bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamical Systems Characterisation and Reduced Order Modelling of Thermoacoustics in a Lean Direct Injection (LDI) Hydrogen Combustor
Authors: Dilip Kumar Ankit , Ezenwajiaku Chinonso , Balachandran Ramanarayanan , Ducci Andrea , Talibi Midhat , Massey James C. , Swaminathan Nedunchezhian 
Published: August 2024

Abstract
Hydrogen is a promising zero-carbon fuel for decarbonised energy and transportation sectors. While carbon emission is not a concern for hydrogen combustion, its higher adiabatic flame temperature poses challenges of mitigating thermal NOx emissions. The wide flammability limits of hydrogen allow a fuel-lean operation, which can reduce NOx emissions. However, lean operation makes the combustion chamber susceptible to thermoacoustic oscillations. In this study, the thermoacoustic instabilities of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor are characterised using dynamical systems theory. The combustor was operated at a range of bulk velocities (30–90 m/s) and equivalence ratios (0.2–0.6), and time-resolved pressure oscillations and integrated OH* chemi-luminescence measurements were taken. The thermoacoustic system reveals a variety of dynamical states in pressure such as period-1 Limit Cycle Oscillation (LCO) with a single characteristic frequency, period-2 LCO with two characteristic frequencies, intermittent, quasi-periodic and chaotic states as either bulk velocity or equivalence ratio is varied. At a bulk velocity of 30 m/s, as the equivalence ratio is gradually decreased from 0.6 to 0.2, the dynamical behaviour follows a sequence from an intermittent state to a period-1 LCO, then to a quasi-periodic state, and eventually reaches a chaotic state. As the equivalence ratio is decreased for a bulk velocity of 60 m/s, the pressure oscillations evolve from a period-2 LCO to quasi-periodic state before flame blows off. The emergence of period-2 and quasi-periodic states indicates the presence of strong non-linear interactions among the cavity acoustic modes. These modes and their spatial behaviour are investigated using a reduced order model which solves the 3D inhomogeneous Helmholtz equation with an n-tau flame model. The analyses show that the period-2 and quasi-periodic states can arise due to the interaction between the plenum and combustion chamber modes indicating that hydrogen flames may excite a wide range of cavity acoustic modes.
Dynamic Characteristics of the Tip Clearance Flow Based on the Leakage Flow Model
Authors: Lin Shiyan , Li Ruiyu , Gao Limin 
Published: August 2024

Abstract
Leakage flow in the tip region significantly affects the turbomachinery performance, such as the efficiency, aerodynamic stability and noise. An accurate and in-depth understanding of the dynamic characteristics of leakage flow is the premise of the flow mechanism analysis and flow control. A simplified three-dimensional multi-wall leakage flow model was employed, which characterizes the unique geometric feature of multiple walls with a tip narrow gap and aerodynamic characteristics, i.e., the shear layer between confined jet and mainstream and the tip leakage vortex (TLV). Subsequently, the wall-adapt local eddy-viscosity large-eddy (WALE LES) simulation was used for the simulation. Based on the Liutex and Spectral proper orthogonal decomposition (SPOD) method, the flow structure, main fluctuation structure and unsteady source of the leakage flow were studied. The results shows that there are TLV, secondary tip leakage vortex (STLV) and induced vortex (IV) in the tip field driven only by the leakage flow. The main fluctuation contains the shake of the TLV’s core, breakdown of the IV and generation of the STLV. Furthermore, the STLV has a crucial influence on the development of the vortex structure and unsteady characteristic of the tip field. Kelvin-Helmholtz instability induced by the strong shear layer under the influence of small disturbances is at the bottom of the explosion. However, this cannot be resolved by the Reynolds-averaged Navier-Stokes (RANS) method.
Experimental Investigations on Carbon Segmented Seals With Smooth and Pocketed Pads
Authors: Jolly Pascal , Arghir Mihai , Kasahara Hidetoshi , Kimura Wataru 
Published: August 2024

Abstract
The present paper introduces experimental results for radial segmented seals operating at high rotating speed. These seals are made of three or more interlocking, carbon-graphite segments, in permanent contact with the rotor while also accommodating its dynamic displacements. Currently, many efforts are made to model these behaviors and for obtaining accurate leakage flow rate and friction torque predictions.
A novel test rig fitted with a casing for measuring leakage and friction torque produced by two carbon segmented seals was developed. The tested seals were composed of three segments. Two types of segmented seals were tested: two seals with flat pads and one seal with pocketed pads. The seals were installed two by two in a casing and were simultaneously tested in a back to back arrangement. The process fluid was air, with a maximum inlet pressure of 0.3MPa, while it was set to ambient at the outlet. The rotor diameter was 100mm with a maximum rotating speed of 24,000rpm. The main measurements were the inlet mass flowrate and friction torque produced by the two seals.
Results show that the seal with pocketed pads produced higher leakage rates but lower friction torque compared to the smooth pads. This suggests that the seal with pocketed pads operated with segments completely lifted from the rotor surface. Mass flow rates measurements during run-up/coast-down tests allowed to highlight a hysteresis effect, which could be the consequence segment tilt. The experimental results could also be useful to validate theoretical models.
Relationship Between Wavy Liquid Film Dynamics and Droplet Formation From Trailing Edge
Authors: Kamada Yoshiaki , Murakami Keito , Wang Zhenying , Inoue Chihiro , Senoo Shigeki 
Published: August 2024

Abstract
Erosion of steam turbine blades due to coarse droplet impingement is a serious problem. The physical relationship is still elusive between the dynamics of wavy liquid film on a wall and the droplet dispersion from the trailing edge. In this study, we experimentally and theoretically investigate the liquid film subjected to the turbulent airflow and following fragmentation process under well-controlled flow conditions, where the airflow velocity is up to 100 m/s, and initial liquid film velocity is 0.06 and 0.10 m/s, and trailing edge thicknesses are 0.5, 1.0, and 2.0 mm. By applying the developed PLIF based method with no use of artificial threshold of brightness, we quantify the film thickness and interfacial friction factor. As the airflow velocity increases, the liquid film instability promotes and the interfacial friction factor increases, much exceeding the Blasius correlation. When the liquid film reaches the trailing edge, several liquid columns extend by the Rayleigh-Taylor instability. We identify that the interfacial friction factor to accelerate the ligament corresponds to the Blasius correlation, distinct from the one on the wavy liquid film upstream. Incorporating the identified two interfacial friction factors, we successfully formulate the diameter of ligament as the characteristic lengthscale of the spreading droplet downstream. Derived formulation for the droplet statistics is well validated by the experimental results of mean and maximum diameters and size distribution.
Comparative Analysis of Total Pressure Measurement Techniques in Rotating Detonation Combustors
Authors: Wei Hongyi , Kayser Tim , Bach Eric , Paschereit Christian Oliver , Bohon Myles D. 
Published: August 2024

Abstract
Current total pressure measurement techniques in RDCs are based on different assumptions and therefore show different applicability for specific RDC operating conditions, and few studies have directly compared these techniques. Therefore, this study comprehensively tested three total pressure measurement techniques: the direct Kiel probe method, the Mach-corrected CTAP method, and the equivalent available pressure (EAP) method under different RDC geometries and mass flow rates, and compared them with their corresponding uncertainties considered. The results show that for all tests in this study, the EAP method shows the largest uncertainty range up to 24%, which is mainly contributed by the load cell calibration process, while the direct Kiel probe method has the lowest uncertainty range, which is consistently below 7%. These uncertainties were incorporated into the comparison between the three techniques via Gaussian process regression, showing that the direct Kiel probe method and the Mach-corrected CTAP method can present EAP-like total pressure. In particular, the total pressure of the SWCC and L modes measured by the three techniques is very comparable. This work shows that the comparability of total pressure techniques depends on the specific RDC environment, and provides the possibility to evaluate the RDC performance with the simplest implementation.
The Onset of Hydrodynamic Instability in Dual Orifice Atomizers
Authors: Kılıçgedik Hıdır Yankı 
Published: August 2024

Abstract
This paper deals with the numerical investigation of inner flow instability in pressure swirl atomizer with a “nozzle within a nozzle” configuration. It begins with an overview of the high fidelity hybrid RANS-LES approach for interface capturing of turbulent multiphase breakdown process. This was followed by a brief discussion on the underlying physical mechanism of the unstable mixing and the transition of this action to Kelvin Helmholtz waves. Three new practical guidelines for instability evaluation were brought to the attention of the readers; flux-based estimation for the time variation of cone angle, sheet deformation ratio and a mathematical analysis of stability based on the standard deviation of the time fluctuating flow characteristics.
The combination of these complementary methods can be used to accurately identify the onset of flow instability. Derived from simple theoretical foundations, these methods have the potential to provide practical benefits for the performance assessment of different injector configurations in industrial applications.
A Physics-Informed Neural Network Surrogate Model for Mistuned Bladed Disks Dynamics
Authors: Fan Yu , Fan Jiasen , Li Anlue , Wu Yaguang , Zhang Yuning , Song Zhiqiang 
Published: August 2024

Abstract
Background: The inevitable mistuning of a bladed disk breaks the cyclic symmetry of the structure and can cause vibration localization and amplitude magnification, thereby seriously reducing the structural reliability. Although numerical simulations based on high-fidelity finite element models can precisely calculate the response under some specific mistuning patterns, repeated calculations of random mistuning cases still bring a significant computational burden, even with ad-hoc reduced-order modeling technologies.
Objective: In this work, we aim to capture the dynamics of randomly mistuned bladed disks using data-driven surrogate models.
Methods: To do that, a physics-informed surrogate model of a designed structural neural network (DS) is proposed, where a “shift” feature from the cyclic symmetry in physics is taken into account for data augmentation. The finite element model of a dummy bladed disk with blade stiffness mistuning is established and taken as an example to test the effectiveness of the surrogate model. Under different training set sizes and excited modes, the performance of the proposed model is compared systematically with a fully connected structural neural network model (FC) and a state-of-the-art deep neural network framework (MS-DNN).
Results: The DS model can accurately predict blade displacement for blade-dominated modes with only 600 training data. The R2 value of the displacement response amplitude reaches 0.99956, and the error of the amplitude magnification factor is only 0.68%. The DS model converges faster and has higher prediction accuracy than the FC model. The DS model is superior to the MS-DNN model concerning the generalization ability.
Study on the Impingement Cooling Structure With the Characteristic of Low Flow Resistance
Authors: Li Changwei , Guo Tao , Liu Cunliang , Zhu Huiren , Li Guodong , Wang Xinyu , Li Jiayu , Liu Shanjie 
Published: August 2024

Abstract
As an efficient cooling method, the impingement cooling in the mid-chord of the aero-engine turbine vane causes the jet to impact the target plate, resulting in a thin boundary layer near the stagnation point and high heat transfer, which other aeroengine internal cooling technologies cannot achieve. Adding pin fins to the target plate is a standard method to improve impingement cooling, but it reduces the coolant flow area in the impingement chamber to increase the flow resistance. This paper proposes a novel structure with low resistance characteristics by adding V-ribs to the target plate. The novel structures’ flow and heat transfer characteristics are studied through numerical simulations and experiments. The Reynolds Averaged Naiver-Stokes (RANS) model is adopted for the 3-D steady-state numerical simulation, and the shear stress transport (SST) k-ω turbulence model is used for closing the governing equations. The main conclusions are that the jet Reynolds number (Rej) and the flow-pitch of the impingement hole are critical factors that affect heat transfer, and the change in the jet-to-plate distance can significantly influence flow resistance. As the jet Reynolds number increases from 2000 to 15000, the average Nusselt number on the impingement target surface increases by a factor of 3.6. The flow coefficient at an impingement distance of 3 is 1.45 times that at an impingement distance of 1. The increase in the jet Reynolds number and the reduction in the flow-pitch of the impingement hole enhance the heat transfer on the target plate by increasing the impingement and wall jet velocities respectively, thereby enhancing the scouring effect. The decrease in pressure in the intake chamber and the corresponding decrease in the pressure gradient in the impingement chamber are the main reasons for the decrease in flow resistance caused by the enlargement of the jet-to-plate distance.
Experimental and Numerical Investigation of Heat Transfer in a Turbocharger Turbine in Consideration of a Diabatic Heat Shield
Authors: Gier Thomas-Sebastian , Luczynski Piotr , Wirsum Manfred 
Published: August 2024

Abstract
Thermal loads play a major role in determining a turbocharger turbine’s lifecycle. The turbine wheel in particular is subject to varying thermal loads, which induce inhomogeneous temperature distributions causing thermo-mechanical stress. In order to calculate these thermal loads the mechanisms governing the heat transfer inside a turbocharger turbine have to be known as precisely as possible. One of these mechanisms is heat transfer from the wheel backside through the heat shield into the bearing housing, which is commonly neglected. This paper aims to fill that gap by exploring the effect of heat transfer through the heat shield of a turbocharger using both experimental and numerical data.
As part of this investigation a brief summary of the experiments with an instrumented turbocharger is presented. These experiments subjected the turbine to several stationary load conditions ranging from minimum to maximum operating points for multiple rotational speeds. Hereby, temperatures in the stationary and rotating parts of the turbine were recorded.
Due to the complexity of the temperature field inside the turbine, experimental data alone does not offer a sufficiently detailed account of the occurring processes, because it is only recorded at discrete points. Therefore, a numerical model is presented, which encompasses both fluid and solid parts of the turbine to enable CHT simulations to be conducted. These simulations allow for a more complete analysis of the heat transfer between turbine wheel and bearing housing due to the availability of data at all locations. To verify the correctness of the numerical results the model is first validated using the experimental data and shown to be a good match. It is then used to analyze heat transfer mechanisms between the backside of the turbine wheel, heat shield and bearing housing, as well as their impact on the temperature field of the turbine wheel.
Challenges in the Production of Fuel Cells for Aviation
Authors: Sperling Patrick , Horstkotte Rainer , Sommer Jan , Gierlings Sascha , Janssen Henning , Herrig Tim , Bergs Thomas , Brecher Christian 
Published: August 2024

Abstract
The influence of increasing resource scarcity and climate change has a significant impact on aviation. Therefore, the European Commission has set ambitious goals with a 75 % reduction in CO2 and a 90 % reduction in NOX as part of the Flightpath 2050 vision. Achieving these goals requires the use of disruptive technologies in aviation, especially in propulsion. In addition to the use of Sustainable Aviation Fuel (SAF), the use of hydrogen is a promising alternative. There is the possibility of using a fuel cell which acts as an energy converter and powers the primary electric drives, offering the potential to fly emission-free, especially for short- and medium-range flights.
However, successful integration of the fuel cell into the aircraft’s powertrain requires a significantly increased gravimetric power density compared to the status quo. Furthermore, the fuel cell and the entire manufacturing process chain must fulfill the stringent safety requirements of aviation. Therefore, the bipolar plate and, respectively, its production process are key elements for the fuel cell.
This paper describes how to establish a basis for the production of the bipolar plate in accordance with aviation requirements. For this purpose, the process chain is explained step by step and for each process step different technology alternatives and corresponding challenges are identified. Finally, an aggregated view of the holistic process chain is given.
Foreign Object Damage of Environmental Barrier Coatings Subjected to CMAS Attack
Authors: Hoffman Leland , Stokes Jamesa L. , Setlock John 
Published: August 2024

Abstract
Foreign object damage (FOD) and attack by calcium magnesium aluminosilicates (CMAS) have been identified as two key damage and failure mechanisms in environmental barrier coatings (EBCs), which are being developed as an enabling technology for silicon carbide (SiC) based composites in gas turbine engines. CMAS exposure at elevated temperatures has been shown to cause premature failure in ytterbium disilicate (Yb2Si2O7) based EBCs. Previously, the effects of foreign object damage were studied on NASA’s Yb2Si2O7-based EBC deposited on SiC. This study aims to understand the synergistic effects of CMAS attack and FOD on the same EBC system. CMAS was loaded onto the EBC at either 2 mg/cm2 or 4 mg/cm2 prior to being fully reacted for 4 hours in a 1316°C furnace. Samples were then impacted at room temperature using a 1.59 mm hardened steel ball with projectile velocities of 50–100 m/s. The impact damage was characterized by depth of the impact crater and length of the EBC delamination as determined by optical profilometry and scanning electron microscopy (SEM) of the cross-sectioned samples. The results of the samples subjected to CMAS attack were then compared to that of the previous study on NASA’s baseline Yb2Si2O7-based EBC. A mechanical assessment of the coatings was also made. Vickers indentation was used to determine coating hardness as well as estimate indentation fracture toughness and nanoindentation was used to estimate the Young’s Modulus.
Effect of Ceramic Matrix Composites on the Thermal Efficiency of a Power Generation Turbine
Authors: Tayade Ashrit , Lynch Stephen 
Published: August 2024

Abstract
Ceramic Matrix Composites (CMCs) offer higher allowable temperatures and reduced weight, making them an attractive prospect for parts in the hot section of a gas turbine engine. As CMCs are increasingly adapted into aero and land-based engines, there is a need to quantify the performance increase based on potential for reduced cooling and increased firing temperatures. In this work, two static hot section components — the first stage turbine vane and the first stage turbine tip shroud (outer casing above the blade) — of a mid-sized power generation engine were modeled. Informed approximations about part geometry and cooling architectures were made to determine cooling requirements of each part. Thermal boundary conditions for the turbine tip shroud and turbine vane were generated as a function of coolant mass flow rate using data from literature and applied to a 2D finite element analysis of the parts to determine maximum temperatures for both metallic and ceramic materials. A gas turbine cycle model was developed to simulate the performance of a mid-sized power generation turbine, and used to determine increase in efficiency due to reduction in cooling requirement for the CMC part compared to a conventional metal superalloy-based part. Potential reduction in chargeable cooling seen for the tip shroud ring was between 0.09% and 0.4% of the compressor mass flow rate, which corresponds to an increase in thermal efficiency between 0.11% and 0.45%. A similar analysis of the turbine vane resulted in a cooling reduction of 10.71% at the maximum turbine entry temperature considered which corresponds to a 3.4% increase in thermal efficiency.
Performance and Control of the Primary Heat Exchanger in a Closed-Loop sCO2 Brayton Cycle With Solid Fuel Combustion
Authors: Schooff Brian , Roy Rajarshi , Smith Fletcher , Tree Daniel , Iverson Brian D. , Chiodo Andrew , Held Timothy J. , Miller Jason , Bowan Brett , Sedlacko Kyle , Johnson Michael , Montgomery Scott , Fry Andrew 
Published: August 2024

Abstract
The supercritical carbon dioxide (sCO2) Brayton cycle has been studied for a variety of heat sources as a replacement for the steam-Rankine cycle with higher thermal efficiency in power plants. The lack of a phase change in this cycle enhances the energy efficiency but also increases the likelihood of overheating of the heat exchanger tubes, especially when using solid fuels. The rapid sensible heating of the working fluid requires careful management of the temperature profile of the heat exchanger tubes inside the boiler. It is necessary to identify the system response of the controlling parameters of the system on the temperature profile of the primary heat exchanger (PHX) which can be used in the development of a model predictive controller (MPC) to manage the PHX surface temperature. A 1500 kWth solid fuel furnace (L1500) was retrofitted with a PHX and turbomachinery to investigate the use of solid fuel combustion with the sCO2 Brayton cycle. The PHX design requires limiting the PHX to a maximum surface temperature of 1089 K (1500 °F) and a maximum rate of change of 100 K/h. CFD modeling and operational data of the L1500 system showed that the firing rate, sCO2 flowrate, and refractory wall temperature significantly impact the temperature profile of the PHX. It is also expected that the amount of excess air will be a critical controlling parameter. Operational data showed that handling measurement noise will be vital to developing a predictive model of the heat transfer to the PHX.