Turbine Disk Research Articles

Deformation mechanism and quantitative characterization of Al2O3 inclusions in powder metallurgy superalloys

By means of implanting inclusions artificially, the evolution law of three-dimensional morphology and size of Al2O3 inclusions in FGH96 powder metallurgy (PM) superalloy during hot iso-static pressing (HIP), hot extrusion (HEX) and hot isothermal forging (HIF) process was investigated by SEM and quasi in situ Micronano-CT. The size change of inclusions during different stages was studied quantitatively, the three-dimensional (3D) morphology of the inclusions was characterized, and the deformation mechanism was proposed. The results showed that the inclusions in powder stage were long stripe or plate-like shape. During HIP, Al2O3 inclusions were mechanically bonded to the alloy matrix, and its chemical composition, morphology and size remained unchanged. During HEX, Al2O3 inclusions were broken and elongated into chain shape due to shear stress. The quantitative relationship between inclusion size after extrusion and extrusion ratio as well as original inclusion size was established. During HIF, the relationship between 3D morphology, size, orientation and deformation of a single inclusion during forging compression was quantitatively characterized by quasi in-situ micronano-CT for the first time. The above evolution law provides theoretical basis and technical support for improving the purity level of powder turbine disk.

Failure correlation evaluation for complex structural systems with cascaded synchronous regression

Failure correlation evaluation of complex structural systems is a complex analysis problem involving multiple disciplinary analyses and multiple response objectives, whose high-nonlinearity performance function makes the traditional methods are difficult to acquire acceptable computing accuracy and efficiency. In this case, a cascaded synchronous regression (CSR) method is proposed by combining the multi-level decomposition cooperation strategy and the random regression tree modeling algorithm. In CSR modeling, the multi-level and multi-stage complex structural system is first decomposed into several correlated single-level and single-stage distributed subsystems; moreover, based on the random regression tree algorithm, the corresponding nonlinear mapping model for each distributed subsystem are established; finally, by performing the CSR-based system reliability simulation and Copula functions, the failure correlation relationships can be quantified. The effectiveness of proposed method is validated by the multi-site and multi-mode failure correlation evaluation of aeroengine turbine disc. The current efforts open up an effective way to realize the high-accuracy failure correlation evaluation of complex structural systems, and shed a light on the structural reliability design theory.

Probabilistic Risk Assessment for Life Extension of Turbine Engine Rotors

Maintaining the component service life beyond its historical limits requires the ability to accurately quantify component reliability and address the uncertainties in material responses. A probabilistic method for predicting the total fatigue life was developed and applied to determine the probability of failure of a Ti-6Al-4V turbine disk component. The total fatigue life incorporates a dual mechanism approach including the crack initiation life and propagation life while simultaneously determining the associated initial flaw sizes. A microstructure-based model was employed to address the uncertainties in material response and relate the crack initiation life with crack size. The propagation life was characterized using both small and large crack growth models to ensure accurate fatigue life prediction. Fatigue life predictions were found to correlate with experimental data at high stress levels. The risk assessment can be used to estimate the expected initial crack sizes from variability in material properties, which can further be used to establish an enhanced inspection planning.

Effects of microstructure and temperature on short fatigue crack propagation behaviour of powder metallurgy superalloy FGH4098 in vacuum

Short fatigue crack propagation (SFCP) behaviour of a powder metallurgy (PM) superalloy (i.e. FGH4098) for aeroengine turbine disc application was investigated at room temperature and 650 °C in vacuum (10−3 pa) by in-situ fatigue test. The SFCP mechanism was analyzed by the microstructural characterization and assessment of the SFCP rate. The results show that the SFCP resistance of fine grained (FG) FGH4098 is slightly better than that of coarse grained (CG) FGH4098 at room temperature due to the hindering effects of grain boundary, and close to that of CG FGH4098 at 650 °C. The temperature exerts more evident influence on SFCP behaviour of FG FGH4098 due to the grain boundary oxidation compared with that of CG FGH4098. In the scenario which grain boundary oxidation is absent or insignificant, SFCP shows transgranular feature and is closely related to slip bands linked to the slip systems with high Schmid factor and/or geometric compatibility factor. Grain boundary oxidation still occurs in both FG and CG FGH4098 alloy and mainly forms Cr oxides at 650 °C, which results in intergranular or mixed-inter-transgranular SFCP and promotes SFCP to some extent for FG FGH4098 alloy.

Comprehensive evaluations of heat transfer performance with conjugate heat dissipation effect in high-speed rotating free-disk system of aero-engines

Thermal boundary conditions of the turbine disk cavity system are of great importance in the design of secondary air systems in aero-engines. This study aims to investigate the complex heat transfer mechanisms of a rotating turbine disk under high-speed conditions. A high-speed rotating free-disk model with Dorfman empirical solutions is developed to evaluate the heat transfer performance considering various factors. Specifically, the influence of compressibility, variable properties, and heat dissipation is determined using theoretical and numerical analyses. In particular, a novel combined solution method is proposed to simplify the complex heat transfer problem. The results indicate that the heat transfer performance of a free disk is primarily influenced by the rotating Mach number, rotating Reynolds number, Rossby number, and wall temperature ratio. The heat transfer temperature and Nusselt number of the free disk are strongly correlated with the rotating Mach number and rotating Reynolds number. Analysis reveals that heat dissipation is a critical factor affecting the accurate evaluation of the heat transfer performance of the turbine disk. Thus, the combined solution method can serve as a reference for future investigations of flow and heat transfer in high-speed rotating turbine disk cavity systems in aero-engines.

A brief review on the status of machining technology of fir-tree slots on aero-engine turbine disk

The machining precision and its consistency of turbine disk fir-tree slots have a direct influence on the performance of aero-engine rotor components. However, the structural dimensions of fir-tree slot are small, and the cutting performance of materials is extremely poor, which lead to great difficulty in machining and very few available machining methods. With the application of new materials in the aero-engines, the machining precision and quality requirements of fir-tree slots are further improved. Therefore, many research achievements on the high-efficiency, high-quality and low-cost machining technology of turbine disk fir-tree slots have been obtained. By summarizing and classifying the machining methods of aero-engine turbine disk fir-tree slots, a brief review on the characteristics of different methods are presented in detail, which provide a reference for selecting the appropriate machining method of turbine disk fir-tree slots in the field of aviation manufacturing. Meanwhile, combined with the research and application status of machining technology of turbine disk fir-tree slots, it is presented that multi-process compound machining is an effective method to realize high-efficiency, high-quality and low-cost precision machining of turbine disk fir-tree slots, such as wire electro discharge machining (wire-EDM) and profiled grinding, wire electrochemical machining (wire-ECM) and profiled grinding, wire-EDM and broaching, milling and broaching.

Turbomachinery design of an axial turbine for a direct fired sCO2 cycle

This paper presents the details of the design process of a 950 MW rated sCO2 turbine for a direct fired sCO2 power plant. The design is made by using a meanline turbomachinery design code, which is then used in a design optimization process using mixed integer distributed ant colony optimization (MIDACO) algorithm. Turbine blade and disk designs and key turbomachinery design metrics are optimized by using a three-step optimization procedure. A single-flow and a double-flow turbine design were made by using the design optimization procedure. The two turbine designs made in this work represent the first publicly available information on detailed turbine parameters for a large-scale sCO2 turbine, which has unique temperature and pressure design requirements compared to the turbine design conditions used in comparable sCO2 cycle literature.

Structural reliability with credibility based on the non-probabilistic set-theoretic analysis

A structural reliability analysis method based on the non-probabilistic credible set model is proposed in this paper. Compared with the probabilistic method, the developed method overcomes the high requirement for the sample size of structural uncertain parameters. Moreover, it surpasses the traditional non-probabilistic reliability analysis method by relating the reliability index to its corresponding credibility. Via introducing the non-probabilistic credible set uncertainty quantification, the distribution range of the required credibility for structural uncertain parameters can be determined by scant samples. Accordingly, the improved uncertainty propagation analysis methods based on the non-probabilistic credible set uncertainty quantification are established to obtain the bounds of structural response by transforming into local coordinate system. The non-probabilistic credible reliability index is constructed and three advanced efficient approaches are developed to calculate that. Moreover, the procedure of structural non-probabilistic credible reliability analysis method is built by combining the above content. Besides, the influence of credibility on non-probabilistic credible reliability is discussed. A cantilever beam example, an aeroengine turbine disk case and a pressure vessel case are utilized to verify the feasibility of applying the proposed approach to various engineering problems.

Advancing asymptotic approaches to studying the longitudinal and torsional oscillations of a moving beam

This paper analyzes the influence of kinetic and physical-mechanical parameters of systems on the characteristics of dynamic processes in moving one-dimensional nonlinear-elastic systems. Improved convenient calculation formulas have been derived that describe the laws of changing the amplitude-frequency characteristics of systems for both a non-resonant case and a resonant one. An important issue of studying the influence of the speed of movement of elements of mechanisms on the oscillations of one-dimensional nonlinear-elastic systems has not been considered in detail until now in the scientific literature. This issue relates to the vibrations of shafts in gears, pipe strings when drilling oil and gas wells, the oscillations of turbine blades and rotating turbine discs, the longitudinal vibrations of the beam as an element of structures. The main reason for this in the analytical study of dynamic processes were the shortcomings of the mathematical apparatus for solving the corresponding nonlinear differential equations that describe the laws of motion of those systems. It was found that in the case of longitudinal oscillations in the moving beam with an increase in the longitudinal speed of the medium to 10 m/s, the amplitude of the oscillation also increases by 13.5 %. However, when the longitudinal velocity of the beam is 5 m/s, the amplitude will increase by only 3 %. It is established that with the growth of the amplitude, the frequency of longitudinal oscillations decreases sharply, and if the system moves at a higher speed, for example, 20 m/s, it reduces the frequency of oscillation by about 13 %. The results reported here make it possible to assess the effect of kinetic and physical-mechanical parameters on the frequency and amplitude of oscillations. The research that involved the asymptotic method makes it possible to predict resonant phenomena and obtain engineering solutions to improve the efficiency of technological equipment.

Adaptive Local Maximum-Entropy Surrogate Model and Its Application to Turbine Disk Reliability Analysis

The emerging Local Maximum-Entropy (LME) approximation, which combines the advantages of global and local approximations, has an unsolved issue wherein it cannot adaptively change the morphology of the basis function according to the local characteristics of the sample, which greatly limits its highly nonlinear approximation ability. In this research, a novel Adaptive Local Maximum-Entropy Surrogate Model (ALMESM) is proposed by constructing an algorithm that adaptively changes the LME basis function and introduces Particle Swarm Optimization to ensure the optimality of the adaptively changed basis function. The performance of the ALMESM is systematically investigated by comparison with the LME approximation, a Radial basis function, and the Kriging model in two explicit highly nonlinear mathematical functions. The results show that the ALMESM has the highest accuracy and stability of all the compared models. The ALMESM is further validated by a highly nonlinear engineering case, consisting of a turbine disk reliability analysis under geometrical uncertainty, and achieves a desirable result. Compared with the direct Monte Carlo method, the relative error of the ALMESM is less than 1%, which indicates that the ALMESM has considerable potential for highly nonlinear problems and structural reliability analysis.

Comprehensive investigations on fluid flow and heat transfer characteristics of a high-speed rotating turbine disk cavity system of aero-engine

Thermal loading management of turbine disks get important attention in the safety of aero-engines due to a large temperature level and gradient differences in the turbine disk cavity. This study conducts a comprehensive evaluation to address complex heat transfer problems in a high-speed rotating turbine disk cavity system, fully considering multiple factors. A theoretical derivation is conducted to fully elaborate the multifactor influencing mechanisms of the system based on similarity criteria and a dimensional analysis method. Notably, a high-speed rotational experimental platform of rotating disk is established to verify the research method's reasonability and the result's accuracy. Furthermore, four dimensionless operation cases are conducted to assess the correlation mechanism of the system performance with a strong rotating flow and heat transfer. The results indicate that the main correlation factors of the disk cavity system performance are the flowing Reynolds number, rotating Mach number, rotating Reynolds number, specific heat ratio, and wall temperature. Moreover, the Rossby number and the swirl ratio are used to evaluate the fluid flow characteristics. With the increase in the flowing Mach number from 0.006 to 0.15 and the rotating Reynolds number from 0.74 × 106 to 14.80 × 106 at 9000 rpm, the Nusselt number on the rotor disk wall enhances to 1639.4 and 1286.9, respectively. However, it decreases to 1001.91 for the rotating Mach numbers in the range of 1800–13,500 rpm. Particularly, the dimensionless heat flux is in the range of 0.0026–1.23 under multifactor effects. In summarizing, the present findings are of importance for improving the thermal management and performance reliability of aero-engines by developing an advanced turbine disk cooling system.

Grinding force during profile grinding of powder metallurgy superalloy FGH96 turbine disc slots structure using CBN abrasive wheel

Grinding force during profile grinding of powder metallurgy superalloy FGH96 turbine disc slots structure using CBN abrasive wheel

Performance Analysis of Rotating Shaft of Air Compressor for Hydrogen Battery

The rotating shaft is the key component of the air compressor connecting the bearing seat and turbine disk for hydrogen battery, and its working reliability affects the safety of the air compressor.The rotating shaft is the key component of the air compressor for hydrogen energy battery connecting the bearing seat and turbine disk, and its working reliability affects the safety and life of the air compressor. The performance analysis and comparison of the typical structure of the rotating shaft of an air compressor are carried out, which provides experimental data for the vibration of an air compressor and lays a theoretical foundation for the relevant design of enterprises.

Couple effects of temperature and fatigue, creep-fatigue interaction and thermo-mechanical loading conditions on crack growth rate of nickel-based alloy

The ambient and high-temperature fatigue crack growth behaviors in C(T) and SENT specimens of Ni-based superalloy for turbine disk application were studied in a wide interval of temperatures 25–750°C using a combination a electro- and servohydraulic test systems and fractographic investigations. The fatigue, creep-fatigue interaction and thermo-mechanical in-phase fatigue (TMF IP) crack growth tests are performed under isothermal and dynamic waveforms loading conditions. The interpretation of the experimental results is given in terms of the traditional stress intensity factors and C-integral as well as new normalized cyclic fracture diagrams. It is found that there are definite temperature-sensitive regions separate for harmonic fatigue and creep-fatigue interaction loading conditions in which the crack growth rate of Ni-based alloy increases sharply. Scanning electron microscopy in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. The couple effect of temperature ranging and isothermal and dynamic waveforms loading conditions on fatigue life was discussed.

Characterization and cause analysis of the “bright spots” on the surface of a GH2674 large-size gas turbine disk

After surface turning process, many surface defects (visually shown as “bright spots”) were found on both sides of the large-size turbine disk. Macro- and microscopic inspections illustrated the distribution of the spots, hardness variation and morphologies inside the spot regions. MC carbides, Laves phases, Mo2C carbides, η phases, G phases were found in the spot regions by SEM, TEM and EDS. The depth of the aggregated precipitates was shown by 3D X-ray tomography. It is indicated that the optic difference of the “bright spots” is due to the change of surface roughness after the cutting tool passed through the segregation regions with higher hardness. The bright spots are essentially freckle defects, which originated from the Ti segregated zones in the ingot. The effect of these defects on the tensile and fatigue properties were further analyzed. The remedial methods are then proposed to alleviate the detrimental effect of the bright spots.

Comparison of wrought and additively manufactured IN718 concerning crack growth threshold and fatigue crack growth behaviour

Rotary components in turbine machinery such as gas turbine blades and discs or turbocharger wheels need to be designed so that high cycle fatigue (HCF) loads are well below the fatigue endurance limit to ensure safe operation. This requires an accurate measurement of the fatigue endurance limit and the related intrinsic fatigue crack growth (FCG) threshold. Furthermore, knowing the FCG threshold is crucial in order to assess the criticality of initial defects (e.g. cavities, carbide nests, etc.). In this study, the influence of the manufacturing route on the FCG threshold and the FCG behaviour at 650 °C in air of the nickel based superalloy IN718 is investigated. For this, a per Laser Powder Bed Fusion (LPBF) process manufactured version is compared to a conventionally wrought IN718 material state, both in the short and long crack regime. To measure crack growth increments of about 1 μm, an alternative pre-cracking and threshold test procedure is proposed for high temperature testing. To assess the behaviour of both material states in the short crack growth regime, cyclic R-curves have been generated taking the influence of two different R ratios into account. A further comparison of the FCG behaviour of the LPBF and the wrought material state is made on the basis of da/dN-ΔKI plots, with a focus on the Paris regime created from both classical FCG tests as well as continued threshold tests. The results observed are discussed in relation to the initial characterization of the two material states, which includes tensile tests at room temperature and at 650 °C as well as microstructural investigations.

A novel non-destructive testing method for turbine disks using dual array ultrasonic transducer.

A novel dual array inspection method for detecting the diffusion bonding defects of superalloy turbine disk has been proposed in this study. The influence of relative position between the planar defect and acoustic source has been analysed, and based on which, the transmission and reception algorithm for the dual array method has been proposed. The time delay law of the dual array transducer for the complex turbine disk structure has been investigated. Finite-difference time-domain theory has been used to establish the numerical model of the dual array method. In the numerical simulations, the novel method has been applied for the superalloy turbine disk specimen with prefabricated defects at the depth of 18.3 m and 28.3 mm. Furthermore, the corresponding experiment has been conducted and verifies the reliability of the simulation. The novel method shows advantages in detecting small diffusion bonding defects in complex structure, assisting the manufacture of superalloy turbine disks, and ensuring the safety of aircrafts.

Effect of inlet flow ratio on heat transfer characteristics of a novel twin-web turbine disk with receiving holes

A new type of twin-web turbine disk (TWD) with receiving holes was designed and the corresponding simulation model was established. The effects of the inlet flow ratio of nozzle 1 to center inlet ( P 1 ) and the flow ratio of nozzle 1 to nozzle 2 ( P 2 ) on the heat transfer characteristics of the system were investigated. The RNG k-ε turbulence model was adopted as the simulation model. Maximum disk temperature ( T max ), the axial and radial temperature uniformity of the turbine disk were used as evaluation indexes. The results showed that T max was the lowest and both the axial and radial temperature uniformity were relatively good when P 1 approached infinity. The effect of P 2 on the heat transfer characteristics of the TWD with receiving holes was investigated by keeping P 1 tending to infinity. Considering comprehensively, when P 2 was equal to 2–3, T max , radial and axial temperature uniformity were relatively good. Compared with the previous optimization results of a traditional TWD done by our group, T max was 8.5 K lower and the maximum axial temperature difference was 4 K lower for the novel TWD. The radial temperature uniformity of the TWD with receiving holes was also better than that of the traditional TWD.

Design of Ni-based turbine disc superalloys with improved yield strength using machine learning

Design of Ni-based turbine disc superalloys with improved yield strength using machine learning

Modelling and predictions of time-dependent local stress distributions around cracks under dwell loading in a nickel-based superalloy at high temperatures

Finite element (FE) analysis modelling of crack configurations was used to provide insights into the role of time-dependent deformation on dwell fatigue crack growth (DFCG) in turbine disc alloys. In particular, the potential influence of time-dependent deformation on fatigue crack growth rates observed during dwell holding periods and the potential crack growth retardation phenomena that can occur for overload-dwell cycles were investigated. The FE model evaluated the mechanical stress state evolution in a two-dimensional cracked geometry subjected to standard dwell and overload-dwell stress waveforms for a given microstructural condition (based on its γ’ particle distribution). Crack-opening stress distributions as a function of dwell time and distance ahead of the crack-tip were interrogated, with the aim to investigate the potential influence of local crack-tip stresses on crack growth during dwell holding periods and the potential for crack growth retardation following overload cycles. Stress distribution profiles predicted by dwell-only simulations showed how quickly local crack-tip stresses relax due to time-dependent plasticity. Characteristic effects of overloads of dwell crack growth resistance observed in experiments were also reasonably well captured. A numerically-derived incubation time was successfully applied in predicting the general trends of achieving more pronounced retardation effects with larger overload factors and extended periods of overloading prior to periods of dwell. FE modelling predicted a significant difference in behaviour between an overload for a given overload factor with a hold time at peak load of 1 s and 10 s. This study emphasises the importance of studying local crack-tip stresses in regards to characterising DFCG behaviour of turbine disc alloys.