoon, the instantaneous wind speed is too large, resulting in the wind turbine speeding, and then the blade fracture accident occurs. At this time, the wind turbine was running under extreme wind speeds, and the speed soared due to the speeding car. Analyze aerodynamic loads at different speeds. It provides an important reference for the design and operation and maintenance of wind turbine blades.

Fault identification method of micro turbine blade based on the order spectral entropy of bearing vibration

In view of the difficulty in identifying the state of the micro turbine blade, this paper uses the order spectral entropy analysis method to extract the characteristic information of the blade fault based on the measured micro turbine bearing vibration data. Firstly, a micro-turbine test bench was established. The normal temperature stable inlet flow was produced by a blower, the high temperature and pressure unstable airflow was generated by turbojet combustion chamber, and the working inlet mode of a micro-turbine with a wide range of speed changes was simulated. The vibration signal of the bearing was collected by shell drilling, a variety of time-frequency domain feature analysis methods based on vibration signal are difficult to effectively identify blade faults under the combined action of unstable airflow and frequent variable speed. In this paper, the bearing vibration data in time domain is converted to the vibration data in angle domain, and then the order amplitude and entropy were compared and analyzed. The results show that the proposed method can effectively identify the blade fracture and fouling faults under the driving of stable and unstable airflow in the speed range of 0–20 000 r min−1. This method provides a new method for micro turbine blade condition monitoring through bearing vibration data.

Study on fracture analysis of rotor blade in thermal power plant

The comprehensive failure analysis of the fractured LP rotor blade was carried out by means of appearance morphology analysis, SEM morphology analysis, mechanical property analysis, chemical composition analysis and microstructure detection. The results show that the second and last stage blades at the low-pressure rotor turbine side are damaged by mechanical collision, resulting in damage and deformation at the steam outlet side of the blades and generating stress concentration areas. The blades are prone to generate crack sources in the stress concentration areas of mechanical damage under the working load, and the cracks continue to expand on the condition of alternative stress, eventually leading to fatigue cracking and fracture of the blades. It is recommended to carefully check the blades at other positions of the LP rotor and deal with the mechanical damage and cracking problems in time. Secondly, foreign matters shall be prevented from entering the turbine with the steam to damage the blades, and the fixed parts inside the cylinder shall be ensured to be firm and not fall off, so as to prevent the recurrence of similar blade fracture.

STRESS ANALYSIS OF VARIOUS DESIGNS OF CENTRIFUGAL PUMP IMPELLERS USING FINITE ELEMENT METHOD

The impeller blade is among the many critical components in a centrifugal pump that affect the efficiency of the pump, as it is the component through which the fluid passes. Therefore, the impeller requires as many analysis as possible to maximise its efficiency. The main requirement is to ensure that the impeller blade can withstand the level of stress thereby reducing the chance of blade fracture. In this paper, 4 different designs of a centrifugal pump impeller were analysed and compared using finite element analysis (FEA) under static analysis. The geometry of centrifugal pump impellers was modelled and analysed using Siemens NX™ software. This analysis provided an insight of performance of design where the blade’s angle, width and shrouds are kept constant throughout the process. Calculations were performed to predict the design discharge and understand the impact on the impeller if the blade angle changes. The analysis revealed that the higher the outlet blade angle is to a point in comparison to the blade at inlet, the higher the head and the higher the pressure at the outlet will be. A pressure load of 1.866 MPa was applied evenly to the impellers with a rotation of 1,100 rpm and a torque of 29.187 Nm. Throughout the analysis, closed impeller blades were set to produce the least stress and displacement in comparison to other designs. Therefore, closed impeller was the best design, where the maximum stress was the lowest (86.09MPa) and can be more reliable in real life application.

Vibration Analysis of 3D printed runner with CNN for using deep learning in hydropower for condition monitoring

Convolutional Neural Networks are deep learning algorithms that are typically used for the classification of images. A black and white image can be represented as the number of rows and columns along with values of intensity for each of components of these rows and columns. Vibration measured with the help of accelerometer can be used to create an image like data. These data can be used for machine learning applications with the help of deep learning. In deep learning techniques, features do not have to be extracted from the data set. The CNN network can generate a feature-like set which can be further classified with a fully connected neural network to give out the probability over the predefined class. The neural networks model is trained with a data set created in laboratory conditions to monitor the unfractured and single blade fracture condition operation state. The paper deals with showing the proof of concept that CNN algorithms can be applied for conditional monitoring of runner blades. The paper mainly focuses on demonstrating that deep learning algorithms can be used as analysis tools for hydropower runners by applying these techniques in scaled versions of 3D printed runners.

Reconstruction of fan blade dynamic loading prior to its fracture

To maintain the functionality of fan blades, it is important to know the distribution of dynamic stresses in the blade, their amplitude and vibration frequency. Understanding of the dynamic loading pattern will allow us to determine under what conditions the engine was operated, to identify and prevent emergencies that could lead to the blade fracture. The purpose of this work is to understand the cause of the fan blade fracture that occurred during the engine ground start. Due to fractographic analysis of blade fragments it was revealed that the fracture occurred due to the initiation of fatigue cracks in blades. The place of crack initiation and parameters of crack growth were established, spectral analysis of the fracture was carried out. To establish the reason of fatigue crack initiation it was necessary to determine the dynamic state of the blades during their destruction. The sections of the second stage of stable crack growth, during which fatigue striations are formed, were determined using the fractographic method. Using the spacing of the fatigue striations and Paris's law, the crack stress intensity range was determined. Modeling of crack propagation in the blade was carried out to define the stress state. The ability to determine the stress intensity factor at each step of crack growth and its comparison with research data made this work possible. The simulation showed under what conditions manifold increase in stresses occurs and made it possible to obtain the expected value of vibration amplitude. Additional modal analysis showed a resonant form that caused the fatigue nature of crack propagation. The demonstrated approach established crack growth conditions and revealed the cause of blade fracture.

Influence of Blade Fracture on the Flow of Rotor-Stator Systems with Centrifugal Superposed Flow

Rotor-stator cavities are often found in turbomachinery; they supply cold air that is bled from the compressor to the turbine blades. The pressure of the outlet of a rotor-stator cavity is axisymmetric under normal circumstances. However, its pressure would be non-axisymmetric in the event of blade fracture. The impact of blade fracture on a rotor-stator cavity with centrifugal superposed flow is studied in this paper. The Euler number E, the rotational Reynolds number Reφ, and the low-pressure zone range θ are investigated and, for the first time, with the non-axisymmetrical boundary conditions employing numerical simulation. The results of the numerical calculations show that after turbine blade fracture, the velocity is more affected in the downstream region at a high radius, especially when the Reφ is large. As for the distribution of the mass flow rate, there may be a critical θc at which the other blades are least affected. The θc would increase as the Reφ or the E increase, and the θc≅0.2 when Cw=10,137, Reφ=5.12×105, and 0.2≤E≤0.4. In addition, the thrust coefficient increases as the E or the θ increases, and the increase in the thrust coefficient does not exceed 4% when the E=0.2 and the θ=0.1 in this paper. However, the moment coefficient on the rotating shaft is almost independent of the E and the θ. An increase in the Reφ will reduce the effect of turbine blade fracture on the thrust and moment coefficients, when the Reφ is small.

Numerical Study on Vibration Response and Fatigue Damage of Axial Compressor Blade Considering Aerodynamic Excitation

Axial compressor blades with a deformed initial torsion angle caused by aerodynamic excitation resonated at the working speed and changed the rule of fatigue damage accumulation. The fatigue life of a blade has a prediction error, even causing serious flight accidents if the effect of torque causing damage deterioration of the blade fatigue life is neglected. Therefore, in this paper, a uniaxial non-linear fatigue damage model was modified using the equivalent stress with torsional shear stress, and the proposed fatigue model including the torsional moment was used to study the compressor blade fatigue life. Then, the blade numerical simulation model was established to calculate the vibration characteristics under complex loads of airflow excitation and a rotating centrifugal force. Finally, the blade fatigue life under actual working conditions was predicted using the modified fatigue model. The results show that the interaction between centrifugal and aerodynamic loads affects the natural frequency, as the frequencies in modes dominated by bending deformation decreased whereas those dominated by torsional deformation increased. Furthermore, the blade root of the suction surface showed stress concentration, but there is an obvious difference of stress distribution and amplitude between the normal stress and the equivalent stress including torsional shear stress. The additional consideration of the torsional shear stress decreased the predicted fatigue life by 4.5%. The damage accumulation rate changes with the loading cycle, and it accelerates fast for the last 25% of the cycle, when the blade fracture may occur at any time. Thus, the aerodynamic excitation increased the safety factor of blade fatigue life prediction.

Study on water erosion and preventive measures of last stage blade of steam turbine

In the background of carbon peak and carbon neutralization, most thermal power plants are more involved in peak regulation and even in-depth peak regulation in order to absorb new energy such as wind power and Solar power. When the turbine is running under low load, the exhaust pressure decreases, which leads to the increase of exhaust humidity. More and more turbine blades have water erosion. The erosion of the last stage blades will worsen the dynamic performance of the turbine, increase the risk of the last stage blade fracture, and threaten the safe operation of the turbine. This paper studies the mechanism of the last stage blade erosion of steam turbine, and analyzes the main factors which influence the erosion with examples. Combined with the mechanism of water erosion, the relevant preventive measures are made for reference of power supply plant.

Research on operating characteristics of a centrifugal pump with broken impeller

The operating characteristics of a centrifugal pump with broken impeller malfunction was studied by tests and numerical simulation. One blade was cut 1/4 as a broken impeller. The energy characteristics, vibration, internal flow, pressure fluctuation, and radial force of the pump were studied in detail. The test results show that as for the pump with broken impeller, the head decreased by 9.85% and efficiency decreased by 1.06% under 1.0 Q0. The vibration increase amplitudes at the outlet flange are the maximum. The APF (axial passing frequency) of all monitoring points increased significantly, and a new frequency – 5APF appeared, except for the inlet of the pump. It can be found that the low-speed region of blade fracture surface is more obvious than other blades through numerical simulation. The radial force of the broken impeller increased obviously and became more concentrated. Due to the broken blade, the peak-to-peak magnitude of pressure fluctuation at the tongue and pump outlet increased by 4.7% and 9.5% respectively. The research results provide some reference for the malfunction diagnosis of centrifugal pump.