Turbine Blade Root Research Articles

Tool wear behavior of vitrified microcrystalline alumina wheels in creep feed profile grinding of turbine blade root of single crystal nickel-based superalloy

Different aspects on the tool wear behavior of profiled vitrified microcrystalline alumina wheels during creep feed grinding of Ni alloy blade root were investigated. Experimental results indicate that the wheel peak regions had the higher wear values than the wheel valley regions by around 21.7%, 42.8%, 34.5%, in terms of the profile heights, circle radii and angles respectively. Furthermore, the wear flats, workpiece material adhesion, and the fractures of grains and bond bridges occurred in the wheel peak regions; while in the wheel valley regions, heavy wheel clogging, fractures of grains, and workpiece material adhesion were produced. Based on the experimental results, an analytical model with the average error of 17.3% to predict the wheel profile wear was finally developed.

Variation of Crystal Orientation and Dendrite Array Generated in the Root of SX Turbine Blades.

The variation of the crystal orientation and the dendrite array generated in the root of the single-crystalline (SX) turbine blades made of CMSX-4 superalloy were studied. The blades with an axial orientation of the [001] type were solidified by the industrial Bridgman technique using a spiral selector at a withdrawal rate of 3 mm/min. The analysis of the crystal orientation and dendrite arrangement was carried out using scanning electron microscopy, X-ray diffraction topography, and Laue diffraction. It was found that the lateral growth of such secondary dendrite arms, which are defined as “leading” and grow in the root at first, is related to the rotation of their crystal lattice, which is the reason for creation of the low-angle boundary (LAB) type defects. The primary crystal orientation of the selector extension (SE) area determines the areas and directions of the lateral growth of the leading arms. Additionally, it was found that in the SE areas of the root, near the connection with the selector, the spatial distribution of the [001]γ′ crystallographic direction has a complex wave-like character and may be related to the shape of the crystallization front.

Wind Field-Based Short-Term Turbine Response Forecasting by Stacked Dilated Convolutional LSTMs

Predicting a wind turbine's responses that correspond to a complex wind field is challenging because the responses are caused by the complex interaction between a dynamically operating mechanical system and a spatially and temporally coupled stochastic wind field. We propose a physics-inspired, data-driven prediction model called stacked dilated convolutional LSTMs (SDCL) that uses a sequence of wind fields (snapshots) as an input to predict future wind turbine responses. A SDCL is composed of a set of dilated convolutional neural networks (CNNs) combined with a long short-term memory (LSTM) to capture the spatial and temporal evolution of the turbulence structure in the input wind field. Notably, a dilated CNN with different dilation ratios along with a corresponding LSTM module, a single component of SDCL, is designed to capture the evolution of an eddy of a certain size in the turbulent wind field. Then SDCL effectively models the evolution of multiple eddies of different sizes. Through a simulation study, we have demonstrated that such a physics-inspired network architecture is effective in processing a complex wind field and thus predicting two representative future wind turbine responses, energy generation and blade root out-of-plane bending moment, more accurately than other standard deep learning architectures.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

On the temperature field in the creep feed grinding of turbine blade root: Simulation and experiments

Although there have been many theoretical, numerical and experimental studies focusing on grinding temperature, very few of them investigated the temperature domain when performing profile grinding of free-form surfaces, where excessive heat can be considered as the key issue due to the long and complex contact zone. In this study, the finite element (FE) based thermal model of the Creep Feed Grinding (CFG) process of Inconel 718 turbine blade root was established in terms of energy partition, material properties, geometry, and thermal boundary. The validation experiments aided with the imbedded thermocouples showed the reasonable match with the experimental results where the average difference was of about 20% proved the simulation feasibility and accuracy. The effects of the blade root profiling and root geometry on the grinding temperature were discussed based on the validated FE model. Considering the research gaps mentioned above, this work is not only expected to be meaningful to deepen the understandings of the temperature field distribution in the CFG of turbine blade root, but also helpful to provide industry guidance to optimize the process physics in precision machining of high-valued parts with complex profiles.

Calculating wind turbine component loads for improved life prediction

Wind turbines life time is commonly predicted based on statistical methods. However, the success of statistics-based maintenance depends on the amount of variation in the system design, usage and load. Life time prediction based on physical models seeks to overcome this drawback by considering the actual design and evaluating the specific usage, load and operating condition of the considered systems. In this paper, a load-based maintenance approach is proposed to predict wind turbines life time. Physical models are used to evaluate load profiles at wind turbine blade root, rotor hub center and tower head. The effects of surface roughness, side winds, yaw misalignment, rotor tilt and blade cone angle, individual blade pitching and wind turbulences are considered and quantified. It is shown that centrifugal, gravity, Euler and Coriolis accelerations dominate the blade root loads. Tilt and cone angle, as well as individual blade pitching, affect the rotor hub and dynamic tower head loads. Further, the actual wind speed distribution is considered which is also proven to be a critical life time prediction parameter. Finally, a set of parameters is proposed that need to be monitored in a specific wind turbine to enable the practical implementation of a predictive maintenance policy.

Novel carbon-fibre powder-epoxy composites: Interface phenomena and interlaminar fracture behaviour

Carbon fibres with three different sizing agents were used to manufacture unidirectional composites based on a powder epoxy resin. Powder epoxy processing was investigated as a route for fast, cost-effective manufacturing of out-of-autoclave composites compared to more time-consuming vacuum infusion technologies. In this work, a heat-activated epoxy powder was used as a resin system in low-cost vacuum-bag-only prepregs for thick composite parts that are required in the renewable energy industry (e.g. wind turbine blade roots). The importance of interfacial bonding between fibres and the matrix is shown and the impact on the ultimate mechanical performance of the manufactured composites demonstrated. The surface characteristics of the sizing on the carbon fibres were investigated using atomic force microscopy (AFM) and Raman spectroscopy. Results showed that the amount of sizing on the fibres' surfaces was inextricably linked with surface roughness and coverage. This in turn influenced the mechanical and chemical interlocking phenomena occurring at the fibre/matrix interface. The composites’ mechanical performance was evaluated using tensile, flexural and interlaminar fracture toughness tests. Fractographic analysis using optical and scanning electron microscopy (SEM) was likewise employed to analyse the fracture surfaces of the tested/failed composites. Interlaminar fracture toughness testing (DCB Mode-I) revealed that the interfacial adhesion differences could alter the fracture resistance of the composites, hence emphasizing the importance of the interfacial bonding strength between the polymer matrix and the carbon fibres.

Cracking, Microstructure and Tribological Properties of Laser Formed and Remelted K417G Ni-Based Superalloy

The K417G Ni-based superalloy is widely used in aeroengine turbine blades for its excellent properties. However, the turbine blade root with fir tree geometry experiences early failure frequently, because of the wear problems occurring in the working process. Laser forming repairing (LFR) is a promising technique to repair these damaged blades. Unfortunately, the laser formed Ni-based superalloys with high content of (Al + Ti) have a high cracking sensitivity. In this paper, the crack characterization of the laser forming repaired (LFRed) K417G—the microstructure, microhardness, and tribological properties of the coating before and after laser remelting—is presented. The results show that the microstructure of as-deposited K417G consists of γ phase, γ′ precipitated phase, γ + γ′ eutectic, and carbide. Cracking mechanisms including solidification cracking, liquation cracking, and ductility dip cracking are proposed based on the composition of K417G and processing characteristics to explain the cracking behavior of the K417G superalloy during LFR. After laser remelting, the microstructure of the coating was refined, and the microhardness and tribological properties was improved. Laser remelting can decrease the size of the cracks in the LFRed K417G, but not the number of cracks. Therefore, laser remelting can be applied as an effective method for strengthening coatings and as an auxiliary method for controlling cracking.

Influence of temperature regimes on stress-strain state of design details

Details of turbomachines come in direct contact with gases, which are at the peak of their temperature. There is a heterogeneous temperature distribution across the detail as a result of changes in temperature and external influences. As is known, the temperature stresses in materials are due to temperature gradients and boundary conditions. However, when designing and determining the bearing capacity of turbomachinery structural elements, other factors, including the heating regime, must be taken into account. The greatest temperature stresses develop during the cycles of heating and cooling. At the same time, the greatest values of temperature gradients and stresses arise in a fairly short period of time, which in turn can cause a temperature fatigue of the material. In addition, high temperatures contribute to the development of creep deformations, which reduce the length of the life cycle of the detail. One of the factors that determines the occurrence of thermal stresses is the nature of the temperature change during the start-up process, which is determined by the start-up curve of the turbine or machine. Start-up curve is the dependence between rotor speed or gas temperature and time. It is especially important for such parts as turbine blades and roots of the blades. Considering that turbomachinery parts must withstand a significant number of start-up cycles, both temperature and mechanical analysis is required. The purpose of this work is to study the effect of the nature of the change of external temperature (start-up curves) on the change in the parameters of the stress-strain state of the fir-tree root of the gas turbine blade under thermoelastoplastic deformation, taking into account the nonhomogenous temperature distribution. The effect of heating regimes on the development of temperature stresses is considered in the paper. The initial relations of the problem of transient thermal conductivity and the problem of thermoelastoplasticity are given. An analysis of the effect of the selection of the start-up curve on the approximated geometry of fir-tree root of the blade was carried out.

Учет остаточных напряжений при расчетах прочности элементов замковых соединений. Часть 2. Влияние остаточных напряжений на напряженно-деформированное состояние хвостовика лопатки турбины

Учет остаточных напряжений при расчетах прочности элементов замковых соединений. Часть 2. Влияние остаточных напряжений на напряженно-деформированное состояние хвостовика лопатки турбины

The development of a novel technique for small ring specimen tensile testing

The wide scale use of small specimens in routine testing programs could significantly reduce material resource requirements (factors of 10 are easily achievable). This is a major benefit to situations where there is not enough material to manufacture conventional, full-size specimens, such as first-stage gas turbine blade roots. However, limitations exist due to concerns over size effects, manufacturing difficulties, uncertainties related to the application of representative loading conditions and complex interpretation procedures of non-standard data. Due to these limitations, small specimen testing techniques have been mostly applied in ranking exercises and to determine approximate or simple material parameters such as Young’s modulus, minimum creep strain rate and fracture toughness. The small ring method is a novel, high sensitivity small specimen technique for creep testing that has been extended in the present work to the determination of tensile material properties. The main advantages of the small ring specimen are that it is self-aligning and has a large equivalent gauge length in comparison to other small specimens, resulting in much higher testing sensitivity. In the present work, this specimen type mimics conventional, full-size, monotonic testing, allowing for observations of elastic and plastic material response to be made. Wrought aluminium alloy 7175-T7153 small rings were tested at room temperature at 5 different loading (displacement) rates and the results compared to conventional, full-size, monotonic specimen equivalents. Finite element analysis was conducted in order to evaluate the equivalent gauge section and equivalent gauge length in the small ring specimen (which varied between circa 0.35–1.4 mm2 and 25–45 mm, respectively) to facilitate these comparisons. An analytical solution has also been derived in order to validate the finite element analysis.

Impact assessment of a wind turbine blade root during an offshore mating process

Single-blade installation is a popular method for installing blades on bottom-fixed offshore wind turbines. A jack-up crane vessel is often employed, and individual blades with their roots equipped with mechanical joints and bolted connections are lifted to the tower-top height and mated with a pre-assembled hub. The final mating phase is challenging and faces significant risks of impact. Due to relative motions between the blade and the hub, substantial impact forces may arise and lead to severe structural damages at root connections, thereby causing delays in the installation task. The present paper considers a realistic scenario of the mating process and investigates the consequences of such impact loads. Here, a single-blade model with tugger lines and a monopile model were established using a multi-body formulation, and relative velocities under collinear wave and wind conditions were obtained. A three-dimensional finite element model was developed for the blade root with T-bolt connections, and an impact investigation was performed for the case in which a guiding connection impacts the hub. The results show severe bending and plastic deformation of the guide pin bolt together with failure of the adjoining composite laminate at the root connection. Based on the type of damage obtained for the different environmental conditions considered, this paper also discusses its consequence on the installation tasks and suggests onboard decision making in case of an impact incident. The results of this study provide new insights regarding the mating phase and can be utilised to establish response-based operational limits.

Effect of Aluminized Coating on Combined Low and High Cycle Fatigue Life of Turbine Blade at Elevated Temperature

Some cracks were detected on the fir-tree root of turbine blade in an in-service aero-engine, and the aluminized coating was considered to be the main cause of these cracks. To study the effect of aluminized coating on fatigue life of turbine blade, the combined low and high cycle fatigue (CCF) tests are carried out at elevated temperature on both aluminized and untreated turbine blades. Probability analysis of test data is conducted and the result indicates that the median life is decreased by 62.2% due to the effect of the aluminized coating. Further study on the mechanism of crack initiation and propagation has been conducted based on fractography and cross section morphology analysis by using scanning electron microscope (SEM), and the results indicate: (1) The aluminized coating consists of two layers, of which the inner layer is considered to contain the σ phase and it reduces the resistance to fatigue of blade. (2) Many cavities are found in the inner layer of aluminized coating, which lead to the initiation of cracks and result in the reduction of crack initiation life. (3) The marker band widths of aluminized and untreated blade are very close, which indicated the aluminized coating may have no effect on the crack propagation life of the blade.

Investigation of Microstructure Properties and Quantitative Metallography by Different Etchants in the Service-Exposed Nickel-Based Superalloy Turbine Blade

In this study, the effect of etchant type and etching conditions on the root and airfoil microstructure of a service-exposed IN738 turbine blade has been investigated. The microstructure of superalloy components used at high temperatures, in addition to the usual microstructural changes, experiences deterioration in micrometer dimensions. In order to investigate these changes, electrochemical etching was performed on the samples with the chemical solution including 80% phosphoric acid, solution containing Cr2O3 and 55% glycerol. Chemical etching was performed with marble and etchant solution containing 60% glycerol. The results in terms of specifying the deterioration effects on microstructure of the blade applied at high temperature, the amount of γ′ phase and the best etchant were investigated. Among the solutions used for chemical etching, the solution containing 10 ml HNO3, 50 ml HCl and 60 ml glycerol was appropriate for detection of segregations and dendrites, and among the electrochemical etching solutions, the Cr2O3 solution was found suitable for specifying γ′ precipitates’ morphology by scanning electron microscopy. In this research, the results of the quantitative analysis of the images provided by these etchants were also investigated.

Analysis of CMSX-4 Single-Crystalline Turbine Blades Root by Electron and X-Ray Diffraction Methods

The root of single-crystalline turbine blade made of CMSX-4 superalloy were studied. The studied blade was produced by the Bridgman technique in industrial ALD furnace at withdrawal rate of 3 mm/min. The samples for investigations were cut from the blade root parallel to the withdrawal direction. Metallographic sections of longitudinal samples planes were prepared for further investigations. The samples were analysed using scanning electron microscopy and the Laue diraction studies. The crystal orientations in macro-scale were determined by analysis of the Laue pattern and local crystal orientations were studied by electron backscattered diraction technique. Morphology of dendrites were examined by analysis of scanning electron microscopy macro-images. Study of subgrain structure was performed by X-ray diraction topography. The sharp parallel contrast bands, visible on the X-ray topograms, were related with dendrite cores, arranged with the same direction. Additionally, the low angle boundaries were formed in certain samples, visible on the topograms as contrast shifts. Step changes of local crystal orientation in certain areas were observed on the electron backscattered diraction maps. The electron backscattered diraction crystal orientation maps were related to the misorientation visualized in topograms.

Finite element analysis of smart wind turbine blades sandwiched with magnetorheological fluid

A brand-new smart wind turbine blade with magnetorheological fluid (MRF) sandwiched was proposed in the research. The three-dimension entity model of a 750 KW wind turbine blades was established through the use of UG software, and three kinds of MRF sandwich layouts were considered into the blade model, that is, at the blade tip, at the blade root and at the whole blade from the root till the tip. The MRF was simplified as Kelvin-Voigt model in order to implement the finite element analysis based on ANSYS software, so that the mode shapes of smart wind turbine blade were revealed under various conditions with three different layout forms of MRF sandwich wind turbine blades. Analysis results showed that the magnetic field would influence the mode shapes of the wind turbine blade with MRF sandwiched, especially the torsion vibration. When the MRF was inserted through the blade from the root till the tip, the blade would dramatically influence the torsion vibration, so that the torsion vibration, which originally would have happened at higher orders, would arise in advance. While the MRF was located at the root of wind turbine blade, the torsion vibration would be postponed to arise at the higher orders. Therefore, the MRF should be located at the blade root, instead of the middle and the tip of wind turbine blade. Smart sandwich wind turbine blade will provide a new way to the vibration control of wind turbine blade.

Vertical Axis Wind Turbine Design Load Cases Investigation and Comparison with Horizontal Axis Wind Turbine

The paper studies the applicability of the IEC 61400-1 ed.3, 2005 International Standard of wind turbine minimum design requirements in the case of an onshore Darrieus VAWT and compares the results of basic Design Load Cases (DLCs) with those of a 3-bladed HAWT. The study is based on aeroelastic computations using the HAWC2 aero-servo-elastic code A 2-bladed 5 MW VAWT rotor is used based on a modified version of the DeepWind rotor For the HAWT simulations the NREL 3-bladed 5 MW reference wind turbine model is utilized Various DLCs are examined including normal power production, emergency shut down and parked situations, from cut-in to cut-out and extreme wind conditions. The ultimate and 1 Hz equivalent fatigue loads of the blade root and turbine base bottom are extracted and compared in order to give an insight of the load levels between the two concepts. According to the analysis the IEC 61400-1 ed.3 can be used to a large extent with proper interpretation of the DLCs and choice of parameters such as the hub-height. In addition, the design drivers for the VAWT appear to differ from the ones of the HAWT. Normal operation results in the highest tower bottom and blade root loads for the VAWT, where parked under storm situation (DLC 6.2) and extreme operating gust (DLC 2.3) are more severe for the HAWT. Turbine base bottom and blade root edgewise fatigue loads are much higher for the VAWT compared to the HAWT. The interpretation and simulation of DLC 6.2 for the VAWT lead to blade instabilities, while extreme wind shear and extreme wind direction change are not critical in terms of loading of the VAWT structure. Finally, the extreme operating gust wind condition simulations revealed that the emerging loads depend on the combination of the rotor orientation and the time stamp that the frontal passage of gust goes through the rotor plane.

Aerodynamic design and analysis of a 10 kW horizontal-axis wind turbine for Tainan, Taiwan

The purpose of the present study is to develop a small-scale horizontal-axis wind turbine (HAWT) suitable for the local wind conditions of Tainan, Taiwan. The wind energy potential was first determined through the Weibull wind speed distribution and then was adapted to the design of the turbine blade. Two numerical approaches were adopted in the design and analysis of the HAWT turbine blades. The blade element momentum theory (BEMT) was used to lay out the shape of the turbine blades (S822 and S823 airfoils). The geometry of the root region of the turbine blade was then modified to facilitate integration with a pitch control system. A mathematical model for the prediction of aerodynamic performance of the S822 and S823 airfoils, in which the lift and drag coefficients are calculated using BEMT equations, was then developed. Finally, computational fluid dynamics (CFD) was used to examine the aerodynamic characteristics of the resulting turbine blades. The resulting aerodynamic performance curves obtained from CFD simulation are in agreement with those obtained using BEMT. It is also observed that separation flow occurred at the turbine blade root at the tip speed ratios of 5 and 7.

Cracks on the Roots of Turbine Blades of the Low-Pressure Turbine in a Steam Power Plant

Abstract Cracks were found in the roots of steam turbine blades of the third blade row (LA-2) of the low-pressure turbine during revision works in a coal-fired power plant. Metallographic examinations reveal pitting corrosion sites, branched cracks, and local plastic deformation at the root of the first load bearing flank radius. The fracture surface was analyzed using light microscopy and scanning electron microscopy (SEM). Finite element (FE) simulations were performed in order to qualitatively represent the stress peak positions on the blade root.

Ultrasonic Wedges for Testing Of Turbine Blade Roots

The integrity of turbine blade roots and attachments is fundamental to the power infrastructure. Therefore, it requires the adoption of appropriate wedges with an effective ultrasonic testing system. Turbine components have complicated geometry which ordinarily impedes proper coupling to the wedge. However, different configurations of the ultrasonic wedge have been developed to obviate this constraint. In this paper, the various types of ultrasonic wedge are reviewed vis-a-vis their conformability to the turbine blade root geometry. Also, the possible application of cylindrical multiple flat-faced wedges is discussed.