bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct and Refined Characterization of Rebound for Irregularly Shaped, High-Speed Particles Incident on Aerospace Grade Titanium
Authors: Weindorf Brandon J. , Ehlers Alix , Lowe Todd , Ng Wing , Caddick Mark , Loebig Jim , Morrison Matthew 
Published: August 2024

Abstract
The observed stochasticity in rebounding trajectories for particle-surface interactions in turbomachinery is often attributed to irregularities in particle shape. However, at higher speeds, plastic deformation of the surface can significantly influence the rebounding particle trajectory. This work explores the interaction between particle shape and surface plastic deformation at high speeds and the effect that it has on the observed spread in rebounding trajectories. Two parameters often used to characterize particle-surface interactions in turbomachinery are the coefficient of restitution (COR) and rebounding angle. A fully time-resolved two-dimensional Particle Tracking Velocimetry (2DPTV) system is employed on a high-speed free jet rig to study particle-surface interactions for 150 μm – 250 μm crushed quartz incident on Grade 4 (Commercial) Titanium. Particle speeds range between 50 m/s and 130 m/s and nominal incidence angles of 30° and 90° are studied. In this work, a novel approach that couples the study of both the particle and particle-surface interactions is discussed. In addition to a full description of the experimental procedure, a source of random uncertainly stemming from particle shape coupled with rotation and inter-pixel effects is presented for both velocity and rebounding angle measurements. Moreover, the sensitivity of particle rebounding trajectories to particle shape is explored. A model from the literature is modified to include the effects that particle shape has on the normal coefficient of restitution. The sensitivity study of particle shape is then expanded to total COR and rebounding angle. It is shown that increases in plastic deformation decrease the sensitivity of the COR (both total and normal) to particle shape, reducing the spread of COR values. In contrast, the spread in rebounding angles is dominated by particle shape irregularities and incidence angle with little dependence on plastic deformation.
Numerical Investigation of Windage Heating in High-Pressure Compressor Shrouded Stator Cavities
Authors: Damgacioglu Altay , Cottier Francois , Gümmer Volker 
Published: August 2024

Abstract
Literature provides valuable insights into the thermodynamic behavior of labyrinth seals, but modelling is still incomplete. In this study, a 3D CFD model of a shrouded stator passage was constructed. Various model variations such as increased wall roughness, fixed temperature boundary conditions and walls with fixed heat flux values have been applied to the model to accurately simulate the heat pickup in the labyrinth seal. The heat pickup in the cavity was then quantitatively analyzed and compared with experimental values and with various methods in the literature. Finally, a coupled CFD-FEM method was used as an additional validation mechanism. The study showed that the flow behavior in the experiments was accurately simulated in terms of core swirl ratios, pressure ratios and total temperature rise. The total temperature rise, on the other hand, can be successfully partitioned between conductive heat transfer and windage heating. Future studies may be required to validate the confidence of this study, especially for a range of engines and test rigs. Additionally, future investigations could focus on enhancing the accuracy of predicting the total temperature increase in inner air seals and exploring the effect of honeycomb structures on flow behavior.
Model-Based Inference of Flame Transfer Matrices From Acoustic Measurements in an Aero-Engine Test Rig
Authors: Eder Alexander J. , Merk Moritz , Hollweck Thomas , Fischer André , Lahiri Claus , Silva Camilo F. , Polifke Wolfgang 
Published: August 2024

Abstract
Flame dynamics in the form of aflame transfer matrix (FTM) is not directly measurable in a test rig, but must be deduced from transfer matrix measurements of the combustion system. The burner-flame transfer matrix (BFTM) approach for estimating the FTM is based on local pressure signals from two microphone arrays located upstream and downstream of the combustor. It combines acoustic transfer matrix measurements in non-reacting and reacting conditions, where the latter implicitly includes the flame dynamics. A simple matrix operation then yields the FTM. However, this approach assumes that there is loss-free wave propagation at a constant speed of sound with no change in cross-sectional area between the microphone locations and the burner/flame. The present work demonstrates the limitations of these assumptions when applied to a test rig with complex features, such as effusion cooling, bypass annulus, and downstream end contraction. To remedy the shortcomings of the BFTM approach, this work proposes a novel method to infer the FTM for complex combustors by combining reactive transfer matrix measurements of the entire combustor with an accurate low-order thermoacoustic network model (LOM) of the test rig. This generalized method reduces to the BFTM approach as a special case.
In this work, the Rolls-Royce Scaled Acoustic Rig for Low Emission Technology (SCARLET) operated under realistic engine conditions (Tin ≈ 825 K, pin ≈ 25 bar, kerosene) is used to analyze the capabilities of the proposed model-based inference method and the limitations of the BFTM approach. In a first step, a LOM based on the geometry and operating point of SCARLET is formulated using a generic FTM. This generic model is used to visualize the limitations of the BFTM approach in terms of various physical and geometrical parameters. Finally, experimental measurement data is used to deduce the FTM of SCARLET using the proposed approach.
Numerical and Experimental Investigation of Steady Flow Distortion in Drooped Turbofan Intakes
Authors: Zhang Yuhan , Dong Xu , Li Zhenyu , Sun Dakun , Sun Xiaofeng 
Published: August 2024

Abstract
In some civil aero engines, steady flow distortion in turbofan intakes is often caused by the non-axisymmetric geometry, mostly droop and scarf, and the trend of shortening the nacelle exacerbates this distortion. Much analysis of previous research has established models for numerically predicting the propagation of modes through the region of steady flow distortion, but experimental measurements of the internal flow field in the intake remain challenging. The main objective of this paper is to demonstrate the feasibility of experimentally investigating the steady flow distortion in drooped turbofan intakes, providing a framework for a deeper understanding of the flow mechanisms in these intakes. Firstly, based on two types of geometrical shape, droop and scarf, three different geometries of intakes are designed, and the steady flow distortions they generate are compared using computational fluid dynamics (CFD). Secondly, the generation mechanism of steady-state distortion will be briefly discussed. Finally, this study designs fan experiments under static inlet conditions. The experiments are conducted on an aspirated fan test rig, and total pressure and static pressure measurements are recorded with a 5-hole Aero-Probe. The research results indicate that the fan experiment is successful in capturing this steady flow distortion. Both droop and scarf type intakes cause minor steady flow distortion at the outlet of the intake, which rapidly decays in the duct.
A Speed Control Method for Hydrogen-Fueled Turbojet Using Improved Internal Model Control
Authors: Pan Mengni , He Ai , Chen Zhixiong , Liu Yuan , Hu Zhongzhi 
Published: August 2024

Abstract
Hydrogen is expected to be widely used in aviation, but accurately measuring its flow rate remains challenging due to its compressibility, potentially compromising engine performance. Prolonged operation of aero-engines in high-temperature environments can alter the health parameters of the engine’s gas path, potentially leading to performance degradation or even damage. Maintaining good dynamic quality of aero-engine speed is crucial despite uncertainties in hydrogen measurement and engine degradation. This paper proposes an internal model control algorithm and designs a robust speed controller that considers these uncertainties. Simulation results demonstrate that, unlike traditional PI methods where the relationship between robustness and design parameters is unclear, the proposed speed controller exhibits strong robustness. Even in the presence of uncertainties in metering and engine degradation, it effectively maintains speed control robustness.
A Modal Analysis of Spray Structures From a Transversely Injected Liquid Jet in Subsonic and Supersonic Crossflows
Authors: McKelvy Aubrey J. , Braun James , Paniagua Guillermo , Choquet Etienne , Andre Thierry , Falempin Francois 
Published: August 2024

Abstract
Flow instabilities in high-Reynolds flows are difficult to characterize because the increasingly chaotic interactions of fluid particles allow for larger variety and superpositions of flow patterns. These are especially underexplored in transversely injected liquid jets, which are a popular mixing strategy for high-Reynolds gaseous flows. This study utilizes proper orthogonal decomposition (POD) to identify periodic flow patterns in experimental spray images. A liquid ethanol jet is injected into both a linear subsonic (Mach 0.25 to Mach 0.7) and an expanding Mach 2 gaseous crossflow with plain-orifice injectors of 0.5, 1, and 2 mm diameter. The subsonic test section is rectangular with a 50 cm length and a 23 × 17 cm cross section; a contoured insert is installed in this rectangular test section to generate the supersonic flow path with a 2.54 × 23 cm throat area. Across both regimes, crossflow mass flows vary from 0.5 to 12 kg/s with injectant momentum flux ratios between 0.3 and 180. Reynolds numbers scaled by the injector diameter varied between 4,000 and 52,000. A high-speed camera is used with backlit, shadowgraph, and schlieren imaging systems to collect transmittance contours of the spray at 50 kHz. Unique ‘dagger’ and ‘hump’ shaped spray features are identified and correlated with the shear breakup regime of turbulent and semi-turbulent liquid jets and the catastrophic breakup regime. The same features are identified as ‘advection modes’ with the POD along with a ‘breathing mode’ corresponding to a low frequency oscillation of the mean penetration, and the mode images provide an accurate representation of the phase-averaged size and shape of these periodic spray structures. A characteristic length is used to normalize the peak POD frequencies and produces a mapping that places the three breakup regimes in specific groupings of Weber number and momentum flux ratio.
Exploiting a Transformer Architecture for Simultaneous Development of Transition and Turbulence Models for Turbine Flow Predictions
Authors: Fang Yuan , Reissmann Maximilian , Pacciani Roberto , Zhao Yaomin , Ooi Andrew S. H. , Marconcini Michele , Akolekar Harshal D. , Sandberg Richard D. 
Published: August 2024

Abstract
Previous studies have shown the potential of using a multiobjective CFD (computational fluid dynamics)-driven machine-learning approach to train both transition and turbulence models in RANS (Reynolds averaged Navier-Stokes) calculations for improved turbine flow predictions (Akolekar et al., GT2022-81091; Fang et al., GT2023-102902). However, conducting CFD-driven training incurs a high computational cost as thousands of RANS calculations are required if the starting guesses are taken from an initial population of randomly generated models. This paper, for the first time, adopts a transformer technique, belonging to the class of natural language processing models, in gene expression programming (GEP), to expedite the training process for transition and turbulence models. The efficacy of utilizing the transformer is investigated for two scenarios. In one, we introduce previously trained models to randomly generated ones in the initial population of candidate models, facilitating the generation of models with a higher likelihood of achieving lower cost function values from the outset. In the other scenario, assuming that no suitable information is available from pre-training, a dynamic approach is employed at certain training iterations, where models exhibiting significant errors are excluded and replaced by those trained on the fly by the transformer and demonstrating smaller errors. Additionally, we incorporate mathematical operators such as minimum, maximum, and exponential functions, along with a technique called a rolling window, to avoid nested functions in the trained models. This enhances the flexibility in constructing trained models while still allowing us to delve into the underlying physics and provide recommendations for developing physical models. Finally, we also introduce two additional physical features that serve as training inputs for the turbulence model that contribute to smaller errors. With these enhancements to the previous GEP framework, model training is accelerated considerably and the models found show improved performance for both training and previously unseen testing cases.
Reduction of the Emission Footprint of Gas Turbines in Future Energy System Scenarios Through Optimized Hydrogen Admixture Strategies
Authors: Goßrau Christian , Petersen Nils Hendrik , Wirsum Manfred 
Published: August 2024

Abstract
Within the energy sector, the mitigation of climate change necessitates a paradigm change towards the replacement of conventional with sustainable power generation technologies. Due to the inherent volatility of renewable power generation technologies, dispatchable components, such as gas turbines (GT) will have to be used increasingly for residual load balancing. In addition, GTs are expected to operate fewer hours per year, more flexibly, and at lower capacities. However, fuel utilization in GT is inherently linked to emissions. As a potentially CO2-free energy carrier, hydrogen is a promising fuel for GTs and manufacturers are working on suitable combustor technologies. However, the availability of large quantities of CO2-free H2 remains unclear in the near future. Other pollutants such as NOx and emissions due to incomplete combustion are formed differently in part-load. Therefore, optimizing natural gas substitution based on available H2 quantities and load profiles can improve the overall emission footprint beyond just reducing CO2 emissions.
In this study, a physical-based gas turbine performance model and an emission calculation tool are used to derive an optimized H2 admixture strategy for different load profiles. Characteristic load demand scenarios are derived from actual load profiles of gas power plants and the emission footprints are comprehensively evaluated by different environmental impact categories. In general, the emission footprint is increased significantly and moderately for capacity reduction and flexibility increase of GT operation. The availability of H2 in the near future is derived from forecasts for Germany, and the corresponding quantities are allocated to the partial loads according to the optimized strategy. In most scenarios, the addition of H2 is associated with a reduction in emissions compared to conventional fossil fuel operation. The greatest leverage of H2 admixture in reducing the environmental footprint is found when applied from the lowest load up, thus assisting in the start-up and shut-down process.
Preventing Tilting Pad Fluttering by Using Elastic Pad Fixation
Authors: Schüler Eckhard , Faulhaber Stephan 
Published: August 2024

Abstract
Tilting pad fluttering is a well-known phenomenon in journal and thrust bearings. It can occur on unloaded pads where the buildup of hydrodynamic pressure is not or not sufficiently achieved, which can be attributed to several causes. In severe forms of pad fluttering there is repetitive contact between the pad and the shaft. This can lead to bearing damages and, in the case of journal bearings, trigger subsynchronous rotor vibration with high amplitudes. There are various approaches to solving the problem, some of which relate to the elimination of existing pad fluttering. Proactive approaches are also described in the literature, but these are often associated with restrictions or certain disadvantages, meaning that these measures are not always applied in practice. To investigate a new approach, tilting pad fluttering was first caused and measured during experimental investigations on a conventional bearing. The bearing was then modified with the design solution “elastic pad fixation” which reliably prevented tilting pad fluttering without impairing the general properties and performance of the bearing.
Prediction of Soot in an RQL Burner Using a Semi-Detailed JetA-1 Chemistry
Authors: Lameloise Etienne , Cuenot Bénédicte , Riber Eleonore , Perrier Aurélien , Cabot Gilles , Grisch Frédéric 
Published: August 2024

Abstract
The present work proposes a methodology to include accurate kinetics for soot modeling taking into account real fuel complexity in Large Eddy Simulation (LES) of aeronautical engines at a reasonable computational cost. The methodology is based on the construction of an analytically reduced kinetic mechanism describing both combustion and gaseous soot precursors growth with sufficient accuracy on selected target properties. This is achieved in several steps, starting from the selection of the detailed kinetic model for combustion and soot precursors growth, followed by the determination of a fuel surrogate model describing the complex real fuel blend. Finally the selected kinetic model is analytically reduced with the code ARCANE while controlling the error on flame properties and soot prediction for the considered fuel surrogate. To perform all evaluation and reduction tests on canonical sooting flames, a Discrete Sectional Model (DSM) for soot has been implemented in Cantera. The resulting code (Cantera-soot) is now available for the fast calculation of soot production in laminar flames for any fuel. The obtained reduced kinetic scheme is finally validated in a Rich-Quench-Lean (RQL) burner of the literature in terms of soot prediction capabilities by comparison of LES coupled to the Lagrangian Soot Tracking model (LST) with measurements. Results show a significant improvement of the soot level prediction when using the reduced more realistic kinetics, which also allows a more detailed analysis of the soot emission mechanisms. This demonstrates the gain in accuracy obtained with improved reduced kinetics, and validates the methodology to build such schemes.
Optimization of a Battery Electric Hybrid Propulsion System for a Short Range Aircraft
Authors: Schroeter Jonas , Armbrüster Fabian , Schaber Reinhold , Gümmer Volker 
Published: August 2024

Abstract
In this paper, a serial electric hybrid propulsion system with a technology level of an entry into service in 2035 is designed and evaluated in a multidisciplinary way. The propulsion system is targeted for a 70-passenger regional aircraft with an typical mission of 400nm. The boundary conditions are set in the LuFo VI project TELEM.
In a novel approach the complete propulsion system consisting of propulsors, electric motors, electrical system, generator, batteries, gas turbine and nacelles is modelled. With this approach the propulsion system can be optimized regarding a given figure of merit and tailored to the specific boundary conditions in a multi-design point approach for all relevant operating points. Design rules for an electro-hybrid propulsion system were developed, which can consider any degree of hybridization in any operating point. In addition to the thermodynamic and aerodynamic design, weights, nacelle geometry, drag, thermal management, emissions and operating costs can be assessed, resulting in an integrated propulsion system design. Individual dependencies between the disciplines, such as the dependence of the nacelle drag on the performance of the thermal management are taken into consideration during the multi-design point sizing of the components. This allows the evaluation of the multidisciplinary figure of merit “block energy”.
Effect of Water Injection on Turbofan Engine Compressor Operation and Aerodynamics
Authors: Zawadzki Natan , Szymański Artur , Igie Uyioghosa 
Published: August 2024

Abstract
Water injection (WI) can potentially remedy aircraft-related nitrogen oxide (NOx) pollution around airports and substantially extend the hot section’s life. No high-fidelity study exists examining the effects of deploying compressor water injection (CWI) on turbofans — an engine type dominating the civil aviation market. The available analytical work is bound to several limitations, such as uniform droplet size distribution, simplified droplet transport and no phase coupling. Effects of local changes in the gas composition, interaction of turbulence with dispersed phase and the underlying loss production mechanism of wet compressions are neglected and thus remain unquantified.
The present work investigated the effect of WI on key performance and aerodynamic parameters in a fully integrated compressor of a generic turbofan engine using Computational Fluid Dynamics (CFD) analysis. The compressor layout comprised a fan stage and two core stages called booster. Water was injected behind the fan rotor at the inlet to the booster. Take-off operation was simulated at dry conditions and a range of wet scenarios with 1% and 2% water-to-air mass injection rates and varying droplet diameters from 10 to 20 microns.
Effects on the stage-by-stage compressor performance are discussed in detail, including water distribution, mass flow, temperature, pressure ratio, and efficiency. Particular attention was paid to the aerodynamic effects, which are impossible to obtain based on analytical results. Furthermore, the detailed droplet evolution inside the compressor was scrutinised, including particle residence time, change in size and distribution due to evaporation and interaction with compressor flow and components. The outcomes showed that water injection can result in favourable conditions for compressor operation. Furthermore, a reduction in compressor delivery temperature of up to 40 degrees Kelvin was predicted if finely atomised water was injected.