bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cavity Impact on the Base Flow Unsteadiness for a High-Speed Exhaust System
Authors: Tsentis Spyros , Goulos Ioannis , Prince Simon , Pachidis Vassilios , Zmijanovic Vladeta 
Published: August 2024

Abstract
Future propulsion systems will be essential to enable sustainable high-speed flight and routine space access. Such concepts usually employ base-embedded, convergent-divergent nozzles and cavity regions to facilitate their mission, thus altering the flow dynamics at the base notably in comparison to contemporary launch vehicles. This paper presents a numerical investigation on the impact of a cavity region on the base flow unsteadiness for a sub-scale, high-speed exhaust system at over-expanded mode. The fully-installed model in the test section of a wind tunnel is employed to facilitate an ongoing experimental campaign. The Delayed Detached Eddy Simulation turbulence modeling approach is utilized to investigate the flow at the base. The configuration featuring the cavity is directly compared to a baseline apparatus, where the cavity has been removed, thus allowing for the impact of the cavity to be identified. Results show that the cavity region can reduce the base pressure fluctuations up to 20% and acts in a damping-like manner for the base flow unsteadiness. The total energy of the pressure fluctuations spectrum at the base can be reduced by as much as 38% compared to the baseline configuration. However, the impact of the cavity on the time-averaged pressure distribution at the base is negligible. Finally, the cavity is found to have a notable effect on the nozzle side loads, which are are reduced by an order of magnitude compared to the baseline case, and behave in an axisymmetric manner. This indicates that the cavity could act as a passive flow control mechanism for side loads reduction.
Fan Non-Synchronous Forced Vibration Under Crosswind
Authors: Chennuru Venkata Y. T. , Corral García Roque , Rodríguez-Blanco Salvador , Vahdati Mehdi , Zhao Fanzhou 
Published: August 2024

Abstract
In this paper, a new aeroelastic phenomena for fans, referred to as Non-Synchronous Forced Vibration (NSFV), is presented. This type of aeroelastic instability can occur at high crosswind conditions when the flow at the intake lip separates and the disturbances caused by flow separation become unsteady. The results show that in presence of unsteady separation in the intake, the fan can experience non-synchronous frequency excitations, which can result in resonant response in modes that are not identified by the Campbell diagram. The findings are corroborated by aeroa-coustic theories. To the best knowledge of authors this is the first time that fan forced response due to unsteady distortion is studied and the findings can unlock some of unexplained and unexpected vibrations experienced by engines.
Effect of Leading Edge Erosion on the Tip Leakage Flow in a Compressor Cascade
Authors: Stein Thomas , Leitner Markus W. , Staudacher Stephan 
Published: August 2024

Abstract
The interaction between tip leakage flow and passage flow in axial compressor blade rows creates complex flow mechanisms that impair flow stability. Caused by erosion of the compressor blades, these flow mechanisms become time dependent. Especially the compressor tip regions experience erosion-related surface loss owing to the particle-laden flow inside the engine. The corresponding reduction in chord length varies in height and leads to varying shapes of eroded compressor blades. It is likely that these impact the engine’s operability. The optical accessibility of flow structures in water was exploited by analyzing four blade tip geometries at different angles of incidence in a linear compressor cascade. The impact of these geometries on the tip flow structures is analyzed by observing the movement of inked fluid elements in space and time. Particle Tracking Velocimetry (PTV) is used to obtain 3D trajectories of both stable and unstable flows. Whilst the non-eroded blade geometry shows stable vortex formation, a notable change in the flow characteristics is observed for particular erosion patterns. In these cases, the tip leakage flow exhibits unsteadiness, featuring fluctuations and unstable flow phenomena. A large blockage of the flow passage occurs due to a vortex breakdown.
Redistribution of Purged Cavity Air Inside a Turbine Exit Vane Frame due to the Interaction With the Main Airflow
Authors: Schien Malte , Lopez Pablo , Bratusek Lukas , Heitmeir Franz , Marn Andreas 
Published: August 2024

Abstract
As a consequence of enhanced pressure ratios and combustion exit temperatures for higher jet engine efficiencies, the exit temperature of the Low Pressure Turbine (LPT) increases, too. To prevent hot gas from entering the rim seal cavity between the LPT’s last stage rotor and the Turbine Exit Vane Frame (TEVF), purge air is needed.
The present work investigates the spatial redistribution of purged cavity air inside an annular Turbine Exit Vane cascade due to its interaction with the main airflow. For this purpose, experimental investigations have been conducted using aerodynamic 5-hole pressure probes and the CO2 trace gas technique. Furthermore, numeric results yield better insights into the flow’s characteristics.
Three operating conditions are investigated, representing the aircraft’s states: take-off, maximum climb, and cruise.
It is shown that the interaction between the purge fluid and main airflow is mainly dominated by the ingress upstream of the vane’s leading edge and the egress at locations of lower static pressure. Inside the vane passage, the cross-flow pressure gradient mainly determines the cavity fluid’s pathway.
At off-design conditions, purge fluid does not contribute significantly to the cascade’s total pressure loss.
Ignition of Aged Lubricants in a Shock Tube
Authors: Abulail Matthew , Juárez Raquel , Petersen Eric L. 
Published: August 2024

Abstract
Lubricants experience harsh conditions which result in degradation of the oil. To imitate similar conditions, Mobil DTE 732, a common gas turbine lubricating oil, was subjected to high temperatures for an extended period of time, until thermal degradation occurred, indicated through the creation of coke. Samples were taken throughout this process, with the sample that was tested having been exposed for 78 hours. Utilizing an endwall injector system, the samples were ignited behind reflected shock waves in the High-Pressure Shock Tube at Texas A&M University. The injector system utilizes the incident wave to increase the temperature of the lubricant past its vaporization temperature, thereby vaporizing the fuel prior to the arrival of the reflected shock. Using this system, the base Mobil DTE 732 and the 78-hour sample produced from the coking test were tested at 1.06 to 1.58 atm and between 1171 and 1373 K. The ignition delay times of the samples were recorded utilizing pressure rise and hydroxyl chemiluminescence located in the sidewall of the shock tube. Upon the analysis of the results, there were negligible changes in the ignition behavior of the fuel, based on ignition delay time. However, changes in the combustion behavior were experienced, such as an absence of two-stage ignition and lower viscosity for the post-coke sample.
Experimental Studies on Lean Blowout Limits for a Hydrogen-Enriched Methane-Fueled Trapped Vortex Combustor
Authors: Verma Nikhil , Ravikrishna R. V. 
Published: August 2024

Abstract
In light of stringent emission regulations and environmental considerations, hydrogen is being considered a viable alternative to replace hydrocarbon fuels. However, hydrogen combustion poses challenges regarding NOx emissions, combustion instability, flashback, and blowout limits. The present study aims to investigate the lean blowout of TVC using methane-hydrogen blends with varied hydrogen concentrations. Furthermore, the flame dynamics near lean blowout in the TVC is achieved by reducing the equivalence ratio and studied in detail using high-speed OH*-chemiluminescence (5 kHz), emissions, and temperature measurements. A trapped vortex combustor is considered for the present study because of its numerous advantages: reduced emissions, improved flame stabilization, increased combustion efficiency, exceptional high-altitude re-ignition capabilities, and operating in lean burn or RQL combustion modes. The lean blowout limit is achieved by reducing the equivalence ratio in the cavity inlet until the blowout event occurs, while the equivalence ratio in the main flow is set to zero. The findings reveal significant changes inflame structure as the lean blowout limit is approached. At higher equivalence ratios, the heat release zone is observed to be distributed within the cavity. However, near the lean blowout limit, the heat release zone is confined to the cavity jet shear layer, which is observed to stabilize near the aft wall of the cavity. As the percentage of hydrogen increases, a significant decrease in the lean blowout limit is observed, accompanied by lower hydrocarbon and CO emissions. Thus, the present study demonstrated a broadening of the operating range of the trapped vortex combustor with lower emissions when hydrogen concentration increases.
Non-Parametric Surrogate Model (NPSM) for High-Dimensional Aerodynamics Optimization
Authors: Cao Jiajun , Xu Liping 
Published: August 2024

Abstract
An non-parametric surrogate model for high-dimensional aerodynamic optimization is introduced in this paper. It directly builds a mapping relationship between surface meshes of objects and the two-dimensional (2D) distributions of flow variables. NPSM utilizes Graph Neural Networks (GNNs) to extract performance-sensitive geometric features from surface meshes according to the feedback of prediction errors. With this geometric information, NPSM can predict 2D distribution of flow variables with Convolutional Neural Networks (CNNs) rather than only several scalar performance metrics. This process reduces the uncertainties caused by manual parameterization of high-dimensional geometries, such as fuselage, wings and blades in turbomachinery. The mapping relationship established by NPSM enables the Non-Parametric Sensitivity Analysis (NPSA) via Automatic Differentiation (AD), which can derive sensitivity of each mesh vertex rather than sensitivity of geometric parameters. This sensitivity information makes NPSM explainable, and provides more information for redistribution of geometry control points. To safeguard the robustness of optimization, a design classifier is designed to utilize the latent space built by NPSM to identify predictable designs. In this paper, two cases are used to demonstrate NPSM. The symmetric bumps case is used to demonstrate the methodology and functionalities of NPSM. The capability of processing high-dimensional geometries is demonstrated with the low-pressure (LP) steam turbine rotor.
Impact of Hydrogen Fuel Retrofits to Gas Turbine Performance and Hot Gas Path Components
Authors: Kapoor Riddhi , Bullard Timothy , Shoraka Amir , Hsia Kuo-Ting 
Published: August 2024

Abstract
Hydrogen is gaining prominence as a carbon reduction strategy for gas turbines by end users and equipment manufacturers within the power generation industry. The cost of new gas turbine units is restrictive, and many are already in service with remaining life. Therefore, there is a growing interest in retrofitting existing gas turbines that historically run on conventional fuels like natural gas and liquid oil. Though many gas turbine combustors currently run on small amounts of hydrogen, such older units have not been specifically designed to use high quantities of hydrogen as a fuel. Among the many technical challenges of implementing hydrogen on existing units is the potential impact on performance and on hot gas path components’ durability. The effects on performance can vary depending on the existing combustion system configuration, as some combustors utilize water or steam injection, and some operate in a dry mode. The current study provides insights into retrofitting dry combustors (i.e., without water or steam injection for emissions control), their influence on gas turbine performance, and potential implications to the hot section components. Two analytical models are employed. The first is a gas turbine performance code used to assess the effects of fuel composition changes on performance parameters such as output, heat rate, firing temperature, exhaust temperature, etc. The second is a thermal fatigue cycle model used to study the effects of the varied combustion products, including high amounts of H2O, on the turbine components.
From Early Development to Industry’s Successful Adoption, the Journey in Additive Manufacturing Cooling Technology for Improved Gas Turbine Capabilities
Authors: Vogel Gregory , Borja Michele , Zangara Mark , Hunt John 
Published: August 2024

Abstract
The power industry is a critical sector that fuels the global economy, heavily reliant on high-performance industrial gas turbines. Leading manufacturers of turbine hardware are continually investing in cutting-edge technologies to meet the industry’s growing demands. Among these technologies, additive manufacturing has emerged as a game changer.
In its early stages, additive manufacturing primarily focused on aspects such as powder morphology, process optimization and material properties characterizations. However, it quickly paved the way for the creation of innovative cooling designs for gas turbine components. Collaborations with prominent universities conducting fundamental experiments have been instrumental in gaining a deeper understanding of the advantages and challenges posed by these novel cooling design features and how they might perform in real engine conditions.
A significant milestone was reached in 2018 when Power Systems Mfg., LLC (PSM) successfully conducted a groundbreaking technology demonstration, featuring an additively manufactured advanced cooling design airfoil running in a heavy-duty industrial turbine. This demonstration provided valuable insights and experiences that marked a turning point in the gas turbine industry’s acceptance of this transformative technology.
Since that pivotal moment, numerous gas turbine units around the globe have been operating with this adopted technology, with some surpassing the impressive milestone of three years in continuous operations. This paper provides detailed technological information related to the journey and present the latest field experience of an additively manufactured F class row 1 turbine nozzle equipped with advanced cooling solutions, as well as valuable lessons learned from applying additive manufacturing technology to enhance cooling designs, ultimately leading to improved gas turbine efficiency.
Metallurgical Investigation and Failure Analysis in GTD-111 Stage 2 Buckets From an Industrial F-Class Gas Turbine
Authors: Bridges Alex , Shingledecker John , Wang Yongqing 
Published: August 2024

Abstract
A utility experienced cracking in multiple stage 2 buckets (S2Bs) in a large F-class power generation gas turbine after only 7,348 hours and 31 starts following a standard repair and rejuvenation heat treatment cycle. The blades were cast from a directionally solidified (DS) superalloy and the cracking was found in the shroud section of the blade in the Z-notch region. A detailed failure investigation was conducted to determine the failure mechanism and most likely contributing factors to root cause in terms of design, operation, fabrication, and metallurgy. Three blades, two with visible cracks and one without cracks, were subjected to non-destructive and destructive evaluation. Methods consisted of visual inspection, 3-D scanning, physical measurements, chemical analysis, optical metallography, LED surface topological evaluation, and scanning electron microscopy. The failure mechanism was determined to be due to creep with damage propagating along the grain boundaries in a high stress concentration area. Evaluation of precipitate structure and size also confirmed this area exhibited the highest temperature during operations. High temperature creep testing was also conducted in material from the two different casting houses to confirm metallurgical risk did not have a significant impact on creep performance. An evaluation of the operational profile of an entire fleet of GE 7FA units showed that the failed 7F.03 S2Bs were in the highest operating temperature base loaded units. The findings from this work will help better define key factors that influence the high temperature performance of nickel-base superalloys used in the hot section of industrial power generating turbines.
Development and Optimization of a Solid Oxide Fuel Cell Gas Turbine Hybrid System
Authors: Sprengel Michael , Echter Nick 
Published: August 2024

Abstract
Solid Oxide Fuel Cells (SOFC) are an advanced form of fuel cells which can convert hydrocarbon-based fuels into electricity at efficiencies reaching 60%. Fuel efficiency may be increased to 70% or higher by closely integrating a SOFC into the hot gas path of a Brayton cycle gas turbine. SOFCs, unlike more common low temperature fuel cell technologies such as PEM, operate at elevated temperatures between 500°C and 1,000°C, temperatures well suited for integration with turbomachinery.
Fuel efficiency is enhanced through several mechanisms including: (1) operating the SOFC at elevated pressure, (2) by tightly integrating the SOFC between the gas turbine’s compressor and expander, (3) by using the gas turbine’s combustor to oxidize dilute fuel in the anode tail gas further heating the already hot and pressurized cathode tail gas before expanding it through a turbine to create additional power, and (4) by eliminating much of the parasitic balance-of-plant (BOP) required to preheat and circulate air through the SOFC.
The authors are part of a multi-company collaboration to develop and demonstrate a SOFC/GT system with unique elements such as an integrated cathode recuperator and a fuel to AC electrical conversion efficiency exceeding 70%. This paper covers the system’s development with a specific focus on tradeoffs and optimizations throughout the system design.
Turbulence Measurements in Axial Turbines Using Fast Response Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Persico Giacomo , Gaetani Paolo 
Published: August 2024

Abstract
Improving the comprehension of turbomachinery fluid-dynamics is vital to increase their performance, and calls for the development or extension of advanced instrumentation. In this context, novel data acquisition and data reduction techniques have been recently developed at Politecnico di Milano for turbulence measurements performed with Fast-Response Aerodynamic Pressure Probes. These improvements address a gap in the capabilities of such probes, as turbulence data were among the few, yet very important, information they could provide only on a quality level. At first, the technique is validated against hot-wire measurements on a low-speed wind tunnel, where a combustor simulator is inserted with or without an upstream turbulence grid generator. Second, the developed methodology is applied downstream of both the stator and the rotor of a single-stage axial turbine, where the probe robustness and reliability are fully exploited to gain crucial flow information also in a harsh flow environment, where the use of hot wires might be critical. In this paper, the measured turbulence intensity using FRAPP is compared among three different operating conditions obtained by changing the rotor rotational speed. Furthermore, the paper explores the impact of non-uniform stage inlet conditions, that resemble the combustor outlet disturbances, on the stator and rotor flow features.
The regions with the highest turbulence levels are observed in areas characterized by secondary flows, wakes, end-walls, and the residual swirl profile. The stator-rotor interaction contributes to the turbulence generation both downstream of the stator and the rotor. Additionally, an increase in blade loading corresponds to higher intensity in secondary flows, leading to elevated turbulence levels at the rotor exit. The injection of combustor non-uniformities has a diminished impact as the rotor load increases, given that the flow field becomes predominantly influenced by strong secondary flows.
Investigation of Lean Blow Off Limits of a Spray Flame in a Laboratory-Scale RQL-Type Burner
Authors: Nagao Jun , Rajendram Soundararajan Preethi , Kurose Ryoichi , Mastorakos Epaminondas 
Published: August 2024

Abstract
This experimental study explores the stability of an ethanol spray flame under conditions close to lean blow-off (LBO) in a rich-quench-lean (RQL)-type combustor. The combustor has a primary inlet with a swirling air flow and four radially injected dilution air inlets. The split ratio (SR) of primary to dilution air was varied (10:0, 8:2, and 6:4) at different fuel mass flow rates to quantify the LBO conditions. Results showed that there was only a minor difference in the LBO conditions for SRs of 10:0 and 8:2 for all fuel mass flow rates. In contrast, the LBO equivalence ratio increased at SR of 6:4. This is attributed to the different blow-off mechanisms at SR of 6:4 compared to the case of lower dilution, as suggested by the analysis of the blow-off event obtained using high-speed OH* chemiluminescence imaging. Those revealed that the flame started to extinguish downstream and around the spray cone region for SR of 10:0 and 8:2, but the flame first lifted off and then extinguished close to the nozzle at SR of 6:4. The high-speed OH* images were analyzed with Proper Orthogonal Decomposition (POD), which demonstrated different modes of flame fluctuations between conditions far from and close to LBO. The results obtained from this study can be used for validating gas turbine combustor CFD models.
Investigation of Flow Mechanism for Solidity in Typical Modes of Variable Pitch Tandem Cascade
Authors: Sheng Xiaoying , Luo Qiaodan , Xu Huafeng , Yang Chengwu , Lu Xingen 
Published: August 2024

Abstract
Due to the influence of fan geometry and aerodynamic factors, aerospace propulsion systems have difficulty operating above Mach 3.5. Even with a hybrid power system equipped with a turbofan engine, there is an issue of insufficient intermediate thrust. This is attributed to the limited acceptable inflow range of traditional fan layouts. This paper proposes a novel variable pitch tandem fan (VPTF) configuration that has the potential to overcome this limitation and further expand the operating speed range of the fan. Subsequently, based on this scheme, three-dimensional Reynolds averaged Navier-Stokes simulations were conducted for VPTF in transonic mode (Ma1 = 1.5), supersonic mode (Ma1 = 2.5), and windmilling mode (Ma1 = 4). The comprehensive impact of solidity on the performance under these three typical modes was investigated. The results show that solidity primarily affects the shock intensity within the passage, as well as the location and number of interactions with the blade surface, thus influencing the aerodynamic performance and blade loading of VPTF. It was found that when the solidity is chosen around 4.5, VPTF can achieve relatively good performance. At this solidity, it exhibits lower losses and maximum pressure ratio in the transonic mode. The supersonic and windmilling modes also exhibit lower losses.