Gas Turbine Applications Research Articles

Potential Use of Additively Manufactured Swirlers for Gas Turbine Applications

Potential Use of Additively Manufactured Swirlers for Gas Turbine Applications

Gamma prime formation in nickel-based superalloy IN738LC manufactured by laser powder bed fusion

Complex components for high-temperature gas turbine applications require materials that offer a combination of excellent high-temperature strength and oxidation resistance. Nickel-based superalloys with high gamma prime (γ´) volume fractions are particularly suited for these applications, especially combined with additive manufacturing for intricate geometries. Despite the complex thermal history that these materials experience during laser powder bed fusion (LPBF) processing, γ´formation is suppressed when manufacturing IN738LC, which has a medium equilibrium γ´content of about 40–50 vol%. This study follows γ´formation in LPBF IN738LC during subsequent annealing treatments at temperatures ranging from 745 °C to 865 °C, creating an experimentally determined TTT (temperature-time-transformation) diagram. This diagram is largely based on scanning electron microscopy (SEM) imaging supported by Vickers hardness measurements and scanning transmission electron microscopy (STEM) bright field imaging. Atom probe tomography (APT) of the as-built material indicated nm-sized regions depleted in Cr and enriched in Ni, Al, and Ti, but show no characteristic superlattice patterns in TEM diffraction. APT and TEM diffraction analysis of material annealed at 850 °C for 3 min confirmed the presence of the γ´phase but indicated that γ´had formed through spinodal decomposition instead of precipitation.

Machining of additively manufactured alloy 718 in as-built and heat-treated condition: surface integrity and cutting tool wear

AbstractAdditive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

Hydrothermal scenario of buoyancy-driven magnetized multi-walled carbon nanotube-Fe3O4-water hybrid nanofluid flow within a discretely heated circular chamber fitted with fins

This investigation unfolds the hydrothermal changes of magnetized buoyancy-driven multi-walled carbon nanotube (MWCNT)-Fe3O4-water hybrid nanofluidic flow through two centrally placed circular cylinders. Four rectangular T-shaped fins are affixed with the internally placed comparatively small-sized heated cylinder, while the outer cylinder is discretely heated. Four different types of heater-cooler segment arrangements along the outer cylinder periphery are set to execute the investigation. The flow-related leading equations and boundary restrictions are presented and altered to their dimensionless form via suitable similarity transformations. Both nondimensional momentum and energy equations are solved by employing the Galerkin-finite-element technique. Numeric and experimental comparisons are executed to ensure the model’s accuracy. Several streamlines, isotherms, and Nusselt number graphics are revealed to explore the parametric impacts. Results assure accelerated velocity trajectory for Rayleigh numbers, while the flow seems to decelerate for magnetic effect and higher nanoparticle concentrations. Case 1 and Case 3 exhibit higher velocity magnitude and heat transmission out of all four designed cases. Case 1 promotes a 4.68% enhancement in heat transference compared to Case 3 for Rayleigh numbers within the range 104 to 105. Enhanced nanoparticle concentrations assist Case 1 in disclosing 8.13% higher heat transport compared to Case 3. This hydrothermal numeric investigation of natural convective magnetized hybrid nanofluidic inside discretely heated annular chambers might have promising applications in gas turbines, thermal storage devices, heat exchangers, solar receivers, electronic cooling, etc.

Investigating the efficiency of the microwave heating process for the carbothermic synthesis of cobalt/nickel alloys

High energy consumption and its associated pollution fare among the significant issues of metal production systems. Traditional furnaces currently used in the production of alloys. The microwave heating process is a novel approach with numerous advantages compared to the conventional heating processes. On the other hand, cobalt/nickel alloy, is an important alloy with extensive applications in jet engines, gas turbines, and petroleum refining. The present research addressed the efficiency of the microwave heating process for the carbothermic synthesis of cobalt/nickel alloys. Moreover, the morphology of the produced material was evaluated. The synthesis method was based on the reduction of cobalt/nickel oxides to cobalt/ nickel alloys. Two parameters of the reaction time and the composition of the granules containing cobalt/nickel oxides were investigated to assess the efficiency of the reduction process. The results showed a decrease in the oxygen content from 20 to about 10 wt% by prolonging the processing time from 10 to 20 min. XRD analysis also indicated no crystal structure related to nickel oxide in the samples processed for 20 min. The diameter of the crystals also increased by about 71 % by prolonging the reaction time from 10 to 20 min, suggesting the growth of the crystals and enhanced adhesion of the particles. The number of oxygen atoms was also decreased by about 50 % upon increasing the reaction time from 10 to 20 min, indicating a better reduction reaction. A rise in the nickel oxide content in the raw granule from 30 % to 60 %, led to a 3.8-fold enhancement in the number of oxygen atoms in the reduced product.

Options for Improving Performance of Additively Manufactured Nickel-Base Superalloys for Gas Turbine Applications

Abstract Additive manufacturing (AM) has been increasingly used for gas turbine (GT) components over the last decade. Many different components can be successfully designed, printed, and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g., creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys, and there still exists a gap in understanding the high temperature processing–structure–properties–performance relationships of these alloy systems. This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on the resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multistep aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties. The results show that there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3× in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components.

The performances and applications of gas turbines in the aviation industry

This paper focuses on using gas turbines in various industries, particularly aviation, due to their unique power-to-weight ratio. It provides a detailed description of how gas turbines operate based on the thermodynamic Brayton cycle, which includes compressors, combustors, and power turbines. Additionally, the paper analyses both ideal and realistic cycles of gas turbines. Despite numerous advantages, gas turbines have limitations, such as high fuel consumption. However, technological advancements have led to the development of more efficient and quieter gas turbines. The paper explains the classification of jet engines, including turbojets, turboprops, and turbofans, each with specific applications. Moreover, the paper discusses the efforts to reduce the use of fossil fuels in aviation due to the increasing awareness of the impact of climate change. Scientists and engineers are exploring substitute fuels and materials and developing gas turbine systems that maximize work generated with minimal combustion; thus, this paper also highlights the importance of developing more efficient and environmentally friendly gas turbines to reduce the industry's carbon footprint while maintaining their productivity.

Small-scale power generation using stationary gas turbine with renewable energy

This article mainly discusses one of the most important applications of stationary gas turbinesthe small-scale power generation. Micro/Small-scale gas turbines have immense hidden potential due to fuel flexibility, low emissions and maintenance. In recent years, the substantial pressure to address environmental issues has led people to focus more on green technologies, so most of the related applications of micro gas turbines use renewable energy like wind energy or biomass. Small-scale power generation can be applied in commercial and residential areas and areas with worse living conditions, such as rural or remote ones. And it is usually designed to exploit more waste heat for cooling/heating purposes. Anyway, there are still drawbacks exist. These turbines require high angular velocity and advanced electronics that can convert high-frequency electricity. The author surveyed distributed energy generation, biomass power plants and mini/micro gas turbines, some typical examples of small-scale power generation that are also stationary and have combustion processes. This application of stationary gas turbines is relatively more innovative and updated than others, so there are not many reliable researches posted online in recent years. This paper will reference all the researchers who want to work in this field.

Data-augmented modeling for yield strength of refractory high entropy alloys: A Bayesian approach

Refractory high entropy alloys (RHEAs) have gained significant attention in recent years as potential replacements for Ni-based superalloys in gas turbine applications. Improving their properties, such as their high-temperature yield strength, is crucial to their success. Unfortunately, exploring this vast chemical space using exclusively experimental approaches is impractical due to the considerable cost of the synthesis, processing, and testing of candidate alloys, particularly at operation-relevant temperatures. On the other hand, the lack of reasonably accurate predictive property models, especially for high-temperature properties, makes traditional Integrated Computational Materials Engineering (ICME) methods inadequate. In this paper, we address this challenge by combining machine-learning models, easy-to-implement physics-based models, and inexpensive proxy experimental data to develop robust and fast-acting models using the concept of Bayesian updating. The framework combines data from one of the most comprehensive databases on RHEAs (Borg et al., 2020) with one of the most widely used physics-based strength models for BCC-based RHEAs (Maresca and Curtin, 2020) into a compact predictive model that is significantly more accurate than the state-of-the-art. This model is cross-validated, tested for physics-informed extrapolation, and rigorously benchmarked against standard Gaussian process regressors (GPRs) in a toy Bayesian optimization problem. Such a model can be used as a tool within ICME frameworks to screen for RHEAs with superior high-temperature properties. The code associated with this work is available at: https://codeocean.com/capsule/7849853/tree/v2.

Design and optimization of fatigue life studies on induction hardened IN718 alloy for gas turbine applications

ABSTRACT The Inconel 718 (IN718) superalloy is commonly used as a component in industrial gas turbines due to its excellent corrosion resistance and high-temperature properties. Generally, gas turbines experience failure in their service on account of high thermal fatigue. In the present research, specimens of Inconel 718 superalloy are treated at two different temperatures 850℃ and 1000℃ (IHT1 & IHT2) with oil quenching, respectively. The specimens are studied with controlled strain amplitudes for different values 0.6%, 0.7% & 0.8% at room temperature and 800°C. It is noticed that the fatigue lifetimes of induction-hardened specimens are greater than those of untreated specimens at the above-mentioned strain amplitude values at room and elevated temperature, whereas the fatigue life of all the specimens reduces as strain amplitudes increase. Interestingly, the stress difference among the three strain amplitudes gradually decreases as the fatigue test progresses and induction-hardened specimens have cyclic softening behaviour as compared to untreated specimens’ cyclic hardening behaviour. Additionally, the mode of fracture for IN718 superalloys in the current study is entirely transgranular, as shown by the fracture surface observation using a scanning electron microscope (SEM).

Laminar burning velocities and Markstein numbers for pure hydrogen and methane/hydrogen/air mixtures at elevated pressures

Spherically expanding flame propagations have been employed to measure flame speeds for H2/CH4/air mixtures over a wide range of H2 fractions (30 %, 50 %, 70 and 100 % hydrogen by volume), at initial temperatures of 303 K and 360 K, and pressures of 0.1, 0.5 and 1.0 MPa. The equivalence ratio (ϕ) was varied from 0.5 to 2.5 for pure hydrogen and from 0.8 to 1.2 for methane/hydrogen mixtures. Experimental laminar burning velocities and Markstein numbers for methane/hydrogen/air mixtures at high pressures, which are crucial for gas turbine applications, are very rare in the literature. Moreover, simulations using three recent chemical kinetic mechanisms (Konnov-2018 detailed reaction, Aramco-2.0-2016 and San Diego Methane detailed mechanism (version 20161214)) were compared against the experimentally derived laminar burning velocities. The maximum laminar burning velocity for 30 % and 50 % H2 occurs at ϕ = 1.1. However, it shifts to ϕ = 1.2 for 70 % H2 and to ϕ = 1.7 for a pure H2 flame. The laminar burning velocities increased with hydrogen fraction and temperature, and decreased with pressure. Unexpected behaviour was recorded for pure H2 flames at low temperature and ϕ = 1.5, 1.7 wherein ul did not decrease when the pressure increased from 0.1 to 0.5 MPa. Although, the measurement uncertainty is large at these conditions, the flame structure analysis showed a minimum decline in the mass fractions of the active species (H, O, and OH) with the rise in the initial pressure. Markstein length (Lb) and Markstein number (Mab and Masr) varied non-monotonically with hydrogen volume fraction, pressure and temperature. There was generally good agreement between simulations and experimentally derived laminar burning velocities, however, for experiments of rich-pure hydrogen at high initial pressures, the level of agreement decreased but remained within the limits of experimental uncertainty.

Experimental Analysis on the Operating Line of Two Gas Turbine Engines by Testing with Different Exhaust Nozzle Geometries

This paper presents a special analysis study about the gas turbine operating line, and an overall description of a gas turbines project, based on experimental data from two particular applications, in order to convert two different types of aero engines into the same engine configuration. The experimental works were carried out with the aim of converting an Ivchenko AI-20K turboprop and a Rolls-Royce Viper 632-41 turbojet into free turbine turboshaft engines, to be used in marine propulsion, and also to obtain an experimental database to be used in other gas turbine applications. In order to carry out the experimental work, the engines were tested in turbojet configuration, to simulate the free turbine load by using jet nozzles with different geometries of the outlet cross-section. Following the engines’ tests, a series of measured data were obtained, through which it was possible to experimentally determine the operating line of some engine components such as the compressor, turbine, and exhaust jet nozzle. This paper is comprehensive and useful through its scientific and technical guidelines, the operation curves coming in handy in the thermodynamic analysis and testing methodology for researchers dealing with similar applications.

Understanding the Sintering Behavior and its Effect on the Thermal Conductivity of YSZ Coatings for Gas Turbine Applications

Thermal barrier coatings are essential coatings to protect the combustion chamber liner material from harsh environments in modern gas turbines that are used in aerospace and land-based power generation facilities. As there are several different materials to produce thermal barrier coatings, the conventional thermal barrier coating is yttria stabilized zirconia (YSZ). The most common method to manufacture YSZ coating is plasma spraying method due to its flexibility and rapid production capacity. Using plasma spraying, often requires understanding the process parameters effect on the coating structure. As there are many parameters to control coating process the main outcome of all parameters is the particle temperature and velocity during the spraying process hence the coating properties such as hardness, porosity ratio and deposition rates. Furthermore, not only produced microstructure but also during the service conditions sintering behaviour also be considered. Sintering behaviour of thermal barrier coatings results declining of their thermal insulation properties. Therefore, in this study we have evaluated sintering effect of on the thermal conductivity of the plasma sprayed yttria stabilized zirconia coatings. To achieve this objective, we produced free-standing coatings and subjected them to heat treatment, followed by measurements of their thermal conductivities. The results of this study will contribute to a better understanding of the sintering behaviour and its impact on the thermal performance of thermal barrier coatings.

Design and numerical analysis of tensile deformation and fracture properties of induction hardened inconel 718 superalloy for gas turbine applications

Design and numerical analysis of tensile deformation and fracture properties of induction hardened inconel 718 superalloy for gas turbine applications

Waste heat recovery optimization in ammonia-based gas turbine applications

E-fuels are promising alternatives to fossil fuels in the transition towards zero-emission energy system. In this study, a novel chemical-recuperated and humidified gas turbine concept aiming at the application of e-fuel ammonia is proposed to overcome the technical hitches and exploit the waste heat to enhance the cycle performance. The thermodynamic analysis shows that the highest net electrical efficiency (56.7%) under the design conditions exceeds that of the ammonia-fueled Brayton cycle by 20.6%-points. The chemical recuperation of fuel contributes to the efficiency improvement by 7%-points under dry condition, while steam injection provides 8%-points to 12%-points efficiency increase corresponding to the ammonia decomposition ratio of 5%–96%. A non-monotonic relation between the net electrical efficiency and steam-to-air ratio is found to be the result of the competition between the enthalpy change from to the varied steam and air mass flow rates. Analyzing the flame characteristics in the combustor under the design conditions, we found that conditions with high decomposition ratio (>88%) and high steam-to-air ratio (>0.3) exhibit similar flame speed with that of methane fueled combustor and thus existing designs can be reused. The prediction shows the NOx emission can be restricted when the steam-to-air ratio exceeds 0.4.

Phase equilibria in the Ti-Al-W system between 800 and 1300 °C

Within the search for new improved high-temperature materials for gas turbine applications with higher energy saving potential and improved greenhouse gas balance, new Ti-Al-W based alloys have recently been discussed. A basic prerequisite for targeted alloy development is the precise knowledge of the phases and phase relationships that determine the microstructure and mechanical behavior of the material. However, there is not much known about the phase equilibria in the application- and manufacturing-relevant temperature range between 800 and 1300 °C. No information on ternary intermetallic compounds or possible ordering of the cubic (βTi,W) solid solution is reported in the literature. In the present investigation, the Ti-rich part of the Ti–Al–W system between 800 and 1300 °C was studied. Ten different alloys were heat-treated and quenched samples were characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), high-energy XRD (HEXRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Based on these results, a series of partial isothermal sections was established. The investigations show that there is no ternary intermetallic compound in this system and the (W) solid solution forms equilibria with the binary Ti-Al phases.

Multi-objective design of laminated cooling configuration applied in gas turbine based on fuzzy grey relational analysis

Laminated cooling is a compound system consisting of different cooling units that can provide effective protection to the hot components in next generation gas turbines. In the present work, using validated numerical simulations, the influential levels of geometrical parameters in laminated cooling configuration (film hole diameter, pin-fin diameter, impingement hole diameter and film hole inclined angle) on multi-objective functions (overall cooling effectiveness, friction loss and temperature uniformity) are calculated and ranked by fuzzy grey relational analysis (FGRA). The FGRA results indicate that the film hole diameter is the primary influence factor on the overall cooling effectiveness and temperature uniformity, but insensitive to the friction loss. Based on this finding, two novel laminated cooling configurations with revised film-hole shapes, i.e., fan-shaped film holes and discrete rectangular film slots, are proposed to meet the multi-objective requirement. Through calculations, it is proved that the overall cooling effectiveness of the discrete film slots with a width of 0.5 mm can be increased by approximately 20%, whereas the additional friction loss is negligible (the increase of flow resistance coefficient is only 0.06 at mass flow ratio equals to 1.19%). Meanwhile, the acceptable temperature uniformity along with high overall cooling effectiveness, low friction loss can be obtained with the design of the fan-shaped film holes. The present work provides a novel analytical method for the multi-influence-factor problem and multi-objective design of complex laminated cooling system in gas turbine application.

Surface roughness and topography of EDM machining of Inconel 718

An alloy with a nickel–chromium basis known as Inconel 718 is utilised in gas turbine and jet engine applications. The machining of the Inconel 718 is challenging because of its higher strength and hardness. Electrical Discharge machining is the most common operation used for machining Inconel alloys because of its higher accuracy in machining the alloy. The machining accuracy is evaluated by the surface roughness of the material. In this research, the machining of Inconel 718 alloy using the electric discharge machining is done by varying the input parameters. Taguchi design is used for varying the input parameters of Electrical discharge machining. The efficiency in machining is evaluated by measuring the surface roughness of the Inconel alloy. The signal-to-noise ratio analysis optimises process parameters for excellent surface roughness. The analysis of variance is used to determine the impact of each input variable on the surface roughness. The result of this research is helpful for researchers and industries to select the accurate process parameter for machining Inconel 718 alloy.

High-throughput exploration of the WMoVTaNbAl refractory multi-principal-element alloys under multiple-property constraints

Development of next-generation gas turbines requires the design and fabrication of novel high-temperature structural materials capable of operating beyond 1300°C. We propose a high-throughput alloy design framework under multiple-property constraints to discover new refractory multi-principal element alloys (MPEAs) for high-temperature applications. The framework treats the development of MPEAs as a composition-agnostic constraint satisfaction problem, i.e., no prescriptions are made concerning the design space before performing investigatory calculations. We target alloys in the WMoVTaNbAl chemistry space that are predicted to meet constraints on the following properties simultaneously: single-phase stability, density, solidus temperature, yield strength at 1300°C, and ductile-to-brittle-transition temperature. These properties are relevant to both applications in gas turbines and manufacturability. A set of 214 MoNbV-rich alloys meet these relevant constraints. These feasible alloys are investigated with density functional theory (DFT) to provide a fundamental electronic basis for their superior properties. Three compositionally representative alloys from the feasible design space (Mo45Nb35Ta5V15, Mo25Nb50V20W5, and Mo30Nb35Ta5V25W5) are selected with a k-medoids-based design scheme for detailed DFT analysis and experimental characterization. The DFT analysis predicted a single-phase BCC at high temperatures with a high yield strength for all three MPEAs, in agreement with CALPHAD (CALculation of PHAse Diagrams) and experiments, respectively. These three alloys are benchmarked against a public database of 1546 MPEAs. Concerning the aforementioned constraints, the Mo30Nb35Ta5V25W5 alloy outperforms these 1546 MPEAs. The present work demonstrates the ability of the proposed design methodology to identify candidate alloys for a given application under multiple property constraints in a combinatorically vast design space.

Assessment of surface integrity and hole quality in graphene-based NMQL Micro-drilling of ceramic-coated Nimonic 90 for gas turbine applications

Nickel-based superalloys have superior strength properties at higher temperature ranges and thus have become increasingly important in manufacturing gas turbine components for aerospace industry. However, the desire for a larger thrust-weight ratio has raised the typical operating temperature in a gas turbine; thus, thermal barrier coatings are essential. The present work compares the micro-drilling performance of ceramic-coated Nimonic 90 nickel superalloy under dry, flood and 0.5% graphene-based NMQL conditions. The biodegradable acid oil was used as a base oil, and the assessment comprised surface integrity in terms of surface roughness inside the hole and micro-crack formation and hole quality based on the diametrical overcut and taper ratio. Spindle speed (1000, 2000 and 3000 rpm) and feed rate (3, 6, and 9 μm/rev) were changed in three levels, and Taguchi L9 array was applied for the design and analysis of the experiments. Ti-Al-N coated tungsten carbide drill of diameter 700 μm was used, and Analysis of variance (ANOVA) revealed that spindle speed was the utmost important parameter impacting surface roughness, while speed and feed rate both influenced overcut and taper ratio. 0.5% Graphene-based NMQL lubrication condition significantly diminished the surface roughness by 52.67%, overcut by 46.86% and the taper ratio by 48.87% as compared to dry condition. Furthermore, in the NMQL condition, micro-crack development and ceramic layer damage were minimized, resulting in better surface integrity. In addition, burr development was minimized at the hole periphery, and tool wandering was not seen in the NMQL condition. Hence the hole quality was superior in NMQL conditions as compared to the dry and flood lubrication.