bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Characterisation of the Dynamics of Partially Premixed Hydrogen Flames in a Lean Direct Injection (LDI) Combustor
Authors: Ezenwajiaku Chinonso , Balachandran Ramanarayanan , Ducci Andrea , Picciani Mark , Talibi Midhat 
Published: September 2023

Abstract
Hydrogen continues to show significant promise as a zero-carbon energy carrier in the pursuit of global decarbonisation targets. Hydrogen has wide flammability limits which means it can operate at considerably leaner conditions for reduced NOx emissions. However, fuel-lean operation makes these systems more susceptible to thermoacoustic instabilities and flame blow-off. Combustor configurations such as jet-in-crossflow are gaining popularity in industry for 100% hydrogen as they can help mitigate risk of flashback, but detailed characterisation of flame dynamics is still necessary.
In this study, the combustion dynamics of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor were investigated at atmospheric conditions. The combustor inlet consisted of nine circular air channels, with hydrogen injected inwards through two diametrically opposite holes into each air channel. Dynamic pressure and OH* chemiluminescence measurements were employed to study the effect of varying key parameters, such as Reynolds number and global equivalence ratio, on combustor dynamics. High-speed OH-PLIF imaging was conducted to understand flame dynamics.
The results showed that self-excited oscillations were observed at all tested conditions and the dynamical behaviour of the combustor was complex with strong dependency on global equivalence ratio and bulk velocity conditions. The magnitude of self-excited thermoacoustic oscillations initially increased with a decrease in global equivalence ratio, but subsequently decreased at leaner conditions (below global equivalence ratio 0.3). Similar observations were noted for all bulk velocities. High speed OH-PLIF imaging indicated that the heat release oscillations were influenced by vortex-flame roll up and possible global lean extinction events. The results from this work have the potential to inform design efforts towards development of new architectures for stable, low-emission 100% hydrogen combustors.
Performance Investigation of a Bladeless Air Compressor Using Numerical Simulation
Authors: Tiwari Ravi Nath , Traverso Alberto , Pascenti Matteo , Ferrari Mario Luigi 
Published: September 2023

Abstract
In recent years, the demand for lightweight, compact, cost-effective, and low-noise-emission machines has increased significantly. Tesla or bladeless machines can meet the current market’s demands, especially at a small scale. This article examines Tesla compressor performance numerically, which is influenced by a number of factors related to rotor and stator design. This study examines multiple aspects of Tesla’s compressor in order to improve its overall performance, including the rotor, stator impact, and statorless or volute casing. An innovative bladeless rotor has been independently studied and optimized based on the Ekman number and diameter ratio. The disk gap and radius ratio are crucial to the performance of bladeless rotors. The rotor-only analysis determined an isentropic efficiency of 95%, which is in line with expectations.
An optimized rotor is initially simulated with a stator (vane diffuser) and subsequently with a volute casing. In the diffuser case, it has been numerically demonstrated that bladeless compressors can achieve an overall efficiency up to 53%. It should be noted, however, that compressor performance depends on the number of diffuser vanes and the stator-rotor interaction. With an increase in diffuser vanes, overall performance may be affected by a significant increase in frictional losses and stator-rotor interaction. In order to improve performance, the volute casing is examined, which reveals that efficiency is improved by 3%–5% as compared to the best-vaned diffuser case. Even if the final choice of the designer will depend on the performance requirements and level of complexity acceptable for the specific application, this study demonstrates that Tesla compressor with volute, i.e. statorless, overperform any vaned diffuser configuration both in terms of efficiency and pressure ratio.
Lean Flame Stabilization With Nanosecond Plasma Discharges in a Gas Turbine Model Combustor
Authors: Blanchard Victorien P. , Roqué Frédéric , Scouflaire Philippe , Laux Christophe O. , Ducruix Sébastien 
Published: September 2023

Abstract
This paper presents an experimental study of lean flames stabilization with nanosecond repetitively pulsed discharges. The two-stage, swirled-stabilized, multipoint injector BIMER operates at atmospheric pressure with methane-air mixtures in the present study. It is representative in its design of a realistic lean premixed prevaporized injector of gas turbine engines operated at a lab-scale level. The lean blow-off extension with plasma is characterized. The combustion efficiency and the pollutant emissions are quantified near blow-off with and without plasma for 50-kW flames. We show that it is possible to stabilize lean flames down to an equivalence ratio of 0.3, with less than 5 ppm of NOx emitted, thanks to NRP discharges with an electric power that represents less than 0.25% of the flame thermal power. This study also clearly shows that it is necessary to account for the plasma system integration at the early stage of the combustor design to fully benefit from the plasma stabilizing effects on the flame.
LES Modeling of High-Lift High-Work LP Turbine Profiles: Part I: Approach
Authors: Ni Michael , Ni Ron-Ho , Clark John P. 
Published: September 2023

Abstract
The Low Pressure Turbine (LPT), commonly used in both commercial and military engines, generally experiences low Reynolds numbers at high altitude cruise conditions. Understanding the complex flow physics in an LPT stage is critical in providing adequate work output while maintaining target efficiency at low Reynolds number situations.
With the complex laminar to turbulent transition flow physics in mind, the high lift LPT design requires an understanding of the turbulent transition response to design and operating conditions which is not currently met with existing design methodologies. The RANS based turbulence models like k-ω and SST, are not able to provide meaningful transition analysis.
This paper presents Large Eddy Simulations (LES) of 4 LPT cascades airfoils over a range of Reynolds’ numbers from 60,000 to 20,000 compared against 1D experimental data. The objective of the work is to define a controlled numerical procedure that minimizes the number variables affecting the LES. The controlled numerical procedure will then be used to understand the LES time-step size requirements needed for consistent Reynolds Lapse rate characterization. Simulations are run with identical mesh count, mesh topology as well as with identical inlet and exit flow conditions. The Reynolds number was varied through the modification of the Kinematic viscosity, enabling effective evaluations of time-step size sensitivity of LES simulations upon the time-averaged total pressure losses.
Findings include that time step size needs to be small enough to promote the creation of 3D eddies and that the time step size used for the Dual-Time Stepping method needs to be smaller than the convection time step size (ΔTc) to provide consistent Pt loss estimation. This methodology is then applied to new cascades and the results presented in Part II.
Predicting Premature Failures in Small Wind Turbines With Recurrence Plots
Authors: Jauregui Juan C. , Torres-Contreras Ignacio 
Published: September 2023

Abstract
This paper presents the application of the Recurrence Plot as an alternative for pre-processing the raw data. The Recurrence Plots can extract the non-linear and transient response and are sensitive to slight variations in the signal frequency, amplitude, and waveform. Thus, it is an alternative technique for improving the sensitivity; consequently, the prognostic algorithms can predict with better resolution. The data were obtained from an experimental 12 m wind turbine. The transmission was instrumented with three accelerometers and three gyroscopes; the generator’s current and voltage were monitored. The difficulty in producing the phase plane using acceleration data is its integration to obtain the kinetic and potential signal energies. This limitation is overcome by integrating the data using the Empirical Mode Decomposition and the shift principle. The results show good sensitivity for predicting variations in the operating conditions and are the basis for other prognostic analyses.
Numerical Assessment of the Effect of Hydrogen Enrichment of a Technically Premixed Swirl-Stabilized Natural Gas Flame
Authors: Pachano Leonardo , Surapaneni Anurag , Both Ambrus , Ax Holger , Petry Niklas , Boxx Isaac , Mira Daniel 
Published: September 2023

Abstract
High-fidelity large eddy simulations (LES) are conducted for lean natural gas flames with different levels of hydrogen enrichment in a technically premixed swirl-stabilized combustor (PRECCINSTA) operated at atmospheric pressure. The modelling approach relies on tabulation of premixed flamelets and presumed-shape probability density functions (PDF) to account for subgrid turbulence-chemistry interactions. Results are presented for non-reacting and reacting conditions with 0, 40 and 50% hydrogen content in the natural gas. The influence of hydrogen-enrichment is investigated here by combining LES with Raman measurements. The assessment of LES shows good predictions of the flame stabilization mechanism, flow field and flame dynamics as compared to experiments. The natural gas flame develops a self-excited flow oscillation characterized as a precessing vortex core, which is well reproduced by the LES. The lean operation of the burner with natural gas shows a stable M-shape flame that transitions to a V-shape fully attached flame as the main fuel is blended with hydrogen. Raman measurements are compared with LES data to examine the flame structure and burning characteristics. It is concluded that hydrogen addition makes the flame more compact, induces higher reactivity of the fuel-air mixture and leads to a stable V-shape flame fully attached to the burner’s nozzle-cone.
Options for Improving Performance of Additively Manufactured Nickel-Base Superalloys for Gas Turbine Applications
Authors: Bridges Alex , Shingledecker John , Clark John , Crudden David , Kirka Michael , Fernandez-Zelaia Patxi 
Published: September 2023

Abstract
Additive manufacturing (AM) has been increasingly used for gas turbine components over the last decade. Many different components can successfully be designed, printed and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g. creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys and there still exists a gap in understanding the high temperature processing-structure-properties-performance relationships of these alloy systems.
This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multi-step aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties.
The results show there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3X in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components.
Numerical Study on the Aeroacoustics of a Propeller-Wing Integration at Various Advance Ratios
Authors: Huang Guangyuan , Sharma Sidharath , Ambrose Stephen , Jefferson-Loveday Richard 
Published: September 2023

Abstract
Driven by increasing demands for a sustainable and ecofriendly future in aviation, Distributed Electric Propulsion (DEP) systems have received much attention for their high aerodynamic efficiency. DEP systems with lower noise emissions are desired by customers and policymakers and therefore it is important to understand the noise generation mechanism, propeller-propeller and propeller-wing interactions of DEP aeroacoustics. In this paper, the effect of flow conditions on the aeroacoustics of a propeller-wing integration is investigated numerically with various advance ratios. The integration consists of a Mejzlik 2-blade propeller installed on the leading edge of a NACA0018 airfoil. The propeller is designed using Clark-Y airfoil sections and a constant pitch with a pitch-to-diameter ratio of P/D = 0.5. Different rotating and forward-flight velocities are studied, corresponding to the advance ratio J ranging from 0.485 to 1.575. A hybrid computational aeroacoustics (CaAA) method is performed, where the near-field aeroacoustics is solved by compressible coarse-grid large-eddy simulations (LES), and the corresponding far-field acoustics is calculated by the Ffowcs Williams and Hawkings (FW-H) equation. The results have shown significant effects of the flow conditions on the propeller-wing integration in terms of the aerodynamic and acoustic features. The aerodynamic performance and near-field flow structures are investigated first. Then the sound generation from the propeller and wing is revealed respectively.
Operational Strategies of 2-Spool Micro Gas Turbine With Alternative Fuels: A Performance Assessment
Authors: Gaitanis Aggelos , Tiwari Ravi Nath , De Paepe Ward , Ferrari Mario Luigi , Contino Francesco , Breuhaus Peter 
Published: September 2023

Abstract
The demand for efficient, cost-effective, and low-emission decentralized electricity and heat production is rapidly increasing. Micro Gas Turbines (mGT) have not yet succeeded in conquering the small-scale combined heat and power (CHP) market. The main reason is that their electrical efficiency is not high enough to maintain a cost-effective operation at low heat demand. A two-shaft intercooled mGT has the potential to meet the current market demand for decentralized power generation. This technology maintains a high level of electrical efficiency even at part load and coupled with its fuel-flexible combustion chamber, makes it an ideal candidate for CHP concepts in a renewable future.
The energy transition however also requires mGTs to be able to run on alternative fuels, such as hydrogen and syngas, which shifts its operating conditions and requires significant modification in the cycle’s part-load control to ensure the stable operation of the components such as the compressor. Therefore, in this paper, performance analysis on a 2-spool mGT is carried out using a mixture of natural gas, syngas, and hydrogen as a fuel. Specific attention is given to the low-pressure and high-pressure compressors and the variation of surge margin by adding hydrogen and syngas into the fuel. Two control strategies of the 2-spool mGT are adopted. In the first scenario, the two shafts have the same rotational speed while in the second one, the shaft speeds are controlled independently. In both part-load strategies, the specific performance of the two compressors keeps high isentropic efficiency which leads to high electrical efficiency at nominal power when natural gas-syngas mixture is used as fuel. When the engine is operated with equal shaft speeds, the maximum performance with 100 vol.% of syngas is observed at 85% of the nominal load while 100 vol.% of hydrogen shows maximum efficiency at an electric load of 63.7%. Also, at electric power lower than 60% of the nominal and for high amounts of syngas in natural gas, the low-pressure compressor (LPC) operates closely to surge line. In the second part-load strategy, the efficiency increases as the load decreases and the LPC runs in an efficient and safe operating region. Moreover, the performance of the 2-spool mGT is significantly influenced by the amount of nitrogen in syngas. At 200 kW, 45 vol.% of nitrogen decreases the airflow rate of the cycle by 7.4% compared to 0 vol.%. The results indicate that the amount of nitrogen in syngas and also the part-load strategies significantly influence the safe operation of the LPC component.
Numerical Study of Radiative Heat Transfer Through Next-Gen Thermal Barrier Coating Topcoats
Authors: Mulla Jaasim , Satpathy Radhakanta , Kaka Fiyanshu 
Published: September 2023

Abstract
With the world coming to terms with the consequences of climate change, the aviation sector has continued pushing towards increased efficiency to lower emissions. Other than the use of eco-friendly fuels, it is a fact that to achieve higher efficiency and thrust, it is essential to raise the turbine entry temperature in the engine. Increased temperatures in the turbine section intensifies the thermo-mechanical stresses on the hot-end components reducing their life exponentially. Higher temperatures also lead to an increased fraction of heat transfer via the mode of radiation, which has been largely neglected in turbine design until recently. Hence, the heat transfer to the substrate needs to be minimized by reflecting or radiating the heat. The goal of this study has been to model the propagation of thermal radiation through a novel thermal barrier coating topcoat focused on reducing radiative heat transport to the super-alloy substrate. The radiation has been modeled with a finite-difference-time-domain approach to gather a broadband response across the target wavelength range. A range of topcoat morphologies were studied numerically, amounting to ≈ 8500 core hours, in search of an ideal structure that minimizes the radiation throughput to the substrate. The study found a strong angle dependency of reflectance with varying pore morphologies. The analysis done in this first of its kind study on the morphology dependence of reflectance in plasma-sprayed alumina coatings is expected to lay the foundation for future research, leading to a more accurate understanding of the mixed modes of heat transfer phenomenon in the turbine environment and higher turbine inlet temperatures.
Numerical and Experimental Investigations on the Leakage Flow Characteristics and Temperature Distributions of Brush Seals
Authors: Song Pengfei , Ma Dengqian , Li Zhigang , Li Jun 
Published: September 2023

Abstract
Investigation on leakage flow and heat transfer characteristics in the bristle pack attaches significant importance to performance enhancement of brush seals. The experimental leakage flow rates were obtained for brush seals with two alternative backing plate configurations at pressure ratio (Rp) up to 2.8 and rotating speed (n) up to 3000 r/min. The leakage characteristics of tested seals were simulated using the RANS equation coupled with porous medium model solutions. The frictional heat effect and heat transfer characteristics of the two brush seals are investigated by means of the porous medium model coupled with the FEA. The calculated leakage flow rates are consistent with the experimental results. The leakage of the two brush seals increases linearly with the increase of Rp and decreases slightly with the increase of n. There will be the blow-down effect in brush seals with the increase of Rp, resulting in bristles extending to the rotating shaft, which slows down the trend of leakage increases with the Rp. The existence of the pressure relief groove can effectively alleviate the hysteresis effect but increase the leakage of brush seals in high pressure drop. The increase in rotating speed can also weaken the hysteresis of brush seals. The aerodynamic force, frictional force and frictional heat flux of two brush seals were calculated according to the experimental conditions. The temperature distribution of two kinds of brush seals were analyzed and discussed. It occurs the stiffening effect in bristles with the existence of pressure drop, which causes a significant increase in the friction between the bristles and the shaft. The friction heat flux increases approximately linearly with the increase of Rp and n, which makes the temperature of the bristles tip increase significantly, but the leakage air can take away part of the friction heat.
Wind Tunnel Experimental Study of the Effects of Blade Number on the Performance and Starting Behavior of a Low Tip-Speed Ratio and Micro-Scale Wind Turbine at Fixed Blade Geometry
Authors: Bourhis Martin , Zhang Shuo , Pereira Michael , Ravelet Florent 
Published: September 2023

Abstract
The effects of the number of blades on the efficiency and starting behavior of low tip-speed ratio micro-scale wind turbines are controversial. In contrast to modern 3-bladed fast large-scale horizontal axis wind turbines, these runners are multi-bladed to increase torque and to perform efficiently in low wind speed conditions. While an optimal number of blades for large-scale wind turbines has been established, it is still under consideration for small wind energy harvesters. The aim of this research is to examine the influence of the number of blades, while maintaining a constant blade chord length, on the power and torque coefficients of micro-scale wind turbines that are specifically designed to work at low tip-speed ratio. Seven 200 mm high-solidity wind turbines with a number of blades varying from 4 to 16 were designed, manufactured, and tested in a wind tunnel to collect the full power and torque coefficients vs. tip-speed ratio characteristics. We found that turbines with a large number of blades are more efficient in low wind speed conditions and have a lower cut-in wind speed than turbines with fewer blades. The experimental results emphasize the existence of an optimal range of blade numbers for our specific blade geometry, between 12 and 14 blades, that decreases the cut-in wind speed while maximizing the power coefficient. Furthermore, we observed that the performance curves of the wind turbines change as the number of blades increases, emphasizing the existence of blade interactions that alter blade aerodynamic properties. In addition, this experimental study provides some guidelines for the development of efficient micro wind energy harvesters.