Turbine Disk Research Articles

Bending of a circular flexible plate taking into account the initial curvature

In this article, an analytical solution of the problem of bending a round plate with an initial curvature is obtained. A round plate with an initial curvature as a structural element is widely used, the calculation of which leads to many questions related to the design of round Foundation plates, turbine disks, flexible shaft connections and other. The nonlinear theory of round flexible plates provides the key to explaining the process of loss of stability, which often leads to complete destruction of the structure. Therefore, there is a high need for analytical methods for solving problems of calculating the stress-strain state of round flexible plates, taking into account the initial curvature. These problems are mathematically reduced to differential equations with variable coefficients, the exact solution of which, as a rule, does not exist. Therefore, the construction of analytical solutions to these problems is very relevant.

Influence of the laser source pulsing frequency on the direct laser deposited Inconel 718 thin walls

The Direct Laser Deposition (DLD) process has shown significant results in manufacturing due to its relevant flexibility to refurbish high-performance components (e.g. turbine blades or disks) or fabricating complex shaped parts. The solidification microstructure during the DLD process, is known to be controllable using different process parameters that induce changes in the grain structure, micro-segregation, and phase transformations. This work focuses on the effect the frequency of the pulsed laser has on the metallurgical characteristics of deposited thin walls. More specifically, the effect of three different pulsing rates (10 Hz, 100 Hz, 1000 Hz) during the deposition of the Nickel-based superalloys Inconel 718 has been studied and the results compared with parts produced by continuous wave laser mode. This work highlights how the pulsing rate significantly affected the thermal history, melt pool shape, grain size and its morphology, segregation region (Nb-enriched), and hardness. Finally, the microhardness was also evaluated and a correlation between the metallurgical characteristics and the pulsing rate was established.

Rigorous uncertainty quantification with correlated random variables from multiple sources

A method of quantification of margins and uncertainties (QMU) is developed for structures with correlated random variables originated from multiple sources. The QMU analysis aims to certify the concerned structure with a prescribed confidence factor (CF), and further determine an adequate design margin. After partitioning correlated random variables into different groups based on their uncertain sources, the multidimensional parallelepiped model is established to describe the uncertainty domain of these correlated random variables. Based on the grouped independent random vectors, McDiarmid’s inequality is applied to realize rigorous uncertainty quantification of the structural performance. The computation of structural uncertainty is formulated as an optimization problem of variables within the multidimensional parallelepiped uncertainty domain. The QMU framework is then established and applied to low cycle fatigue life assessment of aero-engine turbine disc made of GH720Li superalloy. Stochastic parameters involving loads, geometries, and material properties, are chosen as input random variables. It is demonstrated that the turbine disc can be rigorously certified under the given design specification. By contrast, it will provide a wrong certification decision when the correlation of variables is not considered. The assessment provides an effective basis for the design with enough confidence in engineering applications from the perspective of QMU analysis.

A novel metamodeling approach for probabilistic LCF estimation of turbine disk

To improve the computing efficiency and accuracy of probabilistic low cycle fatigue (LCF) estimation for turbine disk, a distributed-coordinated neural network metamodel (DCNNM) is developed. By integrating the proposed neural network metamodel and distributed-coordinated strategy, the mathematical model of DCNNM is studied. The probabilistic LCF estimation theory is introduced in respect of the presented DCNNM. Moreover, the probabilistic LCF estimation for turbine disk is regarded as one case to evaluate the proposed method with respect to various randomness such as material variability, load variation and model randomness. We obtain the distributional traits, reliability degree and sensitivity degree of LCF failure cycle, which provides an effective guidance for the turbine disk life control. By comparing the direct Monte Carlo simulation, support vector regression (SVR), neural network metamodel (NNM), distributed-coordinated SVR (DCSVR) and DCNNM, we observe that the proposed DCNNM approach possesses high efficiency and accuracy for probabilistic LCF estimation of turbine disk. The present effort offers a useful insight for estimating LCF failure from a probabilistic perspective.

Numerical investigation on heat transfer characteristics of twin-web turbine disk-cavity system

A twin-web turbine disk with two rotor-stator cavities and inner cavity system is developed to investigate the effect of nozzle geometrical parameters on both sides, including pre-swirl angle (θ3), radial position (Rd), and inlet flow ratio of of the rotor-stator cavity to inner cavity (P1), on the heat transfer characteristics of the system using the RNG k-ε turbulence model. The maximum disk temperature (Tmax), disk temperature uniformity and local Nu are adopted as evaluation indexes. Nine structures with different θ3 and Rd are designed. The results show that the effect of θ3 is greater than that of Rd. Model 3 with a high-radius nozzle (Rd = 0.8) and small pre-swirl (θ3 = 30°) shows the lowest Tmax and the highest Nu. The axial temperature difference is affected less by θ3 and Rd, i.e., approximately 11 K. The radial temperature uniformity improved with increasing Rd. The Nu on the disk wall increased along the direction of radial temperature gradient increasing. The inlet flow ratio is optimized based on model 3 with different P1. It is revealed that Tmax is the lowest and the radial temperature uniformity is the best when P1 is 1. The axial temperature uniformity is appropriate when P1 is 1 or 2. After optimizing P1, Tmax reduced by 7.1 K, whereas the average temperature of Clip1 and Clip2, TC1 and TC2, reduced by 0.2 and 1.6 K, respectively. The radial temperature uniformity improved slightly, but the axial temperature difference increased by 1.4 K.

An Investigation of Magnetic-field-assisted EDM by Silicon and Boron Based Dielectric of Inconel 706

Inconel 706 is a newly developed superalloy widely used in making gas turbine disk applications owing to its high mechanical strength along with easy fabricability. The conventional machining of 706 material offers lower productivity, poor surface finish and lesser machining efficiency owing to the phenomenon of strain hardening, lower thermal conductivity and excellent temperature capability. In the present study, an effort has been made to machine Inconel 706 by the hybrid EDM technique assisted by fine powder as well as magnetic field (MF). Experiments were performed according to Taguchi L27 orthogonal array (OA) approach. Influence of control parameters such as peak current (Ip), pulse on duration (Pon), pulse off duration (Poff), MF intensity, tool variant and dielectric type on the material removal rate (MRR) and surface roughness (Ra) has been investigated. Analysis of variance (ANOVA) results revealed that Ip has more than 82% contribution to the MRR. Further, Ip (48.40%), copper tool material (20%) and Pon (16.97%) have major influence on Ra. The surface morphology of the machined surface is assessed by FESEM micrographs, which has revealed the formation of melted debris, micro-holes and micro-globules on the machined specimen surface.

Probabilistic life prediction for FCG degradation process of turbine disc with small sample data

A probabilistic fatigue crack growth (FCG) life prediction is conducted on a turbine disc considering small sample data involving material properties and geometric dimensions in this study. Wiener process with two transformed time scales is used to quantify the time-varying dispersion of FCG degradation process. The accuracy of Weiner process model is verified by using the FCG experimental data for standard compact tension (CT) specimens. Then, FCG tests on the component-like specimens are conducted to establish the time-varying FCG model considering geometrical features. During this process, Bootstrap method is introduced to expand the small test samples into larger Bootstrap samples. Meanwhile, the dispersion for geometric dimensions of the small sample is described by using probability box method. Finally, probabilistic FCG analysis is conducted on a turbine disc through using quasi-Monte Carlo sampling method. Results show that the average relative error between the lower bound of Ns and Na is within 20%, and the average relative error between the upper bound of Ns and Na is less than 15%, which further demonstrates the accuracy of probabilistic FCG method.

Integrating Materials Model-Based Definitions into Design, Manufacturing, and Sustainment: A Digital Twin Demonstration of Incorporating Residual Stresses in the Lifecycle Analysis of a Turbine Disk

Abstract Model-based definitions (MBDs) aim to capture both geometric and non-geometric data in digital product definitions using 3D computer-aided design (CAD) models, as a form of product definition baseline, to disseminate product information across different stages of the lifecycle. MBDs can potentially eliminate error-prone information exchange associated with traditional paper-based drawings and improve the fidelity of component details, captured using 3D CAD models. A component’s behavior during its lifecycle stages influences its downstream performance, and if included within the MBD of a part, could be used to forecast performance upfront during the design and explore newer designs to enhance performance. However, current CAD capabilities limit associating behavioral information with the component’s shape definition. This paper presents a CAD-based tool to store and retrieve metadata using point objects within a CAD model, creating linkages to spatial locations within the component. The tool is illustrated for storage and retrieval of bulk residual stresses developed during the manufacturing of a turbine disk acquired from process modeling and characterization. Further, variations in residual stress distribution owing to process model uncertainties have been captured as separate instances of the disk’s CAD models to represent part-to-part variability as an analogy to track individual serialized components for digital twins. The propagation of varying residual stresses from these CAD models within the damage tolerance analysis performed at critical locations in the disk has been demonstrated. The combination of geometric and non-geometric data inside the MBD, via storage of spatial and feature varying information, presents opportunities to create digital twin(s) of actual component(s).

Research on Densification Mechanism of Hot Isostatic Pressing Technology in Nickel-Based Superalloys for Marine Environment

Jiang, Z.; Wang, J., and Cao, D., 2020. Research on densification mechanism of hot isostatic pressing technology in nickel-based superalloys for marine environment. In: Wan, Z. (ed.), Coordinated Sustainable Development in Coastal Areas: Environment and Economy. Journal of Coastal Research, Special Issue No. 109, pp. 100–104. Coconut Creek (Florida), ISSN 0749-0208.Nickel-base superalloy is one of the major materials employed in the manufacturing process of air valve and exhaust system of diesel engine, turbine disk and blade of gas turbine and nuclear power units. The rapid development of modern marine industry is inseparable from the rapid improvement of comprehensive properties of superalloy. In this process, hot isostatic pressing (HIP) technology has been playing a significant role in the application of Nickel-base superalloy. In this paper, the research and application of HIP technology in the field of Nickel-base superalloy are herein summarized, and concluding the effect of HIP technology on densification mechanism and properties of cast superalloy.

Electrochemical cutting of mortise-tenon joint structure by rotary tube electrode with helically distributed jet-flow holes

In aero-engines, mortise-tenon joint structures are often used to connect the blades to the turbine disk. The disadvantages associated with conventional manufacturing techniques mean that a low-cost, high-efficiency, and high-quality nickel-based mortise–tenon joint structure is an urgent requirement in the field of aviation engineering. Electrochemical cutting is a potential machining method for manufacturing these parts, as there is no tool degradation in the cutting process and high-quality surfaces can be obtained. To realize the electrochemical cutting of a mortise-tenon joint structure, a method using a tube electrode with helically distributed jet-flow holes on the side-wall is proposed. During feeding, the tube electrode rotates along its central axis. Flow field simulations show that the rotational speed of the tube electrode determines the direct spraying time of the high-speed electrolyte ejected from the jet-flow holes to the machining area, while the electrolyte pressure determines the flow rate of the electrolyte and the velocity of the electrolyte ejected from the jet-flow holes. The machining results using the proposed method are verified experimentally, and the machining parameters are optimized. Finally, mortise and tenon samples are successfully machined using 20 mm thick Inconel 718 alloy with a feeding rate of 5 μm/s.

Experimental investigation of magnetic-field-assisted electric discharge machining by silicon-based dielectric of Inconel 706 superalloy

Inconel 706 is a nickel–iron-based superalloy having higher mechanical strength along with easiness of fabrication, which makes it suitable for gas turbine disk applications. The current study investigates the hybrid magnetic-field-assisted powder mixed electric discharge machining (MFAPMEDM) process to improve performance in machining Inconel 706. For conducting experiments, an in-house set-up was designed and fabricated. Experiments were conducted according to the Taguchi L9 OA and ANOVA to examine the effect of the peak current (Ip) and pulse duration (P-on/P-off) on the material removal rate (MRR) and surface roughness (Ra) of the machined samples. The quality of the machined surface is assessed using a field emission scanning electron microscope (FESEM), which has revealed the presence of micro-holes, melted debris and micro-globules on the machined specimen surface. The Ra is significantly affected by Ip (49.63%) and P-off (37.12%). Further, Ip has more than 78% contribution to the MRR. Furthermore, a mathematical model has been established to develop the relation between input and output factors.

The Mechanism of Creep during Crack Propagation of a Superalloy under Fatigue-Creep-Environment Interactions.

In this study, we examine the mechanism of fatigue-crack propagation in 718Plus superalloy at 704 °C under fatigue–creep–environment interactions, in this case, a new turbine disc material used in aero-engines at high temperatures. The effect of creep on the fatigue-crack propagation of the superalloy at high temperature was also researched. There was an unusual inhibitory effect on the propagation of fatigue cracks in 718Plus alloy, in which the propagation rate of fatigue cracks decreased with the increase of creep time through exploration of dwell-fatigue-crack growth (DFCG) test with different creep times. In particular, under lower stress intensity factor range (ΔK) conditions, the fatigue-crack growth rate with a 90 s hold-time was one order of magnitude lower than that with a 5 s hold-time. Conversely, the gap between the two DFCGs gradually decreased with the increase of ΔK and the creep effect became less apparent. The mechanism of crack propagation in 718Plus alloy under two creep conditions was investigated from a viewpoint of the microstructure, oxidation rate at high temperature and crack path morphology under different conditions.

Calculation of hybrid reliability of turbine disk based on self-evolutionary game model with few shot learning

A turbine disk design based on uncertainty quantifies the risks and improves the structural reliability. An optimized design issue related to turbine disk fatigue life reliability with subjective and objective multi-source uncertainties is a three-layer nested analysis process, where each iterative step requires a double-layer nested analysis containing probability and improbability. A self-evolution game model is proposed to solve the efficiency problem of the optimized design issue under a specific accuracy requirement. In the initial state, only a few sample points are needed to start the game. In the process of its evolution, the most valuable points are searched automatically, and performance functions are identified only at the points where the game diverges. The maximum failure probability is obtained after game consistency is achieved. Accuracy and efficiency are verified with typical numerical examples. The method is adopted to analyze the hybrid low cycle fatigue reliability of a real turbine disk. It is found that, owing to the elimination of an unnecessary artificial distribution hypothesis, the reliability is lower under the same safety life, and the results are more in line with engineering practice.

Steady and Transient Thermal State of Turbine Disk Estimation for Life Time Monitoring

Abstract In connection with increasing intensification of the working process in a gas turbine engine and increasing requirements for economy, the problem of defining and monitoring the main parts lifetime is becoming more vital. Modern algorithms of the monitoring systems are based on taking into account the levels of part temperature and total equivalent stress throughout the flight cycle. Thermal and stress-strain states of the critical zones of the main parts are determined on the basis of information received from the sensors installed in the engine gas path. Turbine disks are located in the internal cavities of the engine and are cooled by air from the compressor. However, in some designs, the disk cavity can be separated from the place of cooling air bleed by several stages of non-contact labyrinth seals, which will lead to some delay in changing the parameters of the cooling air flow when changing the engine operating mode. It has been observed that if this situation is not taken into account, it can lead to significant errors (more than 40%) in determining the lifetime for the peripheral zone of the disk. At the same time, this error is minimal for the hub and the middle zone of the disk, and the existing monitoring algorithms can be used.

A study on the additive manufacturing of a high chromium Nickel-based superalloy by extreme high-speed laser metal deposition

Nickel-based superalloys have been widely used in manufacturing turbine blades, vanes, and discs of aircrafts and power generators that serve in challenging environment. In order to meet the requirements for rapid manufacturing of these large-scale and high-performance components, the extreme high-speed laser metal deposition (EHLMD) technology have attracted great attention in recent years. The EHLMD technology can significantly improve the efficiency compared with conventional laser metal deposition (LMD). Meanwhile, the solidification condition and the resultant microstructures and mechanical properties can also be dramatically changed. In this study, a high chromium superalloy (K648) has been additively manufacturing by using EHLMD for the first time. The key process parameters and the resulted microstructure and mechanical properties are investigated. The results have shown that the most important factors affecting the height, width, and depth of the single-track deposit of EHLMD K648 superalloy are powder feeding rate, laser power, and scanning speed, respectively. The height and the width of the deposits are the largest when the laser power, scanning speed, and the powder feeding rate are 1400 W, 25 m/min, and 30 g/min. There exist some incomplete fusions in the interlayer region and some pores in the interior region of the multi-track-multi-layer deposits. Columnar grains grow in the build direction within each layer, while equiaxed grains tend to form in the interlayer region. The average value of microhardness of EHLMD K648 superalloy is about 298.1 HV. The ultimate strength of EHLMD K648 superalloy is slightly lower than that of the forging GH648 superalloy but higher than that of the conventional LMD K648 superalloy.

Fatigue crack growth mechanisms in powder metallurgy Ni-based superalloys—A review

Powder metallurgy (PM) Ni-based superalloys are widely used for aeroengine turbine disc applications due to their excellent mechanical properties and good corrosion resistance at elevated temperatures. Understanding the fatigue crack growth (FCG) mechanisms of PM Ni-based superalloys is important for both disc alloy development and life prediction of disc components in these advanced aeroengines where damage tolerance design prevails. FCG in PM Ni-based superalloys is a complicated function of microstructure, temperature, loading conditions and environment and is usually a consequence of the synergistic effects of fatigue, creep and environmental damage. In this review, the mechanisms controlled by microstructural features including grain size, grain misorientation, γ′ size and distribution on short and long FCG behaviour in PM Ni-based superalloys are discussed. The contribution of creep and environmental damage to FCG has been critically assessed. The competing effects of mechanical damage (i.e. fatigue and creep) and environmental damage at the crack tip are microstructure-sensitive, and usually results in transition between transgranular, mixed-trans-intergranular and intergranular FCG depending on the contribution of environmental damage to FCG processes.

Experimental Study on Fatigue-Creep of P/M FGH96 Superalloy with Different Holding Time

The fatigue-creep deformation characteristics and evolutions of microstructure of P/M superalloy FGH96 widely used for the turbine disc of an aero-engine were investigated experimentally. The low cycle fatigue-creep tests with different holding times were performed at 550℃. The influence of the holding time on the stress-strain curve, cyclic strain response, fatigue-creep life and damage mechanism were discussed. The results reveal that the holding time has a significant effect on the fatigue-creep deformation characteristics. As the holding time increases, the hysteretic energy of inelastic strain rises, the steady-state hysteresis curve shifts to the right and the envelope strain and the envelope strain rate increase. Fatigue-creep life decreases firstly exponentially and then stabilizes. The creep damage gradually plays a leading role. The fracture analysis indicates that the introduction of the holding time makes the section appear as a multi-crack source. The fracture mode changes from transgranular fracture to transgranular-intergranular mixed fracture. The slip bands and a small amount of dimples appear in the crack propagation zone and the dimple characteristics of the transient fracture zone are obvious.

A sequential reliability assessment and optimization strategy for multidisciplinary problems with active learning kriging model

The reliability-based multidisciplinary design and optimization is of significance for increasing the quality and economic efficiency in many industrial designs. However, the intensive coupled multidisciplinary analysis and reliability assessment make it impractical for real engineering problems due to the unacceptable computational cost. In this paper, we studied different active learning kriging (ALK) models to approximate the objective function for optimization purpose and the limit state function for reliability assessment purpose. Then, we proposed a sequential reliability assessment and optimization strategy, which satisfies the reliability constraints and then moves to the current optimal point to save the computational resource for optimization iteration, to conduct efficiently the reliability-based multidisciplinary design and optimization. Combined with modified ALK models, the computational cost could be saved by this strategy and it could be demonstrated with a practical case of reliability-based multidisciplinary design and optimization for twin-web turbine disk involving fluid, thermal and structural disciplines.

On the velocity at wind turbine and propeller actuator discs

Abstract. The first version of the actuator disc momentum theory is more than 100 years old. The extension towards very low rotational speeds with high torque for discs with a constant circulation became available only recently. This theory gives the performance data like the power coefficient and average velocity at the disc. Potential flow calculations have added flow properties like the distribution of this velocity. The present paper addresses the comparison of actuator discs representing propellers and wind turbines, with emphasis on the velocity at the disc. At a low rotational speed, propeller discs have an expanding wake while still energy is put into the wake. The high angular momentum of the wake, due to the high torque, creates a pressure deficit which is supplemented by the pressure added by the disc thrust. This results in a positive energy balance while the wake axial velocity has lowered. In the propeller and wind turbine flow regime the velocity at the disc is 0 for a certain minimum but non-zero rotational speed. At the disc, the distribution of the axial velocity component is non-uniform in all actuator disc flows. However, the distribution of the velocity in the plane containing the axis, the meridian plane, is practically uniform (deviation <0.2 %) for wind turbine disc flows with tip speed ratio λ>5, almost uniform (deviation ≈2 %) for wind turbine disc flows with λ=1 and propeller flows with advance ratio J=π, and non-uniform (deviation 5 %) for the propeller disc flow with wake expansion at J=2π. These differences in uniformity are caused by the different strengths of the singularity in the wake boundary vorticity strength at its leading edge.

Research on the Pulsed Eddy Current Sensor of the Crack Depth of Turbine Disk

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