bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of the Dynamical Behaviour of Hydrogen Combustors With Recurrence Quantification Analysis (RQA)
Authors: Alshahrani Ali , Talibi Midhat , Ezenwajiaku Chinonso , Beita Jadeed , Picciani Mark , Balachandran Ramanarayanan , Ducci Andrea 
Published: September 2023

Abstract
Hydrogen has immense potential as a future energy vector for power and propulsion applications. However there are several challenges, including flame stability, flashback and emissions, that impede its widespread use in modern energy systems. Hydrogen systems are required to be operated at fuel-lean conditions to avoid high NOx emissions and flashback issues, however lean operation makes systems more susceptible to thermoacoustic instabilities and lean blow-off (LBO). Understanding these dynamical behaviours is key to develop robust operational strategies.
Recurrence Quantification Analysis (RQA) is an effective tool to study nonlinear dynamics, and has been applied in this study to characterise hydrogen flame behaviour in industry-relevant laboratory-scale combustion systems. RQA was conducted on two different configurations — hydrogen lean direct injection (LDI) combustor and a swirl-stabilised combustor operated on methane-hydrogen blends. RQA was carried out on time-resolved data of (i) pressure measurements in the combustor and (ii) integrated OH* chemiluminescence signals. These commonly used measurements in combustion diagnostics were selected to develop a tool which can be applied easily to other industrial systems.
The effect of H2 blend, bulk velocity, and global equivalence ratio (ϕg) were investigated in this study, and four quantifiable parameters such as Shannon entropy, recurrence rate, determinism, and laminarity were extracted from the RQA, to determine different dynamical behaviours — stable, intermittent, and limit-cycle. High values of Shannon entropy and recurrence rate indicated stable conditions for the swirl-stabilised combustor, while a combination of Shannon entropy and determinism were found to best capture the hydrogen flame dynamics in the LDI combustor. The outcome of this work will allow development of efficient predictive tools for nonlinear data analysis.
Stabilization and Dynamics of Pure Hydrogen Swirling Flames Using Cross-Flow Injection
Authors: Vaysse Nicolas , Durox Daniel , Vicquelin Ronan , Candel Sébastien , Renaud Antoine 
Published: September 2023

Abstract
Hydrogen combustion is currently being considered as a possible means of decarbonization of power generation and air transportation. However, hydrogen raises difficult issues including that of NOx emissions linked to the high flame temperature and that of flashback caused by its high burning velocity. Innovative injection schemes are required allowing operation under lean conditions by enhancing mixing to avoid hotspots. In addition, the flame needs to be stabilized at a distance from solid boundaries to reduce thermal loads and should offer a low sensitivity to disturbances and instability. These issues are investigated with systematic experiments carried out in a single injector laboratory-scale combustor operating at atmospheric pressure, a configuration that was already used to examine the dynamics of spray flames. The atomizer is replaced by a special unit (CFI-X) that allows gaseous hydrogen injection in crossflow and mixing with the air stream set in rotation by a radial swirler. The flame behavior formed by this device is examined as a function of thermal power and global equivalence ratio. The injection head recess is also varied to change the level of mixing in the system and see how it influences thermo-acoustic instabilities. Flame structures visualized through OH* light emission images are used to classify the various flame patterns and distinguish domains where the flame is detached from the injector outlet. Variations of the injection head recess with respect to the outlet, swirl number and chamber length provide a comprehensive view of the operating regimes. It is found that the flames remain attached to the injector at low power and that detached flames are obtained in the high-power range. Dynamical phenomena leading to oscillations coupled by longitudinal chamber modes are observed in an intermediate thermal power range. The corresponding data are interpreted with a stability analysis that defines instability bands for the product of a time delay by the frequency of oscillation. It is found that unstable flames belong to the first of these bands. It is also observed that detached flames that are the most interesting in terms of thermal loads and mixing may also belong to the band of instability but do not give rise to oscillations and are therefore less sensitive to instability.
Is Blue Hydrogen a Better Alternative Than Post-Combustion Carbon Capture for Combined Cycle Gas Turbines? A Thermodynamic Point of View
Authors: Mendoza Morales Maria José , Verhaeghe Antoine , Bricteux Laurent , Blondeau Julien , De Paepe Ward 
Published: September 2023

Abstract
Today, the impact of global warming is more tangible than ever and every sector of society needs to engage in a low-carbon plan of action. For the last few years, increasing the share of variable renewable energy (VRE) has been the strategy of the energy sector to cut CO2 emissions. It requires the energy system to enhance its flexibility, voltage and frequency control, and firm capacity. To maintain the desired stability, combined cycle gas turbine (CCGT) plants come as the ideal candidates. However, if natural gas (NG) remains the primary fuel, the gas turbines (GT) will not comply with carbon emission limits in the future. Decarbonization must, therefore, be implemented in CCGTs. Original equipment manufacturers (OEM) are turning toward hydrogen-fueled GTs. Nevertheless, the production of H2 remains a challenge. In the long run, with a surplus of renewables and the development of more powerful electrolyzers, green or zero-carbon hydrogen could be achievable on a large scale. For the moment, the most mature low-carbon method is steam methane reforming (SMR) combined with carbon capture (CC), producing the so-called blue-H2. Alternatively, post-combustion CC presents another low-carbon solution for CCGTs. However, there is quite some debate is in the literature on the most effective pathway toward CCGT decarbonization. Using multiple Aspen Plus models of an HA-class GT combined with a three-level pressure heat recovery steam generator (HRSG), a CC unit, and an SMR process, the study presented in this paper seeks to assess the performance of both solutions. Simulation results show that for the blue-H2 scenario, the production of blue-H2 has an energy penalty of 24% on the CCGT. On the other hand, post-combustion CC implies an energy penalty of 10%, making the CC-only case the most efficient pathway under the studied conditions.
Flow Control of Turbine Vane Aerodynamics for Gas Turbine Operability
Authors: Dhyani Priyank A. , Jacobs Gustaaf B. , Burnes Dan , Ferguson Tyson 
Published: September 2023

Abstract
An active control of the flow in a turbine is investigated with the objective of an optimal throughflow mass reduction. An array of jets placed at the suction side of a nozzle vane is intended to enhance the effective camber of the vane, thereby reducing the throat area and corresponding throughflow mass. The effect of the jet array’s location is studied parametrically. The jet array’s configuration is also investigated by spatially perturbing the array with harmonic modes. Steady-state nozzle flow simulations at engine conditions are conducted with ANSYS CFX. The injector jet flows are modeled through source points. The jet flow normal to the vane surface leads to a recirculation region that displaces the inviscid flow outside of the viscous, near-wall region. For a jet location upstream of 37% of the chord length, the recirculation region reattaches downstream on the nozzle vane. For a more downstream array location, the flow separates globally. The throat area and throughflow mass reduction is larger for locations near the throat, but relative to the losses measured through the nozzle loss coefficient, the upstream jet array location is more effective and preferred. A jet array placed at the pressure side has an effect similar to a Gurney flap and modifies the Kutta condition. A jet array that is spatially perturbed with a single mode such that the array’s midspan location is more upstream as compared to the location near the end-walls, homogenizes the flow effect of the jet array, i.e., the recirculation region is more uniform.
Role of Turbulence in Modifying the Coherent Heat Release Response of Acoustically Excited Rod-Stabilized Flames
Authors: Karmarkar Ashwini , O’Connor Jacqueline 
Published: September 2023

Abstract
Modern power generation gas turbine engines operate in primarily fuel-lean conditions in order to mitigate harmful emissions. Lean combustion systems, however, are susceptible to combustion instabilities, which arise from a resonant coupling between coherent oscillations in the unsteady heat release rate and the acoustic modes of the combustor. The occurrence of combustion instabilities can severely limit engine performance and operability. To design effective instability control mechanisms, it is critical to understand the response of flames to coherent fluctuations in the velocity and pressure fields of the flow. In addition to coherent oscillations, combustor flow fields also experience high levels of perturbations arising from turbulence, which can significantly alter the flow and flame dynamics. In this work, we study the coherent heat release response of a rod-stabilized flame subjected to longitudinal acoustic forcing at two levels of in-flow turbulence. We systematically vary the amplitude of acoustic excitation at two frequencies — the natural frequency of vortex shedding and its first harmonic — at both turbulence levels. Our results show that the amplitude of the coherent heat release response is strongly dependent on the turbulence intensity. Additionally, the impact of turbulence on the coherent heat release response is a function of the acoustic forcing frequency. These results provide insight into the interaction between coherent and turbulent motions in the flow and their impact on unsteady heat release oscillations in gas turbine combustors.
A Piston Theory-Based Aeroelastic Stability Prediction Toolbox for Radial Turbomachinery
Authors: Iskandar Vincent , Fellows David W. , Bodony Daniel J. , Kang Sang-Guk , Pope Aaron J. , Kweon Chol-Bum 
Published: September 2023

Abstract
Aircraft intermittent combustion engines often incorporate turbochargers adapted from ground-based applications to improve their efficiency and performance. These turbochargers operate at off-design conditions and experience blade failures brought on by aerodynamically-induced blade vibrations. A previously-developed reduced-order model (ROM) leveraging piston theory to compute the stability of general fluid-structural configurations is first presented and summarized. The ROM has been applied to the high-pressure turbine of a dual-stage turbocharger and the results are reviewed as a baseline for new predictions considered in this work. For each operating condition that is investigated, a computational fluid dynamic (CFD) simulation must be performed to inform the fluid loading predicted by piston theory. Interpolation-based approaches are considered to minimize the numerical expense associated with this requirement. The Gaussian-based Kriging interpolation method is presented and explored. The method provides more accurate estimates for the non-linear behavior of the quantities of interest. Kriging also estimates uncertainty and provides confidence levels as part of the interpolation process. A graphical user interface (GUI) that automates the ROM prediction is presented. The GUI presents a rapid means to alter the turbomachine of interest, predict the aeroelastic response associated with a user-specified flight condition and quantify the uncertainty associated with the prediction.
Accounting for Firing Temperature in Combustion Tuning Activities
Authors: Angello Leonard , Perullo Christopher , Nicholson Craig , Harper Jim , Noble David 
Published: September 2023

Abstract
As gas turbines are operated and maintained, it is key to understand engine firing temperatures at cyclical and variable load operations, and more specifically, the tradeoff between engine performance, repair costs and reliability. It is crucial to ensure performance is maintained without sacrificing the life of critical parts.
OEMs traditionally have not provided much information about how tuning activities can impact performance. The current practice of tuning to meet emissions and combustion dynamics, or pulsations, can directly impact output, efficiency, and hot gas path (HGP) component life. A good understanding how and when this can happen can empower users to ensure they get the best performance and understand tradeoffs between performance, operability, and emissions.
To better explain the concept of ‘tuning’, this paper discusses and provides basic tuning guidance common for all gas turbines regarding how tuning steps can impact gas turbine firing temperature, performance, and emissions tradeoffs. A three-step process is described for; 1) assessing if there is evidence of temperature control curve changes; 2) performing a cursory analysis using existing gas turbine instrumentation and operating data to see if there is potential impact on firing temperature / turbine inlet temperature; and 3) examining for evidence of temperature change, whereby a means to analyze time series data using a physics-based model (EPRI gas turbine digital twin) to estimate delta changes in firing temperature pre and post outage is discussed. This process uses software tools available to the authors but is applicable to any trusted analysis toolset.
The paper aims to enhance industry understanding of what is completed during combustion tuning; it provides information about tuning activities impact on gas turbine performance to connect the dots between tuning and performance; and it describes how to conduct a simplified digital twin heat balance analysis to better quantify these impacts.
Turbine Operation and Measurement at DLRs Next Generation Turbine Test Facility
Authors: Pahs Andreas , Söhngen Anna-Samira , König Franz-Xaver , Wolf Torsten 
Published: September 2023

Abstract
Test facilities are important to validate new developments before bringing them into aero engines. The challenge is to have a deep understanding of the individual facility to be able to state measurement uncertainties, boundary conditions and stability to ensure high quality data which allow for comparison with predictions mostly done by simulations. Especially in today’s environment with the big challenge to bring disruptive technologies into service to meet the climate goals.
One large test facility is the Next Generation Turbine test facility (NG-Turb) situated at the German Aerospace Center in Göttingen. Together with Rolls-Royce Deutschland a turbine test rig with the option to use a combustor simulator was operated.
The turbine rig was designed as TRL 6 technology demonstrator with representative cooling scheme, realistic Mach and Reynolds number to determine the turbine characteristics like capacity and efficiency but also to get insight into local flow phenomena. A necessity is the determination of all boundary conditions with mass flow rate, total temperature and total pressure. These must be deduced from different measurements but they are discrete in place and time. A major tool to determine the flow conditions are pneumatic probes which need to be traversed to cover a minimum number of positions for averaging. During that time the operation point of the turbine must be kept as constant as possible. This paper presents the operation of the test rig within the facility including reached stability of operation conditions and thermal behaviour of facility, test rig and flow characteristics.
It is shown that very good stability of boundary conditions is reached but that there are also challenges mainly belonging to thermal gradients which are always present. By improving the instrumentation thermal gradients are resolved and can be taken into account when evaluating the gained turbine characteristics.
Damping Prediction Method for Asynchronous Vibration Modes and Verification by Electromagnetic Excitation for Full Scale Turbine Blade
Authors: Goto Toshiro , Watanabe Toshio , Baba Takeo , Momma Kazuhiro , Miyajima Keiichiro 
Published: September 2023

Abstract
The blades at the end stage of low-pressure turbine (LP-End) become thinner and longer to increase the efficiency and power of steam turbines even under severe conditions. Integral shrouded blades are often used in the low-pressure turbine to increase blade stiffness and get frictional damping to reduce the blade vibration. It is important to predict the frictional damping characteristics of such shrouded blades analytically during the design phase, and many analytical methods have been vigorously proposed.
However, the behavior of the friction damping is complex due to nonlinearities such as contact and sliding, it is difficult to make a high-fidelity model to express the friction. For example, it is important to consider micro-slip phenomena, to initiate sliding due to small excitation force in localized areas, and formulating the contact stiffness. In this paper, with the aim of incorporating damping prediction into the design process, reasonable micro-slip model was developed by predicting the contact conditions during operation in advance, and calculating the damping considering the contact areas of shroud and stub, as well as the distribution of contact forces.
And then, full-scale testing of turbine blades with the electromagnetic excitation system was conducted to validate the analytical method, and vibratory stress and damping of the blades were measured by strain gauges in the test facility. As the result, it was confirmed that the analytical predictions matched well with the measured damping of the high nodal diameter (ND) of the 1st mode by asynchronous excitation.
Short Ducted Fan Diffusers With Integral Splitter Blades
Authors: Hine Rory D. , Farman Judith R. , Grimshaw Sam D. , Taylor James V. 
Published: September 2023

Abstract
To maximise the range of vertical take-off and landing (VTOL) aircraft, the hover efficiency of ducted fan propulsors should be optimised. Diffusers at the outlet of ducted fans increase thrust, for a given power input, by converting otherwise wasted kinetic energy into a static pressure rise. The weight, and therefore length, of diffusers must be minimised to maximise the net thrust added. However, reducing length increases the adverse, axial pressure gradient which increases flow separation and stagnation pressure losses. In this paper, circumferential splitter blades are used to control loading distributions and reduce the size of separations by modifying pressure gradients. The aim is to increase the pressure recovered by short diffusers.
Using 3D computational fluid dynamics (CFD) simulations and pattern search optimisation, the performance and geometric trends of optimised diffusers are mapped as non-dimensional length (L/h) and splitter count (Ns) vary. Two different pressure maximising strategies are identified for diffusers with two splitters (Ns = 2). The first minimises stagnation pressure loss by positioning a splitter near to the hub to inhibit endwall separation. The second maximises the pressure recovered through diffusion by modifying the loading distribution between splitter divided sub-passages. These strategies guide the development of short diffusers for different operational requirements.
To validate simulations, an experimental rig is used to study the inlet and outlet flow fields of short, optimised, Ns = 0 and Ns = 2 diffusers. The experimentally measured stagnation pressure loss suffered by the optimised Ns = 2 diffuser is half that of the Ns = 0 design. This is primarily due to the alleviation of casing endwall separations. Flow mechanisms are identified using CFD simulated limiting surface streamlines and experimental flow visualisation.
Development and Evaluation of Generic Test Pieces for Creep Property Assessment of Laser Powder Bed Fusion Components
Authors: Megahed Sandra , Krämer Karl Michael , Heinze Christoph , Konterman Christian , Udoh Annett , Weihe Stefan , Oechsner Matthias 
Published: September 2023

Abstract
Metal Laser Powder Bed Fusion (PBF-LB/M) allows for high degrees of design freedom and the manufacture of high temperature Ni-based materials, such as IN738LC. The PBF-LB/M microstructure is dependent on several factors, including process parameters, component geometry, build orientation and post-processing steps (e.g. heat treatment). The correlation between the resulting microstructure and these parameters is material specific and not yet fully understood.
In this study, the development of a Specimen Extraction Cube (SEC), based on a generic component with design aspects related to turbomachinery applications, is presented. The SEC allows for the extraction of three samples, one for each of the build orientations: 0° (perpendicular to build direction), 45° (diagonal) and 90° (parallel to build direction).
Specimens extracted from the SEC are mechanically tested and compared to witness samples manufactured in 0°, 45° and 90° build orientation. Particular focus is placed on correlating measured properties and their variations with heat treated microstructures. Creep testing was performed using 240 MPa and a temperature of 850 °C. Microstructural differences and hence differences in mechanical properties are found in extracted and witness samples.
A Computationally Efficient Method for the Thermo-Structural Analysis of a Turbocharger Turbine Wheel Under Engine Transient Operation
Authors: Catalani Iacopo , Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Pini Nicola , Mosciaro Luigi , Mattiello Daniele , Rabbolini Silvio , Hoffer Pierre-Alain 
Published: September 2023

Abstract
The accurate evaluation of thermally-induced stresses is of particular importance for life-cycle analysis of modern turbochargers. Conjugated heat-transfer (CHT), steady-state calculations represent the state-of-the-art, whose temperature distribution is usually imported into a structural solver as a thermal load for carrying out thermo-structural analyses. In the case of transient analyses, however, issues arise. Indeed, due to the different timescales of convective and conductive heat-transfer mechanisms, unsteady CHT simulations are burdened by high computational costs. Moreover, in the specific case of turbocharged engines, the timescales of engine load transients and turbocharger response may differ by a factor of up to 105.
The present study proposes an approach for carrying out transient thermo-structural analyses of the solid domain only, characterized by a physical time in the order of 101 s, without the need for unsteady fluid flow calculations, which would imply the use of a solver timestep in the order of 10−5 s. In the proposed methodology, the effects of the fluid flow in the heat-transfer process are modelled by imposing adequate boundary conditions to wet surfaces of the solid domain with minimum computational effort. Indeed, by performing two steady-state CHT calculations and one steady-state computational fluid dynamics (CFD) calculation, time-dependent boundary conditions can be derived in terms of convective heat transfer coefficient and near-wall fluid temperature. The case study used for model development is a high-performance turbocharger turbine for automotive applications, responding to engine load transients of tenths of seconds. Initially, steady-state CFD and CHT models of the turbine stage are validated against experimental data. Then, transient analyses on the turbine wheel are carried out and their results are imported as thermal loads into an unsteady structural solver, allowing for accurate transient thermo-structural analyses at sustainable computational cost.