Gas Turbine Components Research Articles

Laser surface alloying of Hastelloy X superalloy with Amdry 365 powder: Microstructural evolution and microhardness

Laser surface alloying is a surface modification technique that melts coat powder and substrate with high laser power density. This study aims to improve the properties of Hastelloy X, a Ni-based superalloy used for gas turbine components, by applying a NiCoCrAlY coating using laser surface alloying. The purpose of this study was to investigate the process parameters including laser scanning speed, laser power, and stand-off distance on the microstructure and microhardness of the alloying zones. The findings indicate that different microstructures were formed in different alloying zones such as cellular, columnar, and equiaxed. The results also revealed the presence of β and γ phases in the dendritic and interdendritic regions. The microhardness at the interface was higher than that of the other alloying areas due to the increased content of the Mo element. This study concluded that the properties of Hastelloy X can be improved by using NiCoCrAlY powder through a laser alloying process.

A Digital Engineering Analysis of an Additively Manufactured Turbine Vane

Abstract Additive manufacturing (AM) has transformed the ability to accelerate gas turbine component research and development at a fraction of the cost and time associated with conventional manufacturing. However, whereas prior works have assessed manufacturing variability in cast turbine airfoils, limited data are available to understand the impact of as-built deviations in AM turbine parts. As metal additive airfoils are becoming more prevalent in research turbine architectures, it is increasingly important to understand the effects of potential hardware deviations specific to additively manufactured parts. With this goal in mind, the current study utilizes a digital engineering approach to evaluate the aerodynamic impact of surface deviations on a high-pressure turbine vane design created for research purposes. RANS-based CFD studies derived from structured light scans of as-built turbine vanes are used to quantify performance relative to design intent geometries. Further computational analyses compare results from individual serialized parts with an average vane doublet geometry serving as a surrogate for the entire wheel. Particular emphasis in the study focuses on external surface defects caused by internal cooling features that are inherent through additive manufacturing and how these features can impact the vane performance. Ultimately, this study identifies specific regions of the vane that are subject to increased sensitivity, which benefits future designers intending to use AM as a tool for turbine research and development.

High‐temperature thermal conductivity measurement of porous ceramic coatings with a high heat flux CO2 laser rig

AbstractYttrium‐stabilized zirconia (YSZ) plays a crucial role in thermal barrier coatings widely used to protect metallic components in gas turbine engines against high‐temperature combustion product gases and harsh environments. The thermal conductivity of these coatings is a critical parameter influencing the gas turbine design, performance, and service life. In this study, a laser temperature gradient method is utilized to measure the thermal conductivity of porous YSZ coatings. The method employs specialized laser energy delivery to create a one‐dimensional temperature gradient through the sample thickness, closely simulating the operational condition. This approach provides an effective, direct means to determine the thermal conductivity of high‐temperature heat‐resistant porous ceramic materials.

Scaling Heat Transfer and Pressure Losses of Novel Additively Manufactured Rib Designs

Abstract Rib turbulators are a key cooling feature that enables increased heat transfer on the interior of gas turbine components. As metal additive manufacturing becomes available for developing turbine parts, it is becoming increasingly important to understand how the surface roughness intrinsic to this manufacturing method impacts the performance of rib turbulators. To explore what impact roughness has on rib turbulator performance, several relevant scale test coupons were manufactured on two different additive machines out of IN718. Additionally, several coupons were built at large scales to effectively reduce the relative roughness size impacts and determine scale effects. A range of different wavy broken rib designs, varying both rib wavelength and orientation within a channel were evaluated. Coupon geometry and surface roughness were characterized using both computed tomography scans and optical profilometry. Variations between the print methods were found to have limited impact on the surface roughness, but significant impact on the accuracy to meet the design intent with rib heights varying by 30%. Following characterization, coupons were flow tested and it was found that the ribs that more regularly disturbed the flow as a function of their geometry most significantly enhanced heat transfer and pressure drop. The performance index of the broken wavy ribs was similar to other advanced rib designs, such as broken or V shaped ribs, but augmentations to heat transfer and pressure drop were generally lower. The rib performance was compared as a function of relative roughness, and it was found that increases in relative roughness resulted in increased friction factor and heat transfer, especially at higher Reynolds numbers.

Frequency identification method based on active aliasing of biprobes blade tip timing without once-per-revolution

Rotary blades are the core components of aeroengines, gas turbines and centrifugal compressors. However, due to the complexity of their work environment, monitoring their health is necessary. Blade tip timing (BTT) is an effective non-contact monitoring method for rotating blades. However, conventional BTT rely heavily on once-per-revolution (OPR) signals, which cannot be accurately obtained in complex environments. At the same time, there is a serious under-sampled problem in the BTT signal. Consequently, the extraction of blade vibration parameters from under-sampled BTT signals without relying on OPR signals remains a research hotspot. In this paper, an active aliasing method based on the vibration difference of the blade is proposed to extract the vibration frequency of the blade. In the proposed method, two BTT probes are used to calculate the blade vibration difference, and time delay estimation is used to estimate the approximate value of the natural frequency at small angle delays. Then, a series of aliasing frequencies are generated under various large angle delays. Next, the estimated natural frequency and aliasing frequency are combined to solve the exact natural frequency value. In addition, numerical simulations demonstrate the effectiveness and robustness of the method. Finally, experimental research was conducted on the BTT experimental platform. As a result, this method can accurately identify the inherent frequency of asynchronous vibration of the blades.

Development of the interlayer alloy using for TLP diffusion bonding of GH3230 superalloy based on the CALPHAD method

The hot-end components of aero-engines and gas turbines not only require high-temperature alloys capable of withstanding extreme temperatures, but also demand welds with high-temperature-resistant properties. In this study, the CALPHAD method was employed, utilizing the thermodynamic theory of phase diagrams with Thermo-Calc software and the corresponding database, to design the interlayer composition for superalloy TLP diffusion connections. The optimization aimed to determine the interlayer material's solidus-liquidus and compound phase content, resulting in the selection of a new nickel-based interlayer material containing B as MPD, with Co and W as strengthening elements. Using GH3230 alloy as the research subject, TLP diffusion bonding experiments were conducted at a welding temperature of 1200 °C with a holding time of 4 h. The weld zone exhibited no defects, and the microstructure was identical to that of the GH3230 base metal, consisting entirely of a solid solution. High-temperature tensile tests revealed that fractures consistently occurred in the GH3230 base metal, indicating that the weld's strength significantly exceeded that of the base metal. The average tensile strength of GH3230 high-temperature alloy bar tensile simulated specimens is 899 MPa at room temperature and 213 MPa at high temperature. In addition, the 90° three-point bend test showed no cracking in the weld area, indicating adequate plasticity.

Assessment of Additive Manufactured Micro-Channel Characteristics: Impact of Hydraulic Diameter Evaluation

Abstract Among internal cooling techniques for gas turbines components, skin cooling is recognized as one of the most promising, especially thanks to the spread of additive manufacturing techniques. In this regard, several studies have tried to characterize heat transfer and pressure loss performance of additive manufactured micro-channels, as well as the impact of AM characteristic parameters, mainly in the form of building angle, and resulting surface roughness and channel shape. The open literature offers several correlations in terms of friction and heat transfer coefficient using a representative hydraulic diameter. Despite that, little attention is given on the importance of such characteristic length definition which may lead to under/over estimation of the cooling rates when correlations are used in the design In this work, coupons featuring circular micro-channelswith diameters of 0.5 and 1 mm and different building angles have been tested, to retrieve pressure losses and an average heat transfer coefficient through a lumped approach. The coupons were additive manufactured using the Laser Powder Bed Fusion (L-PBF) technique. Exploiting the experimental survey, the impact of the considered hydraulic diameter was investigated, by comparing different approaches based on a direct measurement. An additional and new approach, aimed at the identification of an “effective” diameter, based on fluid-dynamic considerations, was also considered. The data correlation and the comparison with available correlations from different authors showed the newly proposed approach to provide superior scaling capabilities and, in turn, allowing for the development of more accurate prediction methods

Prediction of the keyhole TIG welding-induced distortions on Inconel 718 industrial gas turbine component by numerical-experimental approach

Welding technologies represent a paramount joining process for ensuring the quality and reliability of critical industrial components; therefore, their innovation constitutes a driving force in realizing increasingly competitive products. A recently developed technology is the keyhole TIG welding, a new high energy–density alternative to the conventional TIG process. A key role in improving innovative manufacturing processes such as the keyhole TIG is covered by numerical simulation; indeed, it allows the development of a process digital twin able to support decisions and work as a predictive tool. Within this framework, the paper deals with the numerical-experimental investigation of the keyhole TIG technology, successfully employed on a simplified mock-up of an industrial gas turbine component consisting of two 6.5-mm-thick Inconel 718 rings. Numerical analysis aimed at predicting welding-induced distortions was performed employing two different computational approaches, namely the moving heat source and the simplified imposed thermal cycle methods. The numerical-experimental comparison of the results demonstrates an innovative approach in the field of the current keyhole TIG numerical simulation since, besides verification of numerical thermal analysis, further substantial validation of the post-weld distortion predictions is provided through comprehensive three-dimensional experimental data. Moreover, the comparative assessment of the two computational approaches and experimental evidence revealed that the imposed thermal cycle method implementation does not compromise the accuracy of welding distortion forecasting in industrial applications such as that investigated. Therefore, it can be regarded as a valuable tool for supporting the process engineer in designing the ideal set-up to comply with a variety of industrial requirements, among them strict design tolerances.

Numerical study of film cooling at the outlet of gas turbine exhaust

Abstract In order to mitigate the potential operational damage risk caused by traditional cooling methods in engineering applications of heavy-duty gas turbine component testing, the film cooling unit and realizable K-epsilon turbulence model were employed. Numerical simulations were conducted for multiple exhaust film holes with varying curvature and pitch-row under different operating conditions. The heat transfer distribution along the flow direction and radial direction of the high temperature wall was analyzed, as well as the influence of heat transfer under different geometrical parameters. The results indicate that for the integrated configuration of large-diameter cooling units, a blowing ratio of 0.3 yields the most comprehensive cooling effect, primarily due to the extensive spatial coverage by the gas film and the weakening of eddy dissipation mechanisms. Additionally, it was observed that with an increase in hole distance ratio for multiple exhaust film holes, cold air could more stably participate in heat exchange with high-temperature flue gas wake at the outlet of the gas film hole; thus, a hole distance ratio of 3.0 provides optimal comprehensive cooling effects.

Background radiation compensation calibration method for film cooling infrared temperature measurement based on BP neural network

The precise non-contact temperature measurement method is essential for studying gas turbine component heat transfer. While infrared thermal imaging provides high-resolution two-dimensional temperature fields, errors arise from the measurement environment's complexity, emissivity variations, and reflection radiation effects. This study utilizes BP neural networks to correct infrared radiation on gas film cooled plates. By modeling background radiation and analyzing infrared emission processes, factors influencing temperature distribution are identified. Experimental data from uncooled plate are used for network training. Experimental measurements were conducted on uncooled plates to obtain training data. A BP neural network was established based on Planck's law and the radiation transmission process to relate the mainstream temperature to the background radiation. Calibration analysis was performed based on experimental data from the cooled plate, achieving the restoration of the two-dimensional temperature field under multiple operating conditions and significantly reducing measurement errors. This method comprehensively considers the entire process of radiation transmission, thereby eliminating background radiation embedded in the infrared images. The obtained measurement results vividly depict the real temperature distribution, offered significant support for gas turbine engineering applications.

Hybrid AI framework for the predictions of film cooling effectiveness distribution with various surface curvatures and compound angles

Film cooling is essential for protecting high-temperature components in gas turbines. For efficient cooling design, it is vital to predict film cooling effectiveness based on flow and geometrical parameters accurately and rapidly. Artificial intelligence (AI) models have recently been popular for this task due to their strong fitting nature. However, standard image-based AI models require significant training data to cover different surface curvatures and compound angles. Moreover, incorporating curvature complicates the input format for these models. Therefore, the current study proposes a hybrid AI framework for the rapid prediction of the film cooling effectiveness distribution under the influence of surface curvature and compound angle, which requires a relatively small amount of training data by integrating film cooling knowledge and different neural networks (Back-propagation neural network and U-Net). The proposed model achieves high accuracy across diverse flow and geometrical parameters, with a mean absolute error of approximately 0.006 or 0.012 for the film holes without or with compound angles on curved surfaces, respectively. The hybrid AI framework offers an accurate and rapid prediction method, offering a valuable tool for turbine cooling design.

Numerical and experimental investigation on flexural properties of selective laser melting (SLM) manufactured strut lattices structures from Ti-6Al-4V and Inconel 625

Lattice structures hold a significant importance in the aerospace industry due to their ability to tailor the physical, thermal, and mechanical properties of complex components for optimal performance. This study is focused on evaluating the flexural properties of four lattice configurations - re-entrant, truncated octahedron, Kelvin, and octet cells - through static finite element analysis (FEA) and experimental three-point bending tests, as well as examining their microstructural features (as they affect the materials’ mechanical properties). High-performance alloys used for gas turbines components manufacturing, Ti-6Al-4 V and Inconel 625, were fabricated using selective laser melting (SLM) process. The necessity of this research resulted from the lack of information in the scientific literature regarding flexural properties of various additive manufactured cell types and metallic materials. The aim was to compile data that could be used to create a comprehensive database for various industrial applications. Findings from both simulations and experimental analyses indicated that the octet cell had the highest performance, with experimentally measured flexural strengths of 878 MPa for Ti-6Al-4V, respective 674 MPa for Inconel 625. Contrarily, the re-entrant cell exhibited the lowest performance, with flexural strengths of 125 MPa for Ti-6Al-4V and 116 MPa for Inconel 625. Failure in the re-entrant cells was attributed to the bending fracture of vertical rods at the connecting nodes or lattice struts, while other cell types experienced damage through a combination of bending and shear mechanisms. Dimensional deviations observed in all specimens were attributed to defects such as surface roughness, the stair-stepping effect, and internal stresses.

High-temperature structural evolution and mechanical properties of oxygen-containing NiCrAlY coatings

NiCrAlY is utilized as a protective coating for gas turbine components at high temperatures. Enhancing the erosion resistance of NiCrAlY coatings can be achieved by optimizing their mechanical properties. In this study, a NiCrAlY coating containing oxygen was deposited by magnetron sputtering and investigated concerning microstructural evolution at 900° C. Oxygen inclusion does not increase the hardness of the NiCrAlY coating in its initial deposited form. When annealing at 900 °C for 1 h, the NiCrAlYO coating develops into a nanocrystalline structure, where Y2O3 is evenly distributed inside the γ/γ′ matrix. This leads to the phenomenon of age-hardening, causing the hardness to increase to 12.4 GPa. Conversely, the hardness of the O-free NiCrAlY coating sharply declines to 9.3 GPa. Moreover, the wear resistance of the NiCrAlYO coating has been enhanced at a temperature of 700 °C, owing to its exceptional mechanical stability.

Effects of surface hardening by laser shock peening and shot peening on a nickel-based single-crystal superalloy CMSX-4

Improving the expected life of nickel-based single-crystal superalloy turbine components by surface hardening treatments including laser shock peening (LSP) and mechanical shot peening (MSP) are of particular interest for mitigation of life limiting damage such as environmental assisted cracking in hot section components of gas turbines. In the present study the effects of LSP and MSP on the surface roughness, microhardness and work hardening of a nickel-based single crystal superalloy CMSX-4® have been assessed. Surface roughness was measured using laser profilometry. The degree of work hardening was measured using electron backscattered diffraction with local misorientation analysis. The analysis showed evidence for a work hardening layer in the MSP sample to a depth of approximately 70 μm. Sets of slip bands extending far into the bulk of the sample were observed in the LSP-treated sample, without any evidence of a work hardening layer. Microhardness measurements used to gauge the depth of residual stress showed that LSP produced a much deeper hardness profile than MSP, with compressive residual stress depths of 1000 μm and 200 μm in LSP and MSP respectively. The retention of hardness after a heat treatment of 50 h at 700 °C was more prominent in the LSP sample than in the MSP sample. LSP and MSP have therefore been shown to be at the opposite ends of the spectrum of surface hardening treatments of CMSX-4, with LSP giving milder hardening, but to a greater depth.

Procedure of Combustion Chamber Airflow Rate Distribution

Combustion systems are the least amenable of all gas turbine components to analyze. Among the literature overview made, it was realized that even though significant steps have been made in improving the combustor design procedure via the use of computational fluid dynamics, much of the design process still relies upon empirically derived rules. These rules include the calculation procedure of the required airflow rate by each zone of the combustion chamber to attain a suitable gas temperature, high values of combustion efficiency, low concentrations of pollutant species together with the determination of liner geometry that matches the chamber required performance goals with the constraints imposed by the engine dimensions [1,2,3, and 4]. The main target of this research work is to identify the proper procedure to distribute a predetermined airflow rate in annular type combustor and to generalize an effective calculation method that formulate and solve the problems in as much simplified and accurate manner as possible. The combustor dimensions and airflow rates in each zone is found in reference [5] and shown in Figure 1. It is designed with central vaporizing unit to deliver 516.3 KW of power with a geometrical constraint of 142 mm & 140 mm overall length and casing diameter, respectively, while the airflow rate is 0.8 kg/sec and the fuel flow rate is 0.012 kg/sec [5, 6].

A techno-economic analysis of future hydrogen reconversion technologies

The transformation of fossil fuel-based power generation systems towards greenhouse gas-neutral ones based on renewable energy sources is one of the key challenges facing contemporary society. The temporal volatility that accompanies the integration of renewable energy (e.g. solar radiation and wind) must be compensated to ensure that at any given time, a sufficient supply of electrical energy for the demands of different sectors is available. Green hydrogen, which is produced using renewable energy sources via electrolysis, can be used to chemically store electrical energy on a seasonal basis. Reconversion technologies are needed to generate electricity from stored hydrogen during periods of low renewable electricity generation. This study presents a detailed techno-economic assessment of hydrogen gas turbines. These technologies are also superior to fuel cells due to their comparatively low investment costs, especially when it comes to covering the residual loads. As of today, hydrogen gas turbines are only available in laboratory or small-scale settings and have no market penetration or high technology readiness level. The primary focus of this study is to analyze the effects on gas turbine component costs when hydrogen is used instead of natural gas. Based on these findings, an economic analysis addressing the current state of these turbine components is conducted. A literature review on the subsystems is performed, considering statements from leading manufactures and researchers to derive the cost deviations and total cost per installed capacity (€/kWel). The results reveal that a hydrogen gas turbine power plant has an expected cost increase of 8.5% compared to a conventional gas turbine one. This leads to an average cost of 542.5 €/kWel for hydrogen gas turbines. For hydrogen combined cycle power plants, the expected cost increase corresponds to the cost of the gas turbine system, as the steam turbine subsystem remains unaffected by fuel switching. Additionally, power plant retrofit potentials were calculated and the respective costs in the case of an upgrade were estimated. For Germany as a case study for an industrialized country, the potential of a possible retrofit is between 2.7 and 11.4 GW resulting to a total investment between 0.3 and 1.1 billion €.

Advanced rare earth tantalate RETaO4 (RE=Dy, Gd and Sm) with excellent oxygen/thermal barrier performance

Thermal barrier coatings (TBCs) materials with lowered thermal and oxygen ion conductivity can provide thermal and oxidative protection for high temperature hot-end components in aeronautical engines and gas turbines. The rare-earth tantalate RETaO4 (RE = Dy, Gd and Sm) ceramics with monoclinic (m) phase were successfully synthesized via spark plasma sintering. Oxygen vacancies responsible for the thermal and oxygen ion conductivities of RETaO4 were demonstrated by atomic-resolution energy dispersive X-ray and X-ray photoelectron spectroscopy. Among the three samples, DyTaO4 has excellent oxygen/thermal barrier performance. Compared to the current service thermal barrier coating material ZrO2-8 wt% Y2O3 (8 YSZ), DyTaO4 has an ultra-low oxygen ion conductivity benefiting from low oxygen vacancy concentration and strong stretching force constants. The intrinsic thermal conductivity of DyTaO4 is 68.2% less than that of 8 YSZ. Additionally, the thermal expansion rate curves indicate that the phase transformation does not happen from room temperature to 1200 °C. The above results demonstrate that high-growth rate thermally grown oxide can be retarded by creating dense DyTaO4 coating with lowered thermal and oxygen ion conductivity.

Particle Bounce Stick Behavior in the Rotating Frame of Reference

Abstract Particle deposition is a major damage mechanism for gas turbine components, especially in the secondary air system. Predicting the transport and deposition of ingested atmospheric contaminants is of great interest in component-level simulations. Bounce stick models predict deposition upon collision with a wall during Lagrangian particle tracking; they consider a range of physical phenomena, including van der Waals forces and plastic deformation. The effect of the rotating frame of reference on particle collision physics has thus far been neglected in the literature despite the significant centrifugal (CF) loads experienced by many components of interest for deposition studies, for example, turbine blades. The collision physics of the rotating frame are discussed here using low-order models and Monte Carlo style simulations. The present work aims to provide a conceptual framework for the inclusion of CF forces in collision physics. No significant effect was found on the rebound velocities of particles experiencing “worst case” CF forces. However, differences were observed in the sticking probability between concave and convex rotating surfaces, where the CF forces act in opposing directions to either push the particle into the surface or detach it. A force-based analogy of the popular critical velocity model was developed to study the phenomenon. It was used in a Monte Carlo style simulation of a rotor disk, finding that the variation of critical velocity due to CF forces was likely to bias deposition toward concave surfaces. The collision physics of the rotating frame were found to be unintuitive, with complex implications for modeling deposition in gas turbine components. However, they were consequential in determining the distribution of deposition through the system, hence should be included in particle deposition simulations in computational fluid dynamics (CFD).

Lotus leaf inspired hierarchical micro-nano structure on NdYbZr2O7 ceramic pellet with enhanced volcanic ash repellence

Volcanic ash dispersed in the air adheres to thermal barrier coatings (TBCs) on the hot section components of gas turbines, posing a severe threat to aviation safety. Here, we report a novel strategy inspired by lotus leaf for mitigating the molten volcanic ash adhesion and corrosion. A hierarchical micro-nano structure composed of arrayed micro-conoids and numerous nanoparticles were constructed on the surface of NdYbZr2O7 ceramic pellet by ultrafast laser direct writing technology, whose morphology could be changed by optimizing the processing parameters. The laser-ablated pellet exhibits larger contact angle of molten volcanic ash than the original one, revealing an enhanced resistance repelling volcanic ash. This phenomenon is primarily attributed to the air trapped in the micro-grooves, together with these nanoparticles. Note that the evolution of viscous force and capillary force with time accelerates the transition of molten volcanic ash from the Cassie state to the Wenzel state and reduces its contact angle. Also, this structure effectively inhibits the infiltration of molten volcanic ash by rapidly developing a reaction layer. These findings are an important step toward the design and development of next-generation silicate ash-repellent TBCs.

Failure investigation of fatigue crack initiation and propagation in compressor blade

Blades are integral components of gas turbines and are subjected to critical conditions, bearing radial forces resulting from rotation. Additionally, they directly interact with high-pressure air. This research investigates the failure of GE-Frame9 compressor blades through experimental analyses. Chemical analysis, metallography, and fractography were performed on the fractured blades. The causes of failure in the first-row blades included rubbing with the casing and bending in the opposite direction of rotor rotation. Furthermore, four rows of compressor blades were extensively damaged, with some breaking at the root area. During the turbine overhaul, a shim plate was placed between the compressor blades' root and disk. Metallography confirmed that placing the shim at the blade-disc connection point resulted in stress concentration at blades root. Fractography of the fractured blade surface indicated signs of fatigue failure, and a correlation was found between the crack initiation site and the impact of the shim plates on the blade root. Fatigue crack initiation occurred due to stress concentration caused by the shim's edge, propagating through the blade root during turbine operation and ultimately leading to complete fracture. These results emphasize the importance of avoiding the placement of shims on inclined surfaces of blade roots and ensuring full contact between the surfaces to prevent stress concentration and subsequent failure.