Blade Bending Research Articles

Design and Optimization of Hybrid Interface Joint in a Composite Fan Blade of Aircraft Engine

Fan blades are one of the most important components of an aircraft engine. Bird strikes on fan blades have always been a cause of worry and it can cause slices of birds hitting other parts of the engine which may lead to greater damages. Bird strikes cannot be completely avoided. However, reduction of the impact of a bird on jet engines can be achieved by suitable design and manufacturing, through the simulation analysis. Although current composite blades can withstand the bird strike impact, some delamination failures are still observed on the trailing edge side of the blade, possibly due to vibration bending modes This paper talks about using two fibers in composite blade instead of the current single fiber one. For this to be feasible, two fiber joints at various locations on the blade have to be properly designed. The design criteria used here is the lowest inter-laminar shear strain level at critical joint locations. Suitable size coupon models in FEA with hybrid joints inside are used to simulate the blade bending with appropriate boundary conditions. The coupon models were developed by using the ANSYS APDL and linear static analysis was performed for different repetitive layups and varying layer by layer joint locations. The coupon joint designs with minimum inter-laminar shear strains are shortlisted to be recommended for use in sub-element and blade models.

The influence of the trailing edge angle of the micro centrifugal impeller on the performance of the centrifugal compressor

In order to study the effect of the trailing edge sweep angle of the centrifugal impeller on the aerodynamic performance of the centrifugal compressor, 6 groups of centrifugal impellers with different bending angles and 5 groups of different inclination angles were designed to achieve different impeller blade trailing edge angle. The computational fluid dynamics (CFD) method was used to simulate and analyze the flow field of centrifugal compressors with different blade shapes under design conditions. The research results show that for transonic micro centrifugal compressors, changing the blade trailing edge sweep angle can improve the compressor’s isentropic efficiency and pressure ratio. The pressure ratio of the compressor shows a trend of increasing first and then decreasing with the increase of the blade bending angle. When the blade bending angle is 45°, the pressure ratio of the centrifugal compressor reaches a maximum of 1.69, and the isentropic efficiency is 67.3%. But changing the inclination angle of the blade trailing edge has little effect on the isentropic efficiency and pressure ratio. The sweep angle of blade trailing edge is an effective method to improve its isentropic efficiency and pressure ratio. This analysis method provides a reference for the rational selection of the blade trailing edge angle, and provides a reference for the design of micro centrifugal compressors under high Reynolds numbers.

Повышение устойчивости дереворежущих пил термопластическим воздействием на распределение остаточных напряжений в полотне

The saw stability in operation defines the ability of the saw blade to resist the forces acting on it in the plane of greatest rigidity. The saw can work reliably only in case of maintaining stable balance, which is achieved through the creation of normalized residual stresses in certain zones of the saw blade by different methods. The stresses balance the forces of external influences. Compressive stresses are created in the central part of the blade to make the circular saw operational. These stresses compensate the forces of centrifugal acceleration, temperature heating of individual zones of the saw blade, external longitudinal and transverse bending forces arising in material processing. In practice, the creation of normalized stresses in the saw disk is traditionally carried out only by local mechanical contact action (forging, rolling) of the saw blade tool on the steel saw blade. It is proposed to form the stressed state of the disk by thermophysical action instead of the traditional mechanical processing of the saw blade. The thermophysical action involves the creation of normalized residual stresses in the saw blade by the concentrated thermal exposure to local differently directed narrow-band zones of straight or deflected shape, mainly radial or along concentric traces, controlling the process in real time. A new approach to the formation of residual stress fields in the saw blade by thermoplastic action enables to radically change the settingup procedure of the circular saw, ensuring its stability in operation.

Effectiveness of the Compound Helicopter Configuration in Rotorcraft Performance Increase

Abstract The article presents the results of calculations applied to compare flight envelopes of varying helicopter configurations. Performance of conventional helicopter with the main and tail rotors, in the case of compound helicopter, can be improved by applying wings and pusher propellers which generate an additional lift and horizontal thrust. The simplified model of a helicopter structure, consisting of a stiff fuselage and the main rotor treated as a stiff disk, is applied for evaluation of the rotorcraft performance and the required range of control system deflections. The more detailed model of deformable main rotor blades, applying the Galerkin method, is used to calculate rotor loads and blade deformations in defined flight states. The calculations of simulated flight states are performed considering data of a hypothetical medium class helicopter with the take-off mass of 6,000kg. In the case of both of the helicopter configurations, the articulated main rotor hub is taken under consideration. According to the Galerkin method, the elastic blade model allows to compute blade deformations as a combination of the blade bending and torsional eigen modes. Introduction of additional wing and pusher propellers allows to increase the range of operational speed over 300 km/h. Results of the simulation are presented as time-runs of rotor loads and blade deformations and in a form of disk distribution plots of rotor parameters. The simulation method can be useful in defining requirements for a high speed rotorcraft.

Pengaruh Jumlah dan Rasio Sudut Lengkung Sudu Terhadap Unjuk Kerja Turbin Angin Savonius Heliks

The helical Savonius is a vertical wind turbine that can utilize wind energy to become a renewable energy source. This study aims to determine the effect of the number of blades and the ratio of blade bends on the performance of the Savonius helical wind turbine. The research was conducted through experimentation using variations in the number of blades 2 and 3 blades. Variation of blade bending ratio H / L = 6/10, 7/10 and 8/10 and variations in wind speed (4.0), (5.2), (6.4) and (7.4) m / s. The turbine performance analysis is reviewed based on the shaft rotation (RPM) of the turbine and the output voltage (volts) generated by the generator connected to the turbine shaft. The results showed that the wind speed, the number of blades, and the blending ratio of the blades affect the performance of the Savonius helical wind turbine. The results of the maximum wind turbine performance test at a variation of 3 blades, a ratio of 6/10, and a wind speed of 7.4 m / s, produce a shaft rotation value of 472.9 rpm and a generator output voltage value of 5.51 volts.
 Keywords: Helical Savonius, number and ratio blade bend, wind speed, performance

Review of Gas Turbine Internal Cooling Improvement Technology

Abstract The higher firing temperature reflects the higher efficiency of the gas turbine. However, using higher temperatures is limited as it may cause a rupture, bending, or failure of the turbine blades. Hence, the development of an effective internal cooling system of the gas turbine blade is essential. At the same time, it is necessary to ensure the lowest possible penalty on the thermodynamics performance cycle. Researchers are working over the years to find out the efficient cooling channel design with high transfer while the lowest pressure drop. They ran several cases both numerically and experimentally. This paper reviews the published research in the various methods of gas turbine internal cooling, such as using rib turbulators, dimples, jet impingement, pin fins, and guide vane, of the gas turbine blade.

FAST.Farm development and validation of structural load prediction against large eddy simulations

AbstractFAST.Farm is a mid‐fidelity engineering tool developed by the National Renewable Energy Laboratory targeted at accurately and efficiently predicting wind turbine power production and structural loading in wind farm settings, including wake interactions between turbines. FAST.Farm is based on several principles of the dynamic wake meandering (DWM) model, but also addresses limitations of previous DWM implementations. Previous FAST.Farm studies have shown the similarities and differences between FAST.Farm and large eddy simulations for rigid turbine cases. The objective of this work is to quantify the ability of FAST.Farm to accurately predict turbine structural response in a small wind farm. This is done by comparing FAST.Farm structural response to SOWFA‐OpenFAST results for three laterally‐aligned turbines. The purpose of this study is to characterize the similarities and differences between FAST.Farm and a higher fidelity model for predicting turbine structural response in a wind farm for differing atmospheric inflows. Strong statistical agreement was found between FAST.Farm and SOWFA‐OpenFAST structural response for the non‐waked upstream turbine, and good agreement was found for the downstream turbines for most structural quantities. Higher differences were seen for downstream turbines with low ambient turbulence intensity or yawed turbines, suggesting areas for FAST.Farm wake dynamics modeling improvements. For all cases and turbines, small statistical differences were seen between blade deflections and bending moments, with larger differences for tower‐top and tower‐base bending moments. Overall, the results establish confidence for applying FAST.Farm to wind farm power and loads analyses and identify areas where further model validations and model improvements should be targeted.

Initial performance and load analysis of the LowWind turbine in comparison with a conventional turbine

We present the preliminary design of a high capacity LowWind turbine rotor with a specific power of 100 W/m 2, a rated power of 3.4MW and a 208m diameter rotor. The turbine is designed for optimal system integration and thus with a considerably increased power production at low to medium wind speed and stopped at 13 m/s. The AEP of the turbine, due to the large swept rotor area, is 40-45% higher than the AEP of a conventional on-shore turbine, the IEA Task 37 reference wind turbine with a 130 m diameter rotor and the same rated power of 3.4 MW. Initial aeroelastic simulations show that the loads of the LowWind turbine are generally higher than on the IEA turbine although comparable for some components at steady wind. For Design Load Case 1.2 (DLC1.2) for normal operation in turbulence we see a typical increase of around 20-40% of tower and rotor fatigue loads. However, this moderate increase for such big increase of rotor diameter is only obtained due to the highly flexible light weight rotor designed with a combination of peak shaving and blade bend twist coupling and for a low stop wind speed of 13 m/s.

Acoustic emission methods for lifetime estimations in aircraft structures

Regularities of acoustic emission (AE) signals’ formation during cyclic loading of turbine blades of different Ni-based superalloys and steel specimens were considered and systematized. AE activity can be related to strain energy density, and for the beginning period of the cyclically loaded blade the value of summarized AE signals Nae recorded in a short time can be used for characterizing the critical state of blade material as blade durability Nf. The lower Nae for a considered time interval, the higher the blade durability Nf. Dependences of lgNf on lgNae were discovered in linear form with a high value of correlation factor. The similar relation between summarized AE signals and durability was demonstrated in the case of a monotonic blade bending with a stress level of 1% higher than in-service stress. For high accuracy of loading, a test-device that enables to load blades with a low velocity of stress level increasing was constructed. Well-known α-criterion appears when registered fatigue crack origination in a blade can be estimated in the number of cycles (Nf)α by the AE signals formation in a short time (Nae)t at the beginning stage of blade cyclic loading.

An insight on VMD for diagnosing wind turbine blade faults using C4.5 as feature selection and discriminating through multilayer perceptron

This paper presents a pioneer study of identifying the wind turbine blade condition based on its vibration pattern. The study used variational mode decomposition (VMD) for signal pre-processing. VMD is an adaptive signal decomposition technique, which can non-recursively decompose a multi-component signal into a number of quasi-orthogonal intrinsic mode functions. This new tool is based on a solid mathematical foundation and can obtain a well-defined time–frequency representation. The main advantage of VMD is, there is no residual noise in the modes and it can avoid redundant modes. Thus, VMD provides a noise-free fault signal for classification. Initially, the obtained vibration data are pre-processed using VMD and then the descriptive statistical features like mean, standard deviation, sample variance, and kurtosis were extracted. After the feature extraction, the dominant features were selected using the C4.5 decision tree algorithm. In this study, multilayer perceptron (MLP) was used for fault classification (blade bend, blade crack, erosion, hub-blade loose connection, and pitch angle twist). Then a comparative study was made with MLP without VMD and MLP with VMD to suggest a better model. From the results, the maximum classification accuracy of 87% was obtained for MLP with VMD when compared to MLP without VMD (76.83%).

Effects of rotor and stator geometry on dissolution process and power consumption in jet-flow high shear mixers

The jet-flow high shear mixer (JF-HSM) is a new type of intensified equipment with special configurations of the rotor and the stator. The mass transfer property and power consumption were studied in the solid-liquid system for a series of JF-HSMs involving different configuration parameters, such as rotor diameter, rotor blade inclination, rotor blade bending direction, stator diameter, and stator bottom opening diameter. The flow characteristics were examined by computational fluid dynamic simulations. Results indicate that the turbulent power consumption of the JF-HSM is affected by the change in rotor blade inclination and stator bottom opening. With the increase in the shear head size and the change in the rotor into a backward-curved blade, the solid-liquid mass transfer rate can be remarkably increased under the same input power. Dimensionless correlations for the mass transfer coefficient and power consumption were obtained to guide the scale-up design and selection of such a new type of equipment to intensify the overall mixing efficiency.

Analysis of the Effect of a Series of Back Twist Blade Configurations for an Active Pitch-To-Stall Floating Offshore Wind Turbine

Abstract For a turbine mounted on a floating platform, extreme induced loads can be increased by up to 1.6 times those experienced by a turbine situated on a fixed base. If these loads cannot be reduced, towers must be strengthened which will result in increased costs and weight. These tower loads would be additionally exasperated for a pitch-to-feather controlled turbine by a phenomenon generally referred to as “negative damping,” if it were not avoided. Preventing negative damping from occurring on a pitch-to-feather controlled floating platform negatively affects rotor speed control and regulated power performance. However, minimizing the blade bending moment response can result in a reduction in the tower fore-aft moment response, which can increase the tower life. A variable-speed, variable pitch-to-stall (VSVP-S) floating semi-submersible wind turbine, which does not suffer from the negative damping and hence provides a more regulated power output, is presented. This incorporates a back twist blade profile such that the blade twist, starting at the root, initially twists toward stall and, at some pre-determined “initiation” point, changes direction to twist back toward feather until the tip. Wind frequency weighting was applied to the tower axial fatigue life trends of different blade profiles and a preferred blade back twist profile was identified. This had a back twist angle of −3 deg and started at 87.5% along the blade length and achieved a 5.1% increase in the tower fatigue life.

Wind turbine asymmetrical load reduction with pitch sensor fault compensation

AbstractOffshore wind turbines suffer from asymmetrical loading (blades, tower, etc), leading to enhanced structural fatigue. As well as asymmetrical loading different faults (pitch system faults etc.) can occur simultaneously, causing degradation of load mitigation performance. Individual pitch control (IPC) can achieve rotor asymmetric loads mitigation, but this is accompanied by an enhancement of pitch movements leading to the increased possibility of pitch system faults, which exerts negative effects on the IPC performance. The combined effects of asymmetrical blade and tower bending together with pitch sensor faults are considered as a “co‐design” problem to minimize performance deterioration and enhance wind turbine sustainability. The essential concept is to attempt to account for all the “fault effects” in the rotor and tower systems, which can weaken the load reduction performance through IPC. Pitch sensor faults are compensated by the proposed fault‐tolerant control (FTC) strategy to attenuate the fault effects acting in the control system. The work thus constitutes a combination of IPC‐based load mitigation and FTC acting at the pitch system level. A linear quadratic regulator (LQR)‐based IPC strategy for simultaneous blade and tower loading mitigation is proposed in which the robust fault estimation is achieved using an unknown input observer (UIO), considering four different pitch sensor faults. The analysis of the combined UIO‐based FTC scheme with the LQR‐based IPC is shown to verify the robustness and effectiveness of these two systems acting together and separately.

A lazy learning approach for condition monitoring of wind turbine blade using vibration signals and histogram features

The main objective of the proposed research study is to discriminate different blade fault conditions which affect the wind turbine blades under operating condition through machine learning approach. A three bladed wind turbine was chosen and the faults like blade bend, blade cracks, blade erosion, hub-blade loose connection and pitch angle twist were considered in the study. This problem is formulated as a machine learning problem which consists of three phases, namely feature extraction, feature selection and feature classification. Histogram features were extracted from vibration signals and feature selection was carried out using J48 decision tree algorithm. Feature classification was performed using lazy classifiers like nearest neighbour, k-nearest neighbours, locally weighted learning and K-star classifier. The results of these classifiers were compared with respect to their correctly classified instances (accuracy percentage) and found that, locally weighted learning yielded a maximum accuracy of 93.83% with a computational time of 0.07 s.

The Influences of Stagger and Pretwist Angles of Blades on Coupling Vibration in Shaft-Disk-Blade Systems

Abstract The influences of stagger angle (α) and pretwist angle (βL) of blades on the coupling vibration among shaft bending and blade bending in a shaft-disk-blade (SDB) system are investigated using a Lagrangian approach in combination with the assumed modes method (AMM). The disk is rigid, and the flexible shaft is supported with two rigid bearings. It is shown that α and βL have variable effects on the coupling vibration because their influences can be increased, reduced, or even completely eliminated for different values of disk location (λ), blade thickness ratio (δ), and blade aspect ratio (γ). To study the coupling vibration in an SDB system, consideration of λ, δ, and γ are very important because those can alter the coupling magnitude, the coupling pattern as well as the predominant modes. Nevertheless, previous researches rarely take into account these parameters. Moreover, in the present work, to investigate the natural frequencies and critical speeds versus λ, δ, and γ, new diagrams are introduced. Also, the relation between the in-plane and out-of-plane motions of the blades with the coupling vibration is precisely analyzed.

Fault Diagnosis of Wind Turbine Blades using Histogram Features through Nested Dichotomy Classifiers

This study makes an attempt of classifying different fault conditions which occurs on wind turbine blade due to environmental stress and high wind speed. “Here three bladed horizontal axis variable wind turbine was used for experimental study and different faults like blade crack, hub-blade loose connection, erosion, pitch angle twist and blade bend was considered. This study had been carried out in three phases namely feature extraction, feature selection and feature classification. Initially vibration signals are noted for different blade conditions and required features are obtained using histogram features. Secondly, from the extracted feature, most dominating feature need to be chosen using J48 decision tree classifier. Later, the selected feature is fed into the classifiers like Nested Dichotomy (ND), Class-Balanced Nested Dichotomies (CBND) and Data near Balanced Nested Dichotomy (DNBND) for classification of the faults. These classifiers are compared with respect to their accuracy to suggest a better model for fault diagnosis on blade. The suggested model can be incorporated in real-time system to monitor the condition of wind turbine blade.

Implementation of Rule based Classifiers for Wind Turbine Blade Fault Diagnosis using Vibration Signals

The fast developing wind industry has revealed a requirement for more multifaceted fault diagnosis system in the segments of a wind turbine. “Present wind turbine researches concentrate on enhancing their dependability quality and decreasing the cost of energy production, especially when wind turbines are worked in off-shore places. Wind turbine blades are ought to be an important component among the other basic segments in the wind turbine framework since they transform dynamic energy of wind into useable power and due to environmental conditions, it get damage often and cause lack in productivity. The main objective of this study is to carry out a fault identification model for wind turbine blade using a machine learning approach through vibration data to classify the blade condition. Here five faults namely, blade bend, hub-blade loose connection, blade cracks, blade erosion and pitch angle twist have been considered. Machine learning approach has three steps namely feature extraction, feature selection and feature classification. Feature extraction was carried out by statistical analysis followed by feature selection using J48 decision tree algorithm. Feature classification was done using twelve rule based classifiers using WEKA. The results were compared with respect to the classification accuracy and the computational time of the classifier.”

Antiretroviral Therapy Interruption and Clinical Outcomes in HIV-infected Adults

Acoustic Emission (AE) method for material state monitoring during fatigue tests was attested for turbine blade durability estimation for different types of superalloys. Average value of summarized AE signals, N̄ae, registered during the beginning of tests and summarized AE-signals, (Nae)01, in the second semi-cycle of blade bending both have good correlation with durability that blades reached at the moment of fracture. The discovered relations between summarized AE signals and durability demonstrated the high value of the correlation factor. For the moment of crack origination, the number of cycles, (Nf)α, can be simulated also by the AE signals, (Nae)t, registered during time interval in several minutes. In all discussed cases, relations between parameters of AE signals and critical values of the cycle’s number for estimating durability introduced with discovered factors.

Theoretical study on the axial excitation force transmission characteristics of marine propellers

There are many researches on exciting forces of propellers. However, most of them have not studied their transmission characteristics (the influence of elastic blades, flexible shafts and bearings on forces during their transmission to the hull). Therefore, in this study, the transmission characteristics of axial exciting force of propellers are studied based on a FSI dynamic model of the fluid-propeller-shaft-bearing system which is established by coupled BEM and FEM. The research results show that elastic blades and the flexible shaft have an important effect on axial exciting force during its transmission to the hull. First, there are two kinds of vibration modes for blade bending vibration, one is jellyfish mode and the other is non-jellyfish mode. The axial exciting force has resonance peak only in the jellyfish mode. Second, the elastic coupling effect between the propeller and the shaft has large effect on the jellyfish mode and has small influence on the non-jellyfish mode. Finally, all these results are validated with analytical solution by simplifying the propeller-shaft-bearing system into a series of mass-spring models. This study can provide theoretical guidance for the optimal design of propeller-shaft-bearing system and minimize the excitation force transmitted to the hull.

Forecasting spare parts demand using condition monitoring information

Purpose The control of an inventory where spare parts demand is infrequent has always been difficult to manage because of the randomness of the demand, as well as the existence of a large proportion of zero values in the demand pattern. The purpose of this paper is to propose a just-in-time (JIT) spare parts availability approach by integrating condition monitoring (CM) with spare parts management by means of proportional hazards models (PHM) to eliminate some of the shortcomings of the spare parts demand forecasting methods. Design/methodology/approach In order to obtain the event data (lifetime) and CM data (first natural frequency) required to build the PHM for the spares demand forecasting, a series of fatigue tests were conducted on a group of turbomachinery blades that were systematically fatigued on an electrodynamic shaker in the laboratory, through base excitation. The process of data generation in the numerical as well as experimental approaches comprised introducing an initial crack in each of the blades and subjecting the blades to base excitation on the shaker and then propagating the crack. The blade fatigue life was estimated from monitoring the first natural frequency of each blade while the crack was propagating. The numerical investigation was performed using the MSC.MARC/2016 software package. Findings After building the PHM using the data obtained during the fatigue tests, a blending of the PHM with economic considerations allowed determining the optimal risk level, which minimizes the cost. The optimal risk point was then used to estimate the JIT spare parts demand and define a component replacement policy. The outcome from the PHM and economical approach allowed proposing development of an integrated forecasting methodology based not only on failure information, but also on condition information. Research limitations/implications The research is simplified by not considering all the elements usually forming part of the spare parts management study, such as lead time, stock holding, etc. This is done to focus the attention on component replacement, so that a just-in-time spare parts availability approach can be implemented. Another feature of the work relates to the decision making using PHM. The approach adopted here does not consider the use of the transition probability matrix as addressed by Jardine and Makis (2013). Instead, a simulation method is used to determine the optimal risk point which minimizes the cost. Originality/value This paper presents a way to address some existing shortcomings of traditional spare parts demand forecasting methods, by introducing the PHM as a tool to forecast spare parts demand, not considering the previous demand as is the case for most of the traditional spare parts forecasting methods, but the condition of the parts in operation. In this paper, the blade bending first mode natural frequency is used as the covariate in the PHM in a laboratory experiment. The choice of natural frequency as covariate is justified by its relationship with structural stiffness (and hence damage), as well as being a global parameter that could be measured anywhere on the blade without affecting the results.