bluuebunny/crossref_metadata_2025_split huggingface dataset:
Techno-Economic Analysis of Hydrogen and Ammonia as Low Carbon Fuels for Power Generation
Authors: Goldmeer Jeffrey , Buck Caroline , Suleiman Baha , Selim Hatem , Tayebi Kamel , Agostinelli Gian-Luigi , Dawood Alaaeldin 
Published: September 2023

Abstract
As the world focuses on the transition to low and zero-carbon energy systems, there are regions of the world that will continue to require imported fuels to meet their energy demands. In countries like Japan, renewable energy is not expected to meet all future energy demand. Therefore, these countries need to transition from importing carbon-based fossil fuels, to importing low or zero-carbon intensity fuels.
Focusing on carbon-free molecules, hydrogen and ammonia are of great interest. Hydrogen can be produced directly via reformation or pyrolysis of natural gas or from electrolysis of water, and because it can be used directly as a fuel. But there are well known challenges associated with hydrogen storage and transport. Due to the limited options for transporting liquid hydrogen, there is a growing interest in using ammonia as a method to ship hydrogen. Multiple countries are considering importing ammonia instead of hydrogen. Once imported the ammonia could be cracked back to hydrogen or potentially used directly in several end use applications, potentially including power generation.
However, there are trade-offs in the use of these fuels. Hydrogen has to be liquefied for transport. Producing ammonia requires added process steps. There are also impacts when using these fuels in a gas turbine. This paper will examine the issues in using these fuels in two parts. The first phase identifies the technical impacts of operating a gas turbine power plant on 100% hydrogen and 100% ammonia. The second phase examines the economic impact of the fuel selection, including the landed cost of the fuel and impact on levelized cost of electricity.
Microstructure and Mechanical Properties of NGB Joints Formed With B/Si Free Braze Alloys
Authors: Huang Xiao , Lowden Paul , Gontcharov Alex , Reis Robyn 
Published: September 2023

Abstract
In this research, boron free nickel-based braze alloys were examined in terms of their microstructure in narrow gap and wide gap configurations. The high temperature tensile properties of the standalone boron free braze alloys along with that of the narrow gap braze (NGB) joints with these alloys were also evaluated. The weldability of the boron free alloys was evaluated using bead-on-plate Tungsten Inert Gas (TIG) welding. NGB (with gap of ∼0.1 mm between two surfaces) was carried out using a substrate of GTD111. In addition, two commercial braze alloys, MTU Amdry 788 (A788) and Liburdi low boron braze alloy LW3PL, were incorporated in the tensile test matrix as baselines for comparison. The results from this study showed that the boron free alloy can be used as traditional braze welding rods for manual weld repair with good weldability. In addition, one of the boron free braze alloys, XH-1, possess higher tensile strengths than A788 braze alloy, due to the presence of gamma prime forming elements (Ti+Al). At 982 °C, NGB joint with XH-1 yielded tensile properties superior to that joined by LW3PL, i.e., higher strength and equivalent ductility. The high temperature tensile properties of the same joints showed similar yield and tensile strength values to that of the base metal GTD111, however, with lower ductility. Further improvement to brazing processes will be undertaken to improve the ductility of the boron free brazed joints in our future studies.
Propulsion Aerodynamics for a Novel High-Speed Exhaust System
Authors: Tsentis Spyros , Goulos Ioannis , Prince Simon , Pachidis Vassilios , Zmijanovic Vladeta 
Published: September 2023

Abstract
A key requirement to achieve sustainable high-speed flight and efficiency improvements in space access, lies in the advanced performance of future propulsive architectures. Such concepts often feature high-speed nozzles, similar to rocket engines, but employ different configurations tailored to their mission. Additionally, they exhibit complex interaction phenomena between high-speed and separated flow regions at the base, which are yet not well understood, but are critical in terms of pressure and viscous forces. This paper presents a numerical investigation on the aerodynamic performance of a representative novel exhaust system, which employs a high-speed, truncated, ideal contoured nozzle and a complex-shaped cavity region at the base. Reynolds-Averaged Navier-Stokes computations are performed for a number of Nozzle Pressure Ratios (NPRs) and free stream Mach numbers in the range of 2.7 &lt; NPR &lt; 24 and 0.7 &lt; M∞ &lt; 1.2 respectively. The corresponding Reynolds number lies within the range of 1.06 · 106 &lt; Red &lt; 1.28 · 106 based on the maximum diameter of the configuration. A decomposition of the drag domain forces exposes the major trends between the constituent elements. The impact of the cavity on the aerodynamic characteristics of the apparatus is revealed by direct comparison to an identical non-cavity configuration. Results show a consistent trend of increasing base drag with increasing NPR for all examined M∞ for both configurations. This is attributed to the jet entrainment effect and to the lower base pressure imposed by the higher jet flow expansion. The cavity region is found to have almost no impact on the incipient separation location of the nozzle flow. At low supersonic speeds of M∞ = 1.2 and high NPRs, the cavity has a significant effect on the aerodynamic performance, transitioning nozzle operation to under-expanded conditions. This results in approximately 12% higher drag coefficient compared to the non-cavity case and shifts the minimum NPR for which the system produces positive gross propulsive force to higher values.
High-Fidelity Simulations and RANS Analysis of a Low-Pressure Turbine Cascade in a Spanwise-Diverging Gas Path - End-Wall Flow Analysis and Loss Generation Mechanisms
Authors: Rosenzweig Marco , Kozul Melissa , Sandberg Richard , Marconcini Michele , Pacciani Roberto 
Published: September 2023

Abstract
In order to increase the impact of cascade tests on the design of low-pressure turbines (LPT), the end-wall geometry must be taken into account. Even if, given the high aspect ratio of LPT bladings, profile loss is expected to be the major loss source, the evolving secondary flow phenomena in the end-wall region can contribute up to 40% of loss generation. In addition, the growth of end-wall boundary layers introduces blockage effects on the otherwise undisturbed, free-stream flow away from the end-walls. Scale-resolving computational fluid dynamics have in the past been able to shed light on the mechanisms driving the evolution of vorticity and loss generation in the end-wall region. The majority of those past studies, however, have been conducted with spanwise-parallel end-walls. The present paper considers the MTU-T161 LPT cascade with spanwise-diverging end-walls, which feature in many real engines. The diverging gas path adds another layer of complexity to the flow field. To study the aerodynamic performance of this cascade, wall-resolved large-eddy simulations (LES) and Reynolds-Averaged Navier-Stokes (RANS) analyses are performed at engine-relevant conditions of isentropic exit Reynolds number of 90,000 and isentropic exit Mach number of 0.6 with proven computational fluid dynamic solvers. Firstly, the LES results are validated against experimental data. Then, in separate simulations, the momentum thickness of the incoming boundary layers is systematically varied, as the resulting end-wall flow downstream of the blade is highly dependent on the state of the incoming end-wall flow. The data-rich results are used to perform a detailed decomposition of the various contributions to loss, to deepen the understanding of loss generation mechanisms in LPT flows in an engine-like, spanwise-divergent gas path. Lastly, a rigorous comparison between the results from LES and RANS shows there is scope for improvement in the capability of standard transition/turbulence closures in accurately reproducing three-dimensional flow features. This is needed if lower-order numerical tools are to be effective in driving the design of next-generation aeronautical LPTs.
A Study of Unsteady Aerodynamic Forces on Last Stage Blades in a Low-Pressure Model Steam Turbine at Very Low Operating Conditions
Authors: Tanuma Tadashi , Okuda Hiroshi , Haraguchi Taiga , Okuno Kenichi , Shibukawa Naoki 
Published: September 2023

Abstract
The relatively higher vibration stress of steam turbine last stage blade which appears at very low load operating condition is investigated in this paper. An unsteady Computational Structural Mechanics (CSM) analysis was conducted using the unsteady Computational Fluid Dynamics (CFD) result as the blade surface Boundary Conditions (BC) of traction in order to reveal the relationship between the aerodynamic unsteady forces and the abrupt increase of the blade vibration stresses. The present FEA model contains the same structures of lacing wires for blade vibration damping as the model steam turbine.
A series of calculations were performed in accordance with a sub-scale test model turbine that precisely simulated an actual large steam turbine. The CFD calculation results were evaluated compared with test data. CFD results for two representative cases explained that under the extremely small flow rate condition where vibration stress increases, several reverse flow cells are generated near the tip of the blades and rotate at a speed slower than the rotational speed. The causal relationship between the aerodynamic excitation force due to this phenomenon and the vibration mode of the long blade and the magnitude of the stress was discussed. It was confirmed that the characteristic vibration mode obtained in the analysis was the same as the vibration mode measured by the test turbine, and the validity of the analysis was confirmed.
Comparison of Equivalence Ratio Fluctuations in a Lean Premixed Combustor for Kerosene and Natural Gas
Authors: Vogel Manuel , Kaufmann Jan , Völkl Vinzenz , Hirsch Christoph , Sattelmayer Thomas 
Published: September 2023

Abstract
Equivalence ratio fluctuations have been identified as a major driving mechanism for thermoacoustic instabilities in lean premixed combustion. In the present study, equivalence ratio fluctuations are determined experimentally from flame chemiluminescence in a lean premixed combustor at atmospheric conditions for kerosene and natural gas combustion. The phase-resolved CH* and CO2* chemiluminescence signals of acoustically excited flames are acquired with an intensified camera equipped with an image doubler and bandpass filters. A calibration chart derived from stationary operation provides the correlation between the global CH*/CO2* ratio and the equivalence ratio for both fuels. Equivalence ratio fluctuations are found to be particularly dominant as long as the convective wavelength of the equivalence ratio wave exceeds the distance between fuel injection and flame. The fluctuations decrease significantly with increasing frequencies and finally become almost negligible. The more complex mixture preparation for liquid fuels compared to gaseous fuels is shown to significantly influence the generation and propagation of equivalence ratio fluctuations. The applied measurement method is validated by investigating externally premixed natural gas combustion, where no equivalence ratio fluctuations are detected. A one-dimensional transport model is employed to analyze the generation and propagation of the equivalence ratio wave. A comparison with the experimental results reveals that the propagation of the equivalence ratio wave can be approximated quite accurately by the model. However, the model fails to predict important features attributed to an interaction of the equivalence ratio wave with swirl fluctuations.
Efficient Unsteady Simulations of Multistage Turbines Using a Flexible Frequency-Domain Approach
Authors: Tartinville Benoît , Vilmin Stéphane 
Published: September 2023

Abstract
Predicting the unsteady nature of the flow within a multistage turbine is of crucial importance for modern design. Indeed, such unsteady interactions can not only affect the turbine global efficiency but also the level of tonal noise and the structural and thermal integrity of the blades. Thermal stresses are of particular importance for turbine blades since the hot streaks coming out of the combustion chamber can severely reduce the blade lifetime.
This paper proposes to demonstrate the capabilities of the nonlinear harmonic method to solve in an accurate and efficient way the unsteady interactions between successive rows, and the propagation of hot streaks from the combustion chamber down to the exit of the low pressure turbine. This frequency-domain approach has been extended to allow for more flexibility in the choice of harmonics, in particular the way the perturbations are propagated through the whole multistage configuration. A special attention has also been paid to reduce the computing time and produce a better parallel efficiency. The high and low-pressure turbines of the KJ66 micro aero-engine have been selected as reference test case.
Full-Scale Demonstration and Validation of a 35 MW Transcritical CO2 Heat Pump
Authors: Wolscht Leonhard , Somaini Reto , Jacquemoud Emmanuel , Jenny Philipp 
Published: September 2023

Abstract
Large-scale industrial heat pumps are an emerging solution for the decarbonization of the district heating sector and its coupling with other thermal (heating or cooling) applications. Hermetically sealed compressors with integrated motors and magnetic bearings secure refrigerant confinement and eliminate thermal losses making them advantageous in large scale heat pump applications. This work presents the thermodynamic and rotordynamic specifics of a large-scale heat pump of 35 MW thermal duty operating with a transcritical CO2 cycle in a full scale testbed setup. Experimental data encompass different operating points at nominal, maximum and part load. Furthermore, fast load changes of more than 66% electrical input power variation prove the suitability of the presented heat pump concept for fast grid stabilisation. The paper discusses the operations’ impact on both the thermodynamic process cycle as well as the rotordynamic key figures. The testbed results show an overall cycle performance with a Lorenz efficiency of 43% and low mechanical unbalance at one third of the allowed vibration limit by ISO. While experiencing unfamiliar pipe vibration patterns the HPU casing vibrations remain well below common limits. This demonstration ensures the technical maturity of industrial-scale heat pumps ready for on-field installation. The experimental data gathered from the test campaign was employed for the successful validation of a dynamic model, that allows for further heat pump transient operation prediction in the future.
Mineral Composition Effects on Dust Deposition at Realistic Engine Conditions
Authors: Wendel Nathanael J. , Subasic Noah P. , Mizer Andrew E. , Bons Jeffrey P. 
Published: September 2023

Abstract
In this paper the role of mineral composition was assessed for Air Force Research Laboratory test dust (AFRL), for deposition in a realistic gas turbine engine environment. Experiments were performed on an effusion cooling test article with a coolant flow temperature of 894K and surface temperature of 1144K. Aerosolized dust with a 0–10 μm particle size distribution was delivered to the test article. The mineral recipe of AFRL was altered such that the presence of each of the five components ranged from 0% to 100%, and capture efficiency, hole capture efficiency, blockage per gram, and normalized deposit height were reported. Results are compared to a previous study of the inter-mineral synergies in an impingement cooling jet at the same temperature conditions. Despite differences in experimental facility flow geometry, overall agreement was found between the trends in deposition behavior of the dust blends. The strong deposition effects that were observed were shown to be related to adhesion forces of particles, mechanical properties, and chemical properties of the dust minerals. Supplemental testing was performed in a high-temperature (1425–1650 K) impinging jet (200–260 m/s) to evaluate mineral effects at hot gas path conditions. Capture efficiency and morphology of dust deposits are reported. The capture efficiency in this regime was shown to correlate well with temperature, with chemical effects being secondary. An attempt was made to predict capture efficiency using chemical assessments such as ratio of bases to acids, Ca:Si ratio, and optical basicity with only modest success.
Analysis of C-Spec Particle Breakage in a Turbine Engine Particle Ingestion Test Cell
Authors: Vlach Tomas , Olshefski Kristopher T. , Bunin David J. , Ehlers Alix M. , Caddick Mark J. , Lowe K. Todd , Ng Wing F. 
Published: September 2023

Abstract
A turboshaft engine test rig based on a Rolls-Royce M250-C20B engine has been developed at Virginia Tech’s Advanced Propulsion and Power Laboratory in cooperation with its government and industry partners. The engine has been instrumented to allow measurement of the effects that dust particles have on the engine (power degradation) as well as the effects that the engine has on the particles (e.g., breakage). The work in this paper presents the first set of data collected from the engine tests and focuses on changes in the shape and size of C-Spec (quartz) dust after passage through the first five stages of the compressor and through the entire engine. Dust samples have been analyzed to determine particle size and shape distributions at the locations of interest and these have been compared with undigested material. These preliminary analyses suggest that average particle volume decreased to ∼5 % of the original size during transit through five stages of the axial compressor. No subsequent change in size and shape occurred, despite these particles then passing through one additional axial stage, the centrifugal stage, and four stages of the turbine section. Moreover, the apparent sphericity of the particles increased slightly in the axial compressor, hinting at the reduction of their erosion potential. The data presented here will assist communities interested in turbine engine environmental damage in understanding the deterioration processes and their prevention. Ultimately, the research will allow for pinpointing such degradation effects to a single compressor stage, resulting in a greater ability to predict engine damage and prevent subsequent loss of human life.
High-Dimensional Uncertainty Quantification of High-Pressure Turbine Vane Based on Multi-Fidelity Deep Neural Networks
Authors: Li Zhihui , Montomoli Francesco , Casari Nicola , Pinelli Michele 
Published: September 2023

Abstract
In this work a new multi-fidelity (MF) uncertainty quantification (UQ) framework is presented and applied to LS89 nozzle modified by fouling. Geometrical uncertainties significantly influence aerodynamic performance of gas turbines. One representative example is given by the airfoil shape modified by fouling deposition, as in turbine nozzle vanes, which generates high-dimensional input uncertainties. However, the traditional UQ approaches suffer from the curse of dimensionality phenomenon in predicting the influence of high-dimensional uncertainties. Thus, a new approach based on multi-fidelity deep neural networks (MF-DNN) was proposed in this paper to solve the high-dimensional UQ problem. The basic idea of MF-DNN is to ensure the approximation capability of neural networks based on abundant low-fidelity (LF) data and few high-fidelity (HF) data. The prediction accuracy of MF-DNN was first evaluated using a 15-dimensional benchmark function. An affordable turbomachinery UQ framework was then built based on the MF-DNN model, the sampling-, the parameterization- and the statistical processing modules. The impact of fouling deposition on LS89 nozzle vane flow was investigated using the proposed UQ framework. In detail, the MF-DNN was fine-tuned based on bi-level numerical simulation results: the 2D Euler flow field as low-fidelity data and the 3D Reynolds-Averaged Navier-Stokes (RANS) flow field as high-fidelity data. The UQ results show that the total pressure loss of LS89 vane is increased by at most 17.1 % or reduced by at most 4.3 %, while the mean value of loss is increased by 3.4 % compared to the baseline. The main reason for relative changes in turbine nozzle performance is that the geometric uncertainties induced by fouling deposition significantly alter the intensity of shock waves near the throat area and trailing edge. The developed UQ framework could provide a useful tool in the design and optimization of advanced turbomachinery considering high-dimensional input uncertainties.
Experimental Investigation of a Multi Tube Burner for Premixed Hydrogen and Natural Gas Low Emission Combustion
Authors: Jaeschke Alexander , Ćosić Bernhard , Wassmer Dominik , Paschereit Christian Oliver 
Published: September 2023

Abstract
Hydrogen as an essential part of future decarbonisation of the energy industry makes it a crucial necessity to replace conventional, natural gas based concepts in gas turbine combustion. This paper presents an experimental study of a multi tube jet flame burner. The study is carried out with natural gas and pure hydrogen fuel at gas turbine relevant conditions at atmospheric pressure. To identify key differences between hydrogen-air and natural gas-air flames on the overall robustness and flame flashback behaviour, air bulk velocity (80–120 m/s), adiabatic flame temperature (1235–2089 K) and air inlet temperature (623–673 K) are varied over a wide range, covering a range of Reynolds numbers of 10.000 to 20.000. Depending on flame temperature, two different flame shapes are observed for natural gas-air flames. The shape of the hydrogen-air flame changes less over the range of flame temperatures tested, but is generally more compact. The process of fuel-air mixing is further investigated by concentration distribution measurements in a water tunnel setup. Therefore, planar laser-induced fluorescence is utilized for visualization. The measured concentration distributions confirm the overall good mixing quality but also give an explanation on the observed flashback behaviour of the different burner designs at reacting tests. The findings of the study are composed in a flashback correlation combining the observed flashback drivers for the burner configurations investigated.