bluuebunny/crossref_metadata_2025_split huggingface dataset:
CO Laser Absorption Measurements During Syngas Combustion at High Pressure
Authors: Cooper Sean P. , Nativel Damien , Mathieu Olivier , Fikri Mustapha , Petersen Eric L. , Schulz Christof 
Published: September 2023

Abstract
Syngas is a desirable fuel for combustion in the Allam-Fetvedt cycle which involves combustion under supercritical-CO2 (sCO2) conditions. While some work has been conducted in collecting ignition delay times at the extreme pressures required by these systems, significant model deficiencies remain. Additionally, considerable barriers in terms of non-ideal gas dynamic effects have been shown for these experiments in shock tubes. Further investigation into the fundamental combustion kinetics of H2/CO/CO2 mixtures is required. Time-resolved speciation measurements for target species have been shown to better aid in improving the understanding of underlying chemical kinetics than global ignition delay time measurements. Therefore, laser absorption measurements of CO were collected behind reflected shock waves during combustion of syngas at 5 and 10 bar and temperatures between 1080 and 2100 K. The mixtures investigated utilized H2-to-CO ratios of 1:1 and 1:4, respectively, each at stoichiometric conditions, allowing for discussions of the effect of initial fuel composition. A ratio of fuel to CO2 of 1:2 was also utilized to represent commercially available syngas. The mixtures were highly diluted in helium and argon (20% He, 76.5% Ar) to minimize thermal effects and to expedite CO thermal relaxation during the experiment. The resulting CO time histories were then compared to modern chemical kinetics mechanisms, and disagreement is seen for this system which is assumed to be fairly well known. This study elucidates particular chemistry that needs improvement in moving toward a better understanding of syngas combustion at elevated pressures.
Forced Response Analysis of a Highly-Loaded Low-Pressure Compressor Stage With Inlet Distortions
Authors: Toracchio Riccardo , Stapelfeldt Sina , Hillewaert Koen , Fontaneto Fabrizio 
Published: September 2023

Abstract
Due to modern evolutions in propulsion, in view of obtaining higher propulsive efficiency, turbofan engines are subjected to ever higher inlet flow distortions. In these systems, structural damage can be induced by distortion patterns with excitation close to the blade natural frequency. To fill the gap currently present in literature about the impact of inlet distortions on the aeroelastic behaviour of engine components, this paper presents an aerodynamic damping and forced-response analysis on a highly-loaded axial compressor subjected to intake total pressure distortions. First, a stability analysis for the vibrational mode with natural frequency close to the resonance condition at the nominal speed of the machine is performed. Blade deformations are then computed through a distortion induced forced-response analysis at different distortion amplitudes. This work aims at studying the aeromechanical behaviour of a modern compressor, highlighting that the amplitude of the blade vibration does not increase linearly with the distortion amplitude.
The Effect of Upstream Unsteadiness on the Unstarting of a Supersonic Inlet Turbine
Authors: Mushtaq Noraiz , Gaetani Paolo 
Published: September 2023

Abstract
A 15% increase in thermal efficiency at medium pressure ratios is promised by rotating detonation engine technology over conventional Joule-Bryton cycles. A supersonic inlet turbine is a viable option to extract substantial work from the highly fluctuating and supersonic flow delivered by the detonating combustor. However, an additional unstarting mechanism based on the generation of a collective shock from the coalescence of leading-edge bow-shock waves further restricts the available design space. Firstly, the effect of unsteady inlet conditions with variable frequency, amplitude, and mean value on collective shock generation is investigated. Then, a fast and cost-effective tool was developed and verified to predict bow shock wave motion from a prescribed inlet Mach trend; the parameters of the transfer function were estimated with a classical identification method based on a step-response CFD simulation. The model was employed to rapidly calculate the maximum amplitude of fluctuations accepted by the supersonic blade row for each frequency and average inlet Mach number. Finally, the influence of the inlet geometric angle, pitch to leading-edge thickness ratio, and static temperature on the model parameters is studied. The preliminary observations of the parametric analysis were confirmed by the rigorous quantitative approach of a global sensitivity analysis based on Sobol sensitivity indices.
Unsteady Pressures During Frequency Lock-in of a Cylinder Experiencing Non-Synchronous Vibrations
Authors: Hollenbach Richard , Sanz Isabelle , Kielb Robert 
Published: September 2023

Abstract
When an unsteady aerodynamic instability coalesces with a natural mode of vibration, Non-Synchronous Vibrations (NSV) can occur. Often in turbomachinery, vortex shedding, or tip gap flow causes frequency lock-in to the compressor or turbine blade bending or torsional natural mode of vibration. This can cause limit cycle oscillation (LCO) and ultimately blade failure. There is no current design tool for NSV that engine manufacturers can use; rather, expensive wind tunnel testing and time-consuming 3D computational fluid dynamics (CFD) are conducted to search for it. While studies have been done on turbomachinery geometry to study NSV, simpler configurations need to be studied first to understand the underlying flow physics. In this work, a cylinder undergoes enforced oscillations transverse to oncoming flow in the von Karman Vortex Street flow regime. The unsteady pressures are studied in both unlocked and lock-in conditions. In this context, this paper attempts to model the unsteady pressures of the lock-in region as a linear combination of unlocked amplitudes. Once the frequency content is collected for multiple cases, the unlocked data is fed into a Multiple Linear Regression to predict the lock-in data, with very good agreement. Previously shown was the coefficient of lift linearly increases with increasing amplitude of oscillation while locked in. The first study validates this finding. However, when unlocked first, the pressure contributions from various frequency ratios linearly combine to recreate the pressure loading for the lock-in cases. Finally, pressure amplitudes for various unlocked amplitude ratios linearly combine to form the same lock-in pressure loading. Unsteady pressures are not measured and do not often appear in literature. In addition, the unsteady pressure contributions have not previously been split up between the enforced motion and the vortex shedding, making this work novel.
Concentrated Solar Power Coupled With Waste Heat Recovery System for Innovative Clinker Calcination Process
Authors: Vesely Ladislav , McLaughlin Luke , Álvarez Francisco , Kapat Jayanta 
Published: September 2023

Abstract
The decarbonization of energy-intensive industries (i.e., cement) is a key challenge to reduce CO2 emissions worldwide and achieve zero-emission production. CO2 emission can happen through three different pathways in a cement plant: directly through (1) use of CO2-emitting heat sources, and (2) emission of CO2 generated in the calcination process, and indirectly through (3) use of electricity from the grid that is not fully green. The decarbonization of the cement process can be carried out by two different approaches (i.e., direct - alternative fuel or energy source and carbon capture systems, indirect - utilization of waste heat). This paper is focused on a novel cement process system that addresses pathways necessary to reduce the CO2-footprint of cement production. The proposed system consists of concentrated solar power (CSP), thermal energy storage (TES), and waste heat recovery systems (WHR). The exhaust stream can be connected with carbon capture and sequestration system (CCS). This allows the cement process to continue in production without downtime. The presented work is a concept study of the proposed system is based on current state of the art of individual subsystems. A complete analysis and optimization are performed for the sCO2 WHR power cycle as well as CSP and TES. The results show potential benefits and disadvantages of the proposed system.
Expansion of Neuber Rule to 3-D Stress States for Anisotropic Materials
Authors: O’Nora Nathan , Day William D. 
Published: September 2023

Abstract
It is often necessary to use finite element analysis (FEA) to understand the stresses experienced by a component when evaluating gas turbine component life. It is necessary to understand the elastic-plastic behavior of the materials for these components, but it may be impractical or cost prohibitive to simulate the inelastic behavior-plastic in FEA due to the much larger computation time. Neuber rule was developed to allow for correlating elastic results to elastic-plastic cases, however, doing so relies upon the use of an effective stress and effective strain calculation in order to be applied. While this works well in isotropic materials, for many anisotropic materials this is poorly suited due to the differences in anisotropy between the failure surfaces, yield surfaces, and plastic flow.
This paper demonstrates the expansion of the Neuber rule expanded to 3-D stress states and 3-D anisotropic material models by applying the rule for each component of the stress-strain relationship. A hydrostatic stress requirement is also used to ensure the resulting elastic-plastic stress-strain behavior is representative of the elastic case used to generate the stress-state. The method is applied to loadings of conventionally cast (CC), directionally-solidified (DS), and single crystal (SX) materials for both simple and complex loadings, utilizing an anisotropic visco-plastic model for the elastic-plastic behavior. Uniaxial results and complex isotropic loadings are compared to the 1-D Neuber rule to ensure that the 3-D expansion simplifies to the 1-D case where expected.
Design of an Environmental Barrier Coating Bond Strength Test Coupon
Authors: Salem Jonathan A. , Mital Subodh K. , Harder Bryan J. , Thompson Aaron C. 
Published: September 2023

Abstract
The bond strength of an environmental barrier coating (EBC) to a substrate such as a silicon carbide fiber/silicon carbide matrix (SiC/SiC) ceramic matrix composite (CMC) is a function of coating application parameters, matrix surface roughness and environmental exposure, which results in the formation of a thermally grown oxide layer (TGO) layer. Current estimates of the EBC bond strength to a substrate are made assuming that the applied force divided by pull tab area is a representative metric. Although this is an expedient method for rapid strength estimates, the process of bonding the EBC to a pull-tab creates thermo-elastic residual stresses that are superimposed with the applied tensile load. Minimization of these stresses via test specimen design should give the most realistic estimate of EBC bond strength. We examine the residual stresses imposed on the EBC by cooling of an adhesive layer bonded to various metal and ceramic tabs. The results are extended to examine the stress distribution in a thermally grown oxide (TGO) layer formed on a Plasma Spray-Physical Vapor Deposited (PS-PVD) Yb2Si2O7 (ytterbium disilicate) EBC. An EBC/substrate coupon that overhangs a titanium or Kovar® pull tab is recommended in order to minimize thermal stresses, avoid edge effects, and provide an acreage strength measurement. The test method is sensitive to changes in substrate surface finish and oxidation time.
On the Performance of Hydrostatic Journal Bearings in Air, Water, and Liquid Nitrogen: Measurements and Predictions
Authors: Jung Hyunsung , Kim Kyuman , Ryu Keun 
Published: September 2023

Abstract
Turbopumps in reusable and low-cost liquid rocket engines require compact and simple hydrostatic (i.e., externally pressurized) bearings to support large static and dynamic loads at high shaft speeds with no bearing DN life limitation. Hydrostatic bearings are one of the key mechanical components for cryogenic turbopumps to improve their reliability and reusability. Hydrostatic bearings offer significantly enhanced durability with very low friction and wear while providing accurate rotor positioning as well as large load and static stiffness characteristics even working with low-viscosity liquids. The current work measures static load characteristics of hydrostatic journal bearings in air (25°C), water (from 25°C to 70°C), and liquid nitrogen (−197°C). Air, water, and liquid nitrogen are used as test fluids for the test bearing to evaluate the effects of fluid properties and temperatures on the bearing performance. A complete set of applied static load, bearing eccentricity, and bearing supply pressure for each test fluid (i.e., air, water, and liquid nitrogen) is presented for the test hydrostatic bearing. Measurements show that the applied static load on the test bearing significantly affects the recorded journal eccentricity ratio, bearing flow rate, and bearing static stiffnesses. Predictions are in good agreement with measurements. The predictable performance of hydrostatic journal bearings in air, water, and liquid nitrogen can further their application in various cryogenic turbopumps for liquid rocket engines.
Sensitivity Analysis of Transient Forced Response of Mistuned Bladed Disks Under Complex Excitation and Varying Rotation Speed
Authors: Tong Jing , Zang Chaoping , Petrov Evgeny 
Published: September 2023

Abstract
During accelerations and decelerations of gas-turbine engines, the transient vibration effects in bladed disk vibration become significant and the transient response needs to be efficiently and accurately assessed.
In this paper, an effective method is developed for efficient calculations of the sensitivity of the transient vibration response for a mistuned bladed disk under varying rotation speeds. The sensitivities are calculated concerning two major factors: (i) the blade mistuning and (ii) the rotor acceleration/deceleration rates. The method uses the large-scale finite element modelling of the bladed disk to accurately describe the dynamic properties of the mistuned bladed disk. The method can be applied for a case when the loading is the transient load, with the amplitude and frequency spectrum changing with rotation speed. The dependency of the modal characteristics on the rotation speed is included in the formulation of the sensitivity analysis method. Efficient reduced order models are used to reduce the computational cost, which can adapt to the effects of the varying rotation speed on the natural frequencies and mode shapes of the mistuned bladed disk under transient conditions. The expressions for the sensitivities are derived analytically which provides high accuracy and speed of the calculations.
The method has been implemented in a computer code and thoroughly verified using a set of test cases. The studies of transient forced response sensitivity have been performed for realistic bladed disk models.
Temperature Measurement of Model Gas Turbine Combustor Using a Multi-Wavelength Pyrometry in Visible and Near Infrared Spectrum
Authors: Haidar Rifat , Lee Jong Guen 
Published: September 2023

Abstract
Continuous control and monitoring of the gas turbine combustor wall is essential for preventing combustor liner from overheating which may significantly damage structural integrity and reduce overall lifespan. In the past half century combustor outlet temperature has risen from 1100 to 1850 K. The continuous increase of severity of operating conditions inside combustor demands for a temperature determination method whose operation and accuracy are not affected by ever rising temperature. Conventional methods such as thermocouples and thermographic phosphor are not only intrusive, but their operation is also either restricted by an upper temperature limit (thermocouple) or measurement accuracy significantly decreases with increasing temperature beyond a certain threshold (thermographic phosphor). In this paper a multi-wavelength pyrometry system is developed which provides a fast, minimally intrusive temperature determination of the combustor wall. This method does not require any prior knowledge of exact emissivity but of the functional relationship between emissivity and wavelength over the spectral region of interest. One of major problems of wall temperature measurement using a pyrometry in combustor is that the emission from the combustor wall is interfered by the emissions from molecular radicals existing in the flame such as CH* (∼431nm), OH* (∼308nm), CO2* (400–600 nm) in the visible range and major species such as H2O (1.4,1.9,2.7,6.3 um) and CO2 (2.7,4.3,15 um) in the infrared region. In this report, a combustor which is made of stainless steel and runs on natural gas is used and the spectrum of flame emission is measured to identify a proper wavelength range (650–800 nm) over which there exists minimal or no interference from flame emission with thermal radiation. Thermal radiation is measured within the mentioned spectral range with spectrometer and camera assembly from the target spot on the combustor wall with temperature ranging from 1000 to 1200K. Measured temperatures are found to be in good agreement with temperatures measured with thermocouple with absolute error being within 5% or less.
Effect of a Passive Flow Control Device on the Performance of an S-Duct Inlet in High Subsonic Flow
Authors: Rider Courtney , Asghar Asad , Allan William D. E. , Ingram Grant , Stowe Robert , Pimentel Rogerio 
Published: September 2023

Abstract
Embedded engines requiring S-duct diffusers as inlets have long experienced flow separation and distortion. This paper presents an investigation of passive flow control with the application on S-duct diffusers. The flow control is in the form of stream-wise tubercles aiming to improve performance through increasing boundary layer momentum and keeping flow attached in previous regions of separation. Tubercles have shown to increase post-stall performance for airfoils and are similarly applied to the suction surface when used in internal aerodynamics. This paper compares results from experimental testing and computational fluid dynamics (CFD) simulations. The experimental results measured surface pressure with static surface ports, and at the exit, total and static pressure measurements were recorded with a 5-hole AeroProbe. The implementation of flow control led to decreased or mitigated separation regions developing into a more uniform pressure at the aerodynamic interface plane. Similar results were evident in the CFD simulation. A k-ω SST model was chosen since it has shown to better predict the separation regions. A high y+ model was used since additional improvement in separation modeling. The same trends were seen in simulated pressure recovery and in swirl when comparing the use of flow control to the baseline duct performance.
Part Load Combustion Testing of a Low NOx Combustor With Hydrogen-Methane Fuel Mixtures
Authors: Beck Griffin , Cunningham Seth 
Published: September 2023

Abstract
Currently, electricity markets are beginning to experience substantial increases in renewable energy generation. Some of these renewable energy sources have a highly variable output in an uncontrolled manner. In order to maintain grid stability, there is a need for power plants to ramp up power supplied to the grid rapidly to make up for drops in renewable generation. This is often termed spinning reserve, but the size of this reserve may need to increase as renewable penetration into the electricity market increases. Small combined heat and power (CHP) plants provide a promising option for meeting this spinning reserve requirement.
In order to operate in spinning reserve while still meeting the heat requirements for the CHP, the gas turbine needs to operate efficiently at very low loads. Efficient, high turndown operations in engines is often limited by the lean flammability limit of the premixed combustion system. This paper discusses experiments carried out to access the benefits on high turndown performance of adding up to 30% hydrogen into the existing engine combustion system. This will help enhance the lean operability range of the gas turbine combustor. Understanding the limits will have a positive two-fold effect. First, the overall efficiency of the gas turbine at part-load conditions will be increased due to the reduced reliance on variable guide vanes (VGV) to maintain a flammable fuel-air ratio. In addition, expanding the lean operating envelope will allow extension of low emissions operation to lower load conditions, which will increase the ability of the gas turbine, operating in a combined heat and power (CHP) application, to efficiently provide power grid support.
Effect of Strip-Fin Height on Jet Impingement Heat Transfer in a Rectangular Channel With Two Jet-to-Target Surface Spacings
Authors: Alzahrani Yasser S. , Wright Lesley M. , Han Je-Chin 
Published: September 2023

Abstract
An experimental investigation of heat transfer performance in a rectangular impingement channel featuring staggered strip-fins was completed. Four configurations were considered to study the effects of varying the strip-fin height (H/d = 1.5 and 2.75) at two jet-to-target surface spacings (z/d = 3 and 6) on the heat transfer, pressure loss, and crossflow magnitude for an impingement channel with in-line, 4 × 12 impinging jets. Also, the effect of the reference temperature choice, either jet inlet temperature or local bulk temperature, for calculating the local heat transfer coefficients was considered. The regionally averaged heat transfer coefficients were measured at seven Reynolds numbers, based on the jet diameter, (10k-70k) utilizing the copper plate experimental method. The results show that the trend of the local Nusselt number distribution varies along the streamwise direction due to the crossflow effect. The crossflow is similar for all Reynolds numbers at a given jet-to-target surface spacing. The discharge coefficients start to decrease below 0.9 after Re = 50k. Finally, empirical correlations were expressed for the area averaged Nusselt number estimation of impingement channels with pin-fin or strip-fin roughness elements.