bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamical Characterization of Thermoacoustic Oscillations in a Hydrogen-Enriched Partially Premixed Swirl-Stabilized Methane/Air Combustor
Authors: Kushwaha Abhishek , Kasthuri Praveen , Pawar Samadhan A. , Sujith R. I. , Chterev Ianko , Boxx Isaac 
Published: September 2021

Abstract
In this study, we systematically analyze the effects of hydrogen enrichment in the well-known PRECCINSTA burner, a partially premixed swirl-stabilized methane/air combustor. Keeping the equivalence ratio and thermal power constant, we vary the hydrogen percentage in the fuel. Successive increments in hydrogen fuel fraction increase the adiabatic flame temperature and also shift the dominant frequencies of acoustic pressure fluctuations to higher values. Under hydrogen enrichment, we observe the emergence of periodicity in the combustor resulting from the interaction between acoustic modes. As a result of the interaction between these modes, the combustor exhibits a variety of dynamical states, including period-1 limit cycle oscillations (LCO), period-2 LCO, chaotic oscillations, and intermittency. The flame and flow behavior is found to be significantly different for each dynamical state. Analyzing the coupled behavior of the acoustic pressure and the heat release rate oscillations during the states of thermoacoustic instability, we report the occurrence of 2:1 frequency-locking during period-2 LCO, where two cycles of acoustic pressure lock with one cycle of the heat release rate. During period-1 LCO, we notice 1:1 frequency-locking, where both acoustic pressure and heat release rate repeat their behavior in every cycle.
Compressor Maps and Coupling: Symmetry, Paradox, and Clarity
Authors: Iwrey Benjamin 
Published: September 2021

Abstract
The most common compressor map framework, referred to here as the β-framework, will be shown to suffer from limitations that grow more troublesome in the multiple-map environment.
When maps are coupled in series in the β-framework, it is very common to find operating points that are physically unrealizable, but these cannot generally be avoided without first generating them. A feasible situation is described in which the β-framework leads to an apparent physical paradox.
In the proposed S-framework, the map itself is recast in terms of independent variables (corrected speed and exit corrected flow) and dependent variables (inlet corrected flow and temperature ratio). The propagation of information in map coupling is split into an upstream-marching corrected flow ‘flux’ and a downstream-marching temperature ‘flux’. Finding the equilibrium operating point requires only finding a simple intersection between curves.
The S-framework is then developed further into a more compact S’-framework that exhibits a natural set of qualitative symmetries. The S- and S’-frameworks are shown to simplify compressor map expression, resolve the problems shown with the β-framework, and aid intuition with regard to off-design phenomena. The resolution of the paradox using the S’-framework is a new description of multistage compressor performance hysteresis.
Development of Turbulent Quantities Inside an Axial Turbine Vane
Authors: Behre Stephan , Kožulović Dragan , Hösgen Christian , Jeschke Peter 
Published: September 2021

Abstract
The paper presents experimental and numerical investigations of the three components of turbulent kinetic energy and its development upstream and downstream of the first vane of 1.5 stage axial flow turbine. The experimental data has been recorded using a miniature hot wire probe, equipped with three 9μm platinized tungsten wires, allowing the determination of the kinetic energy in all three spatial directions. By means of turbulent grids, a total of three different inlet turbulence levels, varying from 0.4 to 4.5%, was created. Extensive field traverses up- and downstream of the first stator have been conducted, covering more than one stator pitch and including both the free stream and the wake. For one inlet condition, a total of three axial positions between the stator and the rotor have been measured to evaluate the development of the composition of the turbulence. The type of turbulence is visualized by making use of the barycentric color map. Detailed investigations of all three fluctuation components reveal that, depending on the anisotropy level and the distribution of energy along the three spatial directions at the stator’s inlet, the velocity gradients within the first stator either promote a production or destruction of turbulent kinetic energy. As a consequence, the distribution of turbulent energy along the three spatial directions is at the stator’s outlet almost identical for the three configurations. Finally, the measurements with focus on the turbulence composition are compared to unsteady CFD simulations using, the, in industrial application, most commonly applied k-w turbulence model. In addition, an Explicit Algebraic Reynolds Stress Model (EARSM) is also applied and compared to numerical and experimental data. However, the paper is focused on the interpretation of the experimental data.
Testing and Acceptance of Semi-Machined Turbine Rotor Forging Elements
Authors: Ingistov Steve , Nagy Douglas 
Published: September 2021

Abstract
Turbine wheels are critical elements and the integrity of their forgings is extremely important. The procurement of wheel forgings utilized oversized outside diameters in order to provide ample amount of material from which test material was cut out. Test specimens were produced in accordance with relevant ASTM standards. Test specimens were divided into three groups; tension, impact and hardness / metallography. Tension and impact tests at sub-zero, room and elevated temperatures were conducted in presence of owner’s inspectors at an independent certified laboratory. Once all specimens passed the tests, the semi-machined forgings were released to the machining facility. Machined forgings were then sent for over-speed tests at sub-zero and elevated temperatures. Over-speed testing under sub-zero temperature was the ultimate test of the forgings. Over-speed testing of the forgings under elevated temperatures served to minimize residual tensile stresses at the bore of the wheel and convert them to beneficial compressive stresses. The above described tests of turbine Elements forging are critical when the owner selects third party producers to reverse engineer and manufacture these elements. This paper details the selection of the tests, the execution of the owner’s acceptance testing program, especially the over-speed tests, and how this helps to ensure the high integrity of critical rotating elements for a mid-size heavy industrial frame gas turbine.
High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils
Authors: Cooper Sean P. , Petersen Eric L. 
Published: September 2021

Abstract
Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (τign). A combination of an extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A clear, two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage τign are compared. Second stage ignition was found to be more indicative of lubricant ignition and was used to compare τign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (&gt; 1275 K); an intermediate, negative-temperature-coefficient-like regime (1230–1275 K); and a low-temperature ignition regime (&lt; 1230 K). Similar τign behavior in the high-temperature regime was seen for both lubricants, and a regression analysis using τign data from both lubricants in this region produced the Arrhenius expression τign(μs) = 4.4 × 10−14exp(96.7(kcal/mol)/RT). While lubricant A was found to be less reactive in the intermediate-temperature regime, Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation. Chemical kinetic modeling was also performed using n-hexadecane models (a lubricant surrogate suggested in the literature). The current models are unable to reproduce the three regimes observed and predict activation energies much lower than those observed in the high-temperature regime, suggesting n-hexadecane is a poor surrogate for lubricant ignition. Additionally, experiments were conducted with Jet-A for temperatures between 1145 and 1419 K around 1 atm. Good agreement is seen with both literature data and model predictions, anchoring the experiment with previously established τign measurement methods and calculations. A linear regression analysis of the Jet-A data produced the Arrhenius expression: τign(μs) = 6.39 × 10−5exp(41.4(kcal/mol)/RT).
Multi-Parameter Prediction for Steam Turbine Based on Real-Time Data Using Deep Learning Approaches
Authors: Sun Lei , Liu Tianyuan , Xie Yonghui , Xia Xinlei 
Published: September 2021

Abstract
Accurate and real-time parameters forecasting is of great importance to the turbine control and predictive maintenance which can help the improvement of power system. In this study, deep-learning models including recurrent neural network (RNN) and convolutional neural network (CNN) for multi-parameter prediction are proposed, and are applied to predict real-time parameters of steam turbine based on data from a power plant. Firstly, the prediction results of RNN and CNN models are compared by the overall performance. The two models show good performance on forecasting of six state parameters while RNN performs better. Moreover, the detailed performance on a certain day show that the relative error of two models are both less than 2%. Finally, the influence of model designs including loss function, training size and input time-steps on the performance of RNN model are also explored. The effects of the above parameters on the prediction performance, training and prediction time of the models are studied. The results can provide a reference for model deployment in the power plant. It is convinced that the proposed method has a high potential for dynamic process prediction in actual industrial scenarios through the above research.
Acoustic-Convective Interference In Transfer Functions of Methane/Hydrogen and Pure Hydrogen Flames
Authors: Æsøy Eirik , Aguilar José G. , Bothien Mirko R. , Worth Nicholas A. , Dawson James R. 
Published: September 2021

Abstract
We investigate the occurrence and source of modulations in the gain and phase of flame transfer functions (FTF) measured in perfectly premixed, bluff body stabilised CH4/H2 and pure H2 flames. The modulations are shown to be caused by flow disturbances originating from the upstream geometry, in particular the grub screws used to centre the bluffbody, indicative of a more generalised phenomenon of convective wave propagation. Velocity measurements are performed at various locations around the injector dump plane, inside the injector pipe, and in the wake of the bluffbody to provide detailed insight into the flow. Peaks corresponding to natural shedding frequencies of the grub screws appear in the unforced velocity spectra and it is found that the magnitude of these convective modes depends on their location. Flame imaging and PIV measurements show that these disturbances do not show up in the mean velocity and flame shape which appear approximately axisymmetric. However, the urms and vrms fields capture a strong asymmetry due to convective disturbances. To further quantify the role of these convective disturbances, hydrodynamic transfer functions are constructed from the forced cold flow, and similar modulations observed in the FTFs are found. A strong correlation is obtained between the two transfer functions, subsequently, the modulations are shown to be centered on the vortex shedding frequency corresponding to the first convective mode. The reason behind the excitation of the first mode is due to a condition that states that for acoustic-convective interaction to be possible, the shedding (convective) frequency needs to be lower than the cut-off frequency of the flame response. This condition is shown to be more relevant for hydrogen flames compared to methane flames due to their shorter flame lengths and thus increased cut-off frequency.
A Novel Deep Learning Model for the Flow Field Reconstruction of An Oscillating Airfoil
Authors: Li Yunzhu , Liu Tianyuan , You Jiarui , Xie Yonghui 
Published: September 2021

Abstract
In this paper, a novel model is presented for reconstructing unsteady periodic fields of velocity vector and pressure scalar over an oscillating foil. This data-driven method based on convolutional neural network can be utilized to accomplish two objections: fields reconstruction from limited measurements and transient aerodynamic characteristics prediction. The verification results of an oscillating foil under low Reynolds number show that this method can accurately reconstruct all the fields only by limited pressure information at probes on the foil surface. The evaluation on aerodynamic characteristics prediction illustrates that our model outperforms four classical machine learning methods. Meanwhile, a well-trained CNN model can almost achieve real-time flow field prediction by leveraging the GPU acceleration. Finally, the exploration of the robustness for the CNN model is conducted on several aspects, including training size, probe layouts, probe numbers and measurement noises.
Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate – The Importance of M-Xylene Within the Combustion of 1,3,5-Trimethylbenzene
Authors: Ramirez Hernandez Astrid , Kathrotia Trupti , Methling Torsten , Braun-Unkhoff Marina , Riedel Uwe 
Published: September 2021

Abstract
The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation.
In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e. temperature, pressure, and fuel equivalence ratios) is presented. The m-xylene reaction submodel was developed based on existing reaction mechanisms of similar species such as toluene and reaction pathways adapted from literature. The sub-model was integrated into an existing detailed mechanism that contains the kinetics of a wide range of n-paraffins, iso-paraffins, cyclo-paraffins, and aromatics.
Simulation results for m-xylene were validated against experimental data available in literature. Results show that the presented m-xylene mechanism correctly predicts ignition delay times at different pressures and temperatures as well as laminar burning velocities at atmospheric pressure and various fuel equivalence ratios. At high pressure, some deviations of the calculated laminar burning velocity and the measured values are obtained at stoichiometric to rich equivalence ratios. Additionally, the model predicts reasonably well concentration profiles of major and intermediate species at different temperatures and atmospheric pressure.
Grid Plate Flame Stabilizer for High Intensity Gas Turbine Combustion: The Influence of the Method of Fuel Injection on Mixing, Flame Development and NOx Emissions
Authors: Quiñonez Arce José Ramón , Andrews Gordon E. , Burns Alan D. , Al-Dabbagh Naman 
Published: September 2021

Abstract
Grid plate flame stabilizers for low NOx emissions have renewed interest in recent years due to their use in low NOx hydrogen gas turbine combustors. For non-premixed grid plate combustion, the difference in flame stabilizer design is in how the grid plate air flow is fueled. In the present work a simple four hole grid plate is investigated using CFD with three methods of fueling the air holes: radially inward fuel injection using 8 fuel nozzles per air hole (Grid Mix, GM 1 and Micromix); central fuel injection (FLOX method); and through a fuel annulus around each air hole (GM2). ANSYS FLUENT CFD predictions for GM2 are compared with axial gas composition traverses inside the combustor and with the mean combustor exit plane emissions. The three methods of fuel injection are also compared using isothermal CFD to determine which of the three methods offer the best mixing quality, which controls the relative NOx emissions. The predictions were for an equivalence ratio of 0.624 for the combustion stage and 0.5 for the isothermal study, using industrial propane. CFD modelling used RANS simulation with Realizable k-epsilon turbulence model, non-premixed combustion with the Steady Laminar Flamelet model. The temperature and mixing profiles obtained for GM2 were in reasonable agreement with the experiments and the other two fuel injection methods were then compared with GM2.
Development of a 25 MWth Flameless Pressurized Oxy-Combustion Pilot
Authors: Schmitt Joshua , Malavasi Massimo 
Published: September 2021

Abstract
The Flameless Pressurized Oxy-Combustion (FPO) cycle, a novel flexible fuel technology, is being developed into a large pilot. This effort seeks to complete the preliminary engineering and planning of a 25 MWth Pilot Plant that will demonstrate the technology for scale-up to a commercial unit. The technology, pioneered by ITEA at the 5 MWth scale, must be brought to a higher technology readiness level (TRL) to be viable at the commercial scale.
The 25 MWth pilot cycle was optimized for cost and technology development and demonstration. Preliminary drawings, layouts, and plans were defined. Process flow diagrams were used to describe the pilot configuration in greater detail. A heat and mass balance with stream data was created. A master equipment list specified the operating conditions for major pieces of equipment within the pilot using this heat and mass balance.
The 25 MWth FPO pilot is assessed for environmental performance. A test campaign is developed to assess the type of test and number of hours required for pilot demonstration. The environmental performance is compared against projected performance at the commercial scale.
This project builds upon extensive evaluation of the techno-economic performance of the FPO technology already performed by ITEA. This includes system improvements, such as the addition of a turbo-expander to the flue gas stream. Some of the performance-enhancing components are not as well defined as others. The primary goal of this effort was to bring all of the core cycle components to the same level of design maturity.
A techno-economic assessment (TEA) evaluated the FPO technology at the commercial scale in comparison to the NETL baseline cases. The reference plants were used in combination with proprietary equipment estimates to build a plant capital cost and cost of electricity evaluation. FPO performed better than the sub-bituminous post-combustion capture cases. Further preliminary estimates of improvements to the FPO cycle show even further gains when compared to conventional carbon capture methods.
Experimental Investigation of a High Velocity Gaseous Jet Injection Into an Oscillating Crossflow
Authors: Song Jinkwan , Wilson Johnathan , Lee Jong Guen 
Published: September 2021

Abstract
This paper presents the experimental results of a gaseous jet injected into an oscillating-air crossflow. The jet to crossflow momentum flux ratios are chosen as 19, 30 and 58, and the mean air crossflow velocities are chosen as 10m/s, 25 m/s, and 60 m/s. The crossflow is modulated at frequencies up to 280 Hz with a maximum crossflow velocity fluctuation of 30% of its mean velocity. Acetone planar laser-induced fluorescence is used to record the instantaneous jet concentration field. Three distinct regions are observed near the injection location (x/d &lt; 18); the jet core, the fast bending zone, and the fully developed plume zone. The location of the end of potential core can be determined primarily by the momentum flux ratio. Based on observations of these three regions, a set of correlations for the trajectory of maximum jet concentration is proposed for the potential core region and for the fully developed plume zone. The potential core responds quasi-steadily to the crossflow oscillation and the fluctuation of penetration of the potential core zone linearly increases with respect to the crossflow velocity fluctuation level. The jet penetration under oscillating crossflow is slightly lower than that under steady crossflow, especially when the mean crossflow velocity is low (10–25 m/s). However, the differences of trajectories between the oscillating and the steady crossflow cases become almost negligible as the mean crossflow velocity increases further. The axial decay of jet concentration under oscillating crossflow occurs at faster rate than that under steady crossflow, indicating that the oscillating air crossflow enhances the mixing between the jet and the crossflow. The vertical jet concentration profile at different axial location confirms that the main effect of crossflow modulation is enhanced mixing of jet with crossflow. However, no noticeable effect of modulation frequency of crossflow on the jet penetration is found.
The Development of Turboexpander-Generators for Gas Pressure Letdown Part I: Design and Analysis
Authors: Khatri Rasish , Liu Jeremy , Sarhan Freddie , Najeeb Ovais , Kajita Hiroshi , Kozuka Mitsuru 
Published: September 2021

Abstract
This paper describes the design and development of an innovative 280 kW and a 125 kW Turboexpander Generator (TEG) for natural gas pressure letdown (PLD) applications. The flange-to-flange TEG is supported by active magnetic bearings (AMB) and uses an advanced thrust balancing scheme to minimize the net load on the thrust bearing. The machine designs for the two TEG frame sizes are very similar to maintain commonality between parts. A review of the high-speed generator (HSG) and AMB design is provided. A complete AMB closed-loop dynamics study is presented, including a comprehensive rotordynamics and controls analysis. The touchdown bearing design is shown and discussed, and design details of the touchdown bearing resilient mount are presented. The touchdown bearings are given resilience with a tolerance ring. A detailed simulation of a rotor touchdown event at full speed is shown. The magnetic bearing controller (MBC) and variable speed drive (VSD) are located approximately 35 m from the TEG, exposed to the outside environment, and are not required to be explosion-proof. The prototype TEGs are intended to be manufactured and tested in Q1 2021. They will be commissioned, and field tested in Q2 2021. A follow-up paper detailing the mechanical testing and field testing of the units will follow in 2022.