bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Conical Cavity on the Load Capacity of Externally Pressurized Steam-Lubricated Journal Bearing
Authors: Liu Zhansheng , Qi Jinlei , Yu Xiangyu 
Published: September 2023

Abstract
Motivated by the urgent need for the development of oil-free and closed-loop turbomachinery in deep-space and deep-sea exploration missions, process-gas lubricated bearing has seen the recent surge of interest due to its numerous advantages. Particularly, externally pressurized steam-lubricated bearing plays an important role in closed-cycle steam turbine, which significantly influences the machine reliability and operating characteristics. In order to achieve effective lubrication and obtain high load capacity, a full understanding of how bearing geometrical parameters and gas properties affect the bearing overall performance is required.
This study mainly proposes a novel design to increase the load capacity of the externally pressurized steam-lubricated journal bearing. Firstly, the correctness of simulation is verified based on a simple bearing model. And with the help of the computational fluid dynamics numerical tool, this paper conducts a detailed fluid flow and heat transfer analysis for inherently compensated steam journal bearing. The computations have been performed for two different gases — air and steam. The bearing diameter is 110mm and it has single-row 8 orifices. Flow field parameters such as pressure distribution, mass flow rate, velocity distribution are presented. Results also reveal the classical pressure depression in the gas film entrance and transonic flow phenomenon in the bearing clearance. Second, based on the lubrication flow analysis, a new conical cavity concept is presented. The study compares the static load capacity performance and flow characteristics of the steam journal bearing with and without the conical cavity. We find that the conical cavity structure can actually improve the static load capacity of the inherently compensated bearing. Finally, the influence of conical cavity angle on the load capacity and mass flow rate is investigated. There are 11 different conical cavity angles which vary from 20 degrees to 70 degrees. The numerical results show that the conical cavity angle almost has no influence on the static load capacity but reduces the mass flow rate when the angle value rises. This study demonstrates that how to design the high load capacity externally pressurized steam-lubricated journal bearing for closed-cycle steam turbine.
Transient Heat Flux Budgeting on a High-Pressure Turbine
Authors: Saavedra Jorge , Lozano Francisco , Paniagua Guillermo 
Published: September 2023

Abstract
This research is focused on the temporal heat flux budgeting on a high-pressure turbine exposed to periodic upstream total flow temperature variations using computational fluid dynamics simulations. A high-pressure turbine vane is exposed to sinusoidal upstream total flow temperature oscillations with peak-to-peak variations around 50K at various frequencies. Transient Unsteady Reynolds Average Navier-Stokes simulations (URANS) are performed, taking advantage of the k-w SST transitional turbulent closure. The transitional kw SST model identifies the transient stagnant conditions’ impact on the velocity and temperature boundary layers, considering its influence on turbulent production and dissipation and thermal convection while minimizing the computational burden. The proposed numerical set-up is verified against experimental pressure and heat flux distributions over a high-pressure turbine vane.
The evolution of the near wall velocity and thermal profiles are described along the periodic operation, identifying the temporal dynamics governing the heat flux distribution. The velocity and static temperature development are also analyzed based on spectral proper orthogonal decomposition to identify the dominant structures responsible for the transient thermal and momentum response. The temporal characterization of the thermal boundary layer and heat flux distribution over the turbine vane enables the design of more efficient flow control and cooling strategies that mitigate heat loading while minimizing the amount of coolant.
Towards an Improved Description of Film-Cooling Heat Transfer Through Anisotropic RANS Modeling: A Combined LES/RANS Contribution
Authors: Laroche Emmanuel , Dupuy Dorian , Duchaine Florent , Gicquel Laurent 
Published: September 2023

Abstract
This study focuses on the physics and the modeling of the heat transfer taking place within the Penn State 777 shaped hole flow configuration. To do so, a dedicated Large-Eddy Simulation conducted with the AVBP solver is carried out and shows good reproduction of the main flow characteristics observed in terms of features and adiabatic effectiveness. This simulation is then more deeply analyzed to conduct an a priori evaluation of the most current heat flux assumptions used in RANS modeling, being the Prandtl analogy and the Daly Harlow hypothesis. Results obtained for this shaped hole configuration confirm previous ones obtained for cylindrical holes, showing the deficiencies of classical RANS models. In particular, it is shown that the equivalent Turbulent Prandtl number usually fixed at 0.9 is here largely overestimated. The most representative value is indeed around 0.5 in most regions of interest. It is also showed that the diffusion process is not the same in all directions, namely the wall normal and transverse directions turbulent diffusion processes differ. A Reynolds-Stress model simulation using the Elliptic Blending Reynolds-Stress Model developed by Manceau is then conducted, combined with different advanced heat flux models. With this new and more advanced model, obtained results show major improvements compared to state of the art RANS simulation using the k-ω SST along with the Prandtl analogy. In particular, the centerline and the lateral effectiveness profiles are considerably enhanced, exhibiting a more representative lateral spreading. The respective contributions issued by the improved Reynolds-stress description and the heat flux models are eventually analyzed. A modified model for the heat flux formulation is hence suggested in an attempt to provide extra improvement compared to Daly-Harlow formulation. In conclusion, this work strongly advocates for the use of anisotropic models either for turbulent stress modeling or turbulent heat flux modeling for the description of film cooling phenomena at stake.
Review and Development of Natural Gas/Hydrogen Fuel Flexible Reduced Chemical Mechanism for High-Order Modeling of Gas Turbines
Authors: Valles Miguel A. , Kessler Iris , Windom Bret C. 
Published: September 2023

Abstract
Green hydrogen produced from water electrolysis is a promising carbon-free energy storage medium that, when blended with natural gas, can be transported in existing natural gas pipeline infrastructure, and utilized in associated power plants to reduce the carbon intensity of existing natural gas-powered systems. However, hydrogen’s high reactivity presents unique challenges related to maintaining stable combustion while balancing low NOx emissions in traditional dry low-NOx combustion systems designed for natural gas fuel. Therefore, there is a need to develop retrofittable combustion technologies that can be adapted to existing gas turbine engines to permit high hydrogen fuel blend ratios. State-of-the-art Computer-Aid Engineering (CAE) tools are needed to study the impact of hydrogen within these devices and to design next-generation novel combustor designs strategies to enable high hydrogen/low NOx combustion. At the heart of these CAE tools is a chemical mechanism to model the combustion reactions and species generated throughout the engine; however, the size of the mechanism is strongly tied to the computational expense. For this reason, it is critical to have a high-fidelity and validated yet tractable mechanism that can be used in advanced computational fluid dynamic modeling approaches while also capturing the key reactions responsible for flame stability and NOx emissions. Many chemical mechanisms exist, each designed for and validated with combustion applications/data under unique conditions. Here we quantitatively compare several of the most common small species chemical mechanisms for suitability in modeling gas turbine engine relevant conditions.
In doing so, we report the results of an extensive literature review comparing existing hydrogen and natural gas chemical mechanisms to a wide range of laminar flame speeds and ignition delay time experimental data. The predictability of existing chemical mechanisms and deficiencies in the validation dataset are discussed. These deficiencies vary from case to case but are noticeable at high pressures (&gt;10 bar) and for blended fuels (natural gas and hydrogen). A large gap was found in current laminar flame speed experimental data at high pressure and temperatures which is also where the largest discrepancies are noticed between existing chemical mechanisms. Preliminary NOx modeling validation for several common NOx chemistry sub-mechanisms was also performed using hydrogen diffusion flame experimental data. Future work will evaluate NOx in natural gas species diffusion flame experiments and laminar flame speed experiments.
Static Characteristics Analysis of Textured Thrust Bearing Based on the Multigrid Algorithm
Authors: Xu Kefan , Zhang Guanghui , Sun Wenlong , Han Jiazhen 
Published: September 2023

Abstract
Carefully designed compliant foil structure or surface texturing can both help improve bearings’ performance. However, little research has been done on their combination: textured gas foil bearing. This paper adopted the modified compressible Reynolds equation as the pressure governing equation of bump-type foil thrust bearing, and the influence of different slip models was discussed. The predicted load capacity agrees with the literature data. This paper further presented the execution time differences between various numerical methods, including the direct, iterative, and multigrid algorithms, when handling the significant discretization effort introduced by texture. The results indicate that the multigrid algorithm performs best, and the execution time is generally reduced by 50% compared to the traditional direct method under the same operating parameters. Besides, further analysis of the textures’ effect on bearings’ performance was carried out based on three distribution types. The results indicate that textures affect all static characteristic parameters more when the relative texture depth increases. For the #1 texture distribution type, the maximum increment of load capacity could exceed 10% when the textures are assumed to be manufactured in the ramp of the top foil. In conclusion, the multigrid is an excellent solution that can balance computational accuracy and efficiency for textured foil thrust bearings. Furthermore, an appropriate arrangement of textures could improve foil thrust bearings’ performance.
The Development and Use of a Natural Gas / Oxygen Burner Rig for Environmental Barrier Coating and Ceramic Matrix Composite Technology Maturation
Authors: Presby Michael J. , Endo Makoto , Fox Dennis S. , Harder Bryan J. , Lee Kang N. , Hoffman Leland C. , Cuy Michael D. 
Published: September 2023

Abstract
This work outlines the development of a new natural gas/oxygen (NG/O2) fueled combustion rig located at the NASA Glenn Research Center for high-temperature environmental durability studies of advanced materials and components at atmospheric pressure. The NG/O2 burner rig can simulate the high-temperature, high-heat flux, and high-velocity thermal environments encountered in gas turbine engines. It also provides the capability to study environmental effects such as water vapor and other foreign contaminants relevant to these applications. The rig is anticipated to bridge the gap between other laboratory methods such as furnaces, jet-fueled burner rigs, high-heat flux lasers, and more expensive engine rig testing. The NG/O2 rig is expected to have maximum sample temperature capabilities over 3,000°F (1,649°C) and result in higher water vapor content compared to our Mach 0.3 to Mach 1.0 jet-A burner rigs which is important for characterizing current and next-generation environmental barrier coatings. This paper will provide an overview of the development of the NG/O2 burner rig, initial characterization, and current research and development efforts on environmental barrier coated ceramic matrix composites.
Simulation of Methane Oxycombustion in Supercritical Carbon Dioxide
Authors: Henry De Frahan Marc T. , Rahimi Mohammad J. , Doronina Olga , Perry Bruce A. , Yellapantula Shashank , Cormier Ian , Day Marc , Martin Michael James 
Published: September 2023

Abstract
The Allam-Fetvedt Cycle (AFC) offers the potential for electricity generation with minimal or even negative carbon emissions by using oxycombustion in supercritical carbon dioxide (sCO2). Because of the extreme high temperatures and pressures encountered in these systems, simulation of oxycombustion requires use of a complex equation of state such as the modified Soave-Redlich-Kwong (SRK) equation, coupled with equally complex correlations for transport properties. The current work simulates a model combustor using both an ideal gas equation of state and the SRK equation of state. The model combustor features a jet of CH4 mixing with and reacting with O2 in the sCO2 ambient. Two jet configurations are considered: one of pure CH4, and one of CH4 mixed with sCO2. Comparison of results shows that key output properties such as combustor temperature and flow distribution are impacted by the choice of equations of state. Inspection of simulation results shows that mixing and reaction rates, as well as the uniformity of the flow, are impacted by the choice of equation of state. These results show that even though use of a complex equation of state greatly increases the computational costs of these simulations, it is critical to accurately capturing the physics of these systems.
Investigation of Water Film Behavior on the Surface of an Airfoil in a High-Speed Flow and Subsequent Ligament Formation and Breakup From the Trailing Edge
Authors: Safiullah S. , Esquivias Brandon , Hickey Brendan , McDonell Vincent , Tabata Soichiro , Senoo Shigeki 
Published: September 2023

Abstract
The breakup of liquid films in high-speed flows are found in many applications. These include pre-filming air blast atomization found in fuel injectors and shedding from airfoils. In this work, the behavior of a liquid film on the surface of a NACA 0012 airfoil placed in a high-speed air flow is investigated. The results complement previous results obtained on time averaged ligament behavior and droplet sizes generated by the same airfoil. A combination of computational fluid dynamic (CFD) simulations and experimental studies were carried out to assess features of water films, including the film thickness, wave speed, droplet shedding, and the dynamics of the sheet. In the present work, air velocities up to 175 m/s were used with water films flows between 1.4 and 2.6 cm2/s. The water film was introduced onto one side of the airfoil surface through a series of 0.5 mm holes separated by 1mm at a location 35 mm downstream of the leading edge of the vane. Experimental results were obtained using four primary tools. The first is a point measurement of the dynamic film thickness using a confocal laser induced fluorescence method. This spatially resolved measurement provides time resolved measurement of the instantaneous liquid film thickness at specific points on the vane surface. This is complimented by time averaged images of the film thickness on the entire vane surface. Third, high speed videos are obtained to study the accumulation and breakup of the liquid at the trailing edge of vane. Finally, laser diffraction is used to document the spray dynamics downstream of the vane. In addition to the experimental results, CFD simulations of the film behavior are also carried out using ANSYS Fluent. The results illustrate that the average film thickness decreases with air velocity and increases with the water flow rate. The results are consistent with the previous study and the current CFD analysis. Frequency analysis suggests that the dominant frequency of liquid film wave, ligament breakup length, drop size and spray concentration increase with the air velocity and is modestly affected by water flow rate. Finally, design tools are provided to predict the average film thickness and dominant frequencies of the film thickness, ligament breakup, spray concentration and droplet average size.
Performance and Emissions Benefits of Cooled Ceramic Matrix Composite Vanes for High Pressure Turbines
Authors: Wehrel Patrick , Schöffler Robin , Grunwitz Clemens , Carvalho Francisco , Plohr Martin , Häßy Jannik , Petersen Anna 
Published: September 2023

Abstract
Ceramic Matrix Composites (CMCs) offer great potential for developing lighter and more efficient aero-engines. Due to their high temperature capability, CMCs are mainly used in the hot gas section in order to replace cooled metallic components and thus save cooling air. Especially CMC vanes for high pressure turbines (HPTs) have been researched and tested in the past. A realistic design approach for cooled CMC vanes is the so-called shell and spar concept. The application of such vanes in HPTs as inlet guide vanes (IGVs) at constant rotor inlet temperature (T41) enables performance and emissions benefits which are assessed by means of a reference engine in this paper. Compared to metallic IGVs, more temperature-resistant CMC IGVs require significantly less cooling air and generate lower cooling losses. A quantitative comparison will be presented. Consequently, the redesign of the reference engine to the setting of a hybrid HPT leads to a reduction in thrust specific fuel consumption (TSFC) by 0.23 % at cruise conditions. Additionally, there is potential to extract the IGV cooling air at a lower pressure level, increasing the cruise TSFC gain to 0.41 %. In the course of the redesign process, the turbine inlet temperature (T4) is reduced by 50 K in order to reach the same T41 with a lower IGV coolant mass flow. Regarding emissions, this leads to a decreased production of nitrogen oxides (NOx). Hence, several NOx emissions parameters can be reduced by more than 4 %.
Effects of Supercritical CO2 Fluid Properties on Heat Exchanger Design
Authors: Lugo Afonso , Turunen-Saaresti Teemu , Tiainen Jonna 
Published: September 2023

Abstract
Supercritical CO2 (sCO2) in industrial applications is a promising solution for the reduction of equipment size and for the potential increasement of overall efficiency. The characteristics of CO2 near the critical point are advantageous for the heat transfer, with high specific heat capacity when compared to conventional liquid or gas coolants. Moreover, dopants can be mixed to CO2, in a blend, to further increase the heat transfer and elevate the critical point of the fluid. Under the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, a heat exchanger was designed using CO2 and blend as working fluids in an innovative power cycle bank of a concentrated solar power (CSP) plant coupled to a water desalination system. In this paper, the innovative heat exchanger is evaluated in terms of the geometry, focusing on heat transfer and turbulence, using computational fluid dynamic (CFD) simulations with SST k-ω turbulence model and real-gas models with REFPROP library for thermodynamic and transport properties. Within each fluid, the diameter of the channels varied from 1.8–2.2 mm and the results are compared to analytical models. The geometry with 1.8 showed a larger pressure drop, but also larger overall heat transfer coefficient. It is observed that both pressure drop and heat transfer decrease with the diameter. Blend as the hot fluid resulted in higher average temperature and heat transfer coefficient, but in lower pressure drop than pure CO2. Nusselt number correlations were compared, showing the decrease of its values with the diameter for pure CO2, while for the blend it was observed higher values for 2.0 mm of diameter, except for Fang and Xu correlation that showed the same trend as the CO2.
Calculation of Thermodynamic Wetness Loss in Steam Turbines Using CFD Simulation
Authors: Hoznedl Michal , Kolovratník Michal , Jun Gukchol 
Published: September 2023

Abstract
In the paper the behavior of wet steam flow is described in three different steam turbines. The first one is the 1100 MW turbine in the nuclear power plant with the pressurized water reactor. The second one is the 660 MW turbine in the fossil fuel power plant with ultra-supercritical steam parameters at the turbine inlet. The last turbine has a nominal output of 34 MW and operates in the municipal waste incinerator. However, this turbine can often also operate even at 2 MW or higher. In all three turbines in the last stage area passages are made for an optical probe to measure steam wetness and primary droplets size, and for a pneumatic probe to determine the pressures, velocities and flow directions. On the basis of experimentally obtained data analyses of thermodynamic wetness loss for all three turbines are performed using numerical flow simulations considering equilibrium and non-equilibrium steam. The condensation model that includes the nucleation rate and droplet growth velocity used in ANSYS CFX is calibrated based on experimentally obtained data. It is evident that the obtained loss patterns depend fundamentally on the turbine type and operating parameters.
Understanding Thermal Unsteadiness in Engine Representative Flows and Improved Methodologies for Derived Heat Transfer Calculations Using Thin-Film Gauges
Authors: Singh Deepanshu , Beard Paul F. , Cardwell David , Chana Kam S. 
Published: September 2023

Abstract
The Oxford Turbine Research Facility (OTRF) is a high-speed rotating transient test facility, that allows unsteady aerodynamic and heat transfer measurements at engine representative conditions. In addition, a variety of inlet temperature profiles can be simulated in the rig including radial distortion, circumferential distortion, and swirl. However, the engine representative flows cause complications in the processing of heat transfer data. The unsteadiness in temperature data was found to significantly rise as temperature distortions were introduced in the NGV inlet profile, to model a lean burn combustor exit. Using the NGV inlet temperature profile survey data, the thermal unsteadiness has been quantified and compared with a Uniform inlet. The experiments with a radially varying NGV inlet temperature profile showed up to nine times higher thermal unsteadiness, compared to the Uniform inlet. The second part of the paper is a continuation of the work presented in a previous paper by Singh et al. [1] and describes improved methodologies for derived heat transfer calculations using thin-film gauges. In addition, the uncertainty associated with the derived heat transfer parameters, such as the heat transfer coefficient and adiabatic wall temperature has been quantified. The refined processing techniques have been demonstrated on casing heat transfer measurements, acquired in the OTRF with two inlet temperature profiles.