bluuebunny/crossref_metadata_2025_split huggingface dataset:
Validation of Filtered Rayleigh Scattering Optical Rake Measurement Techniques in Turbomachinery Applications and Boundary Layers
Authors: Powers Sean W. , Byun Gwibo , Lowe K. Todd 
Published: September 2023

Abstract
Filtered Rayleigh scattering (FRS) is a non-intrusive, laser-based optical technique for measuring 3-component velocity, static temperature, and static density with high spatial resolution and low uncertainty. FRS can be used to derive total values as well as turbomachinery efficiencies. The Virginia Tech team has been developing this seedless technique for simultaneous planar (or line) measurements to overcome the limitations associated with seed-based laser measurement techniques such as laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and Doppler global velocimetry (DGV) as well as limitations with physical probe rakes such as blockage and wake production. This technique is especially attractive in flow cases or environments where the aforementioned seed-based laser measurement techniques are limited or not possible. A combination of specially designed boundary layer total pressure probe rake measurements, FRS optical rake measurements, and computational fluid dynamics (CFD) results in the inlet of a Honeywell TFE731-2 turbofan are presented. Results show that all three techniques (FRS, probe, and CFD) match within approximately 2% root-mean-square error (RMSE). Inlet efficiency was derived and found to be within 2.3% difference for all three techniques.
Performance Assessments of a Novel Oxy-Fuel CO2 Cycle
Authors: Sammak Majed , Thanganadar Dhinesh , Dawood Alaaeldin , Suleiman Baha , Kulkarni Parag 
Published: September 2023

Abstract
This paper presents a novel way of improving CO2 intensity simple cycle gas turbines. We present a novel combined cycle that consists of an integrated semi-closed oxy-fuel gas turbine topping cycle and a sCO2 bottoming cycle. This sCO2 bottoming cycle offers compactness, operation without water or steam, and improves overall cycle performance. The semi-closed oxy fuel gas turbine working fluids are mainly CO2 and water making it feasible to separate CO2 by condensing water vapor. Also, since O2 is used as an oxidizer instead of air in the combustion, NOx emissions are almost zero.
Here we analyze a generic mid-sized oxy-fuel gas turbine cycle. The air separation unit and the CO2 compression were also modeled, and their parasitic loads included in the overall performance.
We further studied three sCO2 bottoming cycle configurations for optimizing the oxy-fuel gas turbine heat recovery. The analyzed sCO2 cycle configurations were simple sCO2, cascade sCO2 and advanced sCO2 cycle.
This paper also studies the oxy-fuel gas turbine integration with sCO2 at different gas turbine pressure ratios varying from 13 to 55 with a turbine inlet temperature of 1500°C.
The advanced sCO2 output was almost 16% higher than simple sCO2 configuration. The overall cycle efficiency for advanced sCO2 was around 10% higher than simple sCO2 configuration in all studied pressure ratios. The study also shows that the overall cycle output and efficiency were almost flat at pressure ratio above 35. The overall cycle output for advanced sCO2 was 110 MW and the overall efficiency was 45.7% at pressure ratio 35.
Furthermore, the study includes a sensitivity study on the advanced sCO2 at pressure ratio 35 and different cooling ambient temperatures. Here we show that the advanced sCO2 cycle output dropped by 19% when the ambient temperature increased from 20°C to 45°C.
The advanced CO2 cycle configuration has shown to be an interesting decarbonization solution for simple cycle gas turbines, more specifically when operating in remote locations with limited access to water or steam.
The paper is based on granted GE patent WO/2023/009161.
Numerical Simulation of Turbulent Premixed Flames Using Thickened Flame Model
Authors: Xia Yu , Newale Ashish , Yadav Rakesh , Verma Ishan , Bessette Didier 
Published: September 2023

Abstract
This work numerically investigates the application of a Thickened Flame Model (TFM) for a premixed methane/air Bunsen flame (Chen F3 flame), using Large Eddy Simulation (LES) for turbulence and Finite-Rate Chemistry (FRC) for combustion. Due to a premixed flame front usually being very thin, a very fine mesh is required to resolve the flame structure if using LES/FRC. The TFM model has therefore been utilized to artificially increase the flame thickness without changing the flame speed, allowing the flame simulation on much coarser meshes. However, the thickening of a flame also reduces the capability of turbulent eddies to wrinkle the flame surface, leading to an underpredicted heat release rate. Efficiency functions have therefore been proposed for TFM to compensate for the reduced flame surface area and the lowered heat release rate. The state-of-the-art efficiency functions require an accurate estimation of the velocity fluctuations at the test filter scale that corresponds to the thickened flame thickness. This work compares different TFM efficiency functions and velocity fluctuation models for the Chen F3 flame, and validates the predicted flow variables against experimental data. The mesh resolution and numerical schemes have been carefully selected, offering a workflow for TFM simulations. The impacts of reaction mechanisms and chemistry acceleration tools, e.g., Dynamic Mechanism Reduction (DMR), on the solution accuracy and computational costs of the present LES/FRC simulations have also been evaluated.
Field Performance of an Innovative AMB-Supported Turboexpander-Generator for Natural Gas Pressure Letdown
Authors: Liu Jeremy , Najeeb Ovais , Hawkins Larry , Khatri Rasish 
Published: September 2023

Abstract
This paper is a follow up to GT2022-82293, which discusses the design validation of an innovative turboexpander-generator (TEG) used for natural gas pressure letdown (PLD). This paper presents the field performance data of the 280kW machine and compares it to predictions. The TEG has a flanged housing that is directly mounted on a pipeline. The high-speed motor is supported by active magnetic bearings (AMB) in the hydrocarbon environment without lubrication. The paper discusses power performance of the impeller and compares it to the power prediction from a mean line aerodynamic analysis presented previously. Additionally, this paper compares magnetic bearing dynamic controls and transfer functions measured in air to those with gas flow in the pipeline; the effect of gas flow on the closed-loop dynamics is discussed. The authors review the thrust balancing design and the axial control current as a function of gas flow. The magnetic current is linearly related to load, and thus gives a good approximation of aerodynamic load vs flow. This paper also presents the results of a non-linear auxiliary back-up bearing high-speed rotor drop simulation and compares it to measured rotor drop data. The drop testing was conducted as part of the design verification of the prototype unit, and the results are discussed in depth in GT2022-82293.
Axial Compressor Map Generation Leveraging Autonomous Self-Training Artificial Intelligence. Phase 2
Authors: Burlaka Maksym , Podlech Sascha , Moroz Leonid 
Published: September 2023

Abstract
This paper discusses a study performed by SoftInWay as part of a Phase II SBIR project funded by NASA.
In contrast with the Phase I project (published in paper GTP-22-1328 [1]) where three discrete compressors were considered, the Phase II study was focused on addressing the problem of axial compressor long development time and cost with the use of AI models capable of predicting the geometry and performance of various multi-stage axial compressors with multiple variable vanes. The applicability of the AI models to various compressors enables the opportunity to avoid iterations between engine cycle analysis and compressor design.
In this paper, automated compressor design and performance generation workflows are described. The approach for autonomous selection of the architectures and hyperparameters of Machine Learning (ML) models is explained. The uncertainty quantification techniques are considered. The developed ML-powered methods for compressor geometry prediction are discussed. The ML models’ accuracy values and representations of typical geometry and performance predictions are given. The utilization of the ML models in engine cycle analysis is discussed.
Guidelines for the Aerodynamic Design of sCO2 Centrifugal Compressor Stages
Authors: Romei Alessandro , Gaetani Paolo , Persico Giacomo 
Published: September 2023

Abstract
This paper explores the viability of established criteria to design centrifugal compressor stages that operate CO2 close to the critical point. The work is split into two complementary studies. At first, several stage configurations are generated by varying characteristic design parameters, such as the inlet and outlet flow coefficient, work coefficient, and stage Mach number. Then, three selected configurations are optimized with a surrogate-assisted evolutionary strategy to refine specific geometrical parameters, which control the meridional shape and splitter location. The stage aerodynamics and performance are assessed with a validated RANS solver based on the homogeneous equilibrium assumption for the two-phase mixture.
One of the key findings of the parametric studies is that designing a stage with a flow coefficient smaller than that suggested by design practices prevents the occurrence of two-phase flows. The onset of a secondary phase at the impeller intake alters the fluid compressibility, producing density gradients across saturated condition that can cause flow separation. Such separation occurs for liquid-like CO2 but not for vapor-like CO2, implying that consolidated design rules can apply to the latter case notwithstanding the presence of condensing flows.
Shape optimizations reveal that modest efficiency improvements can be gained by changing the meridional channel and splitter location. Moreover, the optimization problem is highly multi-modal, as more than 30 different geometries can yield equivalent design efficiency. As a side effect of the optimization, the rangeability is significantly modified. Specifically, increasing the inlet slope angle of the shroud contour extends the operating range at high flow rates but reduces it at low flow rates. Therefore, this geometrical parameter can be controlled to adjust the stage rangeability without compromising design efficiency.
Direct Numerical Simulation of an HPT Stage: Unsteady Boundary Layer Transition and the Resulting Flow Structures
Authors: Wang Taiyang , Zhao Yaomin , Leggett John , Sandberg Richard D. 
Published: September 2023

Abstract
In the present study, we investigate the unsteady boundary layer transition based on the direct numerical simulation (DNS) database of a high-pressure turbine (HPT) stage (Zhao and Sandberg, GT2021-58995), focusing on the transition mechanisms on the rotor blade, which are affected by the incoming periodic wakes and also by the background free-stream turbulence (FST) introduced at the inlet. Based on the fully-resolved DNS flow fields, we are able to provide detailed analysis of the flow structures responsible for the transition, and two distinctive paths to laminar-turbulent transition have been identified. The first path is the typical bypass transition via the instability of Klebanoff streaks, which happens when the transition region is not directly affected by the wake. It is noted that the suction-side boundary layer is disturbed at the leading edge, resulting in the formation of streamwise streaks. These streaky structures endure varicose instability in the region with adverse pressure-gradient (APG), then quickly break down into turbulent spots, which then evolves into fully turbulence. The other transition path is a consequence of the direct interaction between the wake structures and the blade boundary layer, when the wake apex starts to affect the transitional region. To be specific, the wake structures seem to directly interact with the separation bubble in the APG region, causing sudden break down into turbulence. The turbulent boundary layer induced by the periodic wake are usually followed by a calmed region as the wake travels away from the passage. It is also observed that the recovery to a calmed region can be impacted by the FST, as the calmed region in case with no FST is much longer compared to cases with stronger FST.
A Superposition Technique for Predicting Overall Effectiveness With Multiple Sources of Individually Characterized Internal and External Coolant Flows
Authors: Fuqua Matthew N. , Rutledge James L. 
Published: September 2023

Abstract
High performance gas turbine engines rely on intricate cooling schemes to protect turbine components from the high temperature freestream gas. Determining the optimal placement of film cooling holes in optimal locations while remaining mindful of the consumption of precious coolant air is therefore an interesting design challenge. For several decades a method of superposition has been in use that provides a reasonable prediction of the adiabatic effectiveness in a region influenced by multiple rows of film cooling holes acting together if the adiabatic effectiveness distributions resulting from individual rows are already known. This classical superposition technique has been used with success to at least provide a first cut at determining where coolant holes might be placed on turbine components. One of the shortcomings of the method is that it strictly applies only to prediction of adiabatic effectiveness which is indicative of the adiabatic wall temperature, not the actual surface temperature of the turbine component. Indeed, the overall effectiveness, which is indicative of the actual surface temperature is somewhat more complicated as it is influenced not only by the external cooling, but also internal cooling. In the present work, a method of superposition of overall effectiveness data is proposed, thereby allowing prediction of the actual surface temperature distribution on a component. Experimental results show that it is possible to use knowledge of the overall effectiveness distributions resulting from individual internal cooling and associated film cooling holes acting alone to determine how they are likely going to act when combined. This technique shows promise for a turbine designer to use superposition for actual surface temperature prediction, not just adiabatic wall temperature prediction and therefore higher quality initial cooling designs.
Integrated Aerodynamic and Mechanical Design of a Large-Scale Axial Turbine Operating With Supercritical Carbon Dioxide Mixtures
Authors: Abdeldayem Abdelrahman , Paggini Andrea , Diurno Tommaso , Orazi Claudio , White Martin , Ruggiero Marco , Sayma Abdulnaser 
Published: September 2023

Abstract
In this paper, the design of a large-scale axial turbine operating with supercritical carbon dioxide (sCO2) blended with sulfur dioxide (SO2) is presented considering aerodynamic and mechanical design aspects as well as the integration of the whole turbine assembly. The turbine is 130 MW, designed for a 100 MWe concentrated-solar power plant with turbine inlet conditions of 239.1 bar and 700 °C, total-to-static pressure ratio of 2.94 and mass-flow rate of 822 kg/s. The aerodynamic flow path, obtained in a previous study, is first summarised before the aerodynamic performance is evaluated using both steady-state and unsteady 3D numerical models to simulate the aerodynamic performance of the turbine. Whole-annulus unsteady simulations are performed for the last turbine stage and the exhaust section to assess the unsteady loads on the rotor due to downstream pressure field distortion and to assess aerodynamic losses of the diffuser and exhaust section. The potential low engine order excitation on the last rotor stage natural frequency modes due to downstream pressure distortion is assessed. The design of the turbine assembly is constrained by current manufacturing capabilities and the proposed working fluid properties. High-level flow-path design parameters, such as pitch diameter and number of stages, are established considering a trade-off between weight and footprint, turbine efficiency and rotordynamics. Rotordynamic stability is assessed considering the high fluid density related to cross coupling effects. Finally, shaft end sizing, cooling system design and the integration of dry gas seals are discussed.
Thrust Rebalance to Extend Engine Time On-Wing With Consideration of Engine Degradation and Creep Life Consumption
Authors: da Mota Chiavegatto Rafael , Li Yi-Guang 
Published: September 2023

Abstract
Over the years, airlines have consistently attempted to lower their operational costs and improve aircraft availability by applying various technologies. Engine maintenance expenses are one of the most substantial costs for aircraft operations, accounting for around 30% of overall aircraft operational costs. So, maximizing aircraft time between overhaul is crucial to lowering the costs. The engine time on-wing is often limited by the expiration of Life Limiting Parts, performance deterioration, maintenance schedule, etc.
This paper presents a novel method of rebalancing the thrust of engines of an aircraft to maximize the time between overhauls of the aircraft considering the performance degradation and creep life consumption of the engines. The method is applied to a model aircraft fitted with two model engines similar to GT90 115B to test the feasibility of the method with one engine degraded and the other engine undegraded. The obtained results demonstrate that for the aircraft flying between London and Toronto with 5,000 nominal flight cycles given to the engines, the time on-wing of the degraded engine could drop from 5,000 to 2,460 flight days due to its HP turbine degradation (1% efficiency degradation 3% flow capacity degradation), causing the same level of drop of time between overhauls of the aircraft. The time on-wing of the degraded engine could increase from 2,460 flight days without thrust rebalance to 3,410 flight days with thrust rebalance, i. e. around 38.6% potential improvement for the time between overhauls of the aircraft at the expenses of increased creep life consumption rate of the clean engine. The proposed method could be applied to other aircraft and engines.
Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 2: Influence of Different Inlet Guide Vane Configurations
Authors: Sasakaros Marios , Schafferus Markus , Wirsum Manfred , Zobel Arthur , Vogt Damian , Nakos Alex , Beirow Bernd 
Published: September 2023

Abstract
The occurrence of blade vibrations in radial turbines leads to limit cycle oscillations, which in time increase the risk of component failure due to high cycle fatigue. In this context, the precise determination of the resonance operating points and the estimation of the vibration magnitudes are essential for an accurate assessment of the service life of the turbocharger components. In radial turbines forced blade vibrations are primarily flow induced. These vibrations are produced by the non-uniform flow field in the circumferential direction which acts on the blades as a cyclic pressure fluctuation. Previous studies have identified the inlet guide vane (IGV) and the spiral turbine housing as the primary sources of the non-uniform flow field.
In the present study a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed. First, the blade vibration modes were measured experimentally and calculated numerically for the determination of the speed ranges that need to be examined. Subsequently, the vibrations were captured with two redundant measurement systems during real turbocharger operation. Strain gauges were applied on certain blades while eight optical sensors were distributed on the circumference of the turbine shroud for the measurement of the blades tips deflection through a commercial tip-timing system.
In the first part, the blade vibrations caused by the “nominal” IGV are presented. Part 2 analyses the changes of the blade vibrations due to the application of two different IGVs. The first IGV has the same number of vanes as the “nominal” IGV. Nevertheless, it generates additional low engine order excitations by intentionally varying the distance between the vanes. Next, an IGV with a higher number of vanes is employed for the excitation at higher frequencies and thus of higher blade modes. Contrary to expectations, certain synchronous vibrations can be measured in the experiments of all IGVs. These cannot be attributed to the spiral turbine casing.
Modeling a Water-Cooled Printed Circuit Heat Exchanger Condensing CO2 for Use in sCO2 Cycle System Optimization Studies
Authors: Liese Eric , Pidaparti Sandeep 
Published: September 2023

Abstract
This work describes a one-dimensional model of a water-cooled printed circuit heat exchanger (PCHE) condensing CO2. The model is developed for use in cycle optimization studies (e.g., minimizing levelized cost of electricity) as either the main heat rejection cooler and/or a compressor intercooler for recompression closed Brayton supercritical CO2 power cycles. Sensitivity and case studies are used to illustrate the impact of important model parameters, and this includes allowing for independent variation of zig-zag channel wave angles on the CO2 and water side. Results show that for a given CO2 design pressure (and thus saturation temperature), the PCHE design inlet water temperature has a significant impact on the PCHE size. Results also demonstrate that if wave angles are the same on the CO2 and water side, the water side pressure drop will have more influence on determining the optimum PCHE mass than the CO2 side pressure drop. Reducing the water side wave angle to near straight channel flow offers a more compact design for a similar water side pressure drop (and pump power requirement). Cases are also shown for further increasing the compactness and how the PCHE mass is affected along with water pump power.
Nonlinear Response of the Rotor Supported by Gas Journal Bearings Considering Stationary and Rotating Herringbone Grooves
Authors: Kochurov Roman , Moroz Leonid , Martynenko Volodymyr 
Published: September 2023

Abstract
This paper presents an approach to determine the stability of the rotor in herringbone groove gas journal bearings (HGGJB) based on nonlinear transient analysis. The approach considers rotating (on a rotor) or stationary (on a bearing shell) grooves. The bearing gas film model is described by the Reynolds equations. The finite element (FE) method has been applied to obtain an accurate solution for the HGGJB design. The rotor model is discretized with Timoshenko beam finite elements.
A study on the stability of a rotary machine supported by HGGJBs is performed to investigate threshold rotating speeds for the cases of stationary and rotating grooves applying a nonlinear transient analysis procedure. As a result, the influence of rotating grooves on system stability improvement has been investigated. Additionally, the correspondence of the calculated results to the experimental data available in publications and the nonlinear effects presented on Waterfall plots are also discussed in the article.
The presented method is an extension of previously developed techniques that engineers can use for design and calculation purposes. The nonlinear approach allows accurate simulation of coupled rotor-HGGJB systems and has no limitation for designs with a small number of grooves, as the FE method is used for bearings discretization. The method allows the physical effects of rotating/stationary grooves to be accounted for.