bluuebunny/crossref_metadata_2025_split huggingface dataset:
Towards Low NOx Emissions Performance of a 65kW Recuperated Gas Turbine Operated on 100% Hydrogen
Authors: Villatoro Walther , Slope John , McDonell Vincent , Hu Ray , Steele Robert 
Published: August 2024

Abstract
This work supports the development of a low NOx emission 65 kW natural gas turbine capable of operating on 100% hydrogen. This gas turbine has been demonstrated to operate from cold start to full load on up to 30% hydrogen mixed into natural gas with single digit ppm NOx emissions. To reach operation on 100% hydrogen, injectors specifically designed to 1) avoid challenges with flashback and 2) be field retrofittable were developed and tested. The injectors must be designed to prevent flashback while having a high degree of mixing coupled with fuel lean operation to achieve desired low NOx emissions. Successful operation of the engine from cold start to full load on 100% hydrogen was demonstrated. With the successful demonstration of operability, the new injectors serve as a starting point to improve the turbine performance and emissions when operated on hydrogen. To support the development, a chemical reactor network (CRN) is used in conjunction with experimental injector mixing characterization. The CRN analysis predicts NOx using perfectly stirred reactors (PSR). A strategy to account for variation in mixing performance was developed and utilized with the CRN to connect NOx emissions to the injector mixing performance. Fuel concentration profiles produced by different injector designs were measured and the CRN model was used to infer the effects on NOx emission. The CRN model was validated/tuned using measured NOx emissions data from two combustion liners and two injector designs and the corresponding measured injector fuel distributions. The results illustrate how NOx emissions are directly influenced by local fuel rich regions found at the injector outlet. The CRN model can thus be used to screen injector designs and infer NOx performance and will be used to guide the development of injectors for hydrogen that can attain desired fuel distributions, concentrations, and velocities. The results affirm the direction needed to attain improved mixing and to operate at overall leaner conditions made possible by the stabilizing features inherent to hydrogen.
A High-Speed, High-Temperature Micro-Cantilever Steam Turbine for Hot Syngas Compression in Small-Scale Combined Heat and Power
Authors: He Victoria , Van Herle Jan , Schiffmann Jürg 
Published: August 2024

Abstract
Coupling a biomass gasifier with a solid oxide fuel cell system through a high-temperature syngas compressor holds great promise to achieve low-emission, small-scale combined heat and power, since it reduces the number of heat exchangers and increases the system efficiency. However, due to the demanding operating conditions (high temperatures, toxic and explosive gases), electrical motors are not suitable to drive the syngas compressor. Therefore, a high-speed, small-scale cantilever steam turbine that can valorize the system’s waste heat to power the compression is designed and developed. An iterative process involving preliminary design, meanline analysis, commercial tools, and in-house codes is used for the design. The design is then numerically analyzed using computational fluid dynamics. The 2.8 kW cantilever steam turbine with a tip diameter of 21 mm runs up to 210 krpm at temperatures of 525°C while being supported on dynamic steam-lubricated bearings. A low-reaction, full-admission design has been chosen to lower the steam consumption, the axial forces, and the turbine backface leakage. The turbine rotor is made of Ti6Al4V and coated for structural integrity and to withstand high temperatures. Despite the small scale of this design, the results obtained from the established correlations based on large-scale turbines yield a remarkable concordance with the results from the numerical analysis, in particular for the isentropic expansion efficiency prediction.
Evaluations of Superposition Predictions of Adiabatic and Overall Effectiveness for Three Rows of Film Cooling Holes With Differing Hole Geometries
Authors: Ellinger Molly E. , Flachs Elise M. , Kulkarni Ameya N. , Bogard David G. 
Published: August 2024

Abstract
Prediction of film cooling performance on turbine airfoils with multiple rows of film cooling holes based on the measured performance of a single row of holes relies on use of superposition analysis. There have been many past studies of superposition predictions of film cooling adiabatic effectiveness with similar hole shapes, either cylindrical or shaped holes. Recently there has also been a study proposing using a superposition technique to predict overall cooling effectiveness for multiple rows of film cooling holes. In this study, superposition predictions for adiabatic effectiveness and overall cooling effectiveness were evaluated for multiple rows of film cooling holes with varying hole geometries. The test configurations used mimicked the influence of upstream showerhead film cooling holes followed by either baseline 7-7-7 holes or an additively manufactured optimized film cooling hole which included external vortex generators that improved attachment of the coolant jets. Results showed the commonly used Sellers superposition model provided reasonable predictions of adiabatic effectiveness for the more standard 7-7-7 holes, but poor predictions for the optimized holes using vortex generators. Accuracy of the predictions of overall cooling effectiveness based on measured adiabatic effectiveness were found to be good.
Effects of Recess Depth and Orifice Diameter on Pneumatic Hammer Instability in Hydrostatic Thrust Bearings: Analysis and Experimental Validation
Authors: Lim Homin , Kim Kyuman , Ryu Keun 
Published: August 2024

Abstract
Hydrostatic thrust bearings are required in various turbomachinery systems due to their substantial load capacity and superior rotor axial positioning capabilities, which minimize friction and heat generation. However, when lubricated with compressible fluids, these bearings can experience pneumatic hammer instability especially if the recess volume is significant. This study aims to establish design guidelines and experimentally validate the performance of hydrostatic thrust bearings, with a focus on predicting and mitigating pneumatic hammer instability. The research includes an investigation into the static load characteristics of these bearings when operated with air as the lubricant. The analysis in this paper covers the effects of varying supply pressures, recess depths, and orifice diameters on pneumatic hammer instability, as well as on the load capacity, stiffness, and damping coefficients of the bearings. To validate these findings, experiments are conducted using two test bearings with differing recess depths and orifice diameters. The results from both predictive models and experimental data consistently show that a shallow recess depth is effective in preventing pneumatic hammer instability without notably diminishing the bearing load capacity. Nonetheless, modifying the orifice diameter to control pneumatic hammer instability requires careful design consideration, as it might lead to decreased load capacity and stiffness. This research addresses the challenge of preventing pneumatic hammer instability in hydrostatic thrust bearings through a combined approach of numerical analysis and experimental testing. It contributes significantly to the field by offering practical design recommendations for optimizing recess depth and orifice diameter. These guidelines aim to eliminate pneumatic hammer instability while preserving critical performance aspects of hydrostatic thrust bearings, such as load capacity and stiffness.
Impinging Jet Heat Transfer of Liquid Carbon Dioxide at Constant Enthalpy
Authors: Park Seong-Hyeok , Kim Seon Ho , Hsu Wei-Ting , Park Hee Seung , Cho Hyung Hee 
Published: August 2024

Abstract
This study focuses on investigating the heat transfer characteristics of boiling with liquid (subcritical) carbon dioxide impinging jet at identical enthalpy conditions, specifically examining the influence of varying operating pressures on its behavior. The experiments were conducted within a range of operating pressures from 6.37 MPa (0.86 PC) to 7.30 MPa (0.99 PC), slightly below the critical pressure, PC, of 7.38 MPa. Using RTD sensors equipped with a thin film ITO heater, this study measured the wall temperature and wall heat flux at the stagnation point, enabling the calculation of the heat transfer coefficient. The impinging jet, operating at a Reynolds number of 40,000, was directed onto the impinging plate through a 9.4 mm-diameter nozzle. The findings reveal that at the liquid state, the wall temperature at the stagnation point rises in correspondence with the increase in wall heat flux. Moreover, at the given pressure, the wall temperature eventually reaches a saturation point as the wall heat flux continues to increase, leading to the emergence of wall superheat at an operating pressure of 6.37 MPa. However, as the operating pressure increases, the phenomenon of wall superheat diminishes, eventually nearly vanishing.
Cooling System Topology of High-Endurance Dual Stack Proton Exchange Membrane Fuel Cell System for Heavy Duty Trucks
Authors: Nguyen Huu Linh , Yu Sangseok 
Published: August 2024

Abstract
The adoption of proton exchange membrane fuel cell (PEMFC) technology in heavy-duty trucks represents a promising solution for addressing the pressing issues of emissions and sustainability in the transportation sector. Achieving high-endurance operation is critical for the success of these systems, and effective cooling is central to this goal. This paper explores innovative cooling topologies and control strategies designed to extend the endurance and operational longevity of dual PEMFC stack systems in heavy-duty truck applications. To address these issues, a comprehensive analytical model for a dual PEMFC stack system is developed to assess the heat generation within the fuel cell stacks, enabling a meticulous evaluation of the cooling requirements. Two strategies for controlling coolant bypass flow are evaluated, one based on coolant temperature and the other based on stack temperature, during dynamic operation. Three different topologies are designed to achieve efficient cooling systems, and their impact on parasitic power and energy consumption is examined. The results suggest that control strategy in which the bypass valve open ratio is controlled based on the stack temperature, performs better in regulating the fuel cell operating temperature precisely. Among the various topologies, the distributed topology which involves setting up two independent cooling systems for each stack, significantly reduces energy consumption. In particular, it saves up to 71% of energy consumption compared to the integrated topology, where a single cooling system is used for both stacks.
An Innovative Filtering Apparatus for Gas Turbines
Authors: Zanini Nicola , Suman Alessio , Piovan Mattia , Pinelli Michele , Rossin Stefano , Minotti Stefano 
Published: August 2024

Abstract
Air contaminants can severely affect the life of gas turbines. Particles that enter the compressor section can interact with the internal surfaces of the machine leading to the modification of the airfoil shapes and surface roughness. Depending on the particle size and chemical composition, thus the working site of the gas turbine, different degradation mechanisms can occur, such as fouling, erosion, and corrosion. All these phenomena implicate performance drops over time and reduce the reliability of the plant. Multistage filtration systems are usually employed to reduce the contamination at the heavy-duty gas turbine inlet. Inertial separators, wet barriers, self-cleaning filters, and media filters work together in the so-called “filter house” to obtain the most appropriate filtration system according to the contamination of the surrounding environment and the contaminant typology. Inertial separators are more effective against bigger particles (&gt; 10 μm) while media filters can capture smaller ones (&lt; 10 μm). Media filters are commonly installed in the last stages to face the smaller residual particles captured. The continuous exposure to contaminants leads to the increment of the pressure drop and consequently, the media filter replacement is required after having reached a threshold pressure drop. In this work, an innovative particle separator that combines an inertial barrier with a high-voltage electric field is presented. An extensive experimental laboratory-scale campaign is carried out to evaluate the performance of the device against different types of contaminants, particle concentration, and environmental conditions.
Numerical Prediction of Lean Blow Out Event in an Industrial Gas Turbines Through an LES Based CFD Analysis
Authors: M. Rajesh , R. Meloni , A. K. Arun 
Published: August 2024

Abstract
Combustion processes operating under fuel lean conditions can reach very low emissions and extremely high efficiency. However, ultra-lean combustion is more prone to thermos-acoustic instabilities and the flame can even get extinguished by the blowing out of the combustion chamber. Hence the Lean Blow-Out (LBO) limit plays a critical role in the stable performance of gas turbine combustors since it represents the boundary between the flame extinction and the stable flame region. The occurrence of LBO in real engines can significantly reduce the engine availability and operating reliability. Therefore, early detection of LBO is a key performance parameter that needs to be investigated. In this way, the engine can be guided through precautionary actions using a control system, like setting the max air-to-fuel ratio, changing the split among fuel lines, etc.
From a numerical perspective, the unsteady phenomena of LBO are indeed challenging to be captured as the flame is marching towards to the quenching conditions from a stable point. The present work leverages the capabilities of a tabulated chemistry approach in predicting the process of a lean blowout occurring in a swirled technically-premixed flame. One of the experimental events conducted at high pressure and high temperature to understand the LBO event for a given geometry/fuel composition is considered as benchmark condition for the numerical investigation. The paper will presents the validation of the numerical model/approach against the experimental measurements. More in detail, an Extended Turbulent Flame Speed Closure (ETFC) model was implemented to introduce the effect of stretch and heat loss on the partially premixed flame. The exploitation of the numerical results is carried out through the analysis of the main fields like the heat-release rate, the pressure fluctuation and the temperature. The extinction equivalence ratio is predicted quite accurately, showing that the ETFC is suitable for the study of the blow-off for the partially premixed flames, without an increase in computational cost. The presented methodology would serve as the primary benchmark for assessing the models’ effectiveness in capturing the flame dynamics: the approach can be extended/repeated to other operating conditions of the combustor to define the LBO map for a finite TCD range and different fuel split.
Structural Dynamics of an Axial Compressor’s Rear Blisk Drum and Multi-Stage Coupling
Authors: Gambitta Marco , Beirow Bernd , Klauke Thomas 
Published: August 2024

Abstract
Modern turbomachinery compressor design favors the introduction of multi-stage drums to reduce the components’ weight and increase the machine efficiency. The drum design creates a direct connection between the stages, which can lead to a collaboration of the stages in the system structural dynamics. This motivates the investigation of multi-stage coupling for the structure. The objective is to propose a method to characterize such collaboration for coupled components.
To investigate the multi-stage coupling, the analysis of the structural dynamics has to consider the drum system. In consequence, compared to the investigation of individual stages, significantly higher computational costs are expected. Moreover, also when considering the tuned reference geometry, the full drum loses the cyclic symmetrical property of the individual stages due to the different airfoil counts. A reduction method to compute the system modes is investigated, taking advantage of the nominal individual stages’ periodicity. The quality of the results is assessed comparing the computed mode-shapes and natural frequencies with the respective full model of the investigated drum.
The identification and quantification of the coupling is finally crucial to describe the structural dynamics of the drum system. Modes with high coupling show a co-participation of the stages in the dynamics. This implies vibrational responses on a stage due to the excitation of a different drum row. In this work, a formulation for an index is proposed, named coupling strength, to quantify the intensity of this collaboration for each mode. The formulation considers an arbitrary number of stages and can be extended in general to different coupled structures.
Guideline for Large-Scale Analysis of Centrifugal Blower Using Wall-Resolved Large Eddy Simulation
Authors: Tsukamoto Kazuhiro , Kato Chisachi 
Published: August 2024

Abstract
In order to reduce the number of prototypes during product design and accurately predict unsteady phenomena occurring at off-design points, a method for accurately predicting the performance of centrifugal blowers through numerical analysis is required. This paper presents a guideline for accurately predicting the performance of centrifugal blowers using compressible flow analysis with Large Eddy Simulation (LES). In LES analysis, it is important to have a grid resolution that resolves the minimum vortex scale near the wall (referred to as wall-resolved LES) and to consider detailed geometry such as the length of the suction pipe.
The calculations in this study used a model blower, which is a scale model of a single-stage centrifugal blower for use in industrial plants. The model blower was experimentally measured for various parameters such as the blower pressure coefficient, the static pressure rise coefficients of the impeller and vane-less diffuser, the shaft power, and the pressure fluctuations at the inlet of the impeller and the inlet of the vaneless diffuser. The results of these measurements were compared with those obtained from the wall-resolved LES.
The study confirmed that the accuracy of performance prediction can be improved to less than a 4.0% error in the blower pressure coefficient at both design and off-design operating points by resolving the minimum vortex scale with 14.6 billion grid elements and considering the detailed geometry.
Experimental Study of Atomization Feature of Coaxial Parallel Flow Airspray Nozzle in Crossflow
Authors: Li Yue , Suo Jianqin , Ju Hongyu 
Published: August 2024

Abstract
To improve the atomization efficiency of the direct injection nozzle, a ring-shaped air layer is enveloped on the outer side of the liquid jet, forming a structure of co-flowing air atomization nozzle with liquid and gas phases. This paper experimentally studies its atomization characteristics when subjected to cross-flow injection in lateral air streams. The effects of ring-shaped air channel height (0.4mm, 0.7mm, 1.0mm, 1.3mm), different lateral air flow velocities (28.7m/s, 35.9m/s, 43.1m/s), and liquid flow rates (2.5g/s, 4.72g/s, 6.94g/s) on the atomization performance of the nozzle were investigated. Pulsed laser was used as the light source to obtain clear transient images of the liquid spray field. Marvin laser particle size analyzer was employed to measure the particle size at different locations in the liquid spray field. With the constant momentum flux ratio of the liquid-gas jet ensured, a larger ring-shaped air channel height leads to a stronger atomization enhancement effect, resulting in a smaller SMD (Sauter Mean Diameter) of the liquid spray field. The ring-shaped air significantly reduces the influence of lateral air flow velocity and liquid flow rate on the distribution area of the liquid spray field.
Sealing Flow Rate Effects on Unsteady Loss Production in a Low Pressure Turbine Stage
Authors: Barsi Dario , Biassoni Daniele , Lengani Davide , Simoni Daniele , Ubaldi Marina 
Published: August 2024

Abstract
Efforts to increase efficiency in aircraft and power generation turbines have raised turbine inlet temperatures (TIT), necessitating advanced cooling technologies to maintain material integrity. Preventing the ingestion of hot gases into components not suited for high temperatures, like stator/rotor cavity disks, is crucial.
Current gas turbine performance strategies focus on minimizing leakage and optimizing sealing systems. Notably, losses from main flow and cavity interactions are prominent in stator/rotor systems. Using Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, this study explores the unsteady interaction in a low-pressure turbine’s stator/rotor cavity. Numerical simulations of the University of Genova’s cavity rig are validated against experimental results.
The investigation examines stator/rotor interaction effects, including wake ingestion from upstream rotor bars and the blocking impact of downstream rotor bars on cavity sealing. Varied cooling air injection rates in multiple calculations reveal insights into stage efficiency and cavity leakage. Emphasis is on unsteady loss mechanisms downstream of the vane row and in the region where the cavity flow is reintroduced in the main channel, providing a better understanding of losses influenced by cooling flow rates. The analysis of the loss amount along the axial direction demonstrates that losses generated in the vane row are increased prior to entering into the downstream rotor bars, due to cavity main flow interaction. This provide useful information about the production of losses due to sealing flow rate.
Comparison of Rim Sealing Effectiveness in Different Geometrical Configurations
Authors: Orsini Lorenzo , Picchi Alessio , Facchini Bruno , Bonini Alessio , Innocenti Luca 
Published: August 2024

Abstract
The flow field developing inside the stator-rotor cavities of gas turbines is characterized by a complex unsteady behaviour which still requires expensive and time consuming CFD simulations to be accurately modelled. Hence, the experimental characterization of the rim sealing effectiveness by means of scaled down geometries that replicate the rim seals found in actual engines still represent a widely used approach in literature. However, the obtained results can greatly depend on the specific geometry of the tested rim seal. Moreover, different geometrical parameters can vary during the operation of the engine, especially under transient or off-design conditions, thus influencing the resulting effectiveness values. For this reason, the sealing performance of seven different configurations of radial rim seals has been investigated and the obtained dataset has been correlated by using the Orifice Model. Hence, a detailed comparison of the results allowed the evaluation of the impact of different values of axial overlap, different distances between the vanes trailing edge and the blades leading edge and different values of radial gap. In particular, a three times greater axial overlap and a modest increase in the distance between the trailing edge of the vanes and the leading edge of the blades were both found to provide a limited improvement in the sealing performance, with a respective average reduction in Φmin of approximately 5% and 6%. A radial gap 2.4 times greater was instead found to lead to an average increase in the required quantity of sealing flow rate of approximately 44%. Hence, the amount of purge flow required to fully seal a cavity was not found to exhibit a linear increase with the radial gap.