bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation of Seismocardiogram-Derived Cardiac Time Intervals and Heart Rate Variability Metrics Across the Sternum
Authors: Mann Aysha , Rahman Mohammad Muntasir , Vanga Vineeth , Gamage Peshala Thibbotuwawa , Taebi Amirtahà 
Published: August 2024

Abstract
Cardiac time intervals (CTIs) are vital indicators of cardiac health and can be noninvasively assessed using a combination of electrocardiography (ECG) and seismocardiography (SCG), a method of capturing cardiac-induced chest vibrations via accelerometers. SCG signals can be measured from different chest locations. However, more investigations are needed to evaluate the impact of sensor placement on SCG-derived cardiac parameters. This study investigates the effect of accelerometer placement along the sternum on SCG-derived CTI estimations and heart rate variability (HRV) parameters. A semi-automated algorithm was developed to detect SCG fiducial points and seven CTIs from thirteen healthy individuals. Comparative analysis with manually selected peaks and gold-standard ECG was conducted to assess fiducial point detection accuracy. Results indicate the highest recall and precision in aortic valve opening (0.84–1.00 and 0.96–1.00, respectively) and mitral valve closure (0.77–1.00 and 0.93–1.00, respectively) detection. Aortic valve closure (0.43–1.00 and 0.61–1.00, respectively) and mitral valve opening (0.64–1.00 and 0.91–1.00, respectively) detection, although slightly less accurate due to signal intensity variations, demonstrated overall effectiveness compared to manually selected peaks. Furthermore, SCG-derived heart rates showed a high correlation coefficient (r &gt; 0.9) with the gold-standard ECG heart rates. Single-factor ANOVA revealed significant differences (p &lt; 0.05) in SCG-derived CTI estimations based on sensor locations on the sternum, highlighting the importance of sensor placement for accurate assessments.
Axial Flow Fan Performance in a Forced Draught Air-Cooled Heat Exchanger for a sCO2 Brayton Cycle
Authors: Boshoff Francois D. , van der Spuy Sybrand J. , Pretorius Johannes P. 
Published: August 2024

Abstract
An axial flow cooling fan has been designed for use in a concentrated solar power plant. The plant is based on a supercritical carbon dioxide (sCO2) Brayton cycle, and uses a forced draft air-cooled heat exchanger (ACHE) for cooling. The fan performance has been investigated using both computational fluid dynamics (CFD) and scaled fan tests.
This paper presents a CFD model that integrates the fan with the heat exchanger. The objective is to establish a foundation for similar models and to contribute to the development of efficient ACHE units designed for sCO2 power cycles. The finned-tube bundle is simplified, with a Porous Media Model representing the pressure drop through the bundle. Pressure inlet and -outlet boundary conditions are used, meaning the air flow rate is solved based on the fan and tube bundle interaction.
The flow rate predicted by the CFD model is 0.5% higher than the analytical prediction, and 3.6% lower than the design value, demonstrating that the assumptions used in the design procedure are reasonable. The plenum height is also found to affect the flow rate, with shorter plenums resulting in higher flow rates and fan efficiencies, and longer plenums resulting in more uniform cooling air flow.
Partially Cracked Ammonia Mixture Combustion in Gas Turbine Combustors
Authors: Gupta Sreenath , Weathers Timothy , Shahin Tristan , Gejji Rohan , Aithal Shashikant , Hosangadi Ashvin 
Published: August 2024

Abstract
Ammonia is gaining popularity for single fuel use in existing gas turbines, as it is carbonless, has higher hydrogen content per unit volume than liquid hydrogen, and facilitates easy storage and handling. However, the low flame speed of ammonia makes it prone to flame blow off and remains the chief concern for its use in power generation. Following previous studies that have shown improved combustion performance by partially cracking the fuel, in this computational study, efficacy of partially cracked ammonia as a replacement fuel for natural gas is evaluated.
A high-pressure optically accessible combustor operated at ∼10 bar pressure with non-vitiated heated air was used as the test platform. This combustor was equipped with a novel multi-fuel multi-tube micromixing injector (M3 injector). High resolution simulations of the flow fields both in the injector as well as the combustor were performed to understand the fuel mixing in the injector and in the inlet region of the combustor. These modeling results showed that the injector was highly effective for achieving mixture homogeneity at the entrance of the combustor for ammonia and natural gas injection, whereas, for hydrogen an earlier injection facilitating longer residence time would be beneficial. Also, these simulations show that while harnessing waste heat the ideal fuel dissociation fraction is between 0.4 and 0.55 for optimal operation.
Improving a Two-Equation Eddy-Viscosity Turbulence Model for High-Rayleigh-Number Natural-Convection Flows Using Machine Learning
Authors: Haghiri Ali , Xu Xiaowei , Sandberg Richard D. , Tanimoto Koichi , Oda Takuo 
Published: August 2024

Abstract
This study presents data-driven modelling of the Reynolds stress tensor and turbulent heat flux vector for improving unsteady RANS (Reynolds-averaged Navier Stokes) predictions of natural convection problems. While RANS-based calculations are cost-effective, conventional models fail to deliver the requisite predictive precision for high-Rayleigh-number practical engineering flows. To rectify this limitation, a gene-expression programming (GEP)-based machine-learning technique was employed to train novel models using a high-fidelity dataset from a vertical cylinder case with Ra = O(1013), which was generated using LES and validated against experimental data from Mitsubishi Heavy Industries (MHI). The newly developed data-driven closures for Reynolds stress and turbulent heat flux were then used to extend the realisable k-epsilon (RKE) turbulence model. The efficacy of these models was rigorously tested through a full a posteriori approach, involving URANS calculations with the newly constructed closures for the training case and two different testing cases. The results show that for cases with high Ra number (≥ 1011), the Nusselt number, temperature profiles, and velocity profiles exhibit significant enhancements due to the application of the GEP-based closures, initially developed using the Ra = O(1013) training case. However, for cases featuring lower Ra numbers, where standard RANS models already perform relatively well, the utilisation of the current data-driven closures becomes unnecessary, potentially even leading to reduced simulation accuracy. This investigation carries implications for cost reduction in the design process of thermal engineering applications involving high-Rayleigh-number natural convection flows.
A Practical Failure Approach of Burst Assessment of Aero Engine Disc
Authors: Yılmaz Okan Deniz , Savaş Cihan , Baldan Emre 
Published: August 2024

Abstract
The design of aero-engine disc is subjected to stringent regulations owing to their operation under high mechanical and thermal stresses. These structures must be designed as a fail-safe component with the aim of preventing incident. Regulatory authorities compel engine manufacturers to undergo spin-tests or coupon-tests on identical or similar discs to fulfill qualification and certification requirements. Spin-testing of aero-engine discs performs at increasing rotating speed, constant temperature and under vacuum conditions. However, these experiments are both costly and time-consuming.
The purpose of this paper is to present a practical failure approach aimed at replacing physical test facilities with simulations based on both implicit and explicit finite element analysis methods. Typically, burst calculations rely on the average hoop stress in axisymmetric regions. However, stress components in the axial and radial directions may exist in three-dimensional features. The model is employed to predict the burst speed, identify burst locations and role of stress concentration on the disc under varied operation conditions. In order to initiate damage accurately, considerations are given to factors such as crack driving force, plastic deformation, and stress triaxiality. Results obtained from both ANSYS and LS-DYNA solvers are utilized to ensure precise calculations of burst speed, location, and stress concentration factors. The findings of the structural integrity assessment of an aero-engine disc exhibit consistent agreement between each solver in term of crack propagation and the determination of critical speed.
A New Experimental Capability for Electric and Hybrid-Electric Propulsion and Thermal Management Research: The Surrey Aerothermal Test Facility (SATF)
Authors: Hussain Alishaan , Doherty John J. , Pekris Michael J. , Chew John W. , Hayden Paul 
Published: August 2024

Abstract
To support development of electric and hybrid-electric propulsion, the Surrey Aerothermal Test Facility (SATF) has been developed in recent years. The facility allows a powered model to be tested over an operating cycle, with measurement of steady state and transient effects. LabVIEW is used for facility and model control over extended test sequences and for synchronised data acquisition from multiple streams of data from different instrumentation. Novel measurement approaches have also been developed using the facility. These include use of embedded microphones to directly measure fan RPM, as subsequently used in the QinetiQ/Boeing/Surrey EMPAS project. Thrust performance has been investigated based on both direct force measurement and from integration of velocity measurements. IR sensors have been used to measure surface temperature variations on an electric motor, providing evidence of thermal soak-back. Heat flux sensors allow for the monitoring of thermal components and derivation of local heat transfer coefficients.
Use of the facility is highlighted through results presented from a series of Electric Ducted Fan (EDF) studies. An example modular EDF rig is described, which incorporates rotor and stator blade geometries designed using the MULTALL-OPEN turbomachinery design software and manufactured using low-cost 3D-print options.
Application of Interface Reduction Methods to Rotordynamic Casing Models
Authors: Paehr Martin , Panning-von Scheidt Lars 
Published: August 2024

Abstract
As the use of digital twins for the purpose of structural health monitoring increases, so does the demand for high-quality models. In the area of rotating machines, this means that the casing must also be taken into account. These are often geometrically complex assemblies that require the use of finite element models. The models are then reduced in size by established reduction methods like the Craig-Bampton reduction in order to keep the solution time, e.g. for a forced response analysis as low as possible. In case of nonlinear contact forces, e.g. friction in bolted joints, a secondary reduction step has to be applied. Here, three different interface reduction methods are investigated and used for a rotor-casing assembly including frictional damping. The necessary basics and terms are presented. The performance of the methods is evaluated for a linear model on substructure and assembly level and for a nonlinear model on the assembly level. The implementation of the interface reduction within the Harmonic Balance Method is presented and tested for different unbalance excitation cases.
A Rapid Test Facility for Transonic Compressors and Fans
Authors: Wang Tianhou , Taylor James V. , Miller Robert J. 
Published: August 2024

Abstract
This paper provides design recommendations for a rapid test facility for transonic compressors and fans, which aims to enable the testing of new geometries in two weeks at a cost of less than $10k. This compares to current industrial test facilities which typically take years and cost around $10M. The approach is important for its potential to unlock creativity allowing designers to ‘play’ at engine-representative conditions.
This paper is in two parts. The first part aims to physically enable rapid high-speed testing while preserving the key fluid dynamic mechanisms being studied. The complexity of a facility scales with its power input, driven by safety requirements and complex operations. A turboexpander-type subscale facility is designed to reduce the power by a factor of nine while achieving the full Mach number and a half of the full Reynolds number.
The second part aims to shorten the testing cycle time to under two weeks. It analyses the current testing process to identify the time-consuming parts and makes design changes to either eliminate or optimise each process.
The final test facility was demonstrated in a trial where an example rotor geometry with a tip Mach number of 1.2 was manufactured, built, and tested. The new geometry was tested in 2 weeks, incurring a marginal cost of less than $7k.
Accurate Modeling of the Flow Structures in the Gap Between Corotating Disks of a Tesla Turbine
Authors: Pahlavanzadeh Mohammadsadegh , Rusin Krzysztof , Wróblewski Włodzimierz 
Published: August 2024

Abstract
Momentum diffusion and kinetic energy transfer in turbomachinery have always been significant issues. These phenomena have a considerable effect on the performance of the bladeless Tesla turbine. Analyzing the flow inside the gap between the co-rotating disks of the Tesla turbine poses a challenge due to numerous factors, including sub-millimeter length scale, variation of flow cross-section, interactions of body forces arising from the rotation with the turbulence, interactions between the turbine’s inlet nozzles and rotor, and moving walls. Due to the mentioned reasons, the majority of the numerical research devoted to this problem diverges from the experimental data due to the limited accuracy of the implemented models. This research aims to study the flow in the domain that consists of one inlet nozzle and a part of one gap between the disks to reveal the complexity of the flow structures and their impact on the Tesla turbine performance. Large Eddy Simulation (LES) with the Smagorinsky subgrid scale model and k-ω SST turbulence model were employed to simulate the flow. The research compares the flow structure, flow parameters, and its impact on the performance of the system. The mesh strategy is also described since the LES requirements make this simulation computationally expensive and time-consuming. The overall benefit of this method is discussed.
Tribological Evaluation of Coatings for Air Foil Bearing Applications
Authors: Iakovakis Eleftherios , Aliasghari Sepideh , Bonello Philip , Matthews Allan , Burkinshaw Michael , Moore Simon 
Published: August 2024

Abstract
In the pursuit of environmentally friendly and sustainable transportation strategies, proton-exchange membrane fuel cells (PEM-FC) have emerged as a promising technology to decarbonise powertrains especially in heavy-duty vehicles. Oil-free bearings, the so-called Air Foil Bearings (AFBs), are crucial to the robust operation of the PEM-FC by preventing the contamination of the hydrogen fuel cell stack. However, during start-up and coast down of the PEM-FC, there is contact between the top foil of the AFB and the journal, which leads to high friction forces and durability concerns for the AFBs. The objective of this work is to identify the coating system that minimizes the friction forces for AFB applications. With this aim, tribological pin-on-disc tests were performed using coated Inconel discs and coated tool steel pins under room temperature conditions and at 150°C. Additionally, the development of a test rig to measure the tribological performance of coated AFBs under real life applications is discussed. In the pin-on-disc tests, the coated disc represented the top foil of the AFB while the coated pin represented the journal. Four solid lubricants were investigated for the discs, while two types of DLC coatings (monolithic and multilayer) were used for the pins. The worn surfaces have been investigated via microscopy and elemental analysis. The adhesion strength of the coatings was evaluated through indentation (VDI 3198) and scratch tests. The tribosystem of multilayer DLC against sulfur/molybdenum based solid lubricant coating afforded the lowest frictional response and friction stability compared to the other coating systems under evaluation.
Neural Network Application to Rotordynamic Predictions of an Overhung Flexible Rotor
Authors: Deiana Giulio , Vannini Giuseppe , Meazzini Giulia , Cangioli Francesco , Meli Enrico 
Published: August 2024

Abstract
This study focuses on pioneering regressive neural network models to predict lateral dynamics in a centrifugal compressor stage validation test bench. This tool is positioned as a critical resource to be used during the design of the centrifugal stage test, enabling test bench personnel to understand the rotordynamic behavior in terms of critical speeds and vibration amplitudes within the desired operating range. Addressing the demand for swift and manageable solutions for repeatable configurations within defined design parameters motivates this work. While Finite Element Method (FEM) analysis remains valuable, its time-intensive nature, particularly in model definition, drives the search for more time-efficient methods. Machine learning stands as an innovative, streamlined alternative for predicting lateral dynamics, differing from traditional approaches. The adoption of machine learning-based regressive neural networks marks a significant leap in analyzing centrifugal compressor lateral dynamics. This innovation not only boosts operational efficiency but also enhances accessibility and cost-effectiveness in the process.
Surge Detection of Centrifugal Compressor Using CFD Results
Authors: Shahriar Al , Wang Yintao , Yan Jin 
Published: August 2024

Abstract
In this study, a method has been proposed to generate surge lines based on the high-fidelity numerical simulation conducted for a refrigerant centrifugal compressor and later the results are compared against the experimental results. Surge, a violent flow instability at low mass flow rates, is often accompanied by severe detrimental effects including reduced efficiency, safety concerns, noise, and vibration on both the compressor itself and the overall system in which it operates. Conducting experiments for mapping a surge line often requires an extensive amount of time. In this paper, a surge line is mapped for a centrifugal compressor for a wide range of rotational speeds. The behavior of aerodynamically induced radial force and torque are used as the primary criteria for predicting the surge of the compressor. In this study, the pressure ratio and isentropic efficiency of the simulation results closely align with experimental results. Later, the radial displacement of the rotating shaft, a key indicator to identify surge, is obtained in the experiments for an oil-free magnetic bearing compressor. Finally, the surge line based on test data is used for evaluating the accuracy of the proposed method based on simulation results.
Application of Nonlinear Frequency Response Analysis for Windmilling
Authors: Kumar Devesh , Powell Don , Carlson David , Kumar J. S. , Cao Jianming 
Published: August 2024

Abstract
The current best practice across the aero industry is to model the windmilling event in a time-domain analysis. The alternative to time-domain methods is to use frequency response analysis which provides a great deal of information about the system response over the entire range of operation. However, the presence of non-linearities in the system makes it difficult to employ standard frequency response analysis techniques which are linear in nature. If the system contains mild-nonlinearities and the response of the system can be assumed to be periodic (which is usually the case for rotating systems), it is possible to obtain nonlinear frequency response of the system using harmonic balance techniques. Nonlinear harmonic response uses an iterative procedure to find the coefficients for the combination of sinusoids that form the steady-state response. Newton’s method of iteration is employed to solve a system of nonlinear algebraic equations. In addition to the harmonic balance technique, the continuation procedure method is required in the frequency response solver to capture the complete solution that consists of stable and unstable branches. This paper describes the improvements made in MSC Nastran for solving nonlinear windmilling problems and improve its robustness. The enhancements added to the software has made it possible to solve large scale production problems which was not feasible earlier.
Influence of Carbon on Structure and Stress-Rupture Properties of LW4280W and LW4280LCT High Gamma Prime Nickel Based Superalloys for a Tip Repair of Turbine Blades
Authors: Gontcharov Alexandre B. , Lowden Paul , Jena Ashutosh , Brochu Mathieu 
Published: August 2024

Abstract
The influence of carbides on microstructure and stress-rupture properties of high carbon LW4280W and low carbon LW4280LCT welds produced at ambient temperature GTAW at 649°C (1200°F), 872°C (1600), and 927°C (1700°F) are discussed in the current study. The study was powered by the need of using carbon for enhancing of creep strength of welds despite the well-known negative effect of carbides on high gamma prime superalloys weldability. In that context, a maximum carbon content of 0.12 wt.% has been maintained in many commercially available conditionally weldable superalloys. The current study demonstrates that the recently developed LW4280W superalloy with 0.17 wt.% C capable of producing 58–59 vol.% of gamma prime phase upon aging and the low carbon LW4280LCT comprising &lt; 0.1 wt.% C and forming 54–55 vol.% of gamma prime phase during post weld heat treatment (PWHT) have excellent weldability. The high carbon LW4280W welds demonstrated superior creep strength to LW4280LCT welds despite the interdendritic precipitation of complex plate-like TaHf-based carbides during solidification of a welding pool. Our results show that PWHT resulted in a partial fragmentation of plate-like TaHf-based carbides, believed to enhance creep resistance. Despite having similar tensile properties, the time to rupture of test samples manufactured from LW4280W welds at 927°C (1700°F) under stress of 151.7 MPa (22 KSI) exceeded 156 hours while the LW4280LCT welds fractured in 112 hours. Our study also shows that exposure of heat-treated welds to a potential overheating to 1080°C (1975°F) during takeoff of aircrafts for total of 500 hours had little or no effect on the structure and tensile strength of both superalloys. The example of tip repair of turbine blade manufactured from the single crystal material and recommendations for using of LW4280W and LW4280LCT superalloys are provided.