bluuebunny/crossref_metadata_2025_split huggingface dataset:
CFD Simulations of the Unsteady-State Flow Through a 1.5-Stage High-Work Turbine
Authors: Hansen Thorsten , Munktell Erik , Scheuerer Georg , Zhuang Qingyuan , Zwiener Kim 
Published: September 2023

Abstract
Behr et al. [1] have experimentally investigated the unsteady-state flow and clocking effects in a 1.5-stage high-work turbine. Their test rig had a first stator row with 36 blades, a 54-bladed rotor at 2,700 rpm, and a second stator row with 36 blades. They studied four different stator-clocking positions. The present paper computationally investigates the unsteady-state flow through the 1.5-stage turbine by performing CFD simulations with the Simcenter STAR-CCM+ software. The mathematical model of the simulations consisted of the ensemble-averaged unsteady-state mass, momentum and energy equations complemented by the SST turbulence model. The authors applied a quality assessment procedure to the computational results before comparing them to the experimental data and reported the numerical accuracy in the form of the Grid Convergence Index (GCI). The results showed an increase in the calculated efficiencies of the unsteady-state over the steady-state results, bringing data and simulations closer. The total pressure contours at the rotor and second stator exit planes also agreed well with the experiments. Finally, the paper includes simulations of the effects of different stator-clocking positions. The results showed a similar response to the change in stator-clocking position as the experiments.
Measurement of Soot Volume Fraction and Temperature Fields of an Axisymmetric Flame Using an Iterative Image Recreation Method
Authors: Chernov Victor , Cruz Juan Jose , Escudero Felipe , Fuentes Andres 
Published: September 2023

Abstract
A method to recreate an image of a virtual sooting flame is presented. To do this, a spatial field of soot volume fraction and temperature is needed. It is assumed that the dominant emission mechanism is grey body radiation and that the primary soot particles are below the Rayleigh limit. If the spectral and intensity responses of a camera are known, it is possible to recreate the image of the flame by integration of the radiation along the line of sight. The measurement of the soot volume fraction and the temperature is done iteratively — a first guess is proposed, an image is constructed and compared to the real image. If images are different, the soot volume fraction and temperature fields are adjusted and the process is repeated. The iteration procedure is explained. The method is tested on a co-flowing laminar diffusion flame of ethylene and air. The results are compared to other, more established methods. It appears that the proposed method reproduces well soot volume fractions, while there is a noticeable disparity in the temperature results.
Structural Characterization of a Rapid-Prototyped Inlet Particle Separator Model for Aerodynamic Lab Testing
Authors: Castaldi Marco , Mayo Ignacio , Demolis Jacques , Eulitz Frank 
Published: September 2023

Abstract
Inlet Particle Separators (IPS) are filters installed in helicopter and turboprop engines to prevent the ingestion of dust, sand and other debris when operating in extreme conditions. However, the performance and limitations of those systems have to be investigated before their installation in the aircraft. For this reason, the IPS testing is a primary concern for engine manufacturers: unfortunately, the organization of conventional experimental campaigns might be too lengthy and in conflict with the stringent industrial timescales. Hence, the IPS can be fabricated by means of polymer additive manufacturing to shorten the testing cycle time and reduce costs, but this poses a threat in terms of mechanical rig integrity. This paper proposes a complete approach for the structural characterization of an IPS made of FullCure720 and HP PA 11, analyzed using the same tools and procedures of classical metal structures. This method employs fluid structure interaction to ensure safe operability during testing, and can be applied in early design phases to plan low-risk experimental campaigns. Starting from the structural collapse of the rig at high Reynolds number, its safety under both steady and unsteady loading conditions is assessed. The maximum inlet total pressure allowed in the system is determined and some structural reinforcements are analyzed to prevent failure in future tests. The results confirm the existence of weak regions even with stiffer components, and the impossibility of operating the facility at high Reynolds number with the current design.
Aerodynamic Forcing Analysis of Aerodynamically Mistuned Outlet Guide Vane Assemblies
Authors: Merson Jacob , Stapelfeldt Sina 
Published: September 2023

Abstract
The next generation of aero engines feature a more compact design with a shorter distance between the fan rotor and bypass outlet guide vane (OGV) assembly. As such, potential forced response due to rotor-stator interactions has become a more significant concern with regards to high cycle fatigue and component lifespan. It has been shown that deploying a non-axisymmetric OGV configuration is able to reduce the first engine order (1EO) forcing on the fan’s blades.
This paper explores the effects that a non-axisymmetric OGV configuration has on the aerodynamic forcing on the vanes themselves. A low pressure system representative of a modern low-speed fan with different non-axisymmetric OGV patterns is simulated and forcing amplitudes on the OGV stator vanes recorded. Six different non-axisymmetric patterns are generated: three with sinusoidally distributed varied stagger angles of up to 1, 2, and 4 degrees with a one-lobed (circumferential wavenumber m = 1) pattern and an additional three with the same stagger angle distributions with a two-lobed (m = 2) pattern. The forcing in assembly modes and on individual blades are analyzed, and the forcing amplitudes compared to those of the tuned (i.e. identical) OGV configuration. It is shown that aerodynamically mistuning an OGV assembly typically results in a relative increase in forcing amplitudes on most of the individual OGVs, with a maximum forcing amplitude increase of 50% on specific OGVs when configured in the two-lobed, 4 degree re-staggered sinusoidal pattern.
Flow Interaction Between Cascade and Flow Resistance Medium
Authors: Lin Tong , Sarimurat Mehmet , Dang Thong Quoc 
Published: September 2023

Abstract
This paper investigates the effects of flow-interaction between a rotor and a high-resistance medium (HRM) on both rotor and system performance within the 2D cascade limit using computational fluid dynamics (CFD). Two configurations were studied: the Rotor/HRM configuration, where the HRM is located downstream of the rotor, and the HRM/Rotor configuration, where the HRM is located upstream of the rotor. The results indicate that fan performance increases from the interaction effect, along with an extension of the stall margin. However, the pressure drop across the HRM is increased due to an increase in velocity magnitude and non-uniformity, which can lower system overall performance. In the HRM/Rotor configuration, the presence of an upstream close-coupled HRM induces a high-velocity jet around the blade which is more significant on the suction surface and appears to delay flow separation, resulting in an extension of the stall margin. In the Rotor/HRM configuration, the boundary-layer thickness on the blade surfaces is reduced, resulting in delaying stall. In both cases, flow non-uniformity and the presence of swirl velocity in the HRM increases the pressure loss across it.
Best Practices From Hydrogen Fuel System Retrofit
Authors: Pigon Travis , Cloyd Scott , Springer Chaya , Boggs James , Shiraiwa Takashi , Yamazaki Shinichi 
Published: September 2023

Abstract
Hydrogen co-firing is increasingly being considered as a viable solution for the decarbonization of Gas Turbine Power Plants. Enabling this capability at existing natural gas-fired plants requires a hydrogen fuel system retrofit. Hydrogen has a higher propensity to leak and ignite when compared to natural gas. Additionally, when blending hydrogen, hazardous area classification and materials do not necessarily comply with the industry regulations and standards for power plants that run on 100% natural gas. Considering these challenges, the conventional procedures and tests used for natural gas must be reconsidered for the application of hydrogen to achieve a safe, compliant, and cost-effective retrofit.
This paper summarizes best practice recommendations and lessons learned from the successful retrofit and demonstration of a hydrogen fuel system for co-firing at a Southern Company/Georgia Power combined cycle plant featuring Advanced Class M501G gas turbines. As the paper discusses, the methods applied during the project are not new to the industry. However, it was necessary to employ a more controlled and, at certain points, inventive process to address the challenges presented by the unique properties of hydrogen.
Advanced Polytropic Efficiency and H-S Diagram Application
Authors: Wettstein Hans E. 
Published: September 2023

Abstract
The polytropic efficiency is the best quality measure for compressing or expanding engines for compressible fluids. Compressor- and gas-turbine 1D cycle performance simulation methods use it preferably. In steam expanding engine simulation the isentropic efficiency definition is dominating. However, the polytropic efficiency is well applicable for steam expansion based on recent papers of the author [1], [2]. Most applications of polytropic efficiency assume adiabatic change of state. In current turbomachinery, external heat exchange in the blading is often negligible due to short residence time and established external insulations. However, in (historic) reciprocating engines as well as in some current concepts external heat exchange plays an important role forcing to understand this effect as well. This paper aims at understanding the effects of external heat exchange on the polytropic efficiency calculated with a recursive numeric integration algorithm for any finite pressure ratio in expansion.
I select as a teaching appliance a historically well-documented reciprocating Uni-(directional)-flow steam engine involving steam condition with condensation (assuming equilibrium). The older reciprocating steam engines (with alternating flow direction in the cylinders) have both internal heat exchange and external heat losses during expansion. “Our” uniflow engine was a considerable historic improvement step including internal heat exchange in a documented manner. This allows demonstrating the features and the interpretation of the polytropic efficiency based on the use of the current IAPWS steam data.
The Role of Diffusive Mixing in Current and Future Aviation Fuels at Relevant Operating Conditions
Authors: Di Sabatino Francesco , Wan Kevin , Manin Julien , Capil Tyler , Hicks Yolanda , Gander Alex , Crua Cyril 
Published: September 2023

Abstract
With aviation’s dependence on the high volumetric energy density offered by liquid fuels, Sustainable Aviation Fuels (SAFs) could offer the fastest path towards the decarbonization of aircrafts. However, the chemical properties of SAFs present new challenges, and research is needed to better understand their injection, combustion and emission processes. While efforts such as the United States National Jet Fuel Combustion Program (NJFCP) that investigated several aspects in detail, certain processes were unfortunately beyond the reach of this program. One of them in particular is about droplet evaporation at relevant pressures and temperatures, and this represents the focus of the present manuscript. To address this gap we characterized the evaporation and mixing of spray droplets injected into well-controlled thermodynamic environments at conditions relevant to modern and next generation aero-engine combustors. We tested three fuels from the NJFCP, namely an average Jet A fuel (A-2), an alcohol-to-jet fuel containing highly branched dodecane and hexadecane type components (C-1), and a blend made of 40 % C-1 and 60 % iso-paraffins ranging from 9 to 12 carbon atoms (C-4). We also tested a single component normal alkane: n-dodecane, as well as an advanced bio-derived cyclo-alkane fuel: bicyclohexyl. The time evolution of fuel droplets was monitored using high-speed long-distance microscopy in a specific configuration that enabled sharp images to be acquired at these extreme conditions. The collected images were processed using a purposely-developed and trained machine learning (ML) algorithm to detect and characterize the droplets’ evaporation regime. The results revealed different evaporation regimes, such as classical and diffusive. In agreement with previous studies, evaporation regimes appear to be controlled by ambient pressure, temperature, and fuel type. The measurements demonstrate that diffusive evaporation is relevant at high-pressure conditions, such as take-off combustor pressures for modern commercial aircraft engines. However, classical evaporation mostly controls mixing at lower pressure, such as cruise altitude conditions. The ML analysis emphasized that multiple evaporation regimes co-existed at the same operating condition and no significant relationship was found between droplet size and evaporation regime. The findings of this work constitute a database for validating spray and droplet models that are necessary for implementing lower emissions fuels in aero-engines.
Characterization of High-Pressure Hydrogen Leakages
Authors: Cerbarano Davide , Lo Schiavo Ermanno , Tieghi Lorenzo , Delibra Giovanni , Minotti Stefano , Corsini Alessandro 
Published: September 2023

Abstract
Reduction of gas turbines carbon emissions relies on a strategy for fueling the engines with pure or blended hydrogen. The major technical challenges to solve are i) the adjustments to the engine and in particular the combustion chamber and ii) a series of issues to solve to guarantee safe operations. In fact, compared to natural gas, hydrogen fueling implies higher risks of explosion in case of leak in the turbine enclosure and a more careful design of the ventilation system. Thus, a deeper comprehension of hydrogen leak scenarios is needed to adjust the safe design strategy of the enclosure. To this aim, a series of numerical investigations was carried out to understand how different methane-hydrogen blends (from pure methane to pure hydrogen) behave when leaking from a pipeline with fuel pressure that span from 1.5 to 4.5 MPa. The different fuel blends leaks in form of under-expanded jets were studied under different cross-flow ventilation conditions, with ventilation velocity spanning from 0 m/s to 5m s.
When compared to pure methane, the outcome is a three times longer penetration distance for pure hydrogen axisymmetric flammable clouds, whereas in cross-flow conditions a more complex three-dimensional behavior was found, potentially opening a safety-related concerns discussed in the manuscript.
Swirl Enhancement Effect on Turbine Rim Seal Performance
Authors: Choi Mingeun , Goo Bonhan , Cho GeonHwan , Song Seung Jin 
Published: September 2023

Abstract
In gas turbines, sealing flow is extracted from the high-pressure compressor and supplied into the turbine wheel-space to suppress hot gas ingestion. Such hot gas ingestion is thought to be driven by the difference in either the static pressure or swirl between the mainstream and wheel-space flows. For the first time, experiments have been conducted in a low-speed single-stage axial turbine with a single-radial clearance rim seal and a “swirler” on the rotor disk. The objective is to evaluate the impact of enhanced wheel-space flow swirl on the rim seal performance. The swirler does not affect the mainstream flow. In the wheel-space, however, the swirler reduces static pressure; increases swirl; and improves rim seal performance (i.e., reduces the minimum sealing flow rate needed for hot gas ingestion prevention). Thus, the seal performance improvement occurs with increased difference in pressure and reduced difference in swirl between the mainstream and wheel-space flows. Therefore, it can be inferred that the rim seal performance depends more strongly on swirl than pressure. Preliminary gas turbine cycle performance studies indicate that net cycle efficiency benefits can be obtained.
Effect of Air-Liquid Homogeneous Mixture on the Linear Dynamic Characteristics of a Hydrostatic Journal Bearing
Authors: Voitus Anthony , Arghir Mihai , Hassini Mohamed-Amine 
Published: September 2023

Abstract
Water lubricated hydrostatic journal bearings are widely used to support radial load of pumps in nuclear power plants. In some situations, these pumps may be required to operate with a mixture of water and air. This compressible air-water mixture will alter the dynamic characteristics of the hydrostatic journal bearings and can have a significant impact on the vibration behavior of the entire pump shaft line. The present work is a parametrical investigation of the rotordynamic characteristics of these bearings relative to the volume fraction of the ingested air. The compressibility, the density and the viscosity of the air-water mixture depend on this volume fraction. In order to evaluate this influence, a homogeneous air-liquid mixture model was developed. Moreover, for low viscosity lubricants, inertia effects can also have an important impact on bearing rotordynamic coefficients. Therefore, the flow is modeled first with the Reynolds equation and then with the bulk flow system of equations to evaluate this impact. The results show the variation of the direct and cross-coupling stiffness and of the direct damping with the evolution of inertial effects and of the level of air contamination.
Application of a Multidisciplinary Design Process to Assess the Influence of Requirements and Constraints on the Design of Military Engines
Authors: Matuschek Tomasz , Otten Tom , Zenkner Sebastian , Becker Richard-Gregor , Zamboni Jacopo , Moerland Erwin 
Published: September 2023

Abstract
The design of supersonic military aircraft is a complex multidisciplinary optimization (MDO) process in which the dependencies and strong interactions between engine and aircraft must be imperatively considered. Applying a fully coupled propulsion-airframe design system is a highly challenging task, since it requires a set of numerically stable analysis tools capable of optimizing multiple design variables simultaneously. To improve computational efficiency, the application of low-fidelity design of experiment (DOE) methods aid in narrowing down the selection of suitable combinations of design parameters. This approach allows the division of the multidisciplinary process into subsystems, each of which can be served by specialized engineers. Interactions between the disciplines are then considered by exchanging DOE-based sensitivities.
This paper presents the multidisciplinary design process developed at the German Aerospace Center (DLR), — in which the airframe and propulsion system are designed simultaneously whilst effectively utilizing DOE-based sensitivities. Guiding the work is an application case on the preliminary design of military engine concepts considering its effects on overall integrated aircraft architecture. The design process is used to investigate the influence of important engine parameters such as overall pressure ratio (OPR), bypass ratio (BPR) and turbine entry temperature (T4) on the design of military aircraft. Furthermore, the impacts of thrust requirements and technological constraints of the engine are analyzed.
Viability of Fiber Optic Temperature Sensors Embedded Within Engine-Scale Turbine Blades
Authors: Berexa Emily K. , Fells Julian A. J. , Ireland Peter T. 
Published: September 2023

Abstract
Small variations in temperature across a gas turbine blade can have significant impacts on engine fuel efficiency, power output, and blade life. Therefore, an improved understanding of the temperature distribution on the surface of and within a gas turbine blade supports optimization of cooling systems and blade structures. While established methods exist for external blade surfaces, limited methods exist to capture the temperature distribution within the internal structure. Due to the small sizes of blades and the complex cooling configurations they contain, optical access is limited, and sufficient spatial resolution is difficult to obtain. This paper explores the viability of embedding fiber optic temperature sensors within engine-scale turbine blades. Given their minimally invasive nature, potential for multiplexing, and ability to operate in harsh conditions, fiber optic sensors present an opportunity to capture detailed temperature data for research and development or in-situ health monitoring. Specifically, fiber Bragg gratings (FBGs), or narrow band filters which reflect certain wavelengths of light, can be used to sense physical parameters such as strain and temperature. A single optical fiber with a diameter of less than 0.2 mm can contain many FBGs along its length, allowing for measurements with high spatial resolution. Additionally, the high temperature capabilities of FBGs create sensors well-suited for the harsh conditions present in turbine blades. This paper identifies and explores obstacles to the embedding of FBG sensors within engine-scale blades. Three primary challenges include routing through complex configurations, achieving thermal contact between the sensor and blade, and decoupling strain and temperature for embedded measurements. This study evaluates how routing and embedding fiber optic sensors within a blade impact the measurements acquired. Following this study, instrumentation of a cooled, engine-scale blade with fiber optic temperature sensors will be undertaken in a linear cascade at the Oxford Thermofluids Institute.
Initial Numerical Simulations of a Laboratory-Scale Premixed Hydrogen/Air High Swirl Experiment
Authors: Caulfield Christopher J. , Patil Sunil , Arguinzoni Carlo , Ansari Naseem , Palies Paul 
Published: September 2023

Abstract
As decarbonization of combustion systems is critically important, studies focusing on hydrogen combustion are required and undertaken for various future industrial applications. In this context, an experiment located at The Combustion and Propulsion for Aviation Research Center is studied with numerical simulations to get insights into both non-reacting and reacting flow-field. This article presents the computational results of a series of numerical simulations of this laboratory scale fully premixed hydrogen/air experiment. The design of the experiment is first discussed with key components of the setup being described. This setup includes water-cooled bluff-body and upstream plenum for flashback mitigation, axially translatable swirler for combustion instability passive control, and both partially-premixed and fully premixed operating conditions. The simulated operating point corresponds to an equivalence ratio of 0.6, an injector bulk velocity of 13.4 m s−1 and a thermal power of 9 kW. The article discusses results obtained with Reynolds-Averaged-Navier-Stokes (RANS) and Large-Eddy-Simulations (LES) for the non-reacting flow as well as obtained with Stress-Blended Eddy Simulations (SBES) for the reacting flow. State-of-the-art meshing and geometry capabilities are used and lead to a poly-hexacore mesh made for those simulations with a cell count of 6.2 million. The turbulence closure, the combustion and kinetic models used along with the simulations settings are described. The convergence is discussed with two main metrics: mass conservation and residuals monitoring. The results indicate that the current experimental design enables: (i) the formation of a strong inner recirculation zone (IRZ) and an outer recirculation zone (ORZ) as captured by the computations, (ii) the stabilization of a highly swirled premixed hydrogen/air flame which is observed to be compact.