bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms Leading to Stabilization and Incomplete Combustion in Lean CH4/H2 Swirling Wall-Impinging Flames
Authors: Fan Luming , Savard Bruno , Fond Benoît , Durocher Antoine , Bergthorson Jeffrey , Carlyle Spencer , Vena Patrizio 
Published: September 2023

Abstract
In gas turbines, confined highly turbulent flames unavoidably propagate in the vicinity of a relatively cool combustor liner, affecting both the local flame structure and global operation of the combustion system. In our recent work, we demonstrated, using simultaneous [OH] × [CH2O] PLIF and stereo-PIV, that lean CH4/H2 flames at a high Karlovitz number can present a highly broken structure near wall, highlighted by a diffuse CH2O cloud which suggests local quenching and incomplete oxidation. Such high Karlovitz numbers were achieved using an inclined plate, which substantially extended the lean flammability of the low swirl flames. Yet, how a cooled wall acting as a heat sink played a conducive role in stabilizing high Ka flames remains unanswered. In addition, the origin of the CH2O cloud is also unclear. Hence, in this work, we look to better understand the stabilization mechanisms for lean and ultra-lean flames on the same configuration, and how they may change with a parametric variation of plate incident angle, plate-nozzle distance, and bulk velocity up to the critical values that lead to flame blow off. The results show that the impinging swirling flow creates a low speed region that helps hold the flame, while the wall prevents mixing with ambient cold air. The production of diffuse CH2O, which indicates the occurrence of local quenching, is associated with a mean strain rate K beyond the extinction strain rate Ke. For CH4 flames, most of the reaction zones reside within |K|/Ke &lt; 1; for 70% H2 flames at ϕ = 0.4, the reaction zones are highly broken and scattered in a large area where |K|/Ke &lt; 8, the interspace of which is fully filled by CH2O. In other words, high H2 fraction flames appear to be more robust to persistent strain rate, thus extending their stability envelope. However, these flames can subsist as highly broken flames featuring strong incomplete combustion.
Role of the Equivalence Ratio on Soot Formation in a Perfectly Premixed Turbulent Swirled Flame: A Combined Experimental and LES Study
Authors: Maffina Aurora , Roussillo Mathieu , Scouflaire Philippe , Darabiha Nasser , Veynante Denis , Candel Sebastien , Franzelli Benedetta 
Published: September 2023

Abstract
The understanding of processes that govern soot production in aero-engines is fundamental for the design of new combustion systems with low environmental impact. For this, the development of numerical models that allow for soot accurate prediction for a limited computational cost is required. Many combustors, more specifically those used in aero-engines, feature rich flame regions typically exploited in the so-called Rich-Quench-Lean (RQL) technology. Thus, it is important to complete the data on soot formation in turbulent flames that exist in the literature, by considering rich turbulent flames operating in the premixed mode. To this purpose, a model scale swirled combustor, called EM2Soot, was designed at the EM2C laboratory to analyze soot production under perfectly premixed rich conditions. In this work, the effect of the equivalence ratio on soot production in this burner is experimentally characterized and numerically simulated. Measurements of Planar Laser Induced Fluorescence of Polycyclic Aromatic Hydrocarbons (PLIF-PAH) were performed to examine soot precursors presence, whereas soot volume fraction is measured with Planar Laser Induced Incandescence (LII). Large Eddy Simulations (LES) are carried out using an analytically-reduced chemistry for the gas phase simulation in combination with a three-equation model for the solid phase description. By considering a range of equivalence ratios, the soot volume fraction from the experiments was found to reach a maximum near ϕ = 1.8, whereas a lower level of soot volume fraction was measured for lower and for higher equivalence ratios. The large eddy simulations performed in parallel are found to be in qualitative agreement with experimental data in terms of PAHs location and soot presence. The soot volume fractions fv are notably overestimated with respect to the LII measurements, suggesting the need for improved modeling schemes. However, the numerical results correctly retrieve a reduction of soot production for the highest considered equivalence ratio value and can be used to explain the experimental behaviour. Results indicate that LES gives access to a qualitative understanding of the interactions between flame, turbulent flow, and precursors governing soot formation in this system.
Application of Closed-Loop Output Error System Identification to an SOFC Gas Turbine Hybrid Using a Cyber-Physical Approach
Authors: Amoafo Mychal , Zhou Nana , Bonilla-Alvarado Harry , Tucker David 
Published: September 2023

Abstract
Dispatchable hybrid integrated energy systems provide opportunities for meeting the flexibility essential to the transition of the power sector to net-zero carbon. Integrated energy systems have shown promise in meeting the dispatch challenges resulting from the increasing penetration of intermittent renewable power generation in the energy grid. While these integrated cycles offer high part-load efficiency and high slew rates, the coupling of such disparate technologies creates integration issues and multiple control states. To extend the application of more simplified controllers, like PID, in hybrid power systems, adaptive control will be necessary. Implementation of classic system identification at multiple states in equipment with developing technologies represents significant risk.
A Closed-Loop Output Error (CLOE) system identification method was applied to a hardware test facility at the National Energy Technology Laboratory. The CLOE system identification method was used to develop open loop transfer functions from a closed-loop process using the controller gains. Experiments were carried out using the hardware of the integrated energy system to test and validate the CLOE methodology. The coefficients of each CLOE transfer function were compared to open loop transfer function from formal system identification performed at 100% and 50% load respectively to determine the value of the method in reducing risk associated with controller development in hybrid power systems.
The Impact of Oxidation-Induced Degradation on Materials Used in Hydrogen-Fired Microturbines
Authors: Romedenne Marie , Pillai Rishi , Dryepondt Sebastien , Pint Bruce 
Published: September 2023

Abstract
Hydrogen-fueled microturbines are being considered as part of the future green microgrid. However, the use of hydrogen as a fuel presents new challenges for selection and development of suitable high temperature materials for hydrogen combustion. The burning of hydrogen is expected to result in higher operating temperatures and higher than typically observed water vapor contents in exhaust gases versus burning natural gas. In the present work, foil specimens of various Fe- and Ni-based alloys were oxidized in air + 10 % H2O and air + 60% H2O for up to 5,000 h at 700 °C to simulate the exhaust atmosphere of natural gas and hydrogen-fueled microturbines. The impact of alloy composition and water vapor content on the oxidation/ volatilization induced loss of wall thickness was experimentally evaluated. Enhanced external oxidation and volatilization of Cr2O3 and Ti-doped Cr2O3 scales was observed in air + 60% H2O compared to air + 10% H2O. No significant impact of the higher water vapor content was observed on Al2O3 scales formed on Fe-based alumina forming alloys. Lifetime modeling was employed to predict the combined effects of water vapor content, gas flow rates, temperature and alloy composition on the oxidation-induced lifetime of the investigated materials.
Unsteady Investigation of Intermediate Turbine Ducts Under the Influence of Purge Flows
Authors: Merli Filippo , Krajnc Nicolas , Hafizovic Asim , Schien Malte , Göttlich Emil 
Published: September 2023

Abstract
The aerodynamic flow field at the outlet of a high-pressure turbine (HPT) stage in a modern turbofan engine is highly unsteady and strongly influenced by periodic fluctuations from the HPT rotor, also interacting with the HPT stationary vanes. Downstream of the last HPT stage, the flow enters the intermediate turbine duct (ITD), where new unsteady components are generated, due to the interaction between the incoming flow and the struts supporting the ITD.
This paper illustrates the differences between the unsteady flow behavior in two state-of-the-art ITD configurations for turbofan engines: the turbine center frame (TCF), with symmetric strut fairings (typically adopted in conventional dual-spool engines), and the turbine vane frame (TVF), which is commonly used in geared turbofan engines and incorporates the first low-pressure turbine (LPT) vane row inside the duct.
The experimental results discussed in this work are conducted in the Transonic Test Turbine Facility, situated at Graz University of Technology. To achieve engine-representative operating conditions at the ITD inlet and outlet sections, the tested setups include not only the ducts (TCF or TVF), but also the last HPT stage and the first LPT stage row. Additionally, the test rig features a secondary air supply system, capable of feeding purge air to every stator-rotor cavity in the test vehicle, with independent mass flow and temperature control.
Unsteady measurement data at the inlet and outlet of the two duct configurations are acquired with fast-response aerodynamic pressure probes, for two purge flow conditions. Azimuthal mode decomposition is applied to phase-averaged data at selected radial positions, to isolate and quantify the contribution of different interaction modes to the overall unsteady flow field.
Experimental Investigation on Overall Effectiveness of Flat Plate Combined Impingement Cooling With Film-Cooling of Diffusion Slot Holes
Authors: An Bai-Tao , Hu Jia-Jun , Liu Jian-Jun 
Published: September 2023

Abstract
An experimental investigation on the overall effectiveness of combined film-impingement cooling was performed on single-row and double-row flat plate models. The experiments were carried out in a low-speed wind tunnel using a temperature-sensitive paint (TSP) measurement technique. The temperature difference between the mainstream and the cooling air was approximately 40°C, which corresponds to a coolant-to-mainstream density ratio of 1.13. The mainstream Reynolds number based on flat plate width was approximately 2.8 × 105. Three film hole geometries, including typical fan-shaped hole and diffusion slot holes with cross-sectional aspect ratios of 3.4 and 4.9, were combined with impingement cooling with an impingement hole number to film hole number ratio of 3.2. Five blowing ratios from 0.5 to 2.5 were tested and compared. The Biot number on the mainstream side was in the range of approximately 1.7 to 3.4, depending on the cooling performance. It is shown that under high Biot number conditions, the contribution level of impingement cooling to the overall effectiveness is far less than that of film cooling. Although the trend is consistent, the overall effectiveness difference caused by various hole geometries is lower than that of the adiabatic film cooling effectiveness in magnitude. Regardless of the single-row or double-row configuration, the overall effectiveness of the configurations with diffusion slot holes is always significantly higher than that with fan-shaped holes, in which the diffusion slot hole with a larger AS behaves better.
Implementation of Similarity Principle and Scaling Laws for Low-to-High Speed Mixed Flow Compressor
Authors: Kumar Hemant , Mistry Chetan S. 
Published: September 2023

Abstract
In this paper, the use of the similarity principle has been presented to extrapolate the performance and results for mixed flow compressors application in a small jet or turbofan engines. The similarity principle helps in scaling a single-stage mixed flow compressor model tested at variable operating conditions to different multistage compressors operating to varying conditions through scaling the non-dimensional compressor characteristics. To implement the similarity principle, performance governing parameters were selected and scaling laws were derived, which gives us a degree of freedom for extrapolation of mixed flow compressors. The compressor has been scaled to new specifications using the (ns–π) specific speed-total pressure ratio plot, along the best-efficiency line of the baseline compressor. In this paper, a distinctive approach is taken for validating the scaling laws; the input and output for the scaling laws are target performance (ns–π values) and scaling factors, respectively. The practical use of the scaling laws has been demonstrated by scaling a high-speed mixed flow compressor (maximum total pressure ratio, πmax = 4.55) to new required specifications (π max = 1.03), and examining the conditions under which these laws are applicable. The formulated approach developed for extrapolation of the results from low-to-high speed mixed flow compressors has been justified and tested by comparing the computational results. The impact of dimensions those are not considered (tip gap and splitter blades) for scaling law formulations on flow field distribution is computationally analyzed.
Numerical Investigation of Windage Loss and Heat Transfer in a High-Speed Flywheel Energy Storage System With Slit Wall
Authors: Eltaweel Mahmoud , Herfatmanesh Mohammad Reza 
Published: September 2023

Abstract
Energy storage has recently emerged as a topic of discussion in the context of the energy transition away from fossil fuels. The flywheel energy storage system (FESS) is gaining popularity due to its distinct advantages, which include long life cycles, high power density, and low environmental impact. However, windage loss significantly contributes to total losses in high-speed rotating machines such as the flywheel. Windage loss increases self-discharge, rendering FESS unsuitable for long-term energy storage applications. In the FESS application, the enhancement of heat transfer by the medium within the annulus is crucial. The FESS with a slit wall in the outer cylinder is examined in this investigation to assess the flow field distribution, windage losses, and heat transfer characteristics. The effect of four slit wall geometrical configurations, triangular, trapezoidal, rectangular, and half circle, are investigated in this study. The computational fluid dynamics (CFD) technique is used to model the flow in the annulus of a solid FESS. The results show that the slit wall geometry significantly impacts the distribution of the flow field, the heat transfer process, and windage loss. The fluid is mixed more quickly between the hot and cold sides due to the geometry of the slit wall, resulting in a more homogeneous temperature. As a result, the slit geometry with triangular and rectangular slit walls resulted in the best overall system performance through windage loss reduction and enhanced heat transfer. The findings of this study can assist with the design and optimisation of other rotating machinery with similar flow characteristics.
Partially Cracked Ammonia for Micro-Gas Turbine Application
Authors: Bellotti Daria , Anfosso Chiara , Magistri Loredana , Massardo Aristide Fausto 
Published: September 2023

Abstract
During the last decades, CO2 emissions have increased by 42% with respect to the pre-industrial era. The anthropogenic CO2 is the main source of GreenHouse Gas (GHGs) emissions, contributing, alone, to nearly 30% of global warming effects. The reduction in GHGs emissions to contain the increase in global temperature below 2°C, represents one of the greatest challenges of the XXI century, to ensure the survival of the planet and future generations.
In this energy context, Power to X to Power (P2X2P) solutions are gaining more and more importance in the market considering that, in recent years, the market scenario is increasingly driven by Renewable Energy Sources (RESs). The possibility of storing the exceeding electrical energy production, mainly due to RESs, into hydrogen (H2) or ammonia (NH3) and then turning it back into electricity when RESs power production falls below demand, can improve grid resilience and stability, ensuring, in the meanwhile, a lower environmental impact. Even more, P2X2P represents an innovative solution to increase the flexibility of Gas Turbine (GT) plants, extending their operative range by using alternative carbon-free fuel. Attaining this goal would make GT plants more suitable to trade on the ancillary services market guaranteeing a more secure and clean power system. This study focuses on the use of partially cracked NH3 in micro-Gas Turbine (mGT) applications. To carry out the analysis, a MATLAB/Simulink model has been developed, including also the NH3 storage and the ammonia cracking reactor to simulate an Ammonia To Power (A2P) system. The main thermodynamic parameters, system features, and critical aspects have been evaluated (e.g. the global efficiency, the turbine inlet and outlet temperatures, the power output, etc.) and a comparison between the same system fueled by natural gas and hydrogen has been carried out from the technical and environmental point of view.
Experimental Investigation of Capillary Performance of Additively-Manufactured Lattice Structures for Fluid Wicking Applications
Authors: Kabir Mehdi , Walker Ryan , Eden Chance , Gebre Fisseha , Xu Jiajun 
Published: September 2023

Abstract
In the present study, cylindrical lattice structures of 20 × 40 mm2 (i.e., sample diameter and height, respectively) were fabricated from Maraging Steel (EOS MS1) using the Direct Metal Laser Sintering (DMLS) technique. The lattice structures were designed and fabricated for three different cell topologies, including body-centered cubic, face-centered cubic, and octet truss, with pore opening sizes ranging from 200μm to 1600μm. The present study also experimentally investigates and compares the capillary performance of the printed wick structures, accompanied with characterizing the key porous parameters such as pore size, porosity, permeability, and lattice structures at microscopic scales. Capillary experiments were executed by a rate-of-rise technique to present capillary elevations versus time using methanol as the candidate working fluid of choice with desired merit number to be employed for passive two-phase heat transfer devices for thermal management systems in space applications. Due to the difficulty in locating the meniscus front in lattice structures leading to unreliable data, this work not only takes advantage of an infrared (IR) camera to properly distinguish the front location but also measures the changes in liquid mass wicked into the lattice samples over time, which is another adaptation to the classical capillary rate-of-rise tests.
3D-Fabrication of Hydroxyapatite-Polysaccharide Composite Scaffolds for Bone Tissue Engineering
Authors: O’Malley Ethan , Salary Roozbeh (Ross) 
Published: September 2023

Abstract
The overarching goal of this research work is to synthesize and fabricate mechanically robust, dimensionally accurate, and porous bone tissue scaffolds for the clinical treatment of bone fractures, defects, and diseases. In pursuit of this goal, the objective of the work is to investigate the influence of hydroxyapatite (HA) as well as polysaccharide concentration on the mechanical properties of bone scaffolds, fabricated using pneumatic micro-extrusion (PME) additive manufacturing process. PME has emerged as a high-resolution method for the fabrication of a broad range of biological tissues. This research work tests the following central hypothesis: hydroxyapatite and polysaccharide significantly affect the mechanical properties of PME-fabricated bone scaffolds. A review of literature shows that while hydroxyapatite-polysaccharide composite scaffolds are biocompatible (allowing for mimicking the structure and the function of natural bone), identification of key material and fabrication factors as well as underlying failure mechanisms would be inevitable to achieve mechanically robust, porous bone scaffolds. In this study, based on designed experiments, the HA concentration as well as the polysaccharide concentration (amylose content) were changed in the range of 10–40 % and 7.5–15 %, respectively. Porous bone scaffolds were PME-fabricated using a micro-capillary nozzle having a diameter of 860 μm. In addition, print speed and pneumatic flow pressure were set at 5 mm/s and 300 kPa, respectively. The material deposition was laminar and highly viscous on an unheated glass substrate. Subsequently, the fabricated scaffolds were oven-sintered at 37 °C. It was observed that the compression modulus of the scaffolds decreased with an increase in the HA concentration, while an increase in amylose content led to an increase in the scaffold stiffness. The outcomes of this work pave the way for the fabrication of complex, mechanically robust composite bone tissue scaffolds with tunable medical and functional properties.
Flaw Detection in Wire Arc Additive Manufacturing Using In-Situ Acoustic Sensing and Graph Signal Analysis
Authors: Bevans Benjamin , Ramalho André , Smoqi Ziyad , Gaikwad Aniruddha , Santos Telmo G. , Rao Prahalad , Oliveira J. P. 
Published: September 2023

Abstract
The goal of this work is to detect flaw formation in wire arc additive manufacturing (WAAM). This process uses an electric arc as the energy source in order to melt metallic wire and deposit the new material, similar to metal inert gas (MIG) welding. Industry has been slow to adopt WAAM due to the lack of process consistency and reliability. The WAAM process is susceptible to a multitude of stochastic disturbances that cause instability in the electric arc. These arc instabilities eventually lead to flaw formation such as porosity, spatter, and excessive deviations in the desired geometry. Therefore, the objective of this work is to detect flaw formation using in-situ acoustic (sound) data from a microphone installed near the electric arc. This data was processed using a novel wavelet integrated graph theory approach. This approach detected the onset of multiple types of flaw formations with a false alarm rate of less than 2%. Using this method, this work demonstrates the potential for in-situ monitoring and flaw detection of the WAAM process in a computationally tractable manner.
Sustainable 3D Printing of Organ Replica for Endoscopy Training and Medical Research
Authors: Linke Barbara , Fashanu Felicia , Bashayan Kholoud , Thavi Riddhi , Roeth Anjali A. 
Published: September 2023

Abstract
Additive manufacturing allows wide design freedom and manufacturing of complex parts. For the medical sciences, the fabrication of realistic and patient-specific 3D replica of organs offers exciting opportunities. Organ replicas allow better training, e.g. in endoscopy, open more avenues for medical research and can reduce the need for animal testing. However, the use of plastics for 3D printing inherently produces waste and needs to be considered with respect to a circular economy.
With the example of the upper half of a stomach replica for endoscopy, we showcase the feasibility of using recycled versus new polylactic acid (PLA) versus algae-based PLA as printing materials in a wire extrusion process. Furthermore, the stomach half replica is manufactured with elastic materials by stereolithography and polyjet binding, with the aim of improving the user experience and making the stomach model properties more realistic. This paper discusses printing energy, part dimensions and surface roughness, material recyclability, and waste in the context of the digital thread to enable more sustainable 3D printing practices for 3D organ replicas and a circular economy. We furthermore address post-processing of the 3D printed parts and usability in the context of medical training and research. This is a small case study which will be expanded in the future.