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In this study, performance verification tests were conducted on a small turbojet engine, during which a failure occurred at the root of the centrifugal compressor blades, which are made of aluminum alloy. A detailed disassembly and inspection was carried out to reveal the reason of the failure. It was found that the failure of one blade at the root led to jamming of other blades. Then the jammed blades experience sever rubbing and contact with the intake duct. Experimental measurements of material properties and a retrospective examination of the manufacturing process revealed that the yield strength of the material was lower than the design value, and the fillet radius at the blade root was smaller than specifications. The root cause of the fatigue failure of the compressor blades in this incident was attributed to substandard machining quality and material properties, which leads to crack initiation and fatigue propagation until failure occurred. The experience of identifying the root cause would provide engineering guidance for other small turbojet engines. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating (FBG) sensor has a lot of advantages over the resistance strain gauge and has been used in many applications. However, there are few applications of rotor blade dynamic measurement in helicopter flight. In this paper, a method for blade dynamic strain measurement using an FBG sensor in a helicopter's real flight is presented. The corresponding measurement system is established and can eliminate the effects of the helicopter's electromagnetic environment on the electrical sensing components in the measurement system with the orthogonal frequency-division multiplexing modulation. The measured dynamic strains on the rotor blades of the helicopter in real flight contain six harmonic frequencies with the vibration characteristics of rotor blades, indicating that the established FBG measurement method and system have practical engineering applications. [ABSTRACT FROM AUTHOR]

The problem of the stress–strain state of the lock joint of rotor blades for the intermediate pressure cylinder of a steam turbine is solved by the finite-element method for supercritical steam parameters (over 240 atm and 565 °C). The proposed method involves the stage-by-stage determination of the stress–strain state of lock joint, the 3D problem statement, given contact interaction of elements, temperature loads, and plastic and creep deformations of the elements. The stress–strain state influenced by the plastic deformation of the elements in the joint is described using the plastic flow theory. The results of studying the effect of creep on the stress–strain state of the lock joint are presented. The largest increase in creep strains is observed during the first 50,000 hours. The variations in the nature and level of contact stress on the bearing surfaces of the joint elements due to the redistribution of the stresses and strains in the structure as a whole are shown. [ABSTRACT FROM AUTHOR]

This work is the preliminary part of a research program which is aimed at finding some new methods and design solutions for helicopter main rotor multidisciplinary optimization. The task was to develop a parametric geometric model of a single-blade main rotor applicable for varied methods of numerical aerodynamic modeling. The general analytical assumptions for the parametric main rotor design were described. The description of the main rotor blade parametric design method based on Open GRIP graphical programming was presented. Then, the parametric model of a blade was used for aerodynamic models independently developed for panel method and advanced CFD solver. The results obtained from the CFD simulations and panel analysis for main rotor aerodynamics were compared and assessed using analytical calculations. The calculations and simulations for a single-blade and completed rotor were performed for different helicopter weights and rotor pitch angles. The results of different computer aerodynamic analysis environments were compared for the possibility of their application in an optimization loop. This is preliminary work that describes only a partial problem that could be used in the future as part of a comprehensive methodology for aerodynamic and structural optimization of a helicopter rotor. As an output of the research, new options for main rotor optimization are developed. The combined parametric modeling with aerodynamic analysis, as described in this paper, provide the preliminary design for a main rotor spiral, as an element of the optimization loop. [ABSTRACT FROM AUTHOR]

The effect of the creep of materials of a structure on the nature of the contact interaction between its elements during long-term operation is investigated. The problem of the stress-strain state of the rotor blade interlock for the medium-pressure cylinder of a steam turbine for ultrasupercritical steam parameters (over 240 at and 565°C) is solved using a finite element software package. As a model of creep, a modified model of creep with hardening is considered. The methodology for solving the thermal contact problem of interaction between the interlock elements under creep conditions is based on the application of a contact layer model. The calculation is made for the case of the total loads of the centrifugal forces of blades and the temperature field in which the structural element is operated. The results on the distribution of total strains, equivalent stresse,s and contact stresses during long-term operation are analyzed. The points of time, upon reaching which the permissible strength characteristics of the materials used were exceeded, were determined. A change in the nature and level of contact stresses on the bearing surfaces of interlock elements due to the redistribution of the stress-strain state of the structure as a whole is shown. The moments of the appearance of detachment and absence of contact stresses on individual contact surfaces were determined. The results obtained are compared with the data from the operation, during which the structure was damaged. [ABSTRACT FROM AUTHOR]

In this project work, experiments are carried out in low-speed subsonic wind tunnel and 30-port multitube manometer used to study the aerodynamics characteristic of cambered airfoil model NACA5520 with different velocity range and various angle of attack. Experiments were made to investigate the pressure distribution over the airfoil under velocity range from 5m/s, 10m/s, 15 m/s, and 20 m/s and various x/s locations as 0.25, 0.5, and 0.75. The pressure measurements were taken using a multi-tube manometer and pitot-static tube over the cambered airfoil at different angles of attack. Hence, the distribution of the pressure coefficient (Cp) is calculated for the different operating conditions on the tapered blade. Also, the effect of pressure distribution over the tapered blade at different velocities and AOA is studied in spanwise location of the blade. [ABSTRACT FROM AUTHOR]

Poor understanding of the fluid–structure interaction of a wind turbine blade is a well-known bottleneck in the development of the wind power industry. The degree to which different blade vibration modes influence the fluid fluctuation intensity and the manner of its variation with working conditions remain unknown, which restricts the understanding of fluid–structure interaction and the development of corresponding decoupling methods. To this end, an experiment for synchronously monitoring blade vibration parameters, near-wake flow parameters, and generator output parameters was conducted in the present study. To prevent impacting the characteristics of blade structure and wake flow, an indirect test for identifying the dynamic frequencies was developed. To validate this method, a small wind turbine was utilized to experimentally investigate the influence of different blade vibration modes on the fluid fluctuation in the tip vortex region. The results revealed that the blade vibrations have significant influences on the wake flow fluctuation. They also indicated the differences in the intensities of four types of low-frequency vibrations under static and dynamic conditions. Eventually, the relationship between the intensities of blade vibration modes and those of fluid fluctuation with varying blade rotation speeds was also analyzed. [ABSTRACT FROM AUTHOR]

A multidisciplinary rotor blade design approach, which is suitable for conceptual design, sizing and evaluation of helicopters is presented. Blade outer surface and structural geometry is represented by a geometrical model in which chord, thickness ratio, camber ratio and twist distributions along the blade radial stations can be defined as linear or nonlinear functions. Distribution of the number of laminas for both skin and spar were also defined in the presented model parametrically. Low level fidelity analysis methods were chosen to reduce the computing time. Performance analysis and sizing of the vehicle are performed by an in-house developed code named as ROTAP based on BEMT. Airfoil aerodynamic characteristics are calculated by Xfoil, a well-known panel method software. Structural analyses are performed by 1D finite element method approach. Cross-sectional properties of the composite beam are calculated by VABS software and displacements under the loads are calculated by the GEBT. All these programs are modified and embedded into the developed code and a single program with user friendly interface emerged. Developed algorithm and tool can be used for performance and structural strength calculations during the rotor design optimization studies at the conceptual design stage. [ABSTRACT FROM AUTHOR]

In this paper, a synchronous vibration control method was proposed to avoid the high-cycle fatigue fracture of aeroengine rotor blade. Firstly. The harmonic force, causing synchronous vibration, was derived by Fourier series expansion by the mean of simplifying the aerodynamic exciting forces into the periodic rectangular pulse wave forces. It was found that the synchronous vibration can be controlled by adjusting the primary excitation forces parameters. Based on this, the additional secondary excitation forces were introduced to control the synchronous vibration caused by primary excitation forces. Secondly, the influences of the number, position, direction, duration of additional secondary excitation forces and the phase difference between additional secondary excitation forces and primary excitation forces on the synchronous vibration control were obtained through theoretical analysis, which was simulated and verified by a single-degree-of-freedom model. Thirdly, a high-speed straight blade test bench was established, and the feasibility of the method in controlling synchronous vibration of rotor blade was proved by adding additional magnet excitation forces on the basis of fixed magnet excitation forces. Finally, the suppression strategy of synchronous vibration of rotor blade by introducing additional secondary excitation forces was given. It can provide theoretical and technical support for effectively controlling the synchronous vibration amplitude and avoiding the high-cycle fatigue fracture of rotor blade in engineering practice. [ABSTRACT FROM AUTHOR]

The main objective of the work is to study the fracture behavior of AA6061-graphite material using both experimental technique and finite element simulation by considering helicopter rotor blade as a case study. From the case study, it has been observed that the helicopter rotor blade, made of AA6061, has been failed at the threaded portion of the hole. Experimental fracture toughness is carried out using the compact tension specimens as per ASTM standard testing procedure. Modeling of compact tension specimens and the threaded portion of the bolt hole was utilized to analyze the fracture toughness using a simulation tool. From the results and the comparison, it is recommended to use AA6061-9wt% graphite material as a replacement of AA6061 in the application of main rotor blades of the helicopter. [ABSTRACT FROM AUTHOR]

• At various wake ages, tip vortices swirl velocity and circulation profile reveal self-similar structures. • Outside of the vortex core, the flow is turbulent whereas the flow regime inside the vortex core is laminar. • At early wake ages, the tip vortices are not fully formed, and as wake ages rise, they continue to develop. • The size of the vortex grows as the wake age rises and the tip vortex wandering becomes aperiodic. A better understanding of downwash flow is required to increase the efficiency of unmanned aerial vehicle sprayers. The tip vortex rolled up by the rotor blade tip rotating at high speed produces a complex induced velocity field, which has an important impact on the downwash flow in the wake of the rotor. Usually, a symmetrical experimental setup with a central rotor support perpendicular to the rotation plane is used in studies on rotating blade wake and vortices, potentially leading to differences in observed wake and vortices in real situations. whereas in reality, the rotor is typically supported by a parallel arm extending below the rotor in the rotation plane. It is crucial to consider these differences for accurate results in analyzing blade rotation. The behavior of the tip vortices, dynamic characteristics, and velocity field of the rotor wake in agricultural drone single-rotor downwash flow was experimentally investigated using particle image velocimetry (PIV) combined with high-speed camera imaging. The dynamics of blade tip vortices at different wake ages and rotational speeds of the rotor, 1000–3000 rpm, were measured and analyzed. The results indicate that in the early stages of a vortex's life, tip vortices generated by rotors do not have an axisymmetric structure, and the swirl velocity in the core decreases logarithmically as the wake age increases. Vortex models were validated by examining the swirl velocity structure of the tip of the vortex. Vortices within the vortex core exhibit a comparable self-similar velocity profile to the Iverson model's laminar profile, despite the transition flow outside the vortex core. With these measurements, the behavior of vortices in the rotor's wake could be described with generalized semi-empirical models. [ABSTRACT FROM AUTHOR]

The most important step in the design of wind turbine and blades is integrated load analysis, which is usually designed to describe a three-dimensional structure using a one-dimensional beam element; represents a three-dimensional blade with aerodynamic and structural information. In this regard, one-dimensional elements are required to accurately represent all the structural properties of a three-dimensional component. Most of the previous methods regarded the blade as a linear structure, resulting in limitations associated with nonlinearities. The geometry of the blades has a significant change along the length, and the composition of the materials used inside the blades is very complex, so these methods are not suitable for extracting the characteristics of the blades. In this paper, a new design scheme of a one-dimensional beam modeling method is proposed based on the blade sectional element concept that is easier and faster to apply without performing nonlinear analysis. In addition, the validation of the accuracy of its numerical analysis results, the total mass and modal analysis results are compared between three-dimensional blade and one-dimensional blade. [ABSTRACT FROM AUTHOR]

This paper develops an improved dynamic reliability model for compressor rotor system, defined as a “unconventional active system” here. First, regarding to the variety of system-component connections, system specific reliability modeling technique is presented, in which the stress and strength are both nonnegative stochastic processes. The new model fully considers the load characteristics of rotor blades, and inherently embodied the effect of the statistical dependence between the failures of the rotor blades. Then, calculated by the new model, the relationship between reliability and time, and that between the hazard rate and time, for a compressor rotor system are discussed, respectively. Comparing to the traditional series system reliability model, the new system reliability model developed in this paper has higher accuracy for compressor rotor system, since the traditional models neglect the difference between compressor rotor system and traditional active system. Moreover, in order to master the cruise characteristics of the aero-plane during reliability analysis of its compressor rotor blade set, a flight cruise is separated into several stages based on the value of Mach number and its change rate, and a subsection solution method is innovatively proposed accordingly. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the accuracy of the new method. The results show that, as to a flight cruise with different stages, the new method is basically reasonable to most of the load histories, especially for the situation with impact loads existing. [ABSTRACT FROM AUTHOR]

In helicopter satellite communication systems, the received signal is blocked by the helicopter rotor blades during propagation, incurring the unstableness of traditional methods of channel estimation due to unknown channel state. To this end, a joint occlusion detection and phase estimation algorithm is proposed by factor graph in this paper. For occlusion detection to acquire channel state, the occlusion channel model is established relying on a Markov chain with a priori blocking ratio, in which the probability distribution of the channel state is calculated by the proposed message-passing algorithm. To obtain the occlusion position and update the blocking ratio, a cross-correlation method is designed. Furthermore, a joint block detection and phase estimation algorithm is developed based on the proposed occlusion detection algorithm to realize phase estimation by iterative receiver, where occlusion detection, phase estimation, and decoding are performed in turn for one turbo iteration and the result of decoding is then sent back to the occlusion detection step for the next iteration. Simulation results show that the proposed algorithm is adaptive to the dynamical change in the blocking ratio and can achieve bit error rate performance that is close to the performance bounds based on perfect channel state. [ABSTRACT FROM AUTHOR]

An induced gas flotation (IGF) machine is a type of water treatment equipment that separates oil droplets or particles from waste-water using the characteristics of floating air bubbles. In general, bubble movement inside an IGF is difficult to predict since the internal flow in an IGF is not linear due to vortex formation and recirculating flow. Furthermore, the actual bubbles are distributed in various sizes and it is very difficult to accurately simulate them. Therefore, the MUltiple-SIze-Group (MUSIG) method is used to correct this in the numerical analysis. The MUSIG method is to divide the bubbles into groups by size. It can predict relatively accurate bubble movements, coalescence and break-up. In this study, numerical analysis with the MUSIG model was conducted on various types of rotor blade configurations to determine water treatment. The results of void fraction, power consumption, air residence time, air mean bubble diameter, and drag coefficient were predicted and compared between the various configuration of rotor blade. Comparison of the results showed that the backward IGF rotor exhibited an increased void fraction by about 2.6 % and a decreased power number by about 37.6 % compared to the values seen using the reference model. [ABSTRACT FROM AUTHOR]

Recent efforts concerning the automation of production processes for wind turbine rotor blades involve several new challenges. The technical fabrics used present specific features in handling due to their limp characteristics. Because of the steady growth of modern offshore wind turbine dimensions, larger rotor blade mold surfaces have to be covered with technical fabrics which influence the size and the weight of the handling systems used for automation. For an economic production of future wind turbine types, an increase in efficiency – by shortening the process cycle times – is crucial. Consequently, the time‐consuming process steps need to be automated. The article focuses on the continuous direct textile layup process and delivers ideas and solutions for the resulting challenges of process steps like storing, cutting and draping a technical textile in an automated rotor blade production. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to determine dependencies between a rotor-blade shape and a rotor performance as well as to search for optimal shapes of blades dedicated for helicopter main and tail rotors. Design/methodology/approach: The research is conducted based on computational methodology, using the parametric-design approach. The developed parametric model takes into account several typical blade-shape parameters. The rotor aerodynamic characteristics are evaluated using the unsteady Reynolds-averaged Navier–Stokes solver. Flow effects caused by rotating blades are modelled based on both simplified approach and truly 3D simulations. Findings: The computational studies have shown that the helicopter-rotor performance may be significantly improved even through relatively simple aerodynamic redesigning of its blades. The research results confirm high potential of the developed methodology of rotor-blade optimisation. Developed families of helicopter-rotor-blade airfoils are competitive compared to the best airfoils cited in literature. The finally designed rotors, compared to the baselines, for the same driving power, are characterised by 5 and 32% higher thrust, in case of main and tail rotor, respectively. Practical implications: The developed and implemented methodology of parametric design and optimisation of helicopter-rotor blades may be used in future studies on performance improvement of rotorcraft rotors. Some of presented results concern the redesigning of main and tail rotors of existing helicopters. These results may be used directly in modernisation processes of these helicopters. Originality/value: The presented study is original in relation to the developed methodology of optimisation of helicopter-rotor blades, families of modern helicopter airfoils and innovative solutions in rotor-blade-design area. [ABSTRACT FROM AUTHOR]

Highlights • The shaft Instantaneous Angular Position (IAP) is calculated using a State Space Model. • More accurate answers are obtained using the IAP for transient conditions. • Tip deflection accuracy is dependant on blade circumferential location. • A new validation approach for BTT tip deflections is presented. Abstract Rotor blade condition monitoring is considered an important aspect of turbomachine management, especially with the current trend of systems operating at higher speeds, loads and temperatures. Blade Tip Timing is a non-intrusive method of performing rotor blade condition monitoring during turbomachine operation. The technique uses sensors embedded into the turbomachine casing in conjunction with a shaft encoder. A BTT system calculates the difference between the true and expected Angle of Arrival (AoA) of each blade at each sensor. This difference can be used in many ways to perform diagnostics. When calculating the AoA, the shaft speed within each revolution is often assumed as constant. This assumption is incorrect for transient conditions such as a run-up. The incorrect assumption leads to errors in the calculated AoAs. This article proposes a more accurate method for calculating the AoA. A state space equation for the shaft Instantaneous Angular Speed and Instantaneous Angular Position is derived and solved using a Kalman filter. The proposed method is validated using laboratory and field tests. [ABSTRACT FROM AUTHOR]

Abstract Very low head (VLH) axial hydraulic turbines classified as micro-hydropower plants are capable of harvesting energy from sites with elevations below 4.5 m. The VLH turbine output power can be controlled by varying the rotational speed and the runner blade opening angles. In this paper, a design method for the VLH runner blade is developed. The numerical simulation of the designed system is presented and validated against the experimental data of an industrial prototype. The procedure is started by determining the velocity components and angles at the inlet and outlet of 2D radial sections, followed by choosing a hydrofoil for each radial section and calculating the hydrodynamic coefficients. The stagger angle and the chord-length of the section are computed using a MATLAB code coupled with XFoil. The multi-section product of 3D spherical radial sections in ANSYS TurboGrid 15.0 meshing tool forms the runner blade and the guide vane. Importing the generated structured grid into ANSYS CFX 15.0 solver, the RANS equations are solved using the SST turbulence model to capture the turbulent structures. The simplified Rayleigh-Plesset equation for bubble growth rate in the homogenous two-phase model is applied to study the cavitation phenomenon for different states of runner opening angles and rotational speeds. The maximum hydraulic efficiencies for most of the runner positions (at constant angular velocity of 40 rpm) are more than 80%. We demonstrate the effects of runner blade opening angle and the turbine rotational speed on the hydraulic efficiency curves and turbine efficiency hill chart. The cavitation simulation demonstrates leading edge and tip gap cavitation in some off-design points at different blade opening angles. Highlights • A very low head (VLH) axial hydraulic turbine is numerically studied. • The VLH power is a function of rotational speed and runner blade opening angle. • A dimensionless analysis (hill chart) of hydraulic efficiency is given with respect to the head and flow rate. • Cavitation locations are predicted using the simplified Rayleigh-Plesset equation. [ABSTRACT FROM AUTHOR]

Unmanned rotorcraft represents a new paradigm in agricultural activities. Rotor-blade design to improve lift performance was necessitated because payload-mounted flights suffer from a lack of lift. A prototype of rotor blade, comprising the V2008B airfoil, was assessed on an agricultural rotorcraft. The lift corresponding to the collective pitch angle (CPA) and rotor speed was measured on field and compared with a base-line blade. Measurements demonstrated that the prototype blade could sustain a maximum payload of 589 N, resulting in a total lift of 1256 N. Thus, an increase of 10.5 % in total lift was accomplished, compared with a base-line of 1137 N. Simulation also indicated that total lift equals 1269 N at CPA = 10°, approximately 1.0 % greater than the experimental lift. However, a practical spray payload would be reduced due to the ground effect and uncertainty, existing during an anchored field experiment. The ground effect from the experimental operation close to the ground would reduce 10 % of the total lift, resulting in 1138 N for hovering. Furthermore, uncertainty existed in stick control inputs and local wind conditions, resulting in fluctuations of rotor speed and payload. The standard deviation of net lift was ±45.33 N; therefore, the minimum net lift of the low envelope assessed from the uncertainty analysis would be 426 N. [ABSTRACT FROM AUTHOR]

This study presents a damage identification method that combines wavelet packet transforms (WPTs) with neural network ensembles (NNEs). The WPT is used to extract damage features, which are taken as the input vectors in the NNEs used for damage identification. An experiment was performed on a helicopter rotor blades structure to verify the proposed method. First, the vibration responses collected by different sensors are decomposed using the WPT. Second, the relative band energy of each decomposed frequency band is calculated and fused as the damage feature vectors. Third, two types of the NNEs are designed. One is based on the backward propagation neural networks (BPNNs) for detecting the damage locations and severities and the other one is based on the probabilistic neural network (PNN) to detect the damage types. Finally, the trained NNEs are employed in damage identification. From the identification outcomes, it is concluded that damage information can be extracted effectively by the WPT and the identification accuracy of the NNEs is better than that of individual neural networks (INNs). [ABSTRACT FROM AUTHOR]

A novel method is proposed to correct errors caused by rotational speed fluctuations in the BTT system. The analysis shows that the traditional BTT measurement using the constant speed assumption has low-frequency error due to the integration effect when the rotational speed fluctuation exists. Therefore, a filtering method based on the periodic non-uniform sampling (PNS) theorem is proposed. The details of the PNS-based method were investigated. The results show recommended order of the digital FIR filter is a length of 4 to 6 revolutions. The process of the PNS-based method for the unsteady state is given. Monitoring the condition number of the delayed phase matrix A is recommended when using the PNS-based method in the unsteady state. The effectiveness of the method was verified by a laboratory experiment and a field test. The laboratory experiment results showed that the error was reduced by 30 to 70 μ m in the steady state. When the blade vibration was weak, the error was even halved. In the unsteady state, the PNS-based method controlled the error below 200 μ m. In the field test, the PNS-based method also achieved the desired effect. The proposed method can significantly improve BTT measurement accuracy, showing great value and the prospect of blade health monitors in turbomachines. [ABSTRACT FROM AUTHOR]

Failure of high-pressure compressor rotor blade in an aero gas turbine engine is analyzed to determine its root cause. Forensic and metallurgical investigations are carried out on the blade and failed parts. The failure of the platform ladder is found to the first in the chain of events that led to the compressor blade failure. The mode of failure in the blade is found to be fatigue and has originated from the damaged region on the leading edge caused by dislodgement of platform ladder. The failure has caused extensive damages in high-pressure compressor module and also in downstream turbine blades as a secondary effect. [ABSTRACT FROM AUTHOR]

Experimental investigations of non-equilibrium spontaneous condensation in transonic steam flows in a linear blade cascade were carried out. The cascade consists of the rotor blades of the low-pressure (LP) steam turbine last stage. The experimental testing facility is a part of a small-scale steam power plant located at the Silesian University of Technology in Gliwice. The steam parameters at the testing facility inlet correspond to the wet steam conditions in a low-pressure steam turbine. Static pressure measurements on the blade surface as well as Schlieren images were used to assess the flow field in the steam turbine rotor tip blade linear cascade for different flow conditions. The experimental results were used to validate an in-house CFD code. [ABSTRACT FROM AUTHOR]

There is growing interest in unmanned aerial pesticide application, which is a new farming paradigm aimed at reducing labor and improving production stability. To alleviate the difficulties being experienced by operators and pilots, researchers are focusing on the lack of lift and are trying to enhance lift by improving rotor airfoil. In this study, with the objective of enhancing the rotor performance of agricultural unmanned helicopters, the performance of basic airfoils was evaluated in a wind tunnel and via computational fluid dynamics simulation. The lift and power characteristics of rotor blades were also evaluated. As airfoil design steps to improve the lift of unmanned helicopter, the characteristics of lift, drag, and power were analyzed via wind tunnel tests for the 400 mm section models of two airfoils, specifically a thick airfoil (V1505A) with blunt nose and a thin airfoil (V2008B) with drooping nose. The V1505A airfoil is appropriate for the inboard region, which requires stable aerodynamics at a high angle of attack. On the other hand, the V2008B airfoil is ideal for the outboard region of the rotor because it has a relatively high dynamic efficiency. Therefore, it is expected that a transitional airfoil blade with a negative twist angle can solve the problems of unmanned aerial pesticide application. [ABSTRACT FROM AUTHOR]

Modal analysis is a crucial parameter in the design process of turbomolecular pumps, as rotor resonance will seriously affect the stability and reliability of the pump. Suitable modeling is important since it will decide the quick and accurate calculation of the rotor modes. This work focuses on the modeling method and the analysis of the rotor blade modes of the turbomolecular pump. A simplified method of the blade modified model is presented, based on the basic invariance principle of the mass and the moment of inertia before and after simplification. The calculated results of the modes are compared with the original model of the rotor blade. Finally, in order to verify the accuracy of theoretical analysis, the pump is fabricated and the modal testing of the rotor blade is carried out. The results show that the first two natural frequencies of the modified rotor model are in good agreement with the experimental results. The errors of the first two natural frequencies of the rotor blade are 1.58% and 0.014%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a theory related to a two-dimensional linear cross-sectional analysis, recovery relationship, and a one-dimensional nonlinear beam analysis for composite wing slender structure with initial twist. Using VABS including a related theory, the design process of the composite rotor blade has been described. Cross-sectional analysis was performed at cutting point including all the details of geometry and material. Stiffness matrix and mass matrix were linked to each section to make 1D beam model. The 3D strain distributions within the structure were recovered based on the global behavior and load of the 1D beam analysis and visualize numerical results. Comparison between the analytical and experimental results shows that the proposed analytical procedure can provide an accurate and efficient prediction of the both deflection, flexural stiffness, strain of multilayer composite slender structure. Verified comparison results can be used to efficiently design accurate complex slender structure properties for detail design and manufacture. These sentences will appear after the conclusion when an article is finally published. [ABSTRACT FROM AUTHOR]

The importance of using Agriculture unmanned helicopters (AUHs), especially for spraying pesticides and fertilizers on any terrain type to ensure crop yields, has been recently acknowledged. Apart from flying these helicopters at a super-low altitude and low speed, using an efficient and optimum rotor blade ensures a uniform and deep penetration of pesticide and fertilizers over a specified area. Accordingly, this work attempts to optimize the rotor blade of an AUH by using coupling statistics and several numerical techniques, including design of experiments, response surface method, and computational fluid dynamics. The experiments are designed using the central composite design method and by selecting the geometric variables that affect the aerodynamic performance of the rotor blade, including the root chord, tip chord, and angle of attack. The angle at the root and tip is optimized in order for the resulting twist to produce a uniform blade loading, achieve maximum lift, and minimize the required hover power. The required aerodynamic forces and limited availability of engine power are identified as constraints. The blade is optimized only when the helicopter is hovering at a persistent rotational speed, and the hover efficiency of the rotor blade with an optimal twist distribution is significantly higher than the baseline. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to monitoring rotor blade flap, lead-lag and pitch using an embedded gyroscope and symmetrically mounted MEMS accelerometers. The central hypothesis is that differential accelerometer measurements are proportional only to blade motion; fuselage acceleration and blade bending are inherently compensated for. The inverse kinematic relationships (from blade position to acceleration and angular rate) are derived and simulated to validate this hypothesis. An algorithm to solve the forward kinematic relationships (from sensor measurement to blade position) is developed using these simulation results. This algorithm is experimentally validated using a prototype device. The experimental results justify continued development of this kinematic estimation approach. [ABSTRACT FROM AUTHOR]

When the helicopter performs maneuvering flight tasks in harsh environments, the speed of turboshaft engine compressor needs to be adjusted constantly, which leads to the deviation between the wear characteristics of blades and that under constant speed conditions, thus affecting the accurate assessment of erosion wear of the compressor blade caused by sand particles. The four typical rotational speed conditions which are most concerned in engineering applications are selected in this paper. The erosion wear characteristics of the compressor blade under full speed conditions are revealed. The results show that the erosion wear distribution area of compressor blades shows a transfer phenomenon under different speed conditions. At the same time, the erosion wear degree of rotor blades under the design speed is obviously higher than that at other speeds, while the blade wear degree decreases to a certain extent under the emergency state speed. [Display omitted] • Erosion wear of aero-blade is studied by combining experiment and simulation. • The particle volume fraction is used to analyses the wear causes of blade. • Erosion wear area shows a transfer phenomenon under different speed condition. • Erosion wear degree of blade is the most serious at the design speed condition. • Wear degree of R2 blades is 37% and 161% higher than that of R1 and R3 ones. [ABSTRACT FROM AUTHOR]

• Two types of failures of steam turbine blades (premature and after long-term operation) are analysed. • Mechanical and fractographic indicators are used to evaluate the current state of operated steel. • An approach to assessing the degree of operational degradation of high-chromium steel is proposed. • The critical state of the steel operated in steam turbine blades is substantiated. The article focuses on the causes of failures of steam turbine rotor blades made of high-alloyed heat-resistant steel 15Kh11MF. Premature failure of blades is caused by technological defects (intensive corrosion-erosion wear of the blade edges, uneven structure and distribution of micro damages) that occurred because of imperfections of welding and/or surface hardening. Cracks initiated from these defects change the natural oscillation frequency of the blades, leading to their resonance and thus overload. The corrosive steam-water mixture in the phase transition zone contributes to the fracture process. Long-term operation of steel in steam turbines leads to the precipitation of carbides along the grain boundaries that weaken the cohesion between adjacent grains with subsequent pore formation and their merging into defects comparable to grain size. Fatigue crack growth resistance of steel reduces as a result of its operation. The effective threshold values of the SIF range decrease more significantly than the nominal ones due to the crack closure effect. It results from the increased roughness of the fracture surface caused by intergranular fragments protruding above the flat fatigue relief. They have been formed during steel's operation along the damaged grain boundaries, and their number progressively increased with the operation time. To assess the current state of operated steel, the structural (the part of intergranular fragments S in the unit area of the fracture surface) and mechanical (a relative loss in fatigue crack growth resistance due to operation) indicators are proposed. The basic relationship between them makes it possible to substantiate the conditions for the safe operation of 15Kh11MF steel in STR blades. [ABSTRACT FROM AUTHOR]

Detailed investigation was performed on the effect of the rotating stall and surge on the fatigue failure mechanisms of the axial compressor first stage rotor blades. The static stress distribution of the blades was analysed using three dimensional (3D) finite element method (FEM). The critical fracture stress was calculated using the linear elastic fracture mechanics. Fractographic observation revealed different fatigue fracture modes corresponding to the different fatigue loads. Results demonstrated that during operation two kinds of fatigue loads can occur which are tension-torsion fatigue and bending fatigue. The tension-torsion fatigue stems from the periodic tension-torsion stress induced by the surge, while the bending fatigue load is caused by the rotating stall. [ABSTRACT FROM AUTHOR]

Due to the high speed and the high power density, the blade strength and the rotor overheating of a turbomolecular pump (TMP) are strongly related to the safety and the stability of the pump operation. For magnetically levitated TMPs, which can obtain an ultra-clean and ultra-high vacuum in comparison to traditional TMPs with oil-lubricated bearings, the rotor strength and overheating are limiting their ultimate pumping speed, since the rotor is only cooled by thermal radiation. This paper focuses on the stress analysis of the pump and the rotor thermal performance evaluation to prevent the permanent magnets (PMs) from irreversible demagnetization at high temperature and to ensure the rotor integrity throughout the whole speed range. The influence of the thickness of the sleeve around the PMs of the rotor shaft on electromagnetic losses and stress is analyzed. Finally, the electromagnetic and thermal tests are implemented on a prototype to verify the theoretical methods and the design concept. The measured maximum pumping speed of the prototype can reach 4180 L /s. [ABSTRACT FROM AUTHOR]

An experimental study was undertaken to understand the problem of roughness-induced boundary layer transition and the sensitivity of boundary layer to the dimensions of DRE (distributed roughness elements). The distances between the DRE and the transition locations in different Reynolds numbers are considered. Experiments were conducted in the rotor blade whirl tower at AVIC ARI. Infrared thermography was employed to detect boundary layer transition on the rotor blade. In order to investigate the impact of the parameters of roughness elements on transition position, a new method was developed to measure the boundary layer transition position quantitatively. A method based on the ratio of turbulent and laminar areas was used to estimate the downstream transition locations. Seven rotational speeds between 300 rpm and 600 rpm were tested with leading to tip speeds between Vtip=25m/s and Vtip = 40m/s respectively. The results showed that, the IRT technique can be used to measure boundary layer transition on the rotor blade of a helicopter or rotor wings. The transition detection method based on the ratio of turbulent and laminar areas is accurate and reliable. The relationship of transition length induced by different height of DRE and Reynolds number is gained preliminary, and as the height of roughness elements increase, the transition length is decreased. [ABSTRACT FROM AUTHOR]

The effects of rotation on film cooling effectiveness and heat transfer coefficient distributions on the suction and pressure surfaces of a gas turbine blade were numerically simulated using large eddy simulation method. The flow is in the low Mach number (incompressible) regime. The suction (convex) side has simple angled cylindrical film-cooling holes; the pressure (concave) side has compound angled cylindrical film-cooling holes. The blowing ratio (BR) is 0.5 on both the suction and pressure sides and the inlet Reynolds number based on the axial chord is 3 × 10 5 . The effects of turbine rotating conditions on the film cooling effectiveness and heat transfer coefficient distributions were investigated at four rotating speeds of 0 rpm, 125 rpm, 250 rpm, and 500 rpm. Air was injected through one row of film holes each on the pressure and suction surfaces. The commercial code STAR-CCM+ was used in the prediction. The results indicate that film cooling effectiveness increases with an increase in the rotating speed. Higher turbine rotating speeds show more local film cooling effectiveness spread on pressure surface. The film cooling effectiveness and Nusselt number distributions were presented along with the discussions on the influences of rotating speed. Results showed that the rotation promotes an earlier boundary layer transition and increases the transition length on the suction surface. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted of the effect of 'butterfly skin' (metallic version of the butterfly scale) with rough internal surface on vibration and aerodynamic performances of a two-dimensional, 100-mm chord, NACA-230 airfoil oscillating through simulation of flare maneuver, in a 250 x 750 mm low-speed straight through a wind tunnel. Attention was initially directed to this problem by observation of the rough surfaces of butterfly wing scale as well as other studies indicating the vibration suppression of flying butterfly and the better lift of these wings by wing appendages. Results indicated that the 'butterfly skin' increased the lift force by a factor of 1.05, and reduced both the duration of vibration by a factor of 1.13, and the frequency of an oscillating airfoil by a factor of 1.5. The modification of the vibration effects on the rotor blade model was due both to an increase in the added mass, which influences the 'the butterfly skin', and to a decrease of the internal air flow velocity by aerodynamically rough surfaces of the air cavity. The total air mass which influences the slender wing with the 'butterfly skin' was represented as the sum of air mass of three geometrical figures: a circular cylinder around the wing and two right-angled parallelepipeds within the air cavity. The "butterfly skin" can have constant clear spacing of the air cavity or tapered air cavity. The interaction mechanism of a 'butterfly skin' with a flow is also described. [ABSTRACT FROM AUTHOR]

• The calculation errors caused by unstable rotation speed are analyzed. • A new method is proposed to eliminate calculation errors of vibration displacement. • The feasibility of EC-BTT method are verified by simulation and experimental data. Rotor blades, being the key part for power and energy conversion, are essential to the safety of turbomachinery. Monitoring the running state of rotor blades is significantly important to ensure the safety of blade operation. The blade tip-timing (BTT) technology has many advantages of non-intrusive measurement being a popular monitor method. The accuracy of vibration data obtained by BTT method is critical to evaluate the running state of blade. However, the blade vibration displacement obtained by the traditional BTT (T-BTT) method and its extended methods still faces the calculation errors caused by unstable rotation speed. To improve the calculation accuracy of blade vibration displacement and minimize the calculation errors caused by unstable rotation speed, the error correction BTT (EC-BTT) method is proposed. In this method, the calculation errors caused by unstable rotation speed are analyzed, and then the calculation errors are eliminated by the derived formula to obtain more accurate vibration displacement data. The EC-BTT method is proved to be feasible and effective by simulation models and a large-scale industry axial fan. The results indicate that the EC-BTT method can eliminate the calculation errors of vibration displacement caused by sudden change and fluctuating speed. The method also can be used in T-BTT and its extended methods. [ABSTRACT FROM AUTHOR]

The results of technical diagnosis of the destruction of renewed rotor blades of a stationary gas turbine plant are described. Visual, fractographical, and metallographical inspection methods were used to determine the causes of the destruction. The causes of the operational destruction were determined. Practical recommendations for preventing similar destructions were formulated. [ABSTRACT FROM AUTHOR]

A novel passive twist morphing concept is examined for helicopter blades. The concept is demonstrated using a thin-walled rectangular composite beam created with symmetric layup to obtain bend-twist property. The twist of a rotor blade is proposed to be actuated though a movable mass at the blade tip which is able to provide a range of lagwise bending moment during rotation as a result of the centrifugal force. First a set of static bending test is performed which provides detailed characterisation of the deformation and strain distribution of the composite beam subjected to a number of bending loads. The results of the experiment fully verify numerical predictions including finite element approach (FE) and beam cross sectional analysis. A series of simulations are then conducted using the verified numerical model to demonstrate how the desired twist can be effectively achieved by manipulating the size and location of the mass. [ABSTRACT FROM AUTHOR]

Recently, agricultural drones have been widely used for precise agricultural control. In the case of drone control, improved coverage and reduced drift potential of chemical sprays are of major concern, and this is greatly influenced by the downwash flow characteristics formed by the rotor blades. In this study, the mean and turbulent flow characteristics of the downwash flow generated by a single blade of a four-sided agricultural control drone were quantitatively evaluated. The blade radius used to generate the downwash flow was 370 mm, and the measurement position was normalized using this length. In addition, the rotational speed of the blade was 3000 rpm, and the velocity components were dimensionlessly expressed using the blade tip velocity (V Btip) corresponding to this rotational speed. The velocity of downwash flow was measured using CTA-type hot-wire anemometry with an X-type probe, and data were collected at a sampling rate of 30 kHz for turbulence characteristics analysis. The mean velocity, vorticity distribution, turbulence intensity, and Reynolds stress of the fluctuation velocity were quantitatively measured. From extensive experimental works, it was revealed that a high axial velocity is formed at a specific position (r/L b = 0.4–0.8) along the blade length. The radial velocity shows an asymmetric distribution in the plane close to the blade, and the tangential velocity is higher in the central part of the downwash flow than in the region of a high axial and negative radial velocity. An asymmetric spiral rotational flow with low axial velocity and low-pressure distribution exists inside the downwash flow due to the shear flow, and the influence of the driving motor almost disappears at the axial position (Z/L b ∼ 1). The averaged mean value of the axial, radial, and tangential velocity components measured at six axial planes and normalized by blade tip velocity (V Btip) is composed of the ratio of the axial velocity component of 12.8%, the radial velocity component of 0.19%, and the tangential velocity component of 1.3%. The maximum values of the turbulence intensity of the axial, radial, and tangential velocity components were estimated as 6.8%, 3.0%, and 4.3%, respectively. [ABSTRACT FROM AUTHOR]

The axial thrust imposed on the shaft of a gas turbine depends upon its rotor blade inlet inclination to the turbine's axial direction: this inclination can change due to the distortions resulting from fouling, aging, tip rubbing, erosion, thermal-fatigue cracks, and corrosion. Relevant influential parameters for an operational gas turbine were measured. Theoretical predictions for the behavior of the same turbine were obtained from computer simulations. The results of both measurements and theoretical predictions were compared and showed qualitative correspondence. The rotor blade profile distortions result in significant increases in the axial thrust on the compressor, which adversely affects the gas turbine's thermodynamic performance, reliability, and operational life. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics (CFD) is coupled with a computational structural dynamics (CSD) to simulate the unsteady rotor flow with aeroelasticity effects. An unstructured upwind Navier-Stokes solver was developed for this simulation, with 2nd order time-accurate dual-time stepping method for temporal discretization and low Mach number preconditioning method. For turbulent flows, both the Spalart-Allmaras and Menter's SST model are available. Mesh deformation is achieved through a fast dynamic grid method called Delaunay graph map method for unsteady flow simulation. The rotor blades are modeled as Hodges & Dowell's nonlinear beams coupled flap-lag-torsion. The rotorcraft computational structural dynamics code employs the 15-dof beam finite element formulation for modeling. The structure code was validated by comparing the natural frequencies of a rotor model with UMARC. The flow and structure codes are coupled tightly with information exchange several times at every time step. A rotor blade model's unsteady flow field in the hover mode is simulated using the coupling method. Effect of blade elasticity with aerodynamic loads was compared with rigid blade. [ABSTRACT FROM AUTHOR]

Abstract: Structural damage occurs in materials subjected to repeated or fluctuating stresses that must be minimized by design to increase fatigue life, and strains distributed in a blade need to be experimentally determined for evaluating stress levels. In order to measure local strains in a rotating blade, efficient signal transmission between a sensor installed on a blade and a stationary interrogator is significantly important. In this paper a strain-independent fibre Bragg grating (FBG) sensor and a rotary optic coupler were used as means of compensating light intensity loss change arising from blade rotation. Working principles of a FBG sensor and a rotary optic coupler were detailed, and procedures for measuring local strains were also described. Eventually, strain distributions were obtained in terms of mean strain and strain amplitude. Measured strains were then directly compared with analytical ones. Experimental procedures and results offer an improved insight into a strain measurement technique for a rotating mechanical system. [Copyright &y& Elsevier]

In the present study, the effect of crossflow transition on the rotor blade performance in hover was investigated numerically. The simulations were conducted for the Pressure Sensitive Paint (PSP) rotor in hover by using a Reynolds-averaged Navier-Stokes (RANS) solver based on unstructured meshes. The k − ω SST model was used for simulating the turbulent flow fields and for calculating the turbulent eddy viscosity. For predicting the laminar-turbulent onset phenomena involving crossflow-induced transition, the γ − Re θ t − CF + transition model was adopted. For the comparison of the transition locations without considering the crossflow transition effect, simulations were also carried out using the γ − Re θ t transition model. The calculations were made for the PSP rotor at collective pitch angles from four to 12 degrees with an interval of two degrees. To investigate the effect of blade tip Mach number, two blade tip Mach numbers of 0.585 and 0.65 were tested. The predicted results such as the transition onset location and the rotor aerodynamic performance in terms of thrust coefficient, torque coefficient and figure of merit were compared with experimental data. It was found that proper consideration of the effect of crossflow transition is critical for the accurate prediction of the laminar-turbulent transition onset location on rotor blades. The figure of merit also compares better with the experimental data when the effect of laminar-turbulent transition is included. With the addition of the crossflow transition, the figure of merit is slightly decreased, particularly at low thrust levels. [ABSTRACT FROM AUTHOR]

Abstract: During a test run of an aeroengine, a low-pressure turbine rotor blade had failed. The turbine blades were made of Ni-base superalloy of CM 247 LC grade and fabricated by DS investment casting. The blades were coated with platinum aluminide. Investigation revealed that the blade had failed by fatigue. It was concluded that the coating on the blade had developed cracks due to excessive bending/vibration, which in turn propagated by fatigue leading to the failure. [Copyright &y& Elsevier]

Abstract: The design of rotating components demands a good understanding of the effect on materials under dynamic stress conditions. Depending on the operating conditions, the components have to possess appropriate stiffness and strength properties to ensure stresses are kept within acceptable limits, and geometrical stability is maintained to ensure correct functioning. The loads may also fluctuate throughout the rotational cycle, inducing fatigue in the component. In addition, any adverse effects of environmental impact have to be taken into consideration. The design is clearly complicated and utilising the most appropriate material or materials is challenging. This paper discusses the design decision-making involved for a rotationally dynamic component using the example of a helicopter rotor blade. The specification and outline design provide the context for evaluating and comparing metallic and composite constructions. [Copyright &y& Elsevier]