Single Blade Research Articles

A novel pyrolytic-graphite-on-silicon device for neutron monochromatization

In the quest of improving neutron scattering instrumentation a new style of dynamically focusing monochromator is proposed where highly oriented pyrolytic graphite (HOPG) crystals are bonded on bendable single crystal silicon blades. This development followed a study of the elastic limit of HOPG that revealed serious technical difficulties when bending thin blades of this very fragile material to achieve dynamical focusing. The critical breakage thickness was found to be less than 0.1 mm for a radius of curvature of 1.5 m. The novel PG-on-Si (POSI) concept replaces the linear arrays of individually oriented HOPG pieces employed in existing devices. It facilitates the integration of two separate HOPG and Si monochromators into a single device. Mechanical tests, X-ray and neutron diffraction studies of the POSI system confirmed the feasibility of these single and dual monochromator designs that feature high performance and augmented functionality at reduced complexity and cost.

Potential eutectic accumulation in single crystal turbine blade due to geometry effect: a numerical study

Inhomogeneous distribution of the eutectic phase in single crystal (SC) turbine blades is detrimental to its mechanical properties. In a recent publication, it was reported that an accumulation of eutectics was observed on the upper surface of solidification units (e.g. shroud of a turbine blade), whereas fewer eutectics were detected at the bottom. This kind of casting defect brings a huge challenge to the production of turbine blades since the accumulated eutectics cannot be dissolved completely by heat treatment. A sample with three pairs of platforms/shrouds was designed to study the geometry effect on eutectic accumulation. In the current study, the simulation was performed by coupling ProCAST with our previously developed multiphase volume-average solidification model. In the first step, the thermal field including radiation in the furnace and heat conductivity in the casing and mould was calculated via ProCAST. Then, the obtained temperature profiles were set as thermal boundary conditions of the casting to predict the eutectic accumulation and formation of freckles. Based on the simulation results, convective plumes arising from the thermosolutal buoyancy transport solute-enriched liquid upward, which causes the solute pile-up and the final eutectic accumulation at the top surface in each platform. Freckles accompanied with eutectic accumulation was also observed at the corner of the sample. The calculated inhomogeneous distribution of the eutectics agrees well with experimental observations. Knowledge about the geometrical effect on eutectic accumulation is extended.

Parametric Bayesian Model for Rotating Blade Frequency Tracking with Single Probe Blade Tip Timing

Parametric Bayesian Model for Rotating Blade Frequency Tracking with Single Probe Blade Tip Timing

Manufacturing of ceramic cores: From hot injection to 3D printing

With the improvement of aero-engine performance, the preparation of hollow blades of single-crystal superalloys with complex inner cavity cooling structures is becoming increasingly urgent. The ceramic core is the key intermediate part of the preparation and has attracted wide attention. To meet this challenge, new technologies that can make up for the defects of long periods and high costs of fabricating complex structural cores by traditional hot injection technology are needed. Vat photopolymerization 3D printing ceramic technology has been applied to the core field to realize the rapid preparation of complex structural cores. However, the industrial application of this technology still needs further research and improvement. Herein, ceramic cores were prepared using traditional hot injection and vat photopolymerization 3D printing techniques using fused silica, nano-ZrO2, and Al2O3 powders as starting materials. The 3D printed ceramic core has a typical layered structure with a small pore size and low porosity. Because of the layered structure, the pore area is larger than that of the hot injection ceramic core, the leaching performance has little effect (0.0277 g/min for 3D printing cores, 0.298 g/min for hot injection cores). In the X and Y directions, the sintering shrinkage is low (2.7%), but in the Z direction, the shrinkage is large (4.7%). The fracture occurs when the inner layer crack expands and connects with the interlayer crack, forming a stepped fracture in the 3D-printed cores. The bending strength of the 3D printed core at high temperature (1500 °C) is 17.3 MPa. These analyses show that the performance of vat photopolymerization 3D-printed ceramic cores can meet the casting requirements of single crystal superalloy blades, which is a potential technology for the preparation of complex structure ceramic cores. The research mode of 3D printing core technology based on the traditional hot injection process provides an effective new idea for promoting the industrial application of 3D printing core technology.

Experimental system for measuring the force load of a single blade pump

Precise evaluation and anticipation of the radial and axial force loads acting on the impeller of a spiral casing pump are essential to ensure that the pump operates efficiently and dependably. This study presents an experimental system for measuring the force load of a single blade pump and explores the fluid mechanics involved in its operation. The experimental system consists of a strain gauge and a data acquisition system, which measures the force load on the blade as the pump rotates. In addition, our investigation delves into various approaches for measuring radial force loads, which include the evaluation of reaction forces on bearings. For the case of experimental measurement of the radial and axial force in the pump bearings, it is necessary to make some design modifications on the pump body. The measurement methodology is based on the principle of a “relaxed” shaft that performs a so-called spherical motion around the rotation axis during pump operation.

Comparison between Forceps, Single Blade Forceps and Manual Extraction of Fetal Head in Elective Caesarean Section: A Randomized Control Trial-Forceps Delivery in Cesarean Section

Comparison between Forceps, Single Blade Forceps and Manual Extraction of Fetal Head in Elective Caesarean Section: A Randomized Control Trial-Forceps Delivery in Cesarean Section

Modeling of the elastoplastic deformation process of single crystal superalloys

The aim of the research is the development and verification of a micromechanically motivated model of elastoplastic deformation of two-phase single-crystal nickel-based alloys, predicting behavior under high-temperature thermomechanical actionswith taking into account the presence of γ and γ' phases. The model is relevant for computations of the stress-strain state of cooled single crystal blades of gas turbine units. The constitutive equations for each of the phases took into account the anisotropy of elastic and plastic properties, the presence of octahedral slip systems, features of the cubic system, and various hardening mechanisms, including kinematic, isotropic and latent ones. The identification of the elastic and plastic constants of the material for the γ and γ 'phases was carried out on the basis of the known stress-strain curves for each phase. The determination of the effective properties and deformation diagrams of a two-phase single-crystal alloy, taking into account the presence of γ-γ'phases, was carried out both on the basis of finite element homogenization for the representative volume element, and using the simplest rheological (structural) models of the material, considering serial and parallel connection of phases. The dependences of the elastoplastic properties of two-phase single-crystal nickel-based alloys on the volume fraction of the γ'phase are determined by computational experiments and analytical estimates. In order to determine the optimal strategy for solving the class of problems under consideration, multivariant computational experiments were carried out for various types of boundary conditions of the homogenization problem, the number of periodicity cells, forms of inclusion of the γ'phase, volume fractions of the γ' phase, types of hardening, variants of rheological models and appropriate recommendations were given. The simulation results using the proposed two-level microstructural model of the material demonstrate a good agreement with the experimental data for the single-crystal superalloy CMSX-4.

MODELING OF CREEP PROCESSES OF SINGLE-CRYSTAL ALLOYS WITH TAKING INTO ACCOUNT OF RAFTING

The research is devoted to the development and verification of a two-level micromechani-cally motivated model of viscoelastic deformation of two-phase nickel-based single-crystal al-loys, predicting behavior under high thermomechanical loading with taking into account the presence of γ and γ' phases. The model is relevant for computations of the stress-strain state of cooled single crystal blades of gas turbine units. The formulation of the constitutive equations for each of the phases considered the anisot-ropy of elastic and viscous properties, the presence of octahedral slip systems, the features of the cubic system, and the presence of viscous properties both below and above the yield stress. Model parameters for γ and γ' phases were identified based on known creep curves for each phase. The effective properties of a single-crystal alloy, considering the presence of γ and γ' phas-es, were determined both based on finite element homogenization for a representative volume and using the simplest rheological (structural) models of the material, considering the series and parallel connection of phases. Based on multivariant computational experiments and analytical estimates, the dependences of the viscoelastic properties of nickel-based single-crystal alloys on the volume fraction of the γ' phase are determined. Phenomenological creep models that take into account the change in the volume fraction and the morphology of γ' inclusions have been proposed. The simulation results using the proposed two-level microstructural model of the material demonstrate a good agreement with the experimental data for the ZhS32 single-crystal heat-resistant alloy.

Underactuated control and analysis of single blade installation using a jackup installation vessel and active tugger line force control

The assembly and installation costs account for a large share in the overall expenditures of an offshore wind farm project. Single blade installation is suitable for large scale wind turbines due to the lower crane capability requirement and lower transportation time. By introducing active tension control on the tugger lines, an automatic single blade installation approach can accomplish operations in higher sea states, reduce the waiting-on-weather time, and improve the operational efficiency. Compared to early research, a more complicated control objective is achieved in this paper, i.e., a two-tugger-line configuration is applied to stabilize the suspended blade in three degrees of freedom during crane rotation and blade root-hub mating processes. The pulleys on the crane boom, i.e., the ends of the tugger lines, are assumed to be fixedly placed, resulting in tugger line time-varying inclinations. A novel backstepping-like controller is designed and proved. It is able to stabilize the blade around its equilibrium and make it track the desired path. Sensitivity studies are conducted to evaluate the influence of the tugger line inclinations. In addition, the influence of the installed blades on a three-blade horizontal wind turbine with a monopile foundation is discussed. The proposed active control setup improves the installation success rate and reduces the risks for blade impacts that may occur during mating.

Microstructure evolution and dynamic recrystallization mechanism induced by grinding of Ni-based single crystal superalloy

Ni-based single crystal superalloy has experienced high temperature and extreme strain rate during grinding process, resulting in white layer and plastic deformation layer on the subsurface. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) techniques were used to characterize the microstructure changes such as dislocation distribution, crystal structure and orientation information at the nanoscale of the ground subsurface. The mechanism of dynamic recrystallization and grain refinement of the single crystal superalloy were obtained. The results show that the high-density dislocation structure is easy to form in the stress concentration areas, which are the nucleation sites of dynamic recrystallization. With the accumulation of misorientation, the subgrain boundaries (SGBs) are transformed into low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs). Moreover, equiaxed nanograins are formed near the top surface due to the cooperation mechanism of dislocation movement and twins. Under the condition of high strain rate, the deformation mechanism of Ni-based single crystal superalloy is continuous dynamic recrystallization (CDRX) dominated by subgrain rotation. This work illustrated the grinding-induced microstructure evolution and mechanism of dynamic recrystallization, which provides theoretical guidance for machining of single crystal blade.

Wake flow characteristics and unsteady performance of a pump-jet propulsor under hull condition

The propulsor is one of the main noise sources of an underwater vehicle. The pump-jet operating under hull condition is in a typical non-uniform strong anisotropic turbulent flow field. In this paper, the wake flow characteristics and unsteady performance of a pump-jet propulsor under hull condition are numerically investigated. Reynolds-averaged Navier–Stokes (RANS) method and large eddy simulation (LES) method are used to evaluate and compare the ability of solving vortex structure, pressure distribution and unsteady force. LES method can capture the interaction between different vortex systems, and the vortex shedding process of the stator wake and appendage wake. These lead to that the frequency spectra of fluctuation pressure have peaks in the low-frequency range for LES method. For unsteady force spectrum, the frequency of maximum amplitude of a single blade is mainly affected by relative intensities of the stator wake and appendage wake. “Humps” appear near the blade passing frequency and its multiples for unsteady force spectrum of the rotor for LES method. The blade passing frequency in the rotor force spectrum is generated by the phase cancelation between different blades. The completeness of rotor blade phase cancelation is mainly affected by the intensity of the non-stationarity in the flow field. Overall, it is sufficient to clarify the hydrodynamic performance and the characteristics of fluctuation pressure distribution of the pump-jet with RANS method. The LES method is necessary to obtain reasonable transient characteristics of the unsteady force and vortex system interaction for the pump-jet under hull condition.

Partially rotating grid method for self-propulsion calculations with a double body ship model

In this paper, partially rotating grid method for predicting self-propulsion characteristics using a double body ship model approach is presented. Partially rotating grid method combines a full-discretized temporal-domain rotating propeller approach with locally introduced non-inertial equation system to reduce overall computation time. Verification and validation of the method are performed in this paper. Numerical self-propulsion simulations are conducted for a single-screw KRISO container ship both in model and full-scale. Obtained results are analyzed in terms of integral (propulsion factors) and local (velocity field) flow characteristics with a focus on ship-propeller interaction and scale effects. To better understand propeller performance and ship-propeller interaction effects, variation of a single blade KT, KQ, and KT/KQ values during one period of rotation are analyzed. The introduced partially rotating grid method proved to accurately predict the integral and local flow characteristics while reducing overall computation time, at cost of reduced accuracy.

DETERMINATION OF THE VOLUME FRACTION OF THE MICROPOROSITY IN NICKEL-BASED SUPERALLOY SINGLE CRYSTALS

Microporosity is a dangerous defect of single crystal gas turbine blades cast from nickel-based superalloys (NBS). The volume fraction of the porosity in single crystal alloys does not exceed a few tenths of a percent, however, it can result in manyfold shortening of the lifetime of the blade material under fatigue loading. We present the results of determining the volume fraction of the porosity in single crystal NBS. Single crystals of NBS CMSX-4 obtained according to the industrial technology of manufacturing the single crystal blades of gas turbines were used as a test object. It is found that the applied methods, with the exception of optical microscopy, have an accuracy sufficient for measuring the volume fraction of the microporosity of about 0.2 %vol. The highest accuracy with a statistical error of about ±0.01 %vol. was attained using the Archimedes method using distilled water as a liquid. The method provides the determination of small (up to a few hundredths of a percent by volume) increase of the porosity during high-temperature creep. The results obtained can be used for precise determination of the porosity in NBS single crystals before and after service. Moreover, the process of high-temperature creep can be modeled using a correlation relationship between an increase in the porosity of single crystal material and the accumulated creep strain.

Comparison of Twin Screw Derotation Type Versus Single Helical Blade Type Cephalomedullary Nail in Trochanteric Fractures in Geriatric Population.

Introduction The aim of this study was to compare the usage of two devices, the twin screw derotation typeand the helical blade type, in intertrochanteric fractures in the geriatric population at a tertiary-level center. Methods Forty-six eligible patients with intertrochanteric fractures operated with the standard proximal femoral nail (PFN) or proximal femoral nail anti-rotation (PFNA2) were included for analysis. This was a retrospective analysis of prospectively collected data over the study period. Demographics, various operative parameters, outcome parameters, and complications were assessed. Medical management of osteoporosis was provided to all patients. The student t-test and chi-square test were used with SPSS V22.0 (IBM Corp., Armonk, NY) for statistical analysis. Results The mean follow-up was 14 months. The hospital stay and Harris hip score were similar in both groups, but the radiation exposure, surgical time, and blood loss were significantly less in the case of PFNA2. Screw cut-out was also not observed in our study. Conclusion Both PFNA2 and PFN are effective in treating unstable trochanteric fractures in terms of functional outcomes. However, PFNA2 is better because it requires less radiation exposure (p<0.05) due to single guidewire use, a short learning curve, less blood loss, shorter surgical time(p<0.05), and fewer complications. We suggest it to be the preferred implant in trochanteric fractures in the geriatric population and other age groups.

Vibration Control of Large Wind Turbine Blades with Unidirectional Cable Pendulum Damper

A unidirectional cable pendulum damper is proposed to mitigate vibration responses of large-scale wind turbine blades in the edgewise direction, and the effectiveness of the proposed device for vibration response control is investigated. First, the configuration and working principles of the vibration damper are introduced. Second, the Euler–Lagrange equation of the single blade vibration damping system with the vibration damper is derived based on the Hamilton’s principle. At last, considering the effect of blade rotation, the wind load that applied on the blade was calculated using the rotating sample spectrum. The dynamic responses of blades are also calculated using the MATLAB/Simulink platform. The peak value and standard deviation of blade responses were taken as evaluation indexes to evaluate the vibration control efficiency of the device with varying the parameters such as the mass ball pendulum length, the fixed pulley block installation position, the stiffness and the pre-stress of the flexible cable. The optimal parameters of the vibration damper are investigated and obtained based on the assumption that no pounding happens between the mass ball of the vibration damper and the inner wall of the blade. Results show that the length of the mass ball pendulum and the installation position of the fixed pulley block, the values of which are within a reasonable range, can ensure the optimal performance of the vibration damper. The displacement of the mass sphere can be effectively reduced by increasing the stiffness of the flexible cable, and the pre-stress shows marginal beneficial effect on the damping performance and the displacement control of the mass sphere. Using the optimum parameters, the vibration damper can keep the mass ball within a safe running distance. The reduction of the peak value and the standard deviation of the blade displacement can reach 89.36% and 89.83%, respectively. The proposed device space can effectively reduce the blade tip response of the wind turbine by occupying less space. Moreover, the size of the device installation space can be changed by adjusting the weight ball swing length, which is suitable for the vibration control of the wind turbine blade edgewise direction.

Numerical Investigation of Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage

Abstract This paper numerically investigates the flow field in the tip region of a highly loaded axial low-speed compressor rotor. The rotor in focus is of a hybrid blade configuration, featuring a tandem profile in the mid-span region and single blade profiles near the endwalls. The simulated 1.5-stage configuration also consists of a single row inlet guide vane (IGV) and a tandem stator. Due to high loading coefficients (Ψ = 0.58) in combination with moderate flow coefficients (ϕ = 0.58), double leakage of the tip leakage vortex plays a major role at all operating conditions. As already shown in the past, double leakage is a stability influencing dominant flow phenomenon in compressor rotors and influencing that can be the key to an efficient working range enhancement on compressor stages. This work introduces a simple and powerful method of enhancing the working range for low-speed rotors under the influence of double leakage. It is shown, that modifications to the pressure side (ps) shape of rotor tip profiles can influence the interaction of the tip leakage vortex with the adjacent blade, comparable to the effects of casing treatments. These unconventional blade shapes result from the transformations from tandem blade configurations to hybrid blades near the endwalls. The resulting single blade profile close to the tip features a convex profile element (an increase in local thickness, called the “belly”), which significantly influences the local static pressure gradients. This unusual pressure-side profiling can change mass flow over the tip and, by correct positioning, may reduce the amount of double leakage and, consequently, increase the rotor’s efficient working range. This work presents the geometry definitions for the hybrid blade single-segments, a detailed analysis of the impact on design and off-design operating conditions together with their underlying flow phenomena, and finally proposes design guidelines for the blade-tip geometries of highly loaded rotors under the influence of double leakage.

Structural Optimization of Single Crystal Turbine Blade Based on Recrystallization Critical Stress

In view of the problem that the surface structural recrystallization (SRR) is very easy to occur in the splitting gap area of the single crystal blade. A method to control the residual stress is proposed that based on the critical stress of single crystal recrystallization, and the structural details are optimized by combined with the numerical calculation and experimental verification. To reduce the residual stress level and change the residual stress distribution in the single crystal blade splitting gap. So as to control the level of residual stress, which is no more than the recrystallization critical stress. Finally, the experimental verification is completed by the optimized blade. The verification results show that the maximum residual stress is reduced by about 10% in the tail splitting region, and the recrystallization structure is completely eliminated in the original structure. It is proved that this method is a great effectiveness to control the structural integrity and surface structure connectivity of the single crystal blade.

Elimination of the Stray Grain Defects of Single Crystal Blade by Variable Wall Thickness Based on Integral Ceramic Mold

The stray grain defect is often found at the platform in the process of directional solidification of single crystal blades because local undercooling easily occurs in this area. A variable wall thickness mold based on stereolithography and gelcasting technology was proposed to solve the local undercooling at the platform. The influence of variable wall thickness mold on the temperature field of the platform during directional solidification was studied via simulation. The numerical simulation results show that variable wall thickness can effectively prevent heat dissipation at the platform, thereby reducing the undercooling and avoiding the formation of stray grains. At the same time, the influence of molds assembly angle on the formation of stray grains was analyzed, and the appropriate molds assembly angle is suggested.

Effect of Heat Treatment on Microstructure Evolution in DD9 Single Crystal Turbine Blade

The microstructural evolution of DD9 single crystal superalloy turbine blade was studied after heat treatment. In comparison to the as-cast microstructures where the sizes of the γ′ precipitates have an obvious difference between the dendritic core and interdendritic regions, the γ′ sizes of the heat-treated microstructures tend to be uniform and more cubic. And in the heat-treated microstructures, the γ′ sizes and the related size dispersion degrees of the dendritic cores are slightly increased, while those of the interdendritic regions are obviously decreased. After all, all the γ′ sizes follow the normal distribution law. With the raise of section thickness, the γ′ sizes tend to increase and the related size dispersion degrees are enhanced during the cooling process after heat treatment, and the γ-γ′ eutectics are dissolved, left little residual eutectics and pores.

Numerical Analysis of the Radial Load, Pressure and Velocity Fields of a Single Blade Pump

The centrifugal screw-type pump is a type of pump which, due to its hydraulic and mechanical properties, is used in several areas of the industry (e.g., for sludge and rainwater disposal). To avoid impeller passage clogging, the 3D impeller geometry is designed as a helically curved blade added to a conical hub. The passability through the fluid canal of the modelled impeller is 100 mm. In this paper, the magnitude of the radial force on an impeller blade is investigated as a function of the flow rate. The digital model was designed in Catia V5 and calculated using the commercial Ansys CFX software. A numerical computational fluid dynamics (CFD) method was used to investigate the performance characteristics of the pump, specifically discussing internal flow conditions such as velocity, pressure and the radial force mentioned above.