Turbine Disk Research Articles

Turbulence distortion and blockage in the induction zone of a horizontal axis turbine

Wind tunnel measurements of the incident turbulent velocity fields and axial forces on a horizontal axis turbine and porous disc analogues are reported. The models were tested in both a simulated atmospheric boundary layer (ABL) and in grid turbulence, allowing for a range of turbulence length scale to rotor diameter ratios to be considered. A theoretical framework to account for the combined effect of distortion and potential flow blocking in the induction zone is presented. In the case of very large length-scale turbulence to diameter ratios, where distortion effects are minimal, a quasi-steady approach is adopted for the effect of blocking. For the small length-scale ratio limit, the method is developed from the classical analyses for rapid distortion of turbulence and blockage from flow through a porous sheet of resistance. For general length-scale ratios, an efficient prediction method based on interpolation between the two length-scale ratio extremes is established. For very large length-scale ratios, a quasi-steady theory without distortion is appropriate for a rotor or disc in a simulated ABL. The small length-scale theory is applicable for tests conducted in grid turbulence. The results of the study can inform the prediction and interpretation of typical measurements of turbulence within the induction zone and the fluctuating loads on a rotor, at both prototype and full scale. This is of particular importance to fatigue load assessments.

Development of ultrasonic phased array technique for inspection of fir-tree type turbine blade root and disc-rim in nuclear power plant

ABSTRACT Steam turbines are crucial in both nuclear and thermal power plants, serving a key role in electricity generation. However, the operational lifespan of these turbines is often limited by failures in the turbine blade roots and disc rims due to fatigue, stress corrosion cracking and creep. Usage of reliable non-destructive technique during in-service inspection of turbine assembly is very important for decision making and safe operation of power plant. The conventional ultrasonic technique which is being employed currently suffers from access limitation, high inspection time and false calls during defect detection due to complex geometry of blade roots and disc rims. To address these issues, an advanced ultrasonic inspection technique using phased array technology was developed, specifically tailored for fir-tree type blade roots and disc rims. Ultrasonic Simulation studies were performed to determine the optimal parameters for phased array probes, ensuring the effective detection and precise sizing of crack-like defects. This manuscript presents the findings from these simulations, along with experimental results from phased array inspections of turbine blade root and disc rim mockup of turbine assembly in nuclear power plant.

Broaching Digital Twin to Predict Forces, Local Overloads, and Surface Topography Irregularities.

Broaching is a key manufacturing process that directly influences the surface integrity of critical components, impacting their functional performance in sectors such as aeronautics, automotive, and energy. Such components are subjected to severe conditions, including high thermomechanical loads, fatigue, and corrosion. For this reason, the development of predictive models is essential for determining the optimal tool design and machining conditions to ensure proper in-service performance. This study, therefore, presents a broaching digital twin based on hybrid modelling, which combines analytical, numerical, and empirical approaches to provide rapid and accurate predictions of the forces per tooth, local overloads, and surface topography irregularities. The digital twin was validated with a critical industrial case study involving fir-tree broaching of turbine discs made of forged and age-hardened Inconel 718. The accuracy of the digital twin was demonstrated by the results: the average error in force predictions was below 10%, and the model effectively identified the most critical teeth and zones prone to failure. It also predicted surface topography irregularities with an error of less than 15%. Interestingly, the relationship between surface topography irregularities and surface residual stress variations across the machined surface was observed experimentally for the first time.

Research on design method of lattice turbine disk based on topology optimization

Abstract As a typical structure of an aero-engine, turbine disk has been used in high-temperature and high-speed environments for a long time, and its mass accounts for a large proportion. Therefore, its lightweight design is urgent. With the development of an aero-engine towards a high thrust-to-weight ratio, the turbine speed continues to increase, and the single-stage load continues to increase, which makes the design of the turbine disk face more problems and challenges. The uniform material turbine disk structure has made it difficult to meet its comprehensive performance requirements. To address this issue, this paper proposes a lattice turbine disk design idea, changing the uniform organization pursued by traditional design and achieving optimal performance through the integration of design innovation and manufacturing process innovation. This paper takes the turbine disk as the research object to establish a lattice turbine disk design method. By using the topology optimization method based on progressive optimization, the cell configuration can be obtained. After that, combined with the structural characteristics of the turbine disk, the design of the dot matrix auxiliary plate disk is realized. Finally, taking a turbine disk as an example, this paper carried out the optimization design of the turbine disk and obtained the lattice disk with better performance, which verified the feasibility of the method.

Study of three-dimensional crack extension in turbine discs of short-life turbojet engines

Abstract A simulation study on the 3D crack extension of short-lived turbojet engine turbine discs was carried out using FRANC3D 3D fracture mechanics software combined with ABAQUS finite element software. By establishing a 3D geometric model of the turbine disc, the crack extension process is simulated by using the sub-model method, and the crack extension behavior and failure mode are analyzed to predict the remaining life of the cracked wheel disc. The results show that the crack expansion path matches well with the crack failure phenomenon of the turbine disc under the actual working conditions; the turbine disc crack is dominated by Type I (open Type) crack expansion, and the stress intensity factors of Type II and Type III are negligible; the crack expansion rate increases slowly with the increase of crack depth, and it rises steeply at the critical value of the fracture failure; and the residual life of the turbine disc is 32 cycles. This study provides empirical analyses for crack monitoring and life prediction of turbine discs and is of great significance for engine maintenance and reduction of end-of-life costs of turbine components.

Aeroengine Disc Simulation Specimen Fatigue Life Prediction Using Modified Critical Distance Theory

The turbine disc is a critical component of an aeroengine, where the mortise experiences severe stress concentration due to the notch effect, making it a vulnerable position for disc fatigue failure. In this study, the simulation specimens were designed based on the mortise structure. Fatigue tests were conducted to explore the failure mechanism under fatigue loading. Elastic-plastic finite element analyses were performed subsequently to investigate the distribution of local mean stress and stress gradient near the notch. Considering the influence of local mean stress and stress gradient, a novel fatigue life prediction method was proposed based on the theory of critical distance (TCD). This method overcomes the disadvantages of the TCD in which the critical distance cannot be determined beforehand and the requirement of a complex iterative process when predicting fatigue life. By using this method, the predicted fatigue life of the simulation specimens under different loads is within ±2 error factor.

Ultrastrong and ductile superalloy joints bonded with a novel composite interlayer modified by high entropy alloy

Diffusion bonding (DB) with interlayers is sought-after for manufacturing high-performance turbine disks of powder metallurgy (PM) superalloys with precise and intricate inner cavity structures. Developing novel interlayer materials is challenging but crucial for enhancing bonding quality and joint properties. We designed a multi-interlayer composite bonding (MICB) method, employing sandwich-structured interlayers of “BNi2/high entropy alloy (HEA)/BNi2”, to join a PM superalloy FGH98. The MICB joint exhibited an ultrahigh shear strength of ∼1132 MPa and exceptional ductility, indicating a typical ductile fracture pattern with numerous dimples. Owing to the introduction of liquid BNi2 interlayer, initial bonding interfaces were eliminated and replaced by newborn grain boundaries (GBs), preventing brittle interfacial fracture. Due to the diffusion of Al/Ti/Ta from the base metals (BMs), massive ordered γ' nanoparticles also precipitated in the joint. Moreover, the addition of HEA foil reduced the stacking fault energy (SFE) of the joint and facilitated the formation of deformation twins (DTs). Thus, during the deformation process, the γ' nanoparticles, and multiple substructures like stacking faults (SFs), Lomer-Cottrell (L-C) locks, DTs, and 9R phases enhanced the work-hardening capability and strengthened the joint. Simultaneously, the multiplication and interaction of DTs induced a softening mechanism of dynamic recrystallization (DRX) during the entire deformation process and dominated when the plastic instability occurred, resulting in numerous adiabatic shear bands (ASBs) consisting of γ/γ' nano-bands, which indicates a significant improvement of the joint ductility.

Flash Sintering of Bimetallic Assemblies for Turbine Disks in Next‐Generation Jet Engines

René 77 and another advanced powder metallurgy nickel‐based superalloy are flash‐sintered and joined to produce a dual‐alloy assembly. This innovative process allows for the sintering of powders to achieve high relative densities or the formation of solid joints in a shorter time than is feasible with conventional diffusion bonding techniques. Examination of the microstructure after heat treatments reveals that diffusion and recrystallization phenomena can modulate the transition zone. The creep properties of both alloys, evaluated using stress relaxation tests, do not seem to differ by more than an order of magnitude, while the higher thermal stability of René 77 compared to Alloy B at 800 °C tips the scales. In tension, base materials show very high properties, while bimetallic specimens exhibit at least higher properties than René 77. However, failure occurs at the bond at high temperatures due to the formation of an oxide film during the bonding process. These encouraging results illustrate the potential and constraints of the flash‐sintering process for producing dissimilar assemblies, which may enhance the properties of next‐generation aero‐engine turbine disks.

Tool wear prediction in broaching based on tool geometry

Abstract The aircraft engine is a safety-critical part of an aircraft. Constructive modifications resulting in ecological and economic improvements of the engine lead to necessary changes in manufacturing processes. The turbine discs in the low-pressure section are made of temperature resistant nickel-based superalloys. For the connection of the turbine blades with the disc, fir-tree slots are machined by broaching. The broaching process achieves high geometrical accuracy as well as process reliable rim zone properties. Alternative manufacturing processes such as milling or wire electrical discharge machining are still the subject of research in many applications and do not yet achieve the required process reliability. Especially in finishing operations, tool geometry is complex. In previous research work, the local rake angle and, as a result, the acting cutting force were determined analytically and empirically. Based on these results, the relationship between tool geometry, cutting force, and tool wear will be investigated in this work to enable a cutting length dependent prediction of tool wear. The aim of this work is a model-based prediction of tool wear for a given cutting length and a previously unknown tool geometry. For this purpose, a method was developed to predict tool wear using empirical test data as well as internal machine data. With the results of this work, it is not only possible to identify critical points on newly developed broaching tools by maxima of the cutting force, but also to predict wear locally, depending on the cutting length.

Simulation method for dynamic characteristics of rotor-support system subjected to environmental loads

An improved finite element method was proposed to investigate the dynamic characteristics of rotor system with environmental loads (temperature and aerodynamic forces) in aeroengines. According to the axial temperature distribution within shaft elements, the polynomials were established for physical properties of material. The derivation for coefficient matrices under thermal loads, and the tensile stiffness matrix considering axial aerodynamic forces were completed, based on the Timoshenko beam theory. A high-pressure rotor was simulated with operating temperature 200∼600∘C, and the magnitude of aerodynamic force is 105N. Furthermore, a squeezed film damper (SFD) was adopted to this rotor-support system, its steady responses were solved by the equivalent coefficient method, and the Newmark-HHT method was utilized to solve the transient responses. The results indicate that the first two critical speeds are reduced by 1.85 % and 2.07 %, which is mainly caused by thermal loads. The rising temperature leads to lower elastic modulus, higher Poisson's ratio and expansion ratio. With the amount of a mass unbalance being 500 g·mm located at the 1st-stage compressor disk (CD1): the 1st resonance peaks at CD1 and turbine disk (TD) increase by 4.56 % and 4.98 %, respectively, and the 2nd resonance peaks at CD1 and TD rise 5.88 % and 5.00 %, separately. Owing to SFD damping, the first two resonance peaks at CD1 and TD decrease by 69 % and 51 %, respectively. Compared to 40 °C, the first two resonance peaks at CD1 increase by 88 % and 55 % at the oil temperature 100 °C. The oil-film damping deteriorates significantly due to the lower oil viscosity in higher temperature. When operating near the first-order critical speed, the transient responses of rotor perform as simple harmonics, circular precession trajectory, dominant rotational frequency, and periodic motions. Overall, the dynamic characteristics of rotor-SFD-support systems exposed to environmental loads can be predicted by the proposed simulation method.

Probabilistic risk assessment of civil aircraft associated failures under condition-based maintenance

Maintenance can improve an aircraft system's reliability over a long operation period or when a component has failed. However, inappropriate maintenance inspection intervals will cause latent failures to be covered or undetected, leading to a large number of unplanned flight disruptions for airlines. In this paper, we present a two-stage framework to assess the associated failure risk of civil aircraft under condition-based maintenance. In the first stage of the framework, the probability of primary functional failure across the lifecycles of the monitored component is determined by analyzing whether the current inspection interval prevents the component from progressing from latent failure to functional failure. In the second stage of the framework, the associated failure probability between components and related systems is formulated by the adjacency matrix. The structure and performance of the proposed model were tested on a case study by run-to-failure data associated with aircraft engines from a large airline. Focusing on the scenario of turbine disk cracking leading to fragment penetration of the fuel tank and causing fire as the consequential fault impact path, the results show that the risk of aircraft fire caused by turbine disk fragments falls within an acceptable range, necessitating the completion of inspections and subsequent monitoring within the stipulated timeframe. The method can be used to readjust the inspection interval, optimize the operation plan, improve the on-time performance of flights, and reduce the risk of aviation accidents.

Multi-Objective Optimization of the Pre-Swirl System in a Twin-Web Turbine Disc Cavity

Enhancing thermal efficiency and minimizing weight are prevailing issues in aero engines. Owing to its hollow structure, the twin-web turbine disc exhibits remarkable weight reduction properties, while its enhanced cooling constitutes a novel challenge. In this study, a twin-web turbine disc cavity system is numerically investigated. To enhance the cooling effect and minimize pressure loss, a multi-objective genetic algorithm and Kriging surrogate model are employed to optimize the radial height of the pre-swirl nozzle and receiver hole in the disc cavity system. The results indicate that the overall performance of Opt-3, derived from the Technique for Order Preference by Similarity to the Ideal Solution method within the Pareto frontier, is superior. This configuration achieves a uniform low distribution of rotor temperatures while maintaining moderate pressure losses. Notably, the maximum temperature is reduced by 21.1 K compared to the basic model, with pressure losses remaining largely unchanged. Additionally, an increase in the flow ratio leads to a reduction in both the maximum temperature and average temperature of the back web while simultaneously increasing the temperature of the front web and augmenting pressure losses. However, it is important to note that the degree of variation in these parameters diminishes with increasing flow ratios.

A modified cyclic elastoplastic constitutive model considering the variational dynamic recovery term of back stress for FGH95 under asymmetrical cyclic loading

The asymmetric cyclic loading process occurs in aero-engine turbine discs. A constitutive model that accurately describes the cyclic elastoplastic behaviour of the material is important for structural design and low cycle fatigue life prediction of turbine discs. In this paper, the low cycle fatigue test of FGH95 was carried out at 620℃ under 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% and 1.1% strain amplitude with strain ratio equal to 0. The material exhibited cyclic hardening followed by cyclic softening at high strain amplitudes and cyclic softening at low strain amplitudes. The mean stress relaxation rate was similar for each strain amplitude. In addition, the evolution of effective stress and back stress was obtained through the method of internal stress division. Then, the relationship between the change in stress amplitude and the change in internal stress was discussed. The results showed that with cyclic loading, cyclic hardening/softening of FGH95 was affected by the competition mechanism of back and effective stresses. Considering that slip deformation and crystal lattice rotation coexist in plastic deformation, the dynamic recovery term of the Abdel-Karim and Ohno model was used. In order to characterize the different magnitudes of back stress change in materials at different plastic strain intervals, a dynamic recovery term coefficient was introduced to the dynamic recovery term and the critical surface of the back stress. The modified model was used to compare with experimental results. Then, it gives a good description of the material’s mean stress relaxation and strain amplitude variation and gives good agreement on the hysteresis loop.

Constitutive model of high-temperature rapid fracture of Si3N4 ceramics for engine turbine discs and their pore insensitivity parameters

ABSTRACT The metallic materials used to manufacture turbine components can potentially be replaced with ceramics such as Si3N4, but the stress on turbine discs is difficult to determine experimentally, which hinders the development and optimization of ceramics. The finite element method solves this problem, but it requires an accurate constitutive model and parameters. Existing methods for determining model parameters lack versatility and do not consider the internal pores of ceramics. This work proposes a method for determining the parameters of the high-temperature rapid fracture constitutive model of ceramics with internal pores based on the results of industrial computed tomography (CT) and high-temperature fracture toughness experiments. The constitutive model for a ceramic with internal pores was selected based on the typical service conditions of turbine discs. Industrial CT was used to measure pore information. A finite element preprocessor was developed to create simulated specimens with pores. The high-temperature fracture toughness of the ceramics was measured. Pore insensitivity was the parameter obtained from the high-temperature constitutive model of ceramics with pores using this method. The maximum relative error between the predicted and experimental flexural strengths was 6.8%. It provides a new idea for determining the parameters of constitutive models for materials with pores.

Topology Optimization of 3D Turbine Disk Considering Thermal Load Based on BESO Method

Topology Optimization of 3D Turbine Disk Considering Thermal Load Based on BESO Method

Genetic Optimization of Twin-Web Turbine Disc Cavities in Aeroengines

Genetic Optimization of Twin-Web Turbine Disc Cavities in Aeroengines

The diminishing positive effect of phosphorus on the creep behavior with the decrease of applied stress in a Ni-Fe-based alloy

Phosphorus can increase the creep and stress-rupture properties of the turbine disk materials served in high stress with short life. However, the effect of P on the creep of boiler tube in advanced ultra-supercritical power plants served in low stress with long life is still unknown. Combining the formula derivation and experimental analysis, the varying effects of P on the creep with the decrease of stress were clarified. The positive effect of P on prolonging the creep rupture life reduces with the decrease of creep stress, even vanishes when the creep stress decreases to 93 MPa, 133 MPa and 140 MPa in the alloy doping 100 ppm, 200 ppm and 400 ppm P, respectively. The degeneration of M23C6 and the dynamic segregation of P at grain boundary during long-term creep under low stress can decrease the deformation coordination between the adjacent grains and the grain boundary binding force, which makes the positive effect of phosphorus on the creep diminish.

An improved adaptive Kriging method for the possibility-based design optimization and its application to aeroengine turbine disk

Possibility-based design optimization (PBDO) can provide theoretical basis for the structural optimal design of fuzzy uncertainty model in engineering, so as to obtain the optimal design variables. The genetic algorithm (GA) based on adaptive Kriging method for PBDO requires high precision in the whole design space, while the region far from the limit state surface (LSS) of the constraint function has little effect on PBDO, thus greatly affects the computational efficiency. In order to improve the efficiency of PBDO, an improved adaptive Kriging method combined with active possibility constraint (I-AK-AC) is proposed in this paper. In I-AK-AC, the enhanced expected improvement learning function is first put forward to promote the convergence efficiency of Kriging model by reducing the accuracy of the region far from the LSS of the constraint function. Whereafter, the active possibility constraint is identified, and only the boundaries of active possibility constraint need to be approximated precisely by Kriging model. By these ways, the convergence speed of Kriging model is further ameliorated without affecting the computational accuracy, and the efficiency of PBDO is significantly improved. Three test examples and an engineering application of aeroengine turbine disk illustrate the validity and accuracy of the proposed I-AK-AC.

A weakest link theory‐based probabilistic fatigue life prediction method for the turbine disc considering the influence of the number of critical sections

A weakest link theory‐based probabilistic fatigue life prediction method for the turbine disc considering the influence of the number of critical sections

Nonlinear dynamics analysis of hydraulic turbochargers in reverse osmosis desalination plants

The hydraulic turbocharger plays a vital role in harnessing the energy stored in brine within reverse osmosis desalination plants. To optimize the efficiency and durability of this equipment, it is crucial to develop accurate dynamic models of the turbocharger rotor. An improved understanding of rotor dynamics enables the integration of innovative technologies such as Hydraulic Energy Management Integration, effectively enhancing efficiencies in systems characterized by small capacities and high rotational speeds. This study presents a dynamic modeling methodology for the hydraulic turbocharger. The analysis involves approximating the turbocharger rotor with an equivalent finite element shaft line model. Verification of the model’s natural frequency is conducted using three-dimensional finite element analysis, employing the ANSYS modal analysis module. Computational fluid dynamics is employed to evaluate the fluid forces, while the Reynolds equation is utilized to assess the journal bearing forces. The resulting model is employed to investigate the nonlinear dynamics of the rotor, examining the impact of various system parameters, including rotational speed, unbalance forces, and shaft geometrical parameters. The results highlight the significance of balancing the turbine and pump disks for optimal performance. Furthermore, the research demonstrates that increasing the shaft length reduces the rotor’s threshold speed, while increasing the shaft diameter initially raises the threshold speed until it reaches a critical value. Beyond this critical value, further increases in shaft diameter lead to a decrease in the threshold speed.