bluuebunny/crossref_metadata_2025_split huggingface dataset:
Micro-Gas Turbine Cycle Configurations for Biomass Combined Heat and Power Plants
Authors: Bollas Konstantinos D. , Efstathiadis Theofilos G. , Mertzis Dimitrios P. , Kalfas Anestis I. 
Published: October 2022

Abstract
The potential of integrating micro-gas turbine systems into biomass micro-Combined Heat and Power (CHP) units is investigated, following a thermodynamic analysis. Various cycle configurations are elaborated, utilising the producer gas of an existing biomass gasification CHP unit, with a capacity of 30 kWe. The reference CHP unit consists of a fluidised bed gasifier coupled with a gas treatment unit, a gas cooler and an Internal Combustion Engine (ICE). The gas cooler operation is entailed with environmental issues, concerning tar condensation and removal. In this paper, alternative approaches of direct fuel combustion, at elevated temperatures, through micro-gas turbine systems are investigated. Five configurations, based on the internally-fired (simple and recuperative μ-GT) or the externally-fired gas turbine (μ-EFGT), as well an additional reheated micro-gas turbine (μ-RHGT) are considered. The μ-EFGT is investigated for two cases: unfiltered (UF) and filtered (F) producer gas fuel. Each configuration is optimised, using in-house solvers, while the components are modelled using turbomachinery and heat exchanger detailed designs. The recuperative μ-rGT and the unfiltered μ-EFGT/UF show a similar electrical efficiency of around 31.5%, while the overall efficiencies are 63% and 74.8% respectively, which is improved by 5%, compared to the ICE. Challenges related to fuel compression, mainly due to the high rotational speed, are expected in the μ-rGT case, while fouling is expected to be a serious challenge in the μ-EFGT/UF case. Both challenges can be addressed by the filtered μ-EFGT, however, this results in lower electrical efficiency, around 26.5%, which is −12% compared to the ICE.
Advanced Thermal Profiling of Turbocharger Compressor Wheels Using Phosphorescence Thermal History Coatings
Authors: Karagiannopoulos Solon , Rode Martin , Peral David , Castillo Daniel , Araguas-Rodríguez Silvia , Rai Kieron , Inomata Ryosuke , Iosifidis Georgios , Feist Jörg 
Published: October 2022

Abstract
Compliance towards future emissions legislation requires internal combustion engines (ICE) to utilize highly efficient combustion concepts (e.g. Miller cycle), which, are often associated with increased boost pressure requirements, leading to increased mechanical stress on turbocharger components. This is especially the case for compressor wheels due to the increased speed and temperature loading. To offer cost competitive products, IHI seeks to further exploit the limits of conventional state-of-the-art materials used in automotive turbochargers and refine their component development processes. While knowledge of the exact boundary conditions under which turbocharger components are operating is essential, the actual material temperature components experience under real operating conditions is a significant source of uncertainty.
Temperature measurements are usually conducted during turbomachinery durability tests to validate thermodynamic models and assess component lifetime. Temperature measurement techniques typically include thermocouples, optical sensors and thermal paints. However, the former methods are limited mostly to stationary components and can only provide point measurements, while the latter only offers low resolution data for short durations and involves highly toxic materials. Thermal History Paint & Coating technology developed by Sensor Coating Systems (SCS) offers a unique solution for thermal mapping in harsh environments. The technology is based on a phosphor material which is applied as a paint or coating on the surface of the components to be measured. The luminescent properties of the coating material are permanently changing depending on the maximum exposure temperature during the test. The THP/C luminescent properties are measured in multiple locations using a laser-based instrumentation system and a robotic arm. High-resolution thermal maps directly on the 3D CAD models of the component are generated.
For this application, the THP material has been applied for the first time on the surface of three turbocharger compressor wheels tested under different cooling conditions. The THP material exhibited excellent durability during testing at high circumferential speeds above 580 m/s. More than 2,000 temperature measurements were obtained on pre-selected locations on the surface of the wheels. The test demonstrates that THP can be used on components with complex geometries such as turbocharger compressor wheels. Additionally, temperatures as low as 120 °C have been resolved for the first time.
Quasi-Two-Dimensional Numerical Model for Shock Wave Reformers
Authors: Madiot Ghislain , Mahmoodi-Jezeh S. V. , Tüchler Stefan , Davidson Mark , Akbari Pejman , Copeland Colin D. 
Published: October 2022

Abstract
The article details a numerical investigation of methane pyrolysis inside a shock wave reformer using a quasi-2-dimensional (Q2D) Reynolds-Averaged Navier-Stokes (RANS) CFD model. This work is in support of the New Wave Hydrogen, Inc. (NWH2) proprietary technology development. To take account of the characteristics of the flow in the presence of shock waves, a simplified approach is proposed that captures the gas dynamics during partial opening with a lower computational cost suitable for the wave reformer design. The model is based on the three-dimensional, compressible, and unsteady Navier-Stokes equation coupled with k-ω - SST turbulence closure. Boundary conditions are implemented through a cell-centered approach with fictitious cells outside of the domain boundaries. The numerical results are compared with solutions from a quasi-one-dimensional (Q1D) unsteady model reported in literature. The simulations show a good agreement between the two different modelling approaches in terms of spatial distribution of the pressure gradient for one complete cycle. It is observed from the Q2D results that the entrance for each passage, especially upon opening of the high-pressure driver gas port, is a location of particular interest in the formation of the shock. The resulting acute pressure gradients induce loss inside the channel, decreasing the maximum temperature during a complete wave cycle by 15%, and consequently, reducing the methane pyrolysis process.
An Innovative Concept for the Complete and Low-NOx Combustion of Non-Carbon Eco-Fuels Using a Thermo-Acoustically-Driven, Hydrogen-Powered Pilot Stage
Authors: Paulitsch Nina , Giuliani Fabrice , Hofer Andrea , Hofer Johannes , Andracher Lukas 
Published: October 2022

Abstract
The problem of climate change, triggered by a high concentration of pollutants in the atmosphere, and the scarcity of fossil resources, increases the need of low emission thermal utilisation of novel, non-carbon eco-fuels such as hydrogen, ammonia (both for energy and propulsion) or hydrogen sulphide (sulphuric acid production). While all of these listed eco-fuels have the potential to decarbonise industry and the energy sector, they also pose demanding challenges regarding combustion. To address these challenges the idea is to combine the advantages of current low-NOx technologies in terms of ultra-lean combustion with a precisely controlled, forced flame turbulence generated by a pulsation actuator. The aim is to develop a safe and highly digitalised combustion technology, including a two-staged burner design for application in the megawatt range with multi eco-fuel capacities and a fully automated control loop for the combustion process.
To achieve effective thermo-acoustic modulation an actuator type siren is used. Further improvements towards the demanding application in industry were done leading to the latest siren model, Siren E. A siren is a robust pulsation apparatus that generates powerful noise levels and effective flow pulsations under elevated pressure and temperature conditions [1–3]. By scanning through a certain frequency range during combustion, one is able to detect eigenfrequencies of the flame which increases flame turbulence when excited. The effective flow control of the siren can guarantee a complete burnout of the partially toxic eco-fuels. In addition, gaseous pollutants such as NOx can be reduced to a minimum, since the flame pulsation process provides the opportunity to run reliably a mixture with an otherwise unstable combustion process. The Siren E with its new features is introduced in this paper in detail. To verify the method for eigenfrequency detection, initial combustion tests are first carried out with propane on the so-called MethaNull test rig. There, the main aspect is to meet the same eigenfrequencies as in a previous work. Then, initial combustion tests with premixed hydrogen are performed up to a thermal power of 10 kW. First, different methods for the injection of hydrogen are tested resulting in a prioritised premixed variant. Using this premixing method in the test setup the response to thermo-acoustic excitation via loudspeaker and siren is investigated. Prior to the experiments, a numerical study was performed on a model representing a simplified pilot stage. All numerical and experimental results are presented in detail in this paper.
Design and Development of a Five-Hole Probe Calibrator and Traverse to Investigate Ingestion in Rotating Cavities of HP Compressors
Authors: Fox Emma C. , Puttock-Brown Mark R. , Davies Simon J. 
Published: October 2022

Abstract
The internal air system is essential within aero-engine HP compressors for cooling and controlling blade tip clearances. Reducing the amount of air diverted from the main flow to the internal system improves the overall thermal efficiency, and so there is a need to understand the interactions of the flow within the compressor cavities. This paper describes the implementation and use of miniature five-hole probes to investigate the ingress and egress of the bore flow in an established engine representative test rig.
The development of an inexpensive but accurate automated calibration device to calibrate different shaped probes over a wide range of pitch and yaw angles is described. The Reynolds number of the calibration flow was matched to the operating conditions of the pressurised test rig. A bespoke traversing mechanism was designed and installed within the shaft of the rig. The traverse enables the probe to move axially across one cavity, radially from the shaft to low cavity region and rotate to align with the local flow direction. Velocity data from a single commissioning test case at Ro = 0.65, Rez = 5.5 × 104, Reθ = 1.6 × 106, βΔT = 0.37 is presented. A Monte Carlo uncertainty analysis of the calibration and data collection procedure was conducted to validate the use of a five-hole probe for axial, tangential and radial velocity measurements in rotating cavities.
Mesh Refinement and Inlet Turbulence Intensity in the Numerical Evaluation of Cooling Effectiveness: A Systematic Study on an Industrial Gas Turbine
Authors: Lo Presti Federico , Winhart Benjamin , Post Pascal , di Mare Francesca , Wiedermann Alexander , Greving Johannes , Krewinkel Robert 
Published: October 2022

Abstract
In this study, the influence of grid resolution and inflow turbulence on the prediction of gas temperature distribution around HP-turbine blades and the effectiveness of cooling flows are assessed by means of a comparative, systematic study with increasing grid resolution, starting from a typical RANS-mesh with progressive refinement, by means of scale-resolving simulations. The investigation is focused on a three-stage industrial gas turbine in the mid-range output class, whereby we restrict our analysis to the first stage, where most of the external cooling flow is injected, this regions being characterized by the highest temperature fluctuations. The extent of these variations and their unsteady characteristics need to be determined to verify if they have a measurable influence on the material temperature. As the interaction of turbulence with cooling flows is a key element in the prediction of cooling effectiveness, turbulence levels play a major role in addition to the grid resolution. Therefore, special attention is paid to the accurate description of turbulence scaling laws and correlations at the turbine inflow. The results of the investigation provide insight in a viable modelling and simulation tool which can be adopted during design cycles and reveals valuable details of the unsteady aerothermal stresses on the HP turbine blades.
Circumferentially Grooved Seal Flow Field Analysis Based on Effective Film Thickness to Improve Bulk Flow Models
Authors: Gibbons Nathaniel , Watson-Kassa Cori , Goyne Christopher , He Minhui 
Published: October 2022

Abstract
Bulk flow modeling of circumferentially grooved seals uses simplified physics models to predict leakage and rotordynamic coefficients more efficiently than full computational fluid dynamics (CFD) simulations, but at the expense of accuracy. Reducing bulk flow modeling inaccuracies, mainly a result of uncertainties in empirical quantities like friction factors and loss coefficients, requires a more fundamental and physical understanding of the flow features and their dependencies. This study utilizes CFD and an effective film thickness, a physical boundary between the jet and recirculating flows, to investigate Reynolds number effects on grooved seal flow fields and shear stresses. Simulations were run using ANSYS CFX for a single groove seal model assuming fully developed flow for a range of pressure differentials and rotor speeds. The effective film thickness boundary was defined by generating streamlines in the jet flow region that traversed the entire axial length of the model. Radial averaging across the local film thickness yielded bulk flow quantities used in processing and analysis. Flow structures, film thicknesses, shear stresses, and net flow expansion into the groove are found to be described completely by the ratio of circumferential to axial Reynolds number and the total resultant Reynolds number. Decreases in leakage with rotor speed are found to be dictated by increased land shear stresses and a decreased role of the groove at inducing pressure drop. An optimal groove aspect ratio between 0.07 and 0.19 is presented based on maximizing expanded film area while retaining a main groove recirculation region. This is the first paper to analyze circumferentially grooved seal flow from the standpoint of the effective film thickness, and by doing so, provides physical insight needed for a full description of the flow behavior. The results presented highlight bulk flow analysis areas where an effective film thickness approach could lead to new, physics motivated model development and the elimination of particular empirical coefficients. The effective film thickness approach thus provides a strong foundation on which substantial improvements in bulk flow modeling accuracy can be achieved.
Attributes of Bi-Directional Turbomachinery for Pumped Thermal Energy Storage
Authors: Chiapperi J. D. , Greitzer E. M. , Tan C. S. 
Published: October 2022

Abstract
In this paper we (i) present a methodology for determining the aerodynamic performance of bi-directional turbomachines for pumped thermal energy storage, i.e., turbomachines designed to operate as a compressor in one direction, and then as a turbine in the opposite direction, (ii) carry out performance computations for such turbomachines, and (iii) propose principles for conceptual design of these devices. Focus is placed on using the energy storage cycle not only to identify the novel requirements placed on bi-directional turbomachines, but also to estimate the effect of these requirements on the efficiency of the energy storage process. In particular, the difference between aerodynamic loading in forward and in backward operation causes the blading to work at incidences leading to performance below maximum efficiency, resulting in a lower round-trip efficiency. The description of the design principles includes determination of the number of stages, definition of non-dimensional parameters for blading selection, and optimization of two-dimensional blading for bi-directional operation. The assessment of stage count shows the relationship between relative Mach number, pressure ratio, and round-trip efficiency. The non-dimensional parameters are assessed through a bi-directional analogue to existing “Smith charts”, for the efficiency of single direction turbomachines, as a function of camber and stagger. The blade shape evaluation and optimization shows how the blade profile can be modified to address the requirements of a bi-directional turbomachine, enabling an increase in round-trip efficiency of 2 percentage points compared to a baseline double circular arc configuration.
Vibration-Based Diagnostic of Aircraft Bearings Operating Under Strong Speed Variations
Authors: Abboud Dany , Griffaton Julien , Marnissi Yosra , Gomez Chirinos Jose Luis , Elbadaoui Mohammed 
Published: October 2022

Abstract
This paper proposes a vibration-based diagnostic methodology for aircraft bearings based on a joint first- and second-order cyclostationary analysis. The idea is to track the first- and second-order content over a predefined operating speed range, instead of ignoring the later or performing the diagnosis on an arbitrary stationary speed. The methodology applies to relatively long vibration signals recorded under strong speed variations, using a sliding window over which fluctuations are low. First, we obtain the time-evolution of the spectral statistics by computing the so-called instantaneous power and coherence spectra reflecting the first and second order content, respectively. Then, we design a time-to-speed transform based on fuzzy logic to transform the previously obtained time-cyclic maps into speed-cyclic maps, expressing the spectral statistics as functions of a predefined operating speed grid of interest. Last, we demonstrate the proposed methodology on a real vibration signal captured from an accessory gearbox of a CFM56 aircraft engine, with multiple bearing faults.
High-Frequency Mode Shape Dependent Flame-Acoustic Interactions in Reheat Flames
Authors: McClure Jonathan , Bothien Mirko , Sattelmayer Thomas 
Published: October 2022

Abstract
Gas turbines featuring sequentially staged combustion systems offer excellent performance in terms of fuel flexibility, part load performance and combined-cycle efficiency. These reheat combustion systems are therefore a key technology for meeting fluctuating power demand in energy infrastructures with increasing proportions of volatile renewable energy sources. To allow the high operational flexibility required to operate in this role, it is essential that the impact of thermoacoustic instabilities is minimised at all engine load conditions. In this case, high-frequency thermoacoustic instabilities in the second “reheat” combustion stage are investigated. Reheat flames are stabilised by both autoignition and propagation and, as a result, additional thermoacoustic driving mechanisms are present compared with more conventional swirl-stabilised combustors. Two self-excited thermoacoustic modes have been observed in a 1MW reheat test rig at atmospheric pressure, one which exhibits limit-cycle behaviour while the other is only intermittently unstable. The underlying driving mechanisms for each individual mode have been investigated previously and, in this paper, the two modes are directly compared to understand why these instabilities are each associated with different driving phenomena. It is shown that, due to the different flame regimes present in the reheat combustor, the potential for flame-acoustic coupling is highly dependent on the thermoacoustic mode shape. Different interactions between the flame and acoustics are possible depending on the orientation of the acoustic pressure nodes and antinodes relative to the autoignition- and propagation-stabilised flame regions, with the strongest coupling occurring when an antinode is located close to the autoignition zone. This provides insight into the significance of the different driving mechanisms and contributes to the ongoing development of models to allow prediction and mitigation of thermoacoustic instabilities in reheat combustion systems, which are crucial for reliable combustor designs in the future.
Analysis of the NOx Emissions Deriving From Hydrogen/Air Combustion in a Swirling Non-Premixed Annular Micro-Combustor
Authors: Mazzotta Luca , Di Gruttola Francesca , Palone Orlando , Gagliardi Gabriele Guglielmo , Borello Domenico 
Published: October 2022

Abstract
The objective of this paper is to analyse the thermal performances and emission levels of a swirling non-premixed annular micro-combustor. A three-dimensional simulation of the internal flow in an annular combustion chamber fuelled by hydrogen/air in non-premixed conditions was carried out through Ansys Fluent 2020 R2. A detailed mechanism involving many species and reactions was required to represent the complexity of the combustion process. A 19-reactions and 9 species mechanism was deemed to be appropriate to predict the combustion characteristics with great accuracy and limited processing resources. The reaction mechanism was implemented in Fluent through Chemkin. This model was then compared with the built-in model of the chemical kinetics, which involves just one reaction. The results showed that the 19-reactions model is more accurate to reproduce the centerline temperature distribution than the default simpler model: the 1-reaction model differs by 230 K compared to the experimental data, while the 19-reactions one only by 80 K. The comparison between the velocity of the mixture inside the combustor with and without combustion was also carried out, providing an estimate of the influence of temperature on the flow field. Finally, to meet the emission limits established by the European Commission in 2015, the thermal NOx and NOx derived by NNH were examined on both the outlet and the centerline of the combustor. The study reveals great potential of hydrogen mixtures in reducing emissions and provides insights on the cooling requirements to guarantee wall materials reliability.
Multilayered Fibre-Matrix Interphases Derived From the Electrophoretic Deposition of Ceramic Nano-Powders
Authors: Robertson Taylor , Huang Xiao , Kearsey Rick 
Published: October 2022

Abstract
A significant challenge within the manufacturing of Ceramic Matrix Composites (CMCs) is the creation of the fibre-matrix interphase which enables the damage tolerant behavior of CMCs. Chemical vapour deposition (CVD) has been a highly successful approach for fabricating fibre-matrix interphases; however, CVD requires capital intensive facilities and hazardous precursors. This work examines electrophoretic deposition (EPD) as an alternative route for the production of fibre-matrix interphases. Four multilayered fibre-matrix interphases (SiC/Al2O3, BN/ZrO2, ZrC/85wt%Al2O3-15wt%ZrO2, and SiC/Si3N4/SiC) were produced through multi-staged electrophoretic deposition of ceramic nano-powders upon SiC fibre bundles. A 25-2 factorial design of experiments is utilized to explore the effect of different levels of the following variables: electric field strength, duration, surfactant, solids loading and binder. Following deposition of the fibre-matrix interphase the fibre bundles are thinly coated with a SiC matrix through a reactive melt infiltration technique. The resultant microcomposites are then subjected to tensile loading until failure to determine which coating and deposition combination are the most likely to yield favorable tensile properties. Additional microscopy is performed to determine the uniformity and thickness of the coatings. The results are then examined to evaluate the suitability of electrophoretic deposition as a production technique for fibre-matrix interphase coatings in CMCs.