bluuebunny/crossref_metadata_2025_split huggingface dataset:
Artificial Intelligence-Based Performance Maps for Expander-Compressor Analysis in Energy Transition Applications
Authors: Lottini Fabrizio , Bicchi Marco , Agnolucci Andrea , Marconcini Michele , Arnone Andrea 
Published: August 2024

Abstract
Limiting the global warming impact requires a drastic reduction of greenhouse gas emissions (GHG) to reach a zero-carbon growth by 2050. Against this backdrop, turbomachinery designers are asked to develop more compact, efficient, and reliable machines. The research focuses on developing machines able to reduce energy losses and overall footprint, thus improving power plants efficiency and operability. To this end, expander-compressors (EC) seem to play a key role in the energy transition and appear a promising technology for high-density plants, especially together with hydrogen (H2) or supercritical carbon dioxide (sCO2) as working fluid. However, when operating conditions changes, a reduction in machine efficiency may be expected, with a consequent degradation of the overall system performance. In order to optimize the operation of the power plant, it is crucial to understand how the variation of the expander-compressor behavior affects the working conditions of the other components of the plant. In this perspective, a fast and reliable way to estimate the EC performance at different operating conditions is necessary. Although the scientific literature shows several studies on mean-line approaches for expanders and centrifugal compressors, the joint use of 1D models with artificial neural networks (ANN) for ECs combined machine is still overlooked. To fill this gap, the prediction of artificial intelligence (AI)-based performance maps is proposed in this work. The tool has been tested in a case study based on a real EC. Results showed a rapid evaluation of EC efficiency while varying the operating conditions.
Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management
Authors: Frey Adam C. , Bosak David , Stonham Joseph , Sangan Carl M. , Pountney Oliver J. 
Published: August 2024

Abstract
Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion provided that the hydrogen reactant is produced renewably. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized.
Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80–200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select “Pareto efficient” coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches.
Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at &lt; 130°C and aliphatics for PEMFCs operating at &gt; 130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing gains in performance at higher operating temperatures.
The two approaches outlined in this paper are useful to PEMFC TMS designers. The FoM enables expedient coolant screening in preliminary TMS design, and the model provides a high-fidelity method for optimal coolant selection.
Combustion Optimization and Burnout of Ammonia-Based Gaseous Fuels in the Constant Pressure Sequential Combustion System Operated in Rich-Quench-Lean Mode
Authors: Heggset Tarjei , Meyer Ole H. H. , Gruber Andrea , Tay-Wo-Chong Luis , Ciani Andrea 
Published: August 2024

Abstract
In the context of fuel-flexible operation of gas turbines, providing on-demand large-scale electric power without incurring in emissions of carbon dioxide, a convenient feature of Ansaldo Energia’s Constant Pressure Sequential Combustion (CPSC) system is the possibility of controlling the amount of fuel independently fed to the two combustion stages depending on the reactivity and combustion characteristics of the fuel itself. Crucially, in the case of ammonia-based fuels, this includes the capability of switching the CPSC operating mode from a conventional Lean Pre-Mixed (LPM) combustion to a Rich-Quench-Lean (RQL) staging strategy that mitigates undesired emissions of atmospheric pollutants (NOx) and greenhouse gases (N2O) emerging from the oxidation of fuel-bound nitrogen. Building upon an earlier numerical-modelling assessment of the CPSC system capability to operate in RQL mode (GT2023-103835) [1], the present work extends the scope of the initial preliminary study with a comprehensive set of additional calculations, based on massively parallel Large Eddy Simulation (LES) performed in conjunction with detailed chemical kinetics. Firstly, it is reported that, according to the numerical modelling predictions, a transition to stable, low-emission combustion of pure (non-decomposed) ammonia in the Multi-Burner First Stage (MBFS) can be achieved following an initial ignition and flame stabilization of a more reactive, partially decomposed ammonia blend. Secondly, it is shown that, at the equivalence ratio investigated, the unburnt fuel fractions emerging from the fuel-rich MBFS flames are completely oxidated by secondary air injected within the Dilution-Air Mixer (DAM) section of the CPSC. Furthermore, it is found that this burnout process occurring in the DAM section of the CPSC does not lead to significant increase of NOx and N2O emissions, thereby confirming the excellent potential of the CPSC to operate cleanly and efficiently with ammonia-based fuels.
Comparative Analysis of the Effect of Two Tower Geometries on Offshore Wind Turbine Wake Aerodynamics
Authors: Simone Albanese , Barnabei Valerio Francesco , Morici Vincenzo , Corsini Alessandro , Castorrini Alessio 
Published: August 2024

Abstract
Rotor-wake interaction and the corresponding power loss are a significant aspect to account for in the development and design of new offshore wind farms. As the wake shed by upstream turbines can induce a substantial reduction in the power generated by the downstream turbines, turbines are located at considerable relative distances, allowing the downstream flows to have a larger space to recover kinetic energy from the freestream flow field. The mechanism of wake recovery is an interesting area of study for wind engineering, being affected by various factors such as mixing with atmospheric and ground turbulence, interaction of the wake flow and tip vortices with fixed structures and obstacles. In this paper, we examine the impact of support structures on downstream turbulent flow and wake recovery for a utility-scale wind turbine operating in an offshore environment. We use the actuator line method to model the rotor, a common approach to simulating wind farms with CFD solvers, while the support structures geometry given by the tower and nacelle is directly resolved by the CFD mesh. The CFD simulation is based on the incompressible k-ω SST-IDDES model, which is a hybrid LES/RANS turbulence model with enhanced wall-modeling capabilities. The numerical modeling is implemented in Open-FOAM and in a dedicated library for the actuator line model to simulate the blade’s aerodynamics. This is further augmented with a finite element model to account for blade elasticity. In the presented investigation, we use the IEA-15MW turbine model. The rotor is mounted on two distinct types of towers: a standard mono-pylon tower and a tripod-style tower.
Investigating the Influence of Non-Uniform Radial Inlet Distortion on the Performance of Counterflow Model Combustor
Authors: Shi Yunjiao , Luo Shaowen , Zhao Ningbo , Yang Ren , Zheng Hongtao 
Published: August 2024

Abstract
As gas turbine technology, design capabilities, and numerical simulation capabilities continue to advance, the boundary conditions at the inlet of the combustion chamber are no longer set as simple uniform inflow. Instead, the impact of upstream compressor exit flow distortion on combustion chamber performance is fully considered. Therefore, this study employs numerical simulation to analyze in-depth the variation patterns of radial distortion at the inlet of a swirl combustor. The research results indicate that radial distortion simultaneously increases the total pressure loss in both cold and hot flow fields. As the distortion peak shifts upward, the total pressure loss increases (by 0.54%), but it has little impact on combustion efficiency and thermal resistance loss. Changes in the distortion peak velocity position affect the separation vortex location in the diffuser section and the penetration depth of dilution holes, thereby influencing flame morphology and outlet temperature distribution. The increase in total pressure loss along the path becomes more pronounced as the flow turns from the diffuser to the combustor, especially under upper peak conditions. The diffuser exhibits the strongest suppression effect on the velocity peaks of the lower peak and middle peak conditions. This study provides valuable insights for establishing accurate boundary condition models that describe the inlet effects of combustion chambers in numerical simulations of gas turbine combustors.
Ammonia and Ammonia/Hydrogen Mixtures Ignition Delay Times and Chemical Kinetic Model Validation at Gas Turbine Relevant Conditions
Authors: Pierro Michael , Dennis Christopher W. , Pothen Alex-Abraham , Hulliger Nikolas , Kelly Tyler , Fraze Matthew , Urso Justin J. , Rahman Ramees K. , Kinney Cory , Winquist Mark , Vega John , Subbaraman Ganesan , Steele Robert , Vasu Subith S. 
Published: August 2024

Abstract
Undiluted mixtures of ammonia/hydrogen (NH3/H2) were auto-ignited inside the University of Central Florida’s high-pressure shock tube, allowing for lower temperature ignition data and realistic fuel concentrations to be experimentally tested and compared to chemical kinetic models. Ignition delay time (IDT) measurements were collected at the conditions relevant to power generation gas turbines (5–20 bar, 1000–1700 K) and across a range of equivalence ratios (0.5–1.5). The data was compared against the 2018 Glarborg et al. model, which contains nitrogen-based chemistry and was previously validated at lower pressures and dilute conditions. The 20 bar experimental IDT data is predicted well by the model, but large deviations were shown for 5 and 10 bar with hydrogen addition. Experimental 5 bar IDTs were measured to be faster than the 10 and 20 bar data, highlighting the unique combustion chemistry of the hydrogen explosion limits. The model failed to capture explosion limit properties at intermediate pressures, where hydrogen pressure-dependence reaction chemistry is prominent. A sensitive analysis was performed to investigate the top reaction pathways predicted by the model and the chain branching reactions H + O2(+M) → HO2(+M) and HO2 + H → 2OH are suggested as key reactions to reinvestigate to improve the 2018 Glarborg et al. model predictions of the hydrogen explosion limits. Furthermore, an improved chemical kinetic model is shown built upon the experimental data. By improving chemical kinetic models, air-breathing hydrogen/ammonia turbine combustor efficiencies can be improved, and nitrogen oxide (NOx) emissions can be lowered to ultimately reduce greenhouse emissions.
A Reactor-Network Framework to Model Performance and Emissions of a Longitudinally-Staged Combustion System for Carbon-Free Fuels
Authors: Gopalakrishnan Harish S. , Maddipati Raj , Gruber Andrea , Bothien Mirko R. , Aditya Konduri 
Published: August 2024

Abstract
Hydrogen and ammonia are considered crucial carbon-free energy carriers optimally suited for seasonal chemical storage and balancing of the energy system. In this context, longitudinally-staged combustion systems represent an attractive technology in power generation for their capability of achieving low NOx emissions while conserving high load and, crucially, fuel flexibility at high thermal efficiency. Such two-stage combustion systems have been successfully implemented for natural gas firing of gas turbines and, more recently, have shown significant potential for clean and efficient hydrogen-firing operation. However, optimal operation with ammonia-based fuel mixtures is yet to be established. In a recent numerical modelling study (GT2023-103835), a novel Rich-Quench Lean (RQL) operational concept was proposed to burn a fuel-rich mixture of partially-decomposed ammonia and air (for equivalence ratios ϕ ∼ 1.1–1.2) in the first stage of a longitudinally-staged combustion system. Complete oxidation of the remaining (hydrogen) fuel is theoretically ensured by dilution-air addition downstream of the first stage combustor and it is confirmed by predictions from ongoing LES calculations (GT2024-128946). However, any operational concept based on these near-stoichiometric combustion conditions, while minimizing undesired prompt NOx and N2O formation by ammonia oxidation, can potentially result in significant, and certainly unpractical, thermal load on the first stage combustor liner that needs to be mitigated. In the present study, we exploit a newly developed reactors-network model to efficiently investigate the NOx-emissions performance of a longitudinally-staged combustion system fired with natural gas, hydrogen or ammonia. Firstly, the reactors network framework is validated with experimental, computational and other similar reactor network results in the literature. Secondly, the optimal air distribution within the longitudinally-staged combustion system is found for clean (low emissions) and efficient (complete fuel conversion) ammonia-firing operation. Thirdly, the consequences of such “ammonia-optimized” air distribution on flame stabilization and NOx emissions in more conventional natural gas- and hydrogen-firing operation are considered. Finally, an optimal air and fuel distribution is suggested for the longitudinally-staged combustion system on the basis that, while still ensuring robust flame stabilization and high turbine inlet temperature, it minimizes NOx emissions for all three fuels considered.
Numerical Analysis of Convective Heat Transfer Processes and Performance Assessment of Lattice and Triply Periodic Minimal Surface Geometries
Authors: Casini Niccolò , Mazzei Lorenzo , Da Soghe Riccardo 
Published: August 2024

Abstract
The increasing relevance of additive manufacturing has sparked interest in lattice and triply periodic minimal surfaces (TPMS) for lightweight, high-performance components. These structures have recently gained attention in thermo-fluid applications for enhanced heat transfer capabilities. Despite their potential, gaps remain in understanding how design affects convective heat transfer. Previous studies show higher friction factors in lattice and TPMS compared to smooth pipes, which nevertheless achieve greater efficiency index due to increased surface area and Nusselt number. This study examines various lattice and TPMS structures, like Gyroid, Diamond, and BCC, alongside conventional channels and pin fins. Using steady-state CFD, it analyses pressure drop and heat transfer covering Reynolds numbers from 10,000 to 40,000, representative of gas turbine cooling applications. Numerical simulations are validated against literature experimental data, confirming good agreement. Results identify the gyroid structure as the most efficient, emphasizing the role of increased wetted area in heat transfer enhancement despite the low fin efficiency provided by Inconel and the small wall thickness.
Effect of Flare Angle in a Counter-Rotating Dual Radial Swirler on the Stability of a Swirl-Stabilized Flame
Authors: Rathod Darshan D. , S. K. Thirumalaikumaran , Kumar Sonu , Panda Pratikash , Basu Saptarshi 
Published: August 2024

Abstract
A novel high-shear injector developed at the National Centre for Combustion Research and Development (NCCRD) is further investigated in the current study. The effect of flare angle on reacting and non-reacting flow field and stabilization of the flame is explored using high-speed OH* chemiluminescence, high-speed stereo particle image velocimetry and simultaneous pressure fluctuation measurements. Flare is the diverging part attached at the end of the injector and the angle of the diverging section is called the flare angle (β). The flare angle is varied in three steps, 0°, 30°, 50°. For each case of flare, 4 cases of inlet Reynolds’s number (Re) and 8 cases of equivalence ratio (ϕ) totalling 32 cases are explored to elucidate the effect of β on flame size and rich and lean blow-off limits. Central recirculation zone (CRZ) which plays a pivotal role in the stabilization of the flame is found to be altered with a change in β. With an increase in β, the CRZ size increases in non-reacting and reacting cases. For β = 0°, the effect of heat addition and the effect of increasing ϕ on CRZ size is very minimal. There is a slight change noticed in CRZ size with increasing ϕ for β = 30° case. The effect of increasing ϕ on CRZ size is found to be very pronounced for the β = 50° case. Non-reacting flow field provides insights into the CRZ formation mechanism, which also changes for different β. Due to the counter-rotating nature of the primary and secondary swirling air, it is possible to qualitatively distinguish among them using the azimuthal velocity component. This distinction provides insights into the mixing distance and its variation with β. Lean blow-off limit deteriorates with an increase in β, and this is delineated using non-reacting flow field data. Reacting flow-field provides valuable insights into the effect of heat addition and the effect of ϕ on flow field at various β. Rich blow-off limit improves with an increase in β, which can be explained using reacting flow field data. Further, the dynamics of the flame and pressure data are reported indicating the presence of thermo-acoustic instability.
Integrated System Modal and Mistuning Identification for Integrally Bladed Rotors
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L. 
Published: August 2024

Abstract
The safety of Integrally Bladed Rotors (IBRs) is often assessed through bench-level vibration tests to measure amplification factors and back-out sector frequency deviations via mistuning identification (ID) algorithms. This process is usually composed of two separate steps. First, a system ID step is completed to identify system modal data. Then, this data is input into mistuning ID algorithms. Errors in identified modal data will then propagate to produce errors in the system’s predicted mistuning. Obtaining robust mistuning estimates then requires larger quantities of accurate modal data. This effort seeks to attain accurate mistuning data by coupling the system and mistuning ID steps into a more parallel, versus serial, process that is capable of identifying many system modes. An iterative Polyreference-Least Squares Complex Frequency-domain (P-LSCF) algorithm finds modal data, and a mistuning ID algorithm obtains mistuning data at each iteration. An outlier detection method is proposed to remove spurious modes that cause erroneous mistuning results. Then, a weighted, least-squares regression approach is employed to remove the impact of sector-specific outlier data. This method reduces errors in identified mistuning parameters from the Fundamental Mistuning Model (FMM) ID algorithm. Furthermore, the approaches eliminate the need for users to determine true versus spurious system modes in each iteration of the P-LSCF algorithm, thus removing ambiguity. The developed approaches are first tested on simulated data from industrial IBRs that provide challenging test cases. Finally, real bench-top Traveling Wave Excitation (TWE) data is obtained, and results are compared across different Engine Order (EO) excitations. Results show the efficacy of the developed approaches and their ability to account for and reduce uncertainty in identified mistuning parameters.
Development of a Reduced Order Model for Double Wall Liner Cooling Schemes
Authors: Karasu Zeki Tuğberk , Kıyıcı Fırat , Erdem Erinc 
Published: August 2024

Abstract
Double wall cooling scheme combines the impingement and effusion cooling schemes and efficient way to deal with higher temperature values. However, its complex structure makes the simulations and experiments more expensive. The present study aims to develop a correlation-based one-dimensional low order model to predict wall temperature values for double wall structures before conducting numerical analysis and experiments. The effusion cooling is modeled by using single hole film cooling correlations, that includes effect of the lateral hole displacements, hole angle and blowing ratio, are combined with a superposition method to represent staggered hole arrays in the axial direction. On the other hand, the effect of impingement cooling is added as a source term. Several experimental data is used for validating the one-dimensional solver. In addition, conjugate heat transfer analysis is conducted for better understanding of the heat transfer mechanism, and comparing the computational time. One-dimensional model and conjugate heat transfer analysis are in a good agreement with experimental data for different double wall cooling configurations. Also, the low order model provides highly accurate results in a remarkably shorter time than the conjugate heat transfer analysis. The low order model proves itself as a promising tool that the industry could quickly adopt to evaluate innovative cooling geometries.
Effect of Gerlach Cross-Section on S-Duct Inlet Performance in High Subsonic Flow
Authors: Frosst Benjamin D. , Asghar Asad , Allan William D. E. , Stowe Robert A. , Pimentel Rogerio , Ingram Grant , Orchard Timothy 
Published: August 2024

Abstract
It was hypothesized in literature that Gerlach re-shaping of the cross-section of S-duct inlet bends may reduce the transverse pressure gradient and mitigate or eliminate flow separation. This paper presents an internal performance evaluation of an S-duct diffuser with Gerlach cross-sectional area compared to a baseline S-duct. The generic baseline test article was a rectangular-entrance S-duct transitioning to a circular exit, a configuration typical of single-engine air vehicles. The important geometric parameters were exit-to-entrance area ratio of 1.57 and an offset-to-length ratio of 0.37. The performance of the intake was evaluated at Ma = 0.80 by measuring the axial static pressure distribution, exit total pressure and three-dimensional velocity at the aerodynamic interface plane. The measurements were used to evaluate and compare the aerodynamic performance of the S-duct variants. The geometries and flow conditions were also simulated numerically and validated using experimental performance metrics. The static pressure recovery decreased for the Gerlach S-duct; however, total pressure recovery improved. This work will contribute to the development of improved performance for S-duct inlets and for predicting the performance of aero-engines and air vehicles at high-subsonic flight conditions.