bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Supercritical CO2 on Steel Ductility at 450°-650°C
Authors: Pint Bruce A. , Pillai Rishi , Keiser James R. 
Published: September 2021

Abstract
The compatibility of ferritic-martensitic (FM) and conventional and advanced austenitic steels with supercritical CO2 (sCO2) is being explored at 450°–650°C to determine their maximum temperature capability. In addition to measuring reaction kinetics and reaction product thickness, bulk carbon content and post-exposure room temperature tensile properties were assessed by exposing both alloy coupons and 25 mm long dogbone tensile specimens. After 1–2 kh exposures in 300 bar research grade (RG) sCO2, ∼9 and 12%Cr FM steels had similar behavior under these conditions. Consistent with the literature, higher Cr and Ni contents in alloy 316H provided lower reaction rates at 450° and 550°C, but limited benefit at 650°C with similar degradation of tensile properties and C ingress observed. An advanced austenitic Nb-modified 20Cr-25Ni alloy 709 provided the best compatibility even at 650°C with no C uptake detected after 1 kh and no significant loss in room temperature tensile properties after exposure. A clear correlation was observed under these conditions between the formation of a thin, protective Cr-rich oxide scale and the prevention of C ingress and tensile property degradation at 650°C.
A Novel Long-Duration Hydrogen Storage Concept Without Liquefaction and High Pressure Suitable for Onsite Blending
Authors: Otto Marcel , Sargunaraj Manoj P. , Riahi Adil , Kapat Jayanta 
Published: September 2021

Abstract
Hydrogen is typically stored as a low-pressure cryogenic liquid or as a high-pressure gas. Both approaches come with technical challenges that complicate the implementation of such systems at the actual power plant scale. Cryogenic liquids can provide high energy and volume densities but require complex storage systems to limit boil-off. That makes such liquid tanks complex, large, and heavy which in turn drives up capital cost. Furthermore, expensive liquefaction equipment is required, too. The liquefaction process is highly energy-intensive, approximately 35% of the fuel energy, hence, reduces the net performance of gas turbine power plants using such hydrogen storage approaches. Conversely, high-pressure gas storage bottles are less complex and can be kept at room temperature. However, they require a thick wall to withstand the high pressure which makes them considerably heavy as well. Furthermore, the energy densities associated with gas storage are dramatically lower than for cryogenic liquids, even at high pressures up to 700 bar.
The present study presents and discusses a novel concept for storing hydrogen to be used in gas turbine power plants. Proposed technology enables the storage of hydrogen close to cryogenic density without the need for high pressure or liquefaction and the delivery to the gas turbine asset can be at engine pressure so that no gas compression is required. It is believed that the capacity of the storage system scales easily so that hydrogen can be stored for long durations from daily to monthly cycles which correspond to 10 to 100 hours, respectively. Besides a SWOT analysis, a system will be described that would integrate into the existing OEM infrastructure and allows the blending of hydrogen and natural gas between ratios between 30% and 100%. Specifications will be provided for the storage system and analyzed for a gas turbine power plant with 100 MW.
Impingement Heat Transfer Innovations and Enhancements: a Discussion on Selected Geometrical Features
Authors: Dutta Sandip , Singh Prashant 
Published: September 2021

Abstract
Impingement heat transfer is considered as one of the most effective cooling technologies that yields in high localized convective heat transfer coefficient. This paper studies different configurational parameters involved in jet impingement cooling such as, exit orifice shape, crossflow regulation, target surface modification, spent air reuse, impingement channel modification, jet pulsation, and other techniques to understand what are critical and how these heat transfer enhancement concepts work. These enhancement factors have been explored in detail by many researchers, including standard parameters such as normalized distance between adjacent jets and jet-to-target spacing, and those known benefits are not repeated here. The aim of this paper is to stimulate the current scientific knowledge of this efficient cooling technique and instill some thoughts for future innovations. New orifice shapes are becoming feasible due to 3D printing technologies. However, the orifice studies show that it is hard to beat a sharp-edged round orifice. Any attempt to streamline the hole shape indicated a drop in the Nusselt number. Reduction in crossflow has been attempted with channel modifications. Use of high porosity conductive foam in the impingement space has shown marked improvement in heat transfer performance. A list of possible research topics based on this discussion are provided in conclusion.
Localized Breakup Instabilities for a Liquid Jet in Crossflow
Authors: Salauddin Sheikh , Flores Wilmer , Otero Michelle , Ahmed Kareem 
Published: September 2021

Abstract
Liquid fuel jet in Crossflow (LJIC) is significant to the aviation industry since it is a vital technique for atomization. The hydrodynamic instability mechanisms that drive a transverse jet’s primary breakup were investigated using modal and traveling wavelength analysis. This study highlights the primary breakup mechanisms for aviation fuel Jet-A. However, the techniques discussed are applicable to any liquid. Mathematical decomposition techniques are known as POD (Proper Orthogonal Decomposition), and MrDMD (Multi-Resolution Dynamic Mode Decomposition) are used together to identify dominant instability flow dynamics associated with the primary breakup mechanism. Implementation of the MrDMD method deconstructs the nonlinear dynamical systems into multiresolution time-scaled components that capture the intermittent coherent structures. The MrDMD, in conjunction with the POD method, is applied to data points taken across the entire spray breakup regimes, which are: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The dominant frequencies of both breakup regimes are extracted and identified. These coherent structures are classified with an associated time scale and Strouhal number. Characterization of the traveling column and surface wavelengths are conducted and associated with a known instability model. It is found that the Plateau-Rayleigh instability model predicts columns wavelengths similar to wavelengths found in dominant modes associated with a capillary breakup. Rayleigh Taylor’s instability model matches well with bag and multimode breakup. Small scale surface wavelengths associated with a shear breakup are correlated to a modified Rayleigh Taylor instability model founded by Wang et al. [1]. Furthermore, an atomization model that predicts the Sauter Mean Diameter associated with the dominant small-scale surface traveling wavelengths is established.
Investigation of Non-Premixed Hydrogen-Oxygen Impinged Jet Flame Under Steam Dilution
Authors: Fan Yong , Tsujimura Taku , Iki Norihiko , Kurata Osamu , Furutani Hirohide 
Published: September 2021

Abstract
Large-scale electric power generation with hydrogen-fired gas turbines is key to the realization of zero-emission society. One challenge of premixed hydrogen combustion is the flashback associated with high burning velocity. On the other hand, non-premixed (diffusion) hydrogen-air combustion produces high level of NOx due to the high flame temperature. In order to reduce NOx, a semi-closed gas turbine cycles employing the hydrogen-oxygen combustion has been proposed. In the present study, we developed a non-premixed hydrogen-oxygen burner with sub-millimeter nozzles to form two oxygen jets impinging on the hydrogen jet at an acute angle. Compared to conventional burners with co-flow jets, forced mixing of hydrogen and oxygen occurs due to the impingement. It is expected that the flame holding as well as the combustion efficiency can be improved. High-speed Schlieren and OH* chemiluminescence images of the hydrogen flame with/without the oxygen jet impingement in a pressure vessel were captured to examine the instantaneous flame structure. Flammability and flame structure have been investigated at various jet velocity and pressure conditions. It was found that without the oxygen jet impingement the flame becomes longer with increasing the hydrogen velocity. Lifted flames were observed at the velocity over 200 m/s. The lift position moves gradually downstream with further increasing the velocity. On the other hand, with increasing the velocity of the oxygen jet impinged to the hydrogen jet, a V-shaped flame front stabilized at the impinging position was observed. It was also found that flame holding is improved at high pressure. Based on the impinged jet flame concept, prototype multi-cluster burners with sub-millimeter nozzle arrays were designed and fabricated using the Inconel alloy 3D printing technology.
Influence of Opposing Dilution Jets on Effusion Cooling
Authors: Creer M. Riley , Thole Karen A. 
Published: September 2021

Abstract
The gas turbine combustion process reaches gas temperatures that exceed the melting temperature of the combustor liner materials. Cooling the liner is critical to combustor durability and is often accomplished with double-walled liners that contain both impingement and effusion holes. The liner cooling is complicated with the interruption of the effusion cooling by large dilution jets that facilitate the combustion process. Given the presence of the dilution jets, it is important to understand the effect that the dilution jet has on the opposing wall in respect to the effusion film. This research includes measurements of the local static pressure distribution for a range of dilution jet momentum flux ratios to investigate the impact that the opposing dilution jet has on the effusion film. The interactions with the effusion cooling were also evaluated by measuring the overall cooling effectiveness across the panel.
Measurements show that the opposing dilution jets did impact the liner at dilution jet momentum flux ratios that were greater than 20. The impacts at high momentum flux ratios were indicated through increased local static pressures measured on the surface of the combustor liner. Furthermore, the dilution touchdown decreased the overall cooling effectiveness of the effusion cooling. Results also indicated that the opposing dilution jets changed position on the liner as the dilution jet momentum flux ratio changes.
Turn-Down Capability of Ansaldo Energia’s GT26
Authors: Jakoby Ralf , Rinn Jörg , Appel Christoph , Studerus Adrien 
Published: September 2021

Abstract
The operational flexibility of heavy-duty gas turbines is of increasing importance in today’s power generation market. Fast start-up, fast loading, grid frequency support, fuel flexibility and turn-down capability are only some of the keywords that describe the challenges for GT manufacturers.
This paper reports Ansaldo Energia’s activities to further reduce the Minimum Environmental Load (MEL) of the GT26. The difficulties related to operation at very low loads and the solutions that were developed are explained. Furthermore, the results of engine validation tests of the new extended Low Load Operation (eLLO) and extended Low Part Load (eLPL) operation concepts are presented.
The enhancement of the operational flexibility of the GT26 is in the focus of Ansaldo’s development activities since many years. Its sequential combustion system is a very good basis for flexible and emission compliant operation down to very low loads. Ansaldo Energia’s Low Part Load (LPL) and Low Load Operation (LLO) concepts are standard products in the GT26 flexibility portfolio and established in the market for many years.
Low Part Load (LPL) operation extends the standard operating range down to low loads by switching off individual burners in the second combustor (SEV combustor). The compressor mass flow can be varied between idle and base load levels.
Low Load Operation is characterized by a combination of idle compressor mass flow and base load temperatures in the first Combustor (EV combustor). The SEV combustor is switched off. LLO is intended to be a “parking point”, where the plant can operate in combined cycle mode during times of low electricity demand.
Ansaldo Energia has conducted a development project in the past two years in order to further reduce the minimum simple cycle and combined cycle loads. The extension of the LLO and LPL operating ranges and their combination into one single feature are the main targets of the project.
Topological Optimization of Piezoelectric Transducers for Vibration Reduction of Bladed Disks
Authors: Fan Y. , Ma H. Y. , Wu Y. G. , Li L. , Tian K. Y. , Zhao Z. M. 
Published: September 2021

Abstract
In this work, we develop a numerical method to determine the best distribution of piezoelectric materials on a given bladed disk, so as to minimize the added mass of shunted piezoelectric dampers. There is no constrain on the shape of piezoelectric materials, and only the overall mass is limited. The method can be applied to a single mode or several modes from the same or different modal groups. The method is based on the fact that the modal damping is solely determined by the modal electromechanical coupling factor (MEMCF) which is related to the modal stress field and the geometric of the piezoelectric materials only. A linear weighting of stress components is proposed as the criterion to determine the priority of locations for piezoelectric materials. The piezoelectric materials are introduced to the FE model by modifying the type and materials parameters of elements if they are embedded to the bladed disks; or by creating an additional layers of elements if they are bonded to the bladed disks. Details for considering multiple modes, handling polarization direction and electrode connection are also presented. The proposed procedure is applied to an empirical bladed disk with NASA-ROTOR37 profile. Results show that 12% damping ratio can be achieved for multiple modes simultaneously, if we locate piezoelectric materials on the blade with 10% added mass. When locate the piezoelectric materials on the disk and the added mass is only 5%, up to 13% modal damping ratio for the disk dominant modes can be achieved.
GT36 Turbine Development and Full-Scale Validation
Authors: Naik S. , Stephan B. , Henze M. 
Published: September 2021

Abstract
This paper describes the full-scale turbine section validation of the GT36 heavy duty gas turbine, which was conducted in a test Power Plant in Birr, Switzerland.
The GT36 Test Power Plant is extensively instrumented with both standard and specialised instrumentation. In the turbine section, specialised instrumentation includes metal and gas thermocouples, thermal paint, pressure sensors, hot gas rakes, strain gauges, five-hole probes, pyrometers and tip timing sensors. Similar specialised instrumentation also exists for the compressor, combustor and the rotor sections. Three major test campaigns were conducted over an extended period, which consisted of both long and short duration tests, including a range of off-design tests.
Within the turbine section, detailed transient and steady-state measurements were obtained of the stage inlet pressures and temperatures, airfoil surface pressures and metal temperatures. These measurements indicated that both the aerodynamic and cooling performances of the turbine blades and vanes are highly consistent and repeatable over a range of operating conditions. Detailed comparisons of the measured engine pressures and temperatures with predictions also indicated that there was generally a very good match in the Mach numbers and metal temperatures for all the turbine blades and vanes.
Centrifugal Compressor Aero-Mechanical Design: A Machine Learning Approach
Authors: Barsi Dario , Perrone Andrea , Ratto Luca , Ricci Gianluca , Sanguineti Marco 
Published: September 2021

Abstract
The present paper presents an enhanced method for multi-disciplinary design and optimization of centrifugal compressors based on Machine Learning (ML) algorithms. The typical approach involves the preliminary design, the geometry parameterization, the generation of aero-mechanical databases and a surrogate-model based optimization. This procedure is able to provide excellent results, but it is time consuming and has to be repeated for each new design. The aim of the proposed procedure is to actively exploit the simulations performed in the past for subsequent designs thanks to the predictive capabilities of the ML surrogate model. A commercial 3D (three dimensional) computational fluid dynamics (CFD) solver for the aerodynamic computations and a commercial finite element code for the mechanical integrity calculations, coupled with scripting modules, have been adopted. Two different compressors, with different geometry and operating conditions, have been designed and two aero-mechanical databases have been developed. Then, these two databases have been joined and have been used for the training and validation of the surrogate model. To assess the performance of this approach, two new compressors have been designed, case 1 with operating conditions between those of the databases used for training and validation and case 2 with operating conditions far above.
The use of an optimizer coupled to the prediction of the surrogate model has enabled to define the “best set” of model parameters, in compliance with aero-mechanical objectives and constraints. The accuracy of the ML algorithm forecast has been evaluated through CFD and FEM simulations carried out iteratively on the optimal samples, with new simulations added to the database for further training of the surrogate model. The results have been presented with reference to cases 1 and 2 and highlight all the benefits of the proposed approach.
Evaluation of Blow-Off Dynamics in Aero-Engine Combustors Using Recurrence Quantification Analysis
Authors: Leung Ho Yin , Karlis Efstathios , Hardalupas Yannis , Giusti Andrea 
Published: September 2021

Abstract
The lean blow-out performance of an engine and the ability to re-ignite the flame, especially at high-altitude conditions, are important aspects for the safe operability of airplanes. The operability margins of the engine could be extended if it was possible to predict the occurrence of flame blowout from in-flight measurements and take actions to dynamically control the flame behaviour before complete extinction. In this work, the use of Re-currence Quantification Analysis (RQA), an established tool for the analysis of non-linear dynamical systems, is explored to reconstruct and study the blow-off dynamics starting from pressure measurements taken from blow-off experiments of an engine rig. It is shown that the dynamics of the combustor exhibit chaotic characteristics far away from blow-off and that the dynamics become more coherent as the blow-off condition is approached. The degree of determinism and recurrence rate are studied during the entire combustor’s dynamics, from stable flame to flame extinction. It is shown that the flame extinction is anticipated by an increase of the degree of determinism and recurrence rate at all investigated conditions, which indicates intermittent behavior of the combustor before the blow-off condition is reached. Therefore, in the configuration investigated here, the determinism and the recurrence rate of the system could be good predictors of blow-off occurrence and could potentially enable control actions to avoid flame extinction. This study opens up new possibilities for engine control and operability. The development of real-time RQA should be addressed in future research.
Fan Stability With Leading Edge Damage: Blind Prediction and Validation
Authors: Gunn E. J. , Brandvik T. , Wilson M. J. , Maxwell R. 
Published: September 2021

Abstract
This paper considers the impact of a damaged leading edge on the stall margin and stall inception mechanisms of a transonic, low pressure ratio fan. The damage takes the form of a squared-off leading edge over the upper half of the blade.
Full-annulus, unsteady CFD simulations are used to explain the stall inception mechanisms for the fan at low- and high-speed operating points. A combination of steady and unsteady simulations show that the fan is predicted to be sensitive to leading edge damage at low speed, but insensitive at high speed. This blind prediction aligns well with rig test data.
The difference in response is shown to be caused by the change between subsonic and supersonic flow regimes at the leading edge. Where the inlet relative flow is subsonic, rotating stall is initiated by growth and propagation of a subsonic leading edge flow separation. This separation is shown to be triggered at higher mass flow rates when the leading edge is damaged, reducing the stable flow range. Where the inlet relative flow is supersonic, the flow undergoes a supersonic expansion around the leading edge, creating a supersonic flow patch terminated by a shock on the suction surface. Rotating stall is triggered by growth of this separation, which is insensitive to leading edge shape. This creates a marked difference in sensitivity to damage at low- and high-speed operating points.
Towards a Machine Learning Based Design for Fouling of an Axial Turbine Vane
Authors: Friso Riccardo , Oliani Stefano , Casari Nicola , Pinelli Michele , Suman Alessio , Montomoli Francesco 
Published: September 2021

Abstract
Computational fluid dynamics (CFD) is increasingly used during the design phase of turbomachinery. Reducing the cost of such computations is one of the major challenges in the industrial field. The multi-physics phenomena and the multidisciplinary interactions needed for the design of the engine components are difficult to be faced with the classical design methods. In addition, the interest of manufacturers and operators of turbomachines in the increase in performance when degradation processes occur is growing. In the aeronautical sector degradation is among the most critical issues, as it can lead to the in-flight shutdown of the engine. In a bid to tackle these big problems, new design methods based on approximation techniques have been developed. These techniques are called surrogate models and are currently the most used design methods for the aerodynamic design of aircraft engines. In this work, the assessment of a surrogate surface built for the purpose of optimizing an HPT vane in degrading conditions is performed. Using machine learning and statistical techniques, a sensitivity analysis is conducted in order to reduce the problem dimensions. The results of the sensitivity analysis are used for a study of the surrogate, with the purpose of obtaining design guidelines when deterioration effects are considered in the design phase. The main outcome of this study is a map, that outlines the best design zone defined by the combination of the most influential parameters.