Life Of Turbine Blades Research Articles

Effect of change in role of an aircraft on engine life

AbstractNew aircraft require years of development from concept to realisation and can be prone to delays. Consequently, military operators take existing fleets and operate them in a different role. The objective of this study is to examine the effect of operating a typical low bypass military fast jet engine, originally designed for a European theatre, in a hot and harsh climate. The specific purpose is to determine the effect on the high-pressure turbine blade life and the life- cycle cost of the engine.A mission profile and respective performance conditions were analysed and modelled using an in-house performance tool. The flow conditions were simulated using ANSYS® FLUENT. A conjugated heat transfer solution was adopted to determine the blade metal temperature. The blade was modelled physically in 3D using SIMULIA® ABAQUS FEA software. The stresses were derived and used to calculate the temperature coupled low cycle fatigue and creep life.A deterioration case was also studied to evaluate the effect of sand and dust ingestion. There was a significant life reduction of approximately 50% due to creep. The reduction in life was inversely proportional to the life cycle cost of the engine depending on the operating conditions. The results were compared with similar engines and summarised in the context of airworthiness regulations and component integrity.

Sensitivity Analysis on Turbine Blade Temperature Distribution Using Conjugate Heat Transfer Simulation

Heat transfer parameters are the most critical variables affecting turbine blade life. Therefore, accurately predicting heat transfer parameters is essential. In this study, for precise prediction of the blade temperature distribution, a conjugate heat transfer procedure is used. This procedure involves three different physical aspects: flow and heat transfer in external domain and internal cooling passages and conduction within metal blade. For the external flow simulation and conduction within metal, three-dimensional solvers are used. However, three-dimensional modeling of blade cooling passages is time-consuming because of complex cooling passage geometries. Therefore, in the current work, a one-dimensional network method is used for the simulation of cooling passages. For validation of the numerical procedure, simulation results are compared with the available experimental data for a C3X vane. Results show good agreement against experimental data. The present paper investigates uncertainties of some parameters that affect turbine blade heat transfer, namely, (1) turbine inlet temperature and pressure, (2) upstream stator coolant mass flow rate and temperature, (3) rotor shroud heat transfer coefficient and fluid temperature over shroud, (4) rotor coolant inlet pressure and temperature (as a result of secondary air system), (5) blade metal thermal conductivity, and (6) blade coating thickness and thermal conductivity. Results show that turbine inlet temperature, pressure drop and temperature rise in the secondary air system (SAS) and coating parameters have significant effect on the blade temperature.

Studies towards development of laser peening technology for martensitic stainless steel and titanium alloys for steam turbine applications

Fatigue is a major life limiting factor affecting service life of low pressure steam turbine blades which, depending on turbine rating, are generally made of martensitic stainless steel or Ti6Al4V alloy. The results of the present study has demonstrated that with respect to conventional shot peening, laser peening brought more than two times longer mean fatigue life of Ti6Al4V alloy. Enhanced fatigue performance of laser peened specimens was attributed to the deeper peened layer and smoother finish. In the case of DIN X20Cr13 stainless steel, laser peening did not register significant improvement in fatigue resistance over shot peening. At maximum test stress of 550MPa, DIN X20Cr13 stainless steel specimens, shot peened and laser peened specimens exhibited comparable fatigue lives. However, at lower magnitude of maximum test stress of 400MPa, laser peened specimens displayed about 30% longer fatigue lives than their shot peened counterparts. Similar fatigue lives of shot peened and laser peened specimens of DIN X20Cr13 stainless steel specimens is attributed to comparable magnitude of surface residual stress and case depth produced by the two peening treatments.

A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device

This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements.

Optimal power dispatch in wind farm with life extension of wind turbine blades as target

The importance of optimal dispatch in wind farm has been increasingly prominent for large-scale wind farms. The blades are integral parts of wind turbines, which have much influence on the wind turbine life. This paper analyzes the force on the wind turbine blades in different conditions and determines the relationship between the wind turbine blades damage value and different operating conditions and the relationship between the wind turbine blades damage value and life of wind turbine blades. With life extension of wind turbine blades as the optimization objective, the optimal dispatch model is established by Dijkstra's algorithm. It is verified that this optimal dispatch model is reliable in the wind farm operation.

Blade loads on tidal turbines in planar oscillatory flow

Characterisation of the unsteady hydrodynamic loads is essential for accurate predictions of the fatigue life and ultimate loads of tidal turbine blades. This paper analyses a set of experimental tests of the hydrodynamic blade root out-of-plane bending moment response to planar oscillatory motion, chosen as an idealised representation of the unsteadiness imparted by waves and turbulence. Phenomena associated with dynamic stall are observed which are sensitive to the oscillatory frequency and velocity amplitude. Flow separation is shown to result in loads significantly greater in magnitude than that for steady flow. Following flow reattachment, the load cycles compare relatively well with Theodorsen's theory for a two-dimensional foil oscillating in heave, suggesting that circulation due to the shed wake dominates the unsteadiness in phase with acceleration, over added mass effects. For attached flow, the effect of unsteadiness is comparatively much smaller. At low frequencies a phase lead over the velocity is observed, compared to a lag at higher frequencies. Multiple frequency oscillations are also briefly considered. Reconstruction of the multi-frequency response using both the steady flow measurements, and the single frequency measured response, is shown to offer a relatively good fit when the flow is attached, for lower frequency combinations.

Determination of Turbine Blade Life from Engine Field Data

It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal mechanical fatigue as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) Thermal-mechanical fatigue, (2) Oxidation/Erosion, and (3) From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L(sub 10) blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to oxidation/erosion equaled that attributed to thermal-mechanical fatigue. The category that contributed most to blade failure was Other. If there were there no blade failures attributed to oxidation/erosion and thermal-mechanical fatigue, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.

Determination of Turbine Blade Life from Engine Field Data

Determination of Turbine Blade Life from Engine Field Data

Failure assessment of Nimonic 80A gas turbine blade

Nickel base superalloys are widely used in applications requiring strength at high temperature. During the operation of gas turbines, the blades and other elements of hot gas path suffer service induced degradation which may be natural or accelerated due to different causes. The failure analysis of the 3MW gas turbine first stage blades made of nickel-base alloy Nimonic 80A is presented. The blade experienced base alloy degradation due to operation at high temperature. Initially the blade was sectioned for metallographic and microhardness test. The microstructure and microhardness was compared in four different blade zones i.e. root, 30%, 60%, and 90% of the total height of the hot region of the blade. On the basis of the observed microstructures and the phases present in the alloy, the main cause of failure was found to be creep damage. Finite element method (FEM) analysis is conducted considering peak loading of centrifugal force and surface (aerodynamic) loads. Based on FEM simulation results, the life of turbine blades is predicted using the Larson–Miller method. Finally to improve the blade life two heat treatment cycles were suggested and applied. The effect of heat treatments on grain size, volume friction of γ′ primary phase, and micro hardness were investigated. A detailed analysis of the coating showed that, the loss of coatings resistant to high temperature is due to oxidation, corrosion, erosion and inters diffusion of coating-substrate, which results in diffusion of alloy elements into the coating.

Stochastic analysis of the influence of tower shadow on fatigue life of wind turbine blade

Fatigue damage accumulation in upwind turbine blades is primarily influenced by turbulence in the inflow. However, the stress reversals during blade passages through the stagnating and deflected mean wind field in front of the tower also contributes significantly. In the paper the lower order statistical moments of the fatigue life of a blade are estimated and compared for a turbine with a tripod tower and a standard mono-tower, respectively. The stagnation zones for each of the legs of the tripod are narrower than for the mono-tower, and hence the stress reversals will be comparable smaller. The blade stresses are calculated from a dynamic mechanical model based on a two dynamic degree of freedom. The self-induced aero-elastic loading and the turbulence loading are modeled by means of a quasi-static model linearized around the operational point, ignoring any memory effects on the load coefficients. However, such memory effects are taken into consideration at the calculation of the aero-dynamic load during tower passage by the use of a rational approximation to the relevant indicial function. Based on Monte Carlo simulations it is demonstrated that the expected damage accumulation per unit of time in the turbine blades are reduced significantly for the tripod when compared to the damage in a comparable mono-tower design.

Research on Microstructure and Property of TiC-Co Composite Material Made by Laser Cladding

Abstract The experiment of laser cladding on the surface of 2Cr13 steel was made. Titanium carbide (TiC) powder and Co-base alloy powder were used as cladding material. The microstructure and property of laser cladding layer were tested. The research showed that laser cladding layer had better properties such as minute crystals, deeper layer, higher hardness and good metallurgical bonding with base metal. The structure of cladding was supersaturated solid solution with dispersed titanium carbide. The average hardness of cladding zone was 660HV0.2. 2Cr13 steel was widely used in the field of turbine blades. Using laser cladding, the good wear layer would greatly increase the useful life of turbine blades.

PS06 小標本数試験データおよび実機検査記録を用いた信頼性設計手法の開発

Probabilistic safety assessment is an effective method to improve the conservative safety factors on low cycle fatigue life of turbine blades used in jet engines. This paper focuses on uncertainties of low cycle fatigue design life result from small samples and surface finishes. Improvement of uncertainty of design fatigue life, reflected from small sample tests, by use of inspection data is verified through Bayesian update and virtual inspection data. Furthermore, tension-compression low cycle fatigue tests on Inconel 718 were conducted with the specimens, of which surfaces were finished Ra 0.8, Ra 6.3, and Ra 12.5. The results indicates strain-amplitude dependence of the influence of surface finishes on low cycle fatigue life. In order to investigate the effect of surface finishing on low cycle fatigue life, local misorientations of surface layer of specimens are measured by EBSD.

Prediction of Wave Loads on Tidal Turbine Blades

Wave loads are one of the main contributors to fatigue loads of tidal turbine blades. Because of this, they are a determinant parameter for calculation of turbine blade life time. To avoid cost associated with oversizing blades or replacing a damaged blade, it is essential to evaluate the loads acting on the turbine, and especially wave loads on the blades, with the best possible accuracy.Experience from wind industry is valuable for horizontal axis tidal turbine design and loads acting on the blade can be estimated using the same methods, even if the loads are different. This article presents the main features of a code written with Matlab, able to predict thrust force and torque on each blade while the turbine is operating in a regular wave field. The quasi-static Blade Element Momentum theory is combined here with an added mass force modeling. The linear wave theory is employed to describe the water particle velocity due to waves. This velocity is, as a first approximation, simply added to a uniform stream velocity to account for wave-current interaction.The analytical results are validated by comparing them with experimental data obtained by testing a 1.475m-diameter rotor towed in a 260m-long wave tank, for different combinations of current speeds and wave characteristics. This emphasizes the importance of wave effects and dynamics in the design of tidal turbine blades.

Use of an orthogonal array based on the Kriging model to maximize the fatigue life of a turbine blade

PurposeApproximation techniques were used instead of expensive computing analysis in a traditional parametric design optimization of a complex system. A Kriging meta‐model was utilized, which enabled the fit of approximated design characteristics for a complex system such as turbine blades that incorporate a large number of design variables and non‐linear behaviors. This paper aims to discuss these issues.Design/methodology/approachThe authors constructed a Kriging meta‐model with a multi‐level orthogonal array for the design of experiments, which were used to optimize the fatigue life of turbine blades under cyclic rotational loads such as centrifugal force. By combining a seven‐level orthogonal array with the Kriging model, the non‐linear design space of fatigue life was explored and optimized.FindingsA computer‐generated multi‐level orthogonal array provided a good representation of the non‐linear design space information. The results show that not only was the fatigue life of the leading edge of the blade root significantly improved, but also that the computing analysis was effective.Originality/valueTo maximize the fatigue life of the turbine blade, the three‐design variables with seven factor levels were optimized via a Kriging meta‐model. As with the optimization technique, a desirability function approach was adopted, which converted multiple responses into a single response problem by maximizing the total desirability.

Robust design of turbine blades against manufacturing variability

Turbine blade life is central to the integrity of the aircraft engine. Manufacturing variability may lead to variations in the expected life and performance of turbine blades. It becomes important therefore to understand these variations and seek new designs that are robust to manufacturing variability. The present work proposes a methodology that employs Free Form Deformation in conjunction with optimisation to generate realistic 3D representations of the manufactured blades using limited measurements available per blade. Lifing estimations on the perturbed geometries show a reduction of around 1.7% in mean life relative to the designed life with a maximum relative reduction of around 3.7%. Following this, the proposed methodology is employed for robust design studies resulting in a better turbine blade design. This design indicates an improvement of around 2% in the designed life, around 3% improvement in mean life and approximately 57% reduction in blade life variability as compared to the current turbine blade design.

A damage prediction of high temperature polymer matrix composites

This work for prediction of damage and life is based on a new micromechanics of failure theory (MMF) and was started a few years ago. Instead of using the unidirectional ply as the building block, it was found that starting with the fiber, matrix and their interface would lead to a much simpler theory. The constituent properties will include two tensile and compressive strengths of matrix and fiber, plus normal and shear strengths covering the interface. The measured storage modulus of the viscoelastic matrix can be linked to the stiffness and strengths of plies and laminates from which creep rupture and fatigue strengths can be derived. One advantage of this approach is that the failure process of plies and laminates can be explicitly defined in terms of fiber, matrix and interfacial failures. No empirical factor is needed. The effect of moderately high temperature is fully integrated in the basic viscoelastic formulation, not accounted for by a knockdown factor. In addition, macro level properties of idealized square, hexagonal and random fiber arrays can be modeled and the resulting medium and scatter of predicted stiffness and strength are in reasonable agreement with available data. This modeling process is generic and can be applied to different material systems at room and elevated temperatures. Examples of metal matrix composites and hybrid composites like Tigr and Glare can be systematically described with no additional constants except the six basic strengths (four for fiber and matrix and two for the interface). First and last ply failures of laminates (FPF and LPF) can be similarly described with explicit definition of the failure modes. The failure process of matrix does not necessarily define the ultimate strengths of plies and laminates. Sophisticated modeling of the local degradation of matrix by micro cracking, ply delamination and fiber micro buckling will be explored with appropriate software packages developed for use by design engineers. In the mean time master curves covering the constituent stiffness and strength as functions of time and temperatures will be developed, measured and analyzed. In the end, failure envelopes of composite laminates in creep rupture and fatigue strength will be illustrated and their use for design be explained. In particular, the failure and life of a composite wind turbine blade is a good test of the predictive power of MMF.

Creep fatigue of a directionally solidified Ni-base superalloy - smooth and cylindrically notched specimens

Turbine blade life modelling is complicated by the presence of notches, dwells, high temperatures, thermal cycles and temperature gradients. Furthermore, directionally so- lidified (DS) Ni-base superalloys are highly anisotropic. This work seeks to characterize the response of the DS Ni-base superalloy CM247LC subjected to isothermal low cycle fatigue at either 750 or 950 °C. This study considers the effects of strain rate, dwells at the maximum temperature, and stress concentrations. Experiments were conducted under uniaxial loading on smooth and cylindrically notched round-bar specimens in both longitudinal and transverse orientations. The location of the creep-fatigue crack is at the maximum Hill's effective stress in the notched specimens. In addition, the notch behaviour is discussed in light of finite element analysis using an anisotropic elastic-crystal viscoplastic material model.

Probabilistic Life Assessment of Gas Turbine Blades

This paper addresses the problem of analyzing measurement data to estimate the variations in turbine blade life in the presence of manufacturing variability. A methodology that employs existing denoising techniques, namely, Principal Component Analysis and Fast Fourier Transform analysis, is proposed for filtering measurement error from the measured data set. An approach for dimensionality reduction is employed that uses prior knowledge on the measurement error obtained from analyzing repeated measurements. The proposed methodology also helps in capturing the effects of manufacturing drift with time and the blade to blade manufacturing error. The filtered data is then used for generating three-dimensional representations of probable manufactured blade shapes from the limited number of available measurements. This is accomplished by using a Free-Form Deformation based approach for deforming a nominal mesh to the desired shapes. Estimations of life on the probable turbine blade shapes manufactured over a span of 1 year indicate a reduction of around 1.7% in the mean life relative to the nominal life, with a maximum relative reduction of around 3.7%, due to the effects of manufacturing variability.

Reliability Study for Creep Life of Single Crystal Turbine Blade under Random Crystal Orientations and Random Loads

For the single crystal (SC) Ni-based superalloys, it is difficult to avoid orientation variation along airfoil stacking line of the SC turbine blade. At the mean time, the loading of turbine blade is uncertainly during the working. In this work, the creep life of the SC turbine blade is determined by the finite element analysis (FEA) based on the crystal slip theory. The orientation variations are measured based larger numbers commercial turbine blade made of SC superalloys. Furthermore, Monte-Carlo method and the forth moment method are presented to analysis the reliability for creep life of SC turbine blade under random crystal orientations and random loads based on the FEA method. The basic variables sensitivity are comprehensively analyzed by the forth moment method.

Computational Modeling of Tip Heat Transfer to a Superscale Model of an Unshrouded Gas Turbine Blade

Control of over-tip leakage flow between turbine blade tips and the stationary shroud is one of the major challenges facing gas turbine designers today. The flow imposes large thermal loads on unshrouded high pressure (HP) turbine blades and is significantly detrimental to turbine blade life. This paper presents results from a computational study performed to investigate the detailed blade tip heat transfer on a sharp-edged, flat tip HP turbine blade. The tip gap is engine representative at 1.5% of the blade chord. Nusselt number distributions on the blade tip surface have been obtained from steady flow simulations and are compared with experimental data carried out in a superscale cascade, which allows detailed flow and heat transfer measurements in stationary and engine representative conditions. Fully structured, multiblock hexahedral meshes were used in the simulations performed in the commercial solver FLUENT. Seven industry-standard turbulence models and a number of different tip gridding strategies are compared, varying in complexity from the one-equation Spalart–Allmaras model to a seven-equation Reynolds stress model. Of the turbulence models examined, the standard k-ω model gave the closest agreement to the experimental data. The discrepancy in Nusselt number observed was just 5%. However, the size of the separation on the pressure side rim was underpredicted, causing the position of reattachment to occur too close to the edge. Other turbulence models tested typically underpredicted Nusselt numbers by around 35%, although locating the position of peak heat flux correctly. The effect of the blade to casing motion was also simulated successfully, qualitatively producing the same changes in secondary flow features as were previously observed experimentally, with associated changes in heat transfer with the blade tip.