bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of the Purge Flow Density Ratio on the Rim Sealing Effectiveness in Hot Gas Ingestion Measurements
Authors: Orsini Lorenzo , Picchi Alessio , Facchini Bruno , Bonini Alessio , Innocenti Luca 
Published: September 2023

Abstract
The rim seals of gas turbines are used to control the ingestion of hot mainstream gas into the wheel space between the rotor disk and the stationary casing. Sealing air, which is generally used to pressurize the cavity space, flows through the seal clearance and then mixes with the flow path in the annulus. Predicting the correct quantity of purge flow necessary to prevent excessive ingestion of hot gases while, at the same time, minimizing the penalties in terms of engine efficiency and stage aerodynamics represents a great challenge for the designers and a crucial point for the design of reliable engines. Such estimate is governed by unsteady phenomena and CFD approaches are still expensive and time-consuming, especially if 3D domains and unsteady conditions have to be simulated. Fundamental test cases, replicating actual engines geometries, are still a valid approach to calibrate correlations or simplified models such as the so-called Orifice Model. However, most of the experimental studies deal with test rigs at room temperature and do not take into account the effect of the density ratio between purge and main flows.
To fill this gap, the present paper reports the impact of the density ratio on the rim sealing effectiveness by performing a non-intrusive diagnostic based on the Pressure Sensitive Paint (PSP) technique on both the stator and rotor side. The analysis was performed on a cold Rotating Cavity Rig, developed for the study of hot gas ingestion, where two different values of density ratio were tested by using N2 (DR = 1) and CO2 (DR = 1.52) as purge flow. The data extracted from the PSP seal effectiveness maps allowed to calibrate the Orifice Model for the stator side and to fit the coefficients of the Buffer Ratio model for the rotor surface at different flow conditions where the Externally-Induced ingress is the dominant mechanism for gas ingestion. The results highlighted the impact of the DR on the seal effectiveness and on the low-order models considered for the data analysis. In the end, it is shown that the obtained results can be used to scale experimental data, generally collected at DR close to one, towards more representative engine values where the difference between the density of purge and main flows cannot be neglected.
High Speed Rotary Atomizer Supported on Porous Type Gas Bearings: Challenges Faced, Operability Demonstration and Load Testing
Authors: Wadhvani Vishal , Bazergui Claude , Mehan Paul , Smith Michael , Michael Anthony 
Published: September 2023

Abstract
A novel “patent-pending” high speed rotary atomizer supported on porous gas bearing technology was designed, fabricated and tested in response to challenges with an existing product on active magnetic bearing (AMB) technology and the desire to keep the design oil-free due to its inherent maintenance/operation benefits. The lessons learnt on the magnetic bearing atomizer system especially in regards to the periodic rotor imbalances the atomizing process imposes on the system, scaling/ cost complexity of the design and the customer complaints/ feedback were at the heart of this new design endeavor on gas bearing technology. This paper describes all these issues in detail and the testing data on this new design is presented along with the challenges/ setbacks faced during the initial stages of prototype testing. Some of the failures experienced during the early stages of prototype testing will be described in detail (especially due to the temperature rise seen inside the machine at high operating speeds) and how some novel design improvements/ measures were undertaken to overcome them. Lastly, the benefits of this new design will be discussed in comparison to other bearing technologies and how they are being leveraged for use in multiple sizes so it can be a truly scalable platform.
Second Edition: Assessment of Current Capabilities and Near-Term Availability of Hydrogen-Fired Gas Turbines Considering a Low-Carbon Future
Authors: Webb Bobby M. , Harper Jim , Steele Robert , Noble David R. , Emerson Benjamin , Wu David , Lieuwen Tim 
Published: September 2023

Abstract
Gas turbines continue to play a vital role in the global push for decarbonization, both for near-term reductions as coal phases out for natural gas operation and long-term transitions to carbon-free fuels. While decarbonization presents a threat to traditional combustion-based power generation, it offers an opportunity for a renewed role of the existing and future gas turbine fleet in a carbon-free future. This renewed role positions gas turbines to help stabilize power grids with large portfolios of intermittent renewable generation sources, with the gas turbines operating on low-carbon fuels such as hydrogen. Historical approaches to decarbonization of gas turbine combustion face hydrogen fuel content limitations, while simultaneously implementing dry, low-NOx (DLN) technologies. In 2020, we presented a review of the current state-of-the-art, and we projected the emerging technologies for DLN, high hydrogen combustion capabilities. In this paper, we revisit those projections and update the current state-of-the-art combustion capabilities through the last three years of development along with new initiatives to push capabilities further. Readers of this paper will take away an understanding of where the field is on low-NOx, high hydrogen combustion. Additionally, an overview takeaway will be understanding of the current capabilities of each of the OEMs and other major players, including the developing technologies and targets that each is working towards for a carbon-free, dispatchable power generation source.
High Altitude Relight Performance of Hydrogen-Air Micromix Combustion Systems
Authors: Treleaven Nicholas C. W. , Puggelli Stefano , Mercier Renaud , Leparoux Julien , Sun Xiaoxiao , Sethi Bobby 
Published: September 2023

Abstract
In order to reduce the environmental impact of commercial aviation, hydrogen is being considered as a replacement fuel for kerosene in commercial aircraft. Due to the significantly different physical properties as compared to kerosene, this change in fuel promotes a potential revolution in the design of the combustion chamber. One of the alternative combustion systems recently proposed for hydrogen is micromix. The micromix injection consists of replacing a single air and fuel injector with many hundreds or thousands of small-scale simplified jet in crossflow type injectors. These simple injectors consists of an air gate that generates a small axial jet and a hydrogen injection hole that introduces the fuel perpendicularly into the path of the injected air. This configuration then leads to a large number of relatively rich partially-premixed flamelets in an otherwise globally lean combustor. The high local mixture fraction enhances flame stability, while the size of the flamelets enhances mixing and reduces the residence time of hot products, leading to low production of nitrous oxides. This relatively revolutionary approach has still to be tested thoroughly over the full range of engine conditions and operability specifications. One such requirement is high altitude relight: the low temperature and pressure of the combustion chamber reduce the laminar fuel speed and turbulence levels up to conditions where ignition using conventional methods may not succeed. This study used high fidelity Large Eddy Simulation to investigate high altitude relight for a micromix system. In particular, two approaches for chemistry description are compared: tabulated chemistry based on premixed flamelets and transported chemistry. Flame kernels of different sizes are computed with both approaches to determine the minimum kernel size required for ignition and a probability of ignition. Results show that due to the small recirculation zones downstream of these injectors, ignition must take place close to the injector face. Tabulated chemistry methods fail to predict ignition and a detailed analysis is proposed to better understand the differences with transported chemistry. A simplified model is also presented that links the probability of ignition with the flame speed and radius of the initial flame kernel.
Effects of Surface Roughness on Three-Dimensional Flow Structure Within Shaped Film Cooling Holes
Authors: Banko Andrew J. , Benson Michael J. , Davidson F. Todd , Zia Wasif , Bordbar Alireza , Boyce Christopher , Veley Emma M. , Thole Karen A. 
Published: September 2023

Abstract
Additive manufacturing (AM) techniques are expanding what is possible for designing and constructing gas turbine components that can handle increasingly harsh operating conditions. However, AM techniques can also introduce surface roughness that is more prominent than conventional manufacturing methods. The influence of this roughness could have an important effect on the performance of film cooling holes. However, little is known experimentally on what happens inside of a film cooling hole since this region is challenging to access with traditional measurement techniques. This study uses magnetic resonance velocimetry (MRV) to observe the in-hole flow structure of a scaled version of a baseline diffuser-shaped hole configuration with and without surface roughness at two blowing ratio conditions. The roughness geometry is derived from computed tomography (CT) scans of a metal-AM diffuser hole. The three-component, three-dimensional, time-averaged velocity field is measured by MRV and includes the flow from the plenum, within the hole, and in the vicinity of the hole exit. The momentum distribution within the diffuser differs between the smooth and rough holes, with peak velocities and flow asymmetry influenced by the surface roughness. Flow along the leeward wall of the diffuser is nearly separated, and the size of this separated flow region is smaller in the roughened cases. These effects are accentuated at larger blowing ratio. These data provide explanatory evidence of how the momentum distribution within smooth and rough holes may impact surface effectiveness results downstream of the shaped holes. CT scans of the surface roughness coupled with the MRV measurements provide non-optical means to characterize the hole geometry and as-built performance of additively manufactured test coupons with important implications for the field.
Test Rig Concept for Evaluating the Performance of a CO2 Immersed Electro-Mechanical Rotor System Utilizing Gas Bearings: Part-1 Mechanical and Electric Machine Design
Authors: Ertas Bugra , Powers John , Gary Keith , Torrey Dave , Zierer Joseph , Baehmann Peggy , Rallabandi Vandana , Adcock Tom , Anandika Nevin , Bidkar Rahul A. 
Published: September 2023

Abstract
This paper presents the mechanical and electric machine design of a 27krpm rotating test rig aimed at reducing technical risks with hermetic oil-free super-critical carbon dioxide (sCO2) turbomachinery. The test rig rotor system is based on a conceptual turbomachine design discussed in a companion paper that evaluates a sCO2 waste heat recovery (WHR) unit for land-based gas turbines at natural gas (NG) compressor stations. The key novelty of the hermetic sCO2 turbomachine concept is the utilization of additively manufactured CO2 gas bearings and a CO2-immersed direct-drive permanent magnet (PM) electric machine. The previous effort on conceptual design identified 3 main technical risks, which included thrust bearing load capacity, rotordynamics, and thermal performance of the system. Therefore, key requirements of the test vehicle include the ability to test the rotor system in a 400psi (27.6 bar) hermetic CO2 operating environment, apply up to 1,500 lbs (6.7 kN) of rotor thrust loads, capability to assess rotordynamics with radial gas bearings, inclusion of instrumentation to assess thrust bearing load capability, and flexibility for varying secondary cooling flows to confirm thermal model predictions. Design topics such as rotordynamics, bearing design, and electric machine design are addressed in the paper, while highlighting critical elements. In addition, additive build trials for Inconel 718 radial and thrust bearings were performed to prove the manufacturability of the bearing design concepts. The results of the design efforts yield a test rig concept with ability to operate at 27,000 rpm, apply thrust loads to 1,500 lbs, deliver CO2 up to 800psi, and modulate cooling flows.
Enhancements to Impingement Heat Transfer Through Nozzle Geometry Modifications
Authors: Ortiz Laura-Cebrian , Acharya Sumanta 
Published: September 2023

Abstract
Jet impingement heat transfer is commonly employed in turbine cooling. The current paper aims to experimentally analyze the enhancement of the heat transfer rate when using a turbulent impinging jet with different nozzle geometries that alter the nozzle exit flow condition and/or enhance unsteadiness/turbulence and induce it into the jet-flow. The nozzle geometry is altered by adding annular trips or axial trips or swirl trips on the internal surface of the nozzle. The measurements are based on a steady state approach with a uniform heat flux boundary condition and infra-red imaging to determine surface temperatures. Data on the local and average Nusselt number are reported for different jet-to-target spacings (H/D = 1.5–12) and Reynolds numbers (Re = 10000–97000). These results are compared with the corresponding baseline round jet geometry. It is observed that nozzles with swirl turbulators provide the greatest enhancement in surface heat transfer.
Evaluation of Pressure Drop and Cooling Effectiveness of Serpentine Channels With Varying Internal Rib Configurations
Authors: Yoon Christopher , Ellinger Molly E. , Bogard David G. 
Published: September 2023

Abstract
Gas turbine airfoils commonly use serpentine passages for internal cooling. To enhance the heat transfer in this internal passage, rib turbulators are often used. There have been many studies of rib turbulators to determine the optimum height, spacing, and angle; but almost all of these studies have been conducted using straight ducts. In this study, computational RANS predictions using the Realizable k-ϵ model and wind tunnel experimentation were used in conjunction to determine the optimum rib turbulator configuration for use in serpentine channels. The serpentine passage configuration had three U-bends and L/DH = 10 for each leg. The channel was placed below a simulated turbine airfoil wall which was flat, and the ribs in the channel were placed on this wall. Computations and experiments were completed with a smooth channel and with ribs at angles of −60°, 90°, and +60°, rib heights of e/H = 0.125 and 0.25, and spacing between ribs of P/e = 4 and 8. Studies were also done using turning vanes in the U-bends to reduce separation regions downstream of the U-bend. A key result from this study was that ribs oriented at −60° would produce similar pressure drops to the smooth serpentine channel. Flow field visualization showed that large separation regions after each U-bend of the serpentine channels were responsible for increased pressure drop, and the −60° ribs helped to redistribute the biased flow. Rib orientations of 90° and +60° experienced larger pressure drops than the −60° ribs both computationally and experimentally. Compared to the smooth channel, the channels with rib turbulators had only a small increase in heat transfer rates, ranging from 4% to 16% for varying rib angles. This small enhancement of heat transfer was attributed to the large heat transfer for the smooth serpentine channel caused by strong vortical flow generated downstream of the U-bends.
Analytical Study on Hybrid Thrust Foil Bearing, Structural Characterization and Measurement of Static Performance
Authors: Ebewele Ehiremen , Kim Daejong , Ki Jeongpill 
Published: September 2023

Abstract
This work presents a novel design of a hybrid thrust foil bearing (HTFB) with an outer diameter of 154mm, along with simulation and test results. The HTFB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. As a result, this bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HTFB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and external loads. The bearing performance was predicted at 40krpm, 3000N axial load, and 6 bar absolute hydrostatic pressure in both hydrodynamic and hybrid modes. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the minimum film thickness compared to hydrodynamic bearing due to the boost effect of hydrodynamic pressure in the main film. The preliminary experimental measurements on load capacity at zero speed agree with the prediction. Rotational tests were conducted at 10krpm, 15krpm and 20krpm. Ultimately, the novel HTFB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.
3D Printing-Enabled Layer Hierarchies
Authors: Song Kenan , Ravichandran Dharneedar , Jambhulkar Sayli , Xu Weiheng 
Published: September 2023

Abstract
Advanced composite materials (ACMs), especially nanoparticle-reinforced polymer composites (NpRPCs), exhibit desirable physical and chemical properties that include low density coupled with directed high stiffness and strength, optimal dimensional stability, superior temperature, and chemical resistance, as well as relatively cost-efficient manufacturing. Successful manufacturing of high-performance nanocomposites depends on the precise control of processing factors, including (i) uniform dispersion of the nanoparticles, (ii) effective matrix-filler interfacial interactions at the molecular level, and (iii) alignment/orientation of the nanoparticle and/or polymer chains. This study highlights a newly designed nozzle for multilayer composite structure fabrication using thermoplastic and thermoset polymers, as well as nanoparticles of various morphologies (e.g., 1D and 2D), which have been used for the scalable fabrication of 1D fibers, 2D coatings, and 3D architectures via 3D printing. Discussion of the nozzle design, layer formation mechanism, and fabrication of functional structures of 1D, 2D, and 3D morphologies will be the focus of this talk. The demonstrations in structural supports, thermal dissipations, electrical conductors, plastics recycling, stimuli-responsive systems, and tissue scaffolds show massive potential in national defense, space exploration, energy storage, and human health.
Print Speed Optimization for UV-Assisted 3D Printing of Lunar Regolith Simulants Composite Inks
Authors: Marnot Alexandra , Cho Jaehyun , Brettmann Blair 
Published: September 2023

Abstract
Direct-ink-write (DIW) 3D printing of dense composite inks is an attractive method of additive manufacturing for Lunar missions using in-situ derived resources. DIW offers a wide degree of freedom for formulation design with multiple methods for solidifying the inks post-extrusion. The use of UV-curing, however, poses certain complications when the loading of particles in the ink reaches levels above 50 vol% due to light scattering, absorption, and reflection. Herein, we investigate the curability of two Lunar regolith simulants, compared against a model system of glass microspheres, as particles in UV-curable inks. Photo-DSC is utilized to assess the degree of cure of the inks at a range of timescales. These results are tied to depth of cure experiments following the ISO 4049 method to verify cure depths meeting a target print layer height and to optimize the speed of printing while maintaining structural integrity. The extent of cure is verified both qualitatively through print shape fidelity and quantitatively through ATR-FTIR. This work not only highlights the importance of particle mineralogy for achievable UV-assisted solidification post-extrusion, but also presents test methods easily adapted to a design of experiment framework that require very little sample volume to identify successful formulations and printing parameters.
The Effect of Voltage on the Initiation of Natural Pulsation in Electrohydrodynamic Jet Printing
Authors: Hawa Angelo , Bahrami Ali , Barton Kira 
Published: September 2023

Abstract
Electrohydrodynamic jet (e-jet) printing is a high-resolution additive manufacturing process that uses an electric field to extract polarizable ink from a nozzle. The high-resolution capabilities of e-jet printing are very favorable for the fabrication of printed electronics and biosensors, which is typically achieved using a highly controllable pulsating jet. In this regime, high voltage pulses are superimposed over a baseline DC voltage, which primes the meniscus for the subsequent pulse. While a higher baseline voltage reduces the response time of the system, values above a certain threshold can cause the printing to transition toward an uncontrollable jetting regime in which the natural dynamics of the ink instigate pulsating jet behavior. To characterize the effect of these unwanted transitions on the final print, key parameters of the natural pulsating jet mode must be identified. This work presents findings on the relevant time constants and volume measurements of jet printing at various subcritical voltages. While the impingement time of the jet was found to be proportional to the applied voltage, the volume of the initial droplet increasingly varied. Conclusions regarding permissible pulse widths and system predictability as a function of voltage were made.
Optimization of Process Parameters and Variability Study in Friction Stir Welding of 6061-T6 Aluminum Alloy and Ti64 Alloy With Interlayer
Authors: Mustafa Saed Enam , Rai Rajiv Nandan 
Published: September 2023

Abstract
Friction stir welding (FSW) of Aluminum (AA6061-T6) and Titanium (Ti64) dissimilar alloys have been carried out in the presence of a 2 microns Copper interlayer. Three levels of tool rotation speed and traverse speed have been selected as variable input parameters. The output parameters considered response variables were the temperature on the Ti side, temperature difference, microhardness, and tensile strength. Taguchi’s L9 array has been used for the experimental design. The Taguchi’s L9 orthogonal array is used in order to estimate the factors that influence the performance criteria and also which factors are more important than others. From the response table, the tool rotation speed has been found as the most influential factor affecting the quality of the welded joint. The signal-to-noise (S/N) ratio indicated that the welded joint’s optimal quality was achieved at 500 rpm and 14 mm/min. The ANOVA analysis found that the p-values of all the response variables are less than the significance level α (0.05). The variability study indicated that the process was under statistical control, and no assignable causes of variability were present. However, the ways and means to reduce inherent variability can be further explored using an improved experimental setup.