bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of NOx Emissions Associated to Non-Premixed Combustion of H2/Natural Gas Blends in a 40MW Heavy-Duty Gas Turbine
Authors: Carusotto Salvatore , Salvadori Simone , Baratta Mirko , Misul Daniela , Labrini Giovanni , Cardile Francesco , Toppino Marco , Valsania Massimo 
Published: September 2023

Abstract
The tightening in the international regulations is leading the energy production sector towards the usage of hydrogen, which is a zero-carbon energy carrier. In the field of gas turbine lifetime extension, a non-premixed approach including hydrogen blending with conventional fuels is the most promising. However, high-temperature spots might occur, thus increasing thermo-mechanical stresses and NOx emissions. Therefore, a reliable evaluation of the impact of hydrogen blends in combustors characterized by non-premixed flames is necessary. In the present work, a 40MW heavy-duty multi-can combustor belonging to EthosEnergy is investigated by means of steady, reactive simulations by using the ANSYS® FLUENT® solver. The combustor geometry is simplified by removing the casing volume, being the flow split among the holes already available. Such simplification allows for paying major attention to the chemical kinetics thanks to the use of the extended reaction mechanism for natural gas developed by NUI Galway. Simulations include the assessment of the natural gas base load configuration together with hydrogen blends up to 50% in volume, while maintaining unaltered the turbine inlet temperature. The obtained data provide some retrofitting guidelines in the field of hydrogen usage in non-premixed combustion and prove for a modified temperature field in the combustor core and close to the basket. A linear increase in NOx emission is also associated to hydrogen addition, thus suggesting the need for NOx abatement technologies (e.g., water injection).
Functionalization of All-Oxide CMC Elements Using 3D Braiding and Pressure Slip Casting for Composite Processing: Approaches to Reduce the Filter Effect of Dense Reinforcement Textiles
Authors: Jung Fabian , Grigat Niels , Vollbrecht Ben , Gries Thomas 
Published: September 2023

Abstract
A key element for the transition to sustainable energy lies in the transformation of the power plant fleet, which is dominated by fossil fuels, towards sustainable energy production from renewable energy sources. An increase in efficiency and reduction of exhaust gas emissions, especially the minimization of CO2 emissions, is possible through the use of new turbine materials which can withstand higher temperature levels. Oxide ceramics are well known for their high stability in aggressive environments, low density, high melting point, high stiffness and great creep resistance, but their brittleness has strongly limited their number of applications. Therefore, the implementation of fiber reinforcement using the 3D braiding process shows great potential to increase the damage tolerance of CMC and consequently the performance of thermal machines significantly.
Currently, the impregnation of 3D braids for the reinforcement of ceramic composites poses a challenge due to the high packing density of the textiles. In order to enable a homogeneous impregnation of the fiber structures using highly viscous ceramic slurries, the CMC research group at RWTH Aachen University’s Institute of Textile Technology (ITA) is investigating the combination of 3D braiding and pressure slip casting for an economical production of all-oxide CMCs. To increase the impregnation quality of dense textiles, this paper describes approaches to reduce the filter effect of braids. The results of an initial investigation into the functionalization of 2D braided reinforcement structures by using support structures and flow aids are described. The effectiveness of the impregnation ability is assessed by evaluating the residual porosity of generated green compacts via μCT analysis.
Effect of Impurities on the Compatibility of Steels in Supercritical CO2 at 450°-650°C
Authors: Pint Bruce A. , Lance Michael J. , Pillai Rishi , Keiser James R. 
Published: September 2023

Abstract
Direct-fired supercritical CO2 (sCO2) power cycles are a pathway to low-CO2 fossil energy but contain high levels of O2 and H2O in the sCO2. The effect of impurities on structural steels was investigated at 450°–650°C in 300 bar sCO2. The test matrix included 9 and 12%Cr ferritic-martensitic (FM) steels and conventional and advanced austenitic steels exposed for 1000–2000 h with and without additions of 1%O2 and 0.1%H2O to simulate the cycle after water removal. For FM steels, the mass gains and scale thicknesses were similar with and without impurities with the formation of thick, duplex Fe-rich scales in all cases including the observation that Fe2O3 only formed with 1%O2. For the austenitic steels, higher mass gains were observed at all temperatures with increased formation of Fe-rich oxides when impurities were added. Carbon ingress was assessed by bulk combustion analysis, glow discharge optical emission spectroscopy and measuring post-exposure room temperature tensile properties. Bulk C content was strongly increased at 650°C but not at 450° or 550°C.
3D Modelling of a Hydraulic Seal With an Oil Feed, Focussing on the Effect of the Jet on the Behaviour of Oil in the Trough
Authors: Warusevitane Achinie , Omar Rajab , Johnson Kathy , Ambrose Stephen 
Published: September 2023

Abstract
Hydraulic seals can be created between two shafts co-rotating at different speeds to provide a zero flow air seal across the annular cavity and these are often used as intershaft seals in aero-engines. These seals are formed between an oil filled trough on the higher speed shaft and a fin on the lower speed shaft that dips into the oil. Rotation is imparted to the sealing fluid within the trough due to the centrifugal force and the seal is able to balance a pressure difference similar to a manometer in operation. To minimize the effects of viscous heating generated by the interaction of the rotating surfaces and the oil, and to reduce oil residence time, a continuous jet-delivered oil feed is usual in aero-engine seals.
Previously published work, has established a successful modelling methodology to evaluate the maximum pressure capability of hydraulic seals when there is no oil feed. Expanding on prior studies, in this current research a relevant continuous through-flow oil feed is added to the seal modelled in Ansys FLUENT to create a model of the oil behaviour in the seal. The numerical simulations are based on a model representative of a hydraulic seal configuration investigated in an experimental study at the University of Nottingham. The CFD study shows the oil flow breaking up into droplets/ligaments followed by the oil film formed around the circumference of the trough using a Volume-of-Fluid (VOF) method when an operational differential pressure is maintained across the seal. Analysis on the size and trajectory of the droplets generated through splashing is reserved for future work.
This paper presents a quantitative evaluation of the disturbance created on the surface by the jet, demonstrating that the greatest disturbance is caused at the point of impact and the oil film thickness is only impacted by a negligible variation of +/− 0.1mm downstream. High quality CFD images of the jet impact behaviour compare with experimental results. The CFD results of the jet penetration and influence of the secondary flow are presented and discussed.
The second part of the paper comprises an investigation into thermal effects including oil-related heat transfer in the modelled hydraulic seal.
Development of a Needle Type Nanosecond Pulsed Plasma Actuator for the Enhancement of Blowout Limits in a Lifted Stabilized Combustor
Authors: De Giorgi Maria Grazia , Bonuso Sara , Mehdi Ghazanfar , Harth Stefan , Ficarella Antonio 
Published: September 2023

Abstract
The lift-off phenomenon in turbulent jet flames has garnered significant attention, but it also presents the risk of fuel leakage and flame blowout. Stabilizing flames remains a significant challenge in aeroengines and gas turbines. Plasma-assisted combustion (PAC) is considered a promising and active technology for practical applications as it has the potential to improve flame stability and reduce pollutant emissions. This study investigates the combustion characteristics of lifted methane/air flames using high-voltage nanosecond and sinusoidal plasma generators. While nanosecond pulsed excitation of cold atmospheric plasmas is thought to offer advantages over sinusoidal excitation, direct comparisons between the two are rare, especially in the field of PAC. A needle-type plasma actuator was used in a swirl combustor near the nozzle exit, and the electrical characteristics and LBO limits of the two different types of plasma generators were compared. The flame structures with plasma discharge were characterized using high-speed chemiluminescence from electronically excited CH* and OH* radicals. Proper Orthogonal Decomposition (POD) of CH* and OH* chemiluminescence images was used to identify the dominant flame structures using different plasma generators.
Study on the Transient Dynamic Characteristics of the Pitch-Regulated Device for Coaxilcopter Under Aerodynamic Loads
Authors: Meng Qingkai , Ke Zhifang , Wei Wei , Zhao Molei , Tu Jinghan , Yan Qingdong 
Published: September 2023

Abstract
Coaxilcopter with variable rotor space can dynamically adjust the parameters such as the angle of attack of blades through the pitch-regulated device, so it can adjust and change flight attitude. However, both the rotor aerodynamics and the structure of the pitch-regulated device are complex, and some of the forces generated by the rotor will act on such device in the form of a hinge moment, which would affect the realiablity of the variable pitch-regulated device and the whole craft.
Therefore, a coaxilcopter with a pitch-regulated device is designed, and the finite element numerical simulation method is promoted to calculate and analyze the transient aerodynamic loads of the rotor under different rotor spaces and unbalanced angle between blades. The hinge moment load results are further applied to the variable pitch-regulated device, and the dynamic characteristics of the variable pitch-regulated device under the action of hinge moment are further studied.
The results show that when the unbalanced angle between the left and right blade would lead to the increase of the hinge moment of both blade, and with the increase of rotor speed, the hinge moment of both the left and right blades gradually increases; When the hinge moment is applied to the variable pitch-regulated device, the steering gear load of the lower rotor is 1.57 times that of the rotor steering gear when the propeller spacing is 0.1R (R is rotor radius); When the propeller spacing is 1.2R, the actuator load of the upper rotor is 6%∼12% different from that of the single rotor mode, indicating that the influence of propeller spacing on the upper rotor is negligible at 1.2R, but the actuator load of the lower rotor is about 35% different from that of the single rotor mode, which has a significant influence. It also reveals that the aerodynamic interaction between rotors would affect the hinge moment, it provides a basis for the design of variable pitch-regulated device, and provides a reference for the variable pitch control strategy of aerodynamic performance, which has practical engineering significance.
Direct-Fired Liquid Air Energy Storage With Carbon Capture
Authors: Pryor Owen , Allison Tim , Conlon William , Thorp Joseph 
Published: September 2023

Abstract
This paper presents a hybrid liquid air energy storage system with a direct-fired gas turbine that incorporates liquid phase carbon capture. By liquifying air when energy prices are low, energy is able to be stored for long durations. It can then be pressurized and used as the oxidizer and primary working fluid in a natural gas combustion turbine system. By staging the post-combustion expansion, the air can be routed through a series of heat exchangers that serve to vaporize the liquid air and separate the carbon dioxide and water before the air is reheated and expanded down to atmospheric conditions. The key features of the cycle are the ability to store energy in the form of liquid air, generate power via using the liquid air in a direct-fired, high-pressure combustion process and extracting the carbon dioxide as a liquid via a staged expansion approach. A preliminary cycle model has been created to examine the potential benefits of the cycle using combustor exit conditions of 1150 °C and 30 MPa, and an intermediate extraction pressure of 1 MPa. The preliminary discharge cycle showed extremely high thermal efficiency of 65% with carbon capture and a stored energy rate of around 1.5 by utilizing liquid air as the storage medium.
Large Eddy Simulation of Hydrogen Flame Stabilization in a Reheat Gas Turbine Combustor
Authors: Cartwright Ethan , Xu Chao 
Published: September 2023

Abstract
Reheat gas turbine combustors utilizing high hydrogen content fuel blends serve as a potentially effective low-emission alternative energy system; however, these combustors operate under unique conditions that lack low-cost models for accurately predicting flame stabilization. A large eddy simulation (LES) with detailed chemistry and adaptive mesh refinement is performed on a simplified geometry of the Ansaldo GT36 sequential combustor with an elevated inlet temperature and vitiated air-hydrogen flow in a rectangular mixing duct and combustion chamber, a configuration previously modeled with direct numerical simulation (DNS) in ref. [15]. Flame characteristics and stabilization are investigated, finding similarity in stabilization mechanism and location, but discrepancies in flame front shape and size as compared to DNS results — likely due to a combination of a reduced flame speed fuel composition from that used in DNS results and too coarse a grid for the highly reactive hydrogen fuel. Various wall treatments are investigated, finding indistinguishable behavior across heat transfer models for Law of Walls models, reduced heat transfer with an isothermal wall indicating unresolved length scales, and expected high near wall temperatures for adiabatic wall. The latter two causing significant differences in flame stabilization location and mechanism as compared to DNS results. Results gathered here validate the feasibility of stabilized sequential combustor LES models which can complement fundamental experimental and DNS results in their application to the design process, though further improvements to the LES model are needed before it can be applied to systematic flame characteristic analysis.
Aircraft Engine Performance Augmented by Wet Compression
Authors: Gkoutzamanis Vasilis G. , Psaropoulos Michalis K. , Kalfas Anestis I. 
Published: September 2023

Abstract
This work presents a systematic thermodynamic study to identify and assess the effects of wet compression stage conditioning in aeroengines. Similar techniques found in the literature are initially reviewed. The performance of a modern two-spool turbofan engine variant is then modelled. To account for the humidification effects, a 0D evaporation model is developed and three fluids (water, jet fuel and liquid hydrogen) are evaluated. The results verify that earlier injection is more effective per mass injected, if water is used. However, upstream injection is limited by the amount of water that can be absorbed from the air stream. If jet fuel is used, injection is not feasible for the conditions studied and is overall limited by its autoignition and solidification temperatures. Hydrogen injection indicates that it may facilitate several valid injection points, at low quantities. A further error propagation analysis is made, to evaluate the model’s sensitivity in ambient conditions. Overall, a comparison of the three fluids indicates hydrogen’s feasibility (up to 15% ΔThrust and −35% for EINOx as compared to water’s up to 12.5% ΔThrust, −28% EINOx for similar injection levels) as compared to the other two fluids.
Stability of a Lateral Contact Between a Rotor and Stator When Rubbing
Authors: Wilkes Jason 
Published: September 2023

Abstract
In many rotating machines, close clearances between a rotor and stator at seals, bearings, and other locations may result in contact between the rotor and stator. The current work investigates a contact phenomenon that can occur in these instances that can become unstable. The contact model is applied to a simple overhung rotor similar to an eye seal on an integrally geared compressor. A stability analysis is presented to determine the threshold speed of instability of the rotor in contact with a stator.
It was determined that a correlation between the change in real part of the eigenvalue with respect to rotor speed exists and is proportional to the coefficient of friction at the rub location. The resulting onset speed of instability is determined through an analytical solution to the real part of the eigenvalue when rotor speed and is zero and contact forces are present. It is interesting, however, that the contact stiffness and damping have no affect on rotordynamic stability of the tool. The analysis was tested by comparison with eigenvalue analysis performed in XLTRC2. The results of the comparison showed that the analytical prediction was accurate to within one percent of the true threshold speed of instability.
Test Rig Concept for Evaluating the Performance of a CO2 Immersed Electromechanical Rotor System Utilizing Gas Bearings: Part-2 Thermal Systems & Flow Loop Design
Authors: Bidkar Rahul A. , Kumar Uttara , Zhang Xiaohua , Sarawate Neelesh , Powers John , Anandika Nevin M. , Ertas Bugra 
Published: September 2023

Abstract
Closed-loop supercritical carbon dioxide (sCO2) power cycles and sCO2 turbomachinery hold promise for waste-heat recovery (WHR) in natural gas (NG) pipeline compression stations. A companion paper [2] develops a cascaded sCO2 thermodynamic cycle (operating between 237 bara, 485 °C and 85 bara, 35 °C) using a two-train hermetically sealed turbomachinery power system as a concept for a WHR bottoming cycle at NG compression stations. The key novelty of the hermetic sCO2 turbomachinery was the inclusion of CO2-immersed gas bearings and a CO2-immersed direct-drive permanent magnet (PM) electric machine, both operating in a high-pressure CO2 environment of 27.6 bara. Operation of immersed gas bearings and the immersed PM electric machine in a high-speed, high-pressure CO2 environment is expected to result in high levels of windage heat generation — that can cause undesired structural distortions in thin-film gas bearings, resulting in compromised load carrying capability. Furthermore, high temperature from the windage heat can lead to structural stresses, loss of stator winding laminate glue and overall deterioration of the electric machine performance. To mitigate these risks experimentally, a companion paper [10] proposes a high-speed hermetically sealed test rig that simulates a highspeed 27krpm rotor supported with three radial gas bearings and a thrust gas bearing. High-pressure CO2 is supplied to the test rig with a Gas Supply Flow Loop that includes gas boosters, regulators, flow meters and chillers for a steady state operation. This paper discusses the thermal analysis model for the test rig. Specifically, as part of the thermal model, we present an ASPEN HYSYS model of the external flow loop that tracks the thermodynamic state of the CO2 gas supplied to the rig. Internal to the rig, the thermal model consists of a fluid-advection network that is thermally coupled with a steady-state thermal conduction solver to predict the windage heat, heat transfer coefficients, metal and fluid temperatures in the rig. The internal fluid advection network uses simple 1D fluid elements and real-gas CO2 properties for internal rig flows as well as commercial CFD software for modeling complex thin-film flows in gas bearings. The thermal model uses the principle of energy conservation to couple the heat flow in the advection network with the surrounding rig structural/rotating parts. The thermal model was implemented using an in-house solver using ANSYS workbench and ANSYS APDL script as the underlying platform. We present baseline temperature predictions for the test rig and quantify the amount of cooling mass flow needed to operate the test rig with its temperature constraints. We study the role of cooling in enabling reliable operation of the gas bearing system and electric machine at various rig internal pressures.
Comparison of Computational Predictions for a Cooled High-Pressure Turbine to Data From a Short Duration Experiment
Authors: Christensen Louis , Celestina Richard , Sperling Spencer , Mathison Randall , Aksoy Hakan , Liu Jong , Nickol Jeremy 
Published: September 2023

Abstract
Cooling of hot gas components is essential to the operation of modern gas turbine engines. To continually improve designs and deploy the next generation of cooling, experimental and predictive capabilities must increase as well to more accurately understand new designs. One region of interest is the squealer tip of the high-pressure turbine blades which encounter high thermal loading. This work will investigate the performance of the film cooling in the squealer tip using both experimental data collected with a high-speed infrared camera as a part of a previously published work and transient conjugate heat transfer simulations of the blade passage.
This work investigates the comparison between the experimental data and numerical predictions. Verification of the conjugate heat transfer model is done by examining the mass flowrate through the passage, pressure and thermal loading on the blade midspan, and temperature distributions on the blade tip. In depth analysis of the spatial temperature distributions on the blade tip is conducted as well. From this work, it can be seen that the infrared measurement system is capable of capturing low spatial frequency temperature distributions with good agreement to the computational predictions. Additionally, the numerical predictions are compared to other simulations of the same blade passage which highlight the ability of conjugate heat transfer analysis to capture the heating of the blade during the experiments further improving predictive capabilities.