bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a Conduction-Free Total Temperature Probe Based on the Two-Wire Thermocouple Concept
Authors: Nares Alcala Roberto Felix , Bhatnagar Lakshya , Paniagua Guillermo 
Published: September 2023

Abstract
Thermocouple measurements suffer from errors due to several heat transfer effects. A dominant error source is conduction error due to a difference in the junction and support temperature. Correction for conduction is critical in both steady and transient temperature measurements. The effect of conduction is reduced by using a high length-to-diameter ratio of the wire, but this becomes unfeasible in high-speed flows due to structural limitations. This paper presents a new procedure to perform thermocouple measurement with unprecedented accuracy using a two-wire thermocouple probe.
Our novel numerical correction method necessitates two temperature readings from two different thermocouple diameters. The temperature values are different because the conduction error is a function of their length-diameter ratio and material properties. The two thermocouple readings combined with Conjugate Heat Transfer Simulations (CHT) are used to correct the temperature readings and deliver the actual temperature of the flow free of conduction error. The Conjugate Heat Transfer simulations are run at different temperature boundary conditions and flow Reynolds numbers. This method is generalizable and can correct conduction errors within 0.1K. The paper includes a comprehensive uncertainty quantification approach based on Monte Carlo simulations. This correction was demonstrated experimentally to measure the inlet temperature of a turbine test rig compared against a standard one-wire thermocouple probe, and the uncertainty of the method was quantified.
Validation and Assessment of a Hybrid VOF-Lagrangian Numerical Methodology for Turbulent Liquid Fuel Jets in High-Speed Crossflow
Authors: Zghal Malika , Gauthier Pierre , Sun Xiaoxiao , Wijesinghe Charith , Sethi Vishal 
Published: September 2023

Abstract
For gas turbine combustors using liquid fuel injectors, introducing the spray into crossflowing air to achieve superior fuel-air mixing characteristics can improve performance and reduce emissions. Robust numerical design tools are needed to accelerate the development of low-emissions technologies. CFD models are used to assess the design, performance, and emissions of novel combustion systems. Atomization modelling is often facilitated by using the Lagrangian approach with breakup models rather than the more complex and computationally expensive higher-fidelity Volume-of-Fluid (VOF) approach. However, breakup models used in state-of-the-art CFD rely on empirical constants that have not yet been fully calibrated for jets in crossflow or for representative gas turbine conditions.
Coupling the Lagrangian and VOF approaches could deliver a better compromise between accuracy and computational cost. Among the few studies conducted on the VOF-Lagrangian approach for jets in crossflow, validation was often limited to the near-field spray trajectory under low Weber numbers using either non-turbulent jets or water at ambient pressure. The predictive capabilities in the far-field region were only validated using deterministic breakup models and for non-turbulent jets under low pressure conditions.
This study proposes and validates a novel numerical methodology for coupling the Lagrangian and VOF approaches using a Stochastic Secondary Droplet (SSD) breakup model with Adaptive Mesh Refinements (AMR) for turbulent liquid fuel jets in high-speed crossflow at more representative conditions. The predictions within both near and far-field breakup regions were validated using experimental datasets at high pressures (1–8 bar), Weber numbers (720–1172) and momentum flux ratios (6–33). The predictive capabilities and computational cost were also compared to the Lagrangian approach used with LES and used with an unsteady RANS numerical methodology previously developed and validated by the authors. The effects of different VOF-Lagrangian transition criteria on the computational cost were also assessed and recommendations have been provided for further improvements. The overall predictive capabilities of LES were significantly improved by the novel hybrid methodology proposed by the authors. Although it tends to underpredict the spray trajectory and Sauter Mean Diameter (SMD), it better captures the SMD in the wake region of the jet and the overall droplet velocities compared to the URANS methodology.
Investigation of High-Pressure Ignition Phenomena of CO2-Diluted Syngas in Shock Tubes
Authors: Mohr Darryl J. , Cooper Sean P. , Hay Matthew K. , Kulatilaka Waruna D. , Petersen Eric L. 
Published: September 2023

Abstract
With the rise in popularity of syngas comes the need to better understand the chemistry and combustion phenomena that occur during its use in applications such as the Allam-Fetvedt cycle that utilizes supercritical-CO2 (sCO2) as a working fluid. Several recent studies have shown significant model discrepancies in ignition delay time (IDT) data of syngas diluted in CO2 from shock-tube facilities. However, undesirable inhomogeneous ignition may occur at high pressures behind reflected shock waves in a shock tube. Understanding these undesirable events and when they arise during CO2-diluted syngas combustion is crucial to produce data for chemical mechanism refinement. To allow for imaging studies of these ignition and combustion events, a new addition has been made to the High-Pressure Shock Tube facility at the TEES Turbomachinery Laboratory at Texas A&M University. This paper presents the findings from that facility during the ignition and combustion of CO2-diluted syngas from reflected-shock ignition experiments. Pressures from 12 to 43 atm were studied in a 0.05 H2 + 0.05 O2 + 0.05 CO + 0.85 CO2 blend. Results from high-speed OH* imaging through the endwall showed evidence of homogeneous ignition and combustion within a central core region, but with a clear delineation between the central core and a concentric band adjacent to the sidewall, likely due to reflected-shock bifurcation. Follow-on imaging experiments are suggested before a complete understanding of syngas-CO2 ignition at high pressures in shock tubes is obtained.
Combustion Analysis of a Can Combustor With CH4/NH3 Blended Fuels for a Micro Gas Turbine
Authors: Shih Hsin-Yi , Ho Sz-Pei , Cheng Cheng 
Published: September 2023

Abstract
Ammonia has been proposed as a hydrogen carrier and a potential alternative fuel to achieve low-carbon emissions. Due to its high ignition energy, limited flammable range, and low heating value compared to hydrogen and typical hydrocarbon fuels, it is challenging to sustain stable ammonia combustion. Blending ammonia with natural gas can increase the possibility of combustion applications. This work is to investigate the combustion performance of a micro gas turbine combustor with CH4/NH3 fuel blends. Results indicated the flame temperature declined with increasing NH3 mole fractions at constant fuel flow rates due to lower heating value of ammonia. To maintain the same power output with increasing NH3 contents, the mass flow rates of the fuel blends were raised, which pushed the flame downstream and resulted in severe temperature fluctuation at combustor exit. At higher NH3 fractions, the high-temperature regions shrank again because of lower residence time for any significant reactions. NOx emission was increased due to fuel-NOx production with NH3 addition. However, the non-monotonic trend of NO emission indicated a competition between thermal-NO and fuel-NO productions. Further considerations of flame stabilization and dilution strategy are essential for the implementation of the fuel blends in this micro gas turbine.
CFD Model and Design for Gas Turbine Inlet Plenum With EGR
Authors: Devi Ravindra , Lorusso Salvatore , Michelassi Vittorio , Scotti Del Greco Alberto 
Published: September 2023

Abstract
‘Exhaust Gas Recirculation’ (EGR) with a ‘Carbon Capture Unit’ (CCU) for an industrial gas turbine is one of the widely explored options towards minimizing the detrimental effect of greenhouse gases on the environment. System level studies of gas turbine combustion system conclude an acceptable EGR volume as high as 80%. Considering the large install base units versus new units, industry focus is on a retrofit solution. Introducing such a large percentage of exhaust gas in the intake system of a heavy-duty gas turbine without affecting the flow distortions at the compressor inlet is a challenge. In the current work, an existing intake system is modified to intake up to 50% exhaust gas. Various designs are evaluated using ANSYS CFX 2021R2, a commercial CFD code; CFD domain extends from air-intake region up to compressor ‘Inlet Guide Vane’ (IGV) leading edge, while including details such as filters and silencer. Filters are modeled as porous media. Mixing of exhaust gas and air is modeled using component mixture model; modeling considerations are elaborated. A retrofit arrangement is designed considering the effect of design features such as position, orientation, and cross section of the exhaust gas duct on the flow physics. CFD analysis results show that the flow distortions levels for total pressure, total temperature, and swirl are as good as the intake system without EGR duct. Compared to designs seen in the literature, the retrofit design is simpler to manufacture and maintain. Design is optimized using splitters to reduce footprint and metal weight. Robustness of the design is assessed for extreme air & gas temperatures, duct approach direction, inlet flow non-uniformity due to upstream duct bends and various EGR percentages.
Secondary Flow Patterns Through a Turbine Vane Frame
Authors: Graiff Mattia , Staggl Marian , Wakelam Christian , Laufer Anna-Lisa , Göttlich Emil 
Published: September 2023

Abstract
The Turbine Vane Frame (TVF) is an integrated component interposed between the High-Pressure Turbine (HPT) and the Low-Pressure Turbine (LPT). It carries structural loads, provides shrouded paths for oil and service lines, guides the flow in the transition from small HPT radius to large LPT radius, and imparts to the flow the level of swirl required by the first LPT stage. Integrating these requirements in a single component offers significant size and weight benefits; it poses however a significant challenge to the aerodynamic design. The TVF takes the form of an S-shaped annular duct with low aspect ratio turning vanes. The strong development of secondary flow within the TVF is therefore a matter of particular interest; the scope of this paper is to expand the understanding of secondary flow patterns with respect to the widely accepted models based on linear blade cascades. Numerical and experimental results are leveraged to obtain insights into the flow structures; a method to evaluate vortical structures from experimental data based on a modified version of the Q Criterion is introduced. Experiments are performed in the Sector Cascade rig at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz Unversity of Technology. Two TVF geometries with differing strut counts are furthermore compared.
Historical Review and Performance Comparison of Hydrogen Oxyfuel Steam Cycles for Thermal Power Plants Considering Current Limitations of Turbomachinery
Authors: Bocandé David , Schatz Markus 
Published: September 2023

Abstract
To face the challenge regarding reconversion of stored green hydrogen into electricity, zero emission oxyfuel hydrogen cycles with steam as a working fluid are very promising in both thermal efficiency and large-scale applicability. Previous studies suggest that with Turbine Inlet Temperatures (TIT) of 1700 °C thermal efficiencies in excess of 70% based on Lower Heating Value (LHV) can be reached. This work starts with a historical review, from the early 80s until today, of the processes proposed in the literature which can be categorized in partly condensing and fully condensing cycles. Also, since the calculations in the literature are based on different assumptions of cycle parameters, component efficiencies and material limitations, a selection of state-of-the-art process and component parameters in the turbomachinery and power plant industry will be established to help identify the technically realizable and promising cycles. Those parameters will also be used as a common base for thermodynamic simulations of the selected cycles and can serve as a reliable reference for further calculations. The simulations show that thermal efficiencies up to 73% are achievable under conditions reflecting the present state-of-the-art and 75% in the near future, considering current development. Mitsubishi’s intercooled topping recuperation cycle shows the highest thermal efficiency with 75% based on LHV. Moreover, a higher TIT goes along with increased cooling demand and thus higher losses in the turbine, counteracting the efficiency increase due to the elevated temperature. A parametric analysis will identify the optimum operating point of each cycle regarding TIT with consideration of the cooling efficiency.
Robust Design of Herringbone Grooved Journal Bearings Using Multi-Objective Optimization With Artificial Neural Networks
Authors: Massoudi Soheyl , Schiffmann Jürg 
Published: September 2023

Abstract
Herringbone grooved journal bearings (HGJBs) are widely used in micro-turbocompressor applications due to their high load-carrying capacity, low friction, and oil-free solution. However, the performance of these bearings is sensitive to manufacturing deviations, which can lead to significant variations in their performance and stability. In this study, design guidelines for robust design against manufacturing deviations of HGJB supported micro-turbocompressors are proposed. These guidelines are based on surrogate model assisted multi-objective optimization using ensembles of artificial neural networks trained on a large dataset of rotor and bearing designs as well as operating conditions. The developed framework is then applied to a series of case studies representative of heat-pump and fuel cell micro-turbomachines. To highlight the importance of rotor geometry and bearing aspect ratio in the robustness of HGJBs, two types of optimizations are performed: one focusing on optimizing the bearing geometry, and the other focusing on both the bearing and rotor geometries. The analysis of the Pareto fronts and Pareto optima of each type of optimization and case study allows for the derivation of design guidelines for the robust design of HGJB supported rotors. Results suggest that by following these guidelines, it is possible to significantly improve the robustness of herringbone grooved journal bearings against manufacturing deviations, resulting in stable operation. The best design achieved ±8 μm tolerance on the bearing clearance, and designs optimized for both rotor and bearing geometry outperformed those optimized for bearing geometry alone. This work successfully identifies guidelines for the robust design of herringbone grooved journal bearings in micro-turbocompressor applications, demonstrating the strength of surrogate model assisted multi-objective optimization. It provides a valuable tool for engineers seeking to optimize the performance and reliability of these bearings.
Comparison of the Flame Dynamics of a Liquid Fueled Swirl Stabilized Combustor for Different Degrees of Fuel-Air Premixing
Authors: Kaufmann Jan , Vogel Manuel , Sattelmayer Thomas 
Published: September 2023

Abstract
This study investigates the flame dynamics of lean premixed kerosene combustion for two different degrees of fuel-air premixing using a swirl stabilized burner with an axially movable twin fluid fuel injection nozzle. Thermal power, equivalence ratio and atomizing air mass flow are varied systematically for both nozzle positions investigated. Measurements of the droplet size distribution at the nozzle exit are provided for all operation points. NOx emission measurements and OH*-chemiluminescence flame images show that stationary combustion characteristics significantly change with the nozzle position. Flame Transfer Functions (FTFs) are presented and interpreted for all operation points. The FTFs for the two configurations differ most in the low frequency range where the influence of the droplet dynamics is expected to be highest. For both configurations, a change in thermal power does not affect droplet size, flame shape, NOx emissions and FTF. The observed trends in response to changes in equivalence ratio and atomizing air mass flow are opposite for both configurations. NOx emissions and flame shape are independent of the atomization air mass flow in the highly premixed configuration but not in the partially premixed configuration. In contrast to this, the FTF is affected by changes of the atomization air mass flow in both configurations, but again the trends are opposite. The observed trends for the highly premixed configuration are modeled and reproduced by a change in the phase relation between the equivalence ratio fluctuations and other instability driving mechanisms.
Turbulent Flame Speed and Flame Characteristics of Lean Premixed H2-CH4 Flames at Moderate Pressure Levels
Authors: Faldella Filippo , Eisenring Sebastián , Kim Taesung , Doll Ulrich , Jansohn Peter 
Published: September 2023

Abstract
Carbon dioxide emissions in gas turbine power generation can be reduced by adding an increasing amount of hydrogen to the existing natural gas-fueled combustion systems. To enable safe operation, more insight on how H2 addition affects turbulent flame speed and other important flame characteristics is needed. In this work, the investigation of hydrogen addition effects on certain flame properties has been carried out in a high-pressure axial-dump combustor at gas turbine relevant conditions. OH planar laser induced fluorescence (PLIF) was applied to retrieve flame front contours and turbulent flame speed. The results show that as the concentration of hydrogen in the fuel mixture increases, turbulent flame speed and flame characteristics change drastically. Two main regimes can be identified: From 0 to 50% vol. hydrogen, the turbulent flame speed increases weakly in an almost linear fashion, while from 50% vol. to 100% vol. the trend sharply changes and the higher reactivity of hydrogen, combined with a lower Lewis number, cause thermal-diffusive instability and preferential diffusion effects to become increasingly strong, leading to very high burning rates. The presented results, help to understand and to define the relevant modifications that are necessary to successfully operate gas turbine combustor systems with high H2 content fuels.
Vibration Control of a Rotor-Magnetic Bearing System on the Moving Base Through H∞ Control
Authors: Zhang Guorong , Liu Mingyang , Zou Hansen , Wang Xikui , Xi Guang 
Published: September 2023

Abstract
Rotor-Active magnetic bearing (AMB) systems installed in an aircraft are supported by a moving base. An optimal controller is required to ensure the stability and ideal vibration response of the rotor-AMB system. In this paper, a rigid rotor-AMB system on an aircraft is modeled by the Lagrange principle. The moving base generates additional stiffness, damping and external forcing terms. H∞ control method is applied to design a controller and compare it with a decentralized PID controller. The flight maneuvers of the dive-pull up and horizontal turn are mainly studied. The results show that when the aircraft is in different flight maneuvers, the H∞ controller has a strong ability to resist base movement disturbance, and the rotor displacement of the H∞ controller is smaller than that of the PID controller. As the flight speed Va and maximum roll angle γm increase, the maximum rotor displacement of the H∞ controller remains almost unchanged, but the peak control current of the AMB also increases and may even exceed the maximum allowable value. Therefore, the effect of base movement disturbance should be fully considered during the design process of the AMB.
Quantitative Definition of Spray Edge With Extinction Diagnostics and Evaluation of Attenuation Coefficient for Liquid Jets in Supersonic Crossflow
Authors: McKelvy Aubrey J. , Braun James , Paniagua Guillermo , Andre Thierry , Choquet Etienne , Falempin Francois 
Published: September 2023

Abstract
We present a quantifiable, reproducible, and repeatable definition of the three-dimensional spray width and depth for a canonical jet in an open-source supersonic crossflow. An expanding Mach 2 dry-air crossflow is generated through a converging-diverging nozzle with a 25.4 mm by 230 mm wide throat area. A one-millimeter injector with ethanol seeding provides the liquid injection. Injector characteristics and losses are quantified through a calibrated cavitating venturi. Momentum flux ratios ranged from 0.1 to 20, and Reynolds number scaled by the injector diameter ranged from 5,000 to 40,000. A shadowgraph setup with a telecentric lens provides uniform magnification for precise and repeatable measurements from injection to 150 mm downstream of the jet. A Phantom v2012 camera with a frame rate of 20 kHz and shutter time of 285 ns was employed. Light transmittance is defined and calculated for each image pixel with a ratio method paired with no-spray images collected immediately before injection. These values are then related to an attenuation coefficient by incorporating spray width profiles collected with cross-sectional Mie-scatter imaging at multiple axial locations with a burst mode laser.
Investigation of the Effect of Blade Passing on Two-Phase Flow Within Discrete Compressor Casing Recirculation Channel Using Particle Image Velocimetry
Authors: Ribeiro Santa Cruz Mendoza Carlos Eduardo , Ozdemir I. Bedii , Helcig Christian , Gümmer Volker 
Published: September 2023

Abstract
Recirculation channels (RC) can improve the aerodynamic operational stability of axial compressors. The performance of compressors using RC is still unascertained during in-service operations, which might be subject to particle ingestion. Due to its inherent unsteadiness, little is known about the two-phase flow structure inside such discrete casing treatments.
The present study provides the first insight into the two-phase flow within an RC via Particle Image Velocimetry, characterizing air and particle motions. The ensemble correlation method is used to obtain averaged flow field data corresponding to different blade positions with respect to the RC, providing the periodic dynamic characteristics of the flow.
Measurements show that the blade passing frequency and operation condition impact the amount of recirculated air, the creation of stagnation and separation points, particle trajectories, and slip velocity inside the RC. As a result, this study shows that a robust RC design should consider the particle-wall interactions that can lead to significant erosion or fouling and possibility of blockage near the inlet.