bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Geometric Parameters for a 100 kW Inward Flow Radial Supercritical CO2 Turbine
Authors: Hoque Syed J. , Kumar Pramod , Gopi Pramod Chandra 
Published: October 2022

Abstract
As an emerging technology, supercritical CO2 (sCO2) power generation systems currently focus on small-scale power generation. Inward flow radial (IFR) turbine is preferred for small-scale power generation due to its efficient and compact design. The influence of design parameters on sCO2 turbine performance can be different from gas turbines due to small size, high rotational speed, and low viscous losses. This paper presents a CFD study to find the optimal value of four geometric design parameters — axial length, outlet-to-inlet radius ratio, number of rotor blades, and velocity ratio for a 100 kW IFR turbine and their effect on the turbine’s performance. The results are compared against well-established gas turbine correlations in the 0.2 to 0.8 specific speed range to review their applicability on sCO2 turbines. The results show significant differences in the optimal value of design parameters compared to gas turbines. sCO2 turbines require fewer blades and a higher velocity ratio for optimal performance. The maximum turbine efficiencies (∼ 82%) are achieved at a lower specific speed of ∼0.4 than gas turbine results ∼ 0.55 to 0.65. Also, high incidence angles ∼ −50° to −55° are required at high specific speeds to counter the Coriolis effect in rotor passage. The results also show the variation of stator, rotor, and exit kinetic energy losses with specific speeds, which shows the cumulative losses are minimum at the specific speed of ∼ 0.4.
Experimental Investigation Into Oil Film Thickness and Behaviour Near an Aero-Engine Bearing
Authors: Sinha Avick , Hann David , Johnson Kathy , Walsh Michael 
Published: October 2022

Abstract
In an aero-engine transmission system, bearings are used for shaft location and load support. These bearings are housed in bearing chambers and oil is supplied to the chamber for lubrication and cooling. To achieve the targets of ACARE Flight-path 2050, improved engine design, including the transmission oil system, is required, necessitating a better understanding of oil flow behaviour and management in the bearing chambers.
The present work focuses on investigating oil flow behaviour on static surfaces near a bearing in a representative, purpose-built test rig, at four angular locations: 0°, 90°, 180° and 270° from top dead centre. The rig was run at shaft speeds up to a rotational Reynolds number of 1.7 × 106, for two oil flow rates and two axial load conditions. The investigation was conducted using high-speed imaging and subsequent detailed image analysis. These are the first experimental results obtained on this facility for film characteristics near the bearing slot at high shaft speeds. The current work has value both in terms of insights into the physics of the oil flow behaviour and also in generating high-quality data for comparison with CFD models.
Three different film regimes were identified based on the shape of the film interface and these have been descriptively characterised as long wave, short wave and uniform film. Median film thickness obtained from image analysis was found to be highest at the 180° location and lowest at the 90° location. At all speed/load conditions investigated, the surface waves were found to be capillary waves.
Carbon Capture: CO2 Compression Challenges and Design Options
Authors: Taher Matt 
Published: October 2022

Abstract
Carbon Capture and Storage are essential technologies to help achieve the ambition of net zero anthropogenic greenhouse gas emissions by 2050 [1]. Independent of the method used to capture the CO2, it remains central to compress carbon dioxide for liquefaction, transportation, and storage. The CO2 stream exiting almost any capture technology is in the gas phase, while it will be transported as a sub-cooled liquid for ship-based transportation or a dense-phase in pipeline-based transportation. The CO2 compression process that involves compressing low-pressure CO2 in gas phase to high-pressure supercritical phase is ‘transcritical’, i.e., with subcritical low-side and supercritical high-side pressure.
This paper is intended to provide a summary of the current CO2 compression technologies and design challenges. Different possible pathways to compress CO2 from subcritical to supercritical conditions are explained. Also, the anomalous behavior of supercritical CO2 and its effect on design and performance of the compression system is highlighted. Inline centrifugal compressors and integrally geared compressors are compared for transcritical CO2 compression applications. Also, the use of centrifugal pumps and reciprocating compressors are briefly addressed.
Method of Analysis for Impact of Input Uncertainty Error Propagation in a Highly Nonlinear System: Applied to Modern Aircraft Engine
Authors: Castaldo Timothy 
Published: October 2022

Abstract
Current methods for compressor vane control in a turbo-jet engine rely on measurements or estimates of compressor inlet temperatures and speed to determine the most favorable compressor stator vane angles over the course of an effectively infinite-horizon control decision process. During each instance of this process, the stator vane angles must be adjusted with a regular frequency to manage compressor efficiency and stability over the course of a flight. The optimality suffers from uncertainty in compressor inlet temperature, though the extent of deviation from optimality is unknown, as is the cost-benefit trade space for addressing this issue. This is an example of a more general problem in systems engineering, which is to estimate the cost of uncertainty in information with respect to its effect on deviations from optimality in infinite- and indefinite-horizon decision processes subject to a stochastic state machine that determines decision outcome. This thesis will develop a methodology for (A) estimating the cost of uncertain information in these kinds of sequential decision processes, (B) characterizing the trade space associated with addressing this problem, and (C) application to the jet engine design refinement problem.
Development of a Laser Igniter for Direct Fired sCO2 Combustor
Authors: Gupta Sreenath , Aithal Shashikant , Hosangadi Ashvin , Weathers Timothy , Fetvedt Jeremy 
Published: October 2022

Abstract
The combustor of a typical Allam-Fetvedt cycle has pressures ranging up to 300 bar and CO2 dilution levels up to 90% by volume, which present a rather challenging environment to ensure reliable ignition. Laser igniters offer improved performance under such adverse conditions, i.e., extend ignitability to a wider range of pressures, equivalence ratios and dilution levels. Additionally, unlike hypergolic igniters laser igniters can be used for ignition multiple times. Additionally, the capability of laser igniters to ignite at higher pressures reduces the relight operation in a power plant from several hours to less than a second. In this paper we report our efforts to design and develop a laser igniter for such combustors. First, high-fidelity CFD modeling was performed for a combustor geometry fueled by coal-derived syngas. Based on the predicted flow field, a laser igniter having a capability to place the ignition kernel at the optimal location was designed and developed. Finally, the performance of the laser igniter was evaluated using several bench-scale tests using premixed mixtures of coal-derived syngas and oxidizers. These bench-scale tests showed that laser ignition was possible over a wide range of equivalence ratios, ϕ = 0.7 to 1.6, and initial pressures up to 50 bar. These tests also showed that multiple ignition kernels form at the focal point along the laser line of sight. Both volumetric ignition and use of multiple ignition pulses (i.e., burst mode) significantly improve ignitability of the fuel-oxidizer mixtures.
Unsteady Gas Dynamics of Radial Turbine Volutes Under Pressure Pulsations
Authors: Yang Bijie , Xue Yingxian , Martinez-Botas Ricardo , Yang Mingyang 
Published: October 2022

Abstract
Turbocharging is the key technique to improve engine-specific power and reduce CO2 emissions of a piston-driven engine. Repeated actions of engine pistons and valves give rise to engine pulsations resulting in intensive unsteady flow in the turbines. Understanding the pulsation effects on a turbine that is steady-flow designed is crucially important for performance enhancement. The present work derives an equation that is capable of evaluating the pulsation effects on the volute-outlet flow angle. Based on the equation, a reduced order model (1-D) is proposed and applied to a single-entry mixed flow turbine. By comparing to 3-D unsteady computational fluid dynamics (CFD), the ability and accuracy of the 1-D model on predicting the unsteady volute-outlet flow angle is verified. The effects of the unsteady flow angle on the turbine performance are further investigated by comparing unsteady and quasi-steady flow field characteristics given by 3-D CFD. The present work unveils the volute unsteady behaviour and explains the unsteady coupling mechanism between the volute and the rotor. The findings can lead to improvement of turbine design methodology under pulsating flow conditions.
Evolution of Turbulence and Its Modification by Axial Casing Grooves in a Multi-Stage Axial Compressor
Authors: Koley Subhra Shankha , Saraswat Ayush , Katz Joseph 
Published: October 2022

Abstract
This paper examines the distribution of turbulent kinetic energy (TKE), normal Reynolds stresses, and production rates of stress components in the JHU refractive index-matched axial compressor at pre-stall and near the best efficiency (BEP) flow rates. Modifications to the turbulence caused by installing semicircular axial casing grooves (ACGs) are also investigated. The stereo-PIV measurements are performed in axial planes covering entire passages, from the hub to the tip, both between and within blade rows. The TKE is highly anisotropic and spatially inhomogeneous, with each of the normal stress components evolving differently. Most of the trends can be explained by examining the dominant production rate terms. Upstream of the rotor, at pre-stall flowrate, the TKE is high in the inlet guide vane (IGV) wakes, and in the tip region. The turbulence increases significantly upon entering the rotor with peak RMS values of axial velocity fluctuations reaching as high as 71% of the spatially averaged mean axial velocity. Near the rotor leading edge (LE), the TKE is elevated over the entire outer 30% of the span, expanding to 50% near the rotor trailing edge. Upon entering the stator, there is a rapid reduction in turbulence in the outer half of the passage aided by negative turbulence production due to axial extension. However, further downstream near the stator trailing edge, the turbulence increases along the lower suction side of the stator blade as the boundary layer separates intermittently. By stabilizing and homogenizing the flow, the ACGs reduce the turbulence production, hence the TKE, in the rotor and the stator. The only exception is an increase in turbulence at the interface between the outflow from the grooves at their upstream end and the passage flow. Near BEP of the untreated endwall, the TKE is much lower in all the investigated planes except for the region influenced by the groove outflow. The TKE downstream of the rotor and the stator for both smooth endwall and with the ACGs appears to be quite similar. Yet, the ACGs cause a reduction in the TKE peak but expand the area of elevated turbulence in the tip region. Distributions of measured eddy viscosity highlight the extreme non-equilibrium conditions over the entire machine, questioning the fundamental assumptions of local equilibrium in eddy viscosity-based Reynolds stress models.
Methodology for the Redesign of Compressor Blades Undergoing Nonlinear Structural Interactions: Application to Blade-Tip/Casing Contacts
Authors: Kojtych Solène , Nyssen Florence , Audet Charles , Batailly Alain 
Published: October 2022

Abstract
Over the past decade, the drive towards more efficient aircraft engines has pushed the boundaries of operating ranges far beyond a linear structural context. Nonlinear interfaces, such as blade-tip/casing contacts, are to be expected in nominal operating conditions. However, current blade design methodologies still rely on empirical structural considerations, often linear, which may lead to costly redesign operations. This work aims at proposing a methodology for the redesign of blades undergoing nonlinear structural interactions. A three-step redesign process is considered: (1) parameterization of an existing blade, (2) update of blade parameters with respect to a surrogate performance criterion and (3) performance check of the optimized blade. An original two-way parameterization method is proposed to parameterize existing blades and generate models from blade parameters. As a proof-of-concept, the redesign of the NASA compressor blade rotor 37 and fan blade rotor 67 with respect to blade-tip/casing contacts is considered. High-fidelity parameterized models of the initial blades are obtained and their dynamic response to contact interactions are analyzed. Geometries are updated with respect to their clearance consumption, as its minimization has shown beneficial effects on the considered contact interactions. The proposed methodology allows to better assess the relevance of this performance criterion in the context of blade-tip/casing contacts.
Analysis of the Condensation Phenomena Within the Radial Turbine of a Fuel Cell Turbocharger
Authors: Wittmann Tim , Lück Sebastian , Friedrichs Jens , Wiśniewski Piotr , Dykas Sławomir 
Published: October 2022

Abstract
Cathode systems of proton exchange membrane fuel cells are tasked with providing compressed air for the fuel cell stack. The exhaust gas from the fuel cell has a pressure potential which can be utilised in a turbine to partially power the compressor. Therefore, a radial compressor and a radial turbine are often combined with an electric motor to form an electric fuel cell turbocharger. The exhaust gas used to operate the turbine is humid and hence prone to condensation. Previous studies on such condensation only investigated a turbine segment and neglected the volute. This study overcomes this simplification and analyses the aerodynamics of the full-annulus flow of volute, stator and rotor. The focus is set on the effect of the circumferential asymmetry on the occurrence and strength of condensation in the turbine rotor. The effect of variations of the rotational speed is also investigated. The main finding is, that such asymmetries or speed changes can have a significant effect for operating points for which they are able to determine the occurrence of condensation. Operating points with no or with certain condensation are less affected.
Azimuthal Instabilities of an Annular Combustor With Different Swirling Injectors
Authors: Rajendram Soundararajan Preethi , Durox Daniel , Renaud Antoine , Candel Sébastien 
Published: October 2022

Abstract
Experiments are carried out on the laboratory-scale MICCA-Spray annular combustor to examine the effects of swirlers on combustion instabilities. This system comprises sixteen spray-swirl injectors and gives rise to instabilities coupled by azimuthal modes. Five types of swirlers producing clockwise rotation and varying in swirl numbers and pressure drops are considered. These swirlers can be broadly categorized into two groups, lower-swirl, and higher-swirl groups, based on their swirl numbers. An arrangement where clockwise and counterclockwise swirlers alternate is also studied. Experiments are performed systematically with liquid heptane at five levels of thermal power and six equivalence ratios. Results reveal that none of the swirlers in the lower-swirl category exhibit instability in the operating region considered, whereas the higher-swirl units feature strong azimuthal instabilities that trace an overall limit cycle envelope with a few short and random bursts. Among the higher-swirl group, a higher pressure drop swirler is associated with a broader instability map. This shows that the transition to instability mainly depends on the swirl number through its effect on the flame structure and that the pressure drop adds to further variations in amplitude and frequency of oscillation. The spin ratio time series indicate that the modes are of mixed type, and that its distribution depends on the operating condition. On specifically comparing the spin ratio distribution between a full set of clockwise rotating swirlers (CR) and a configuration where clockwise and counterclockwise rotating swirlers (CCR) are alternatively placed, it is found that there is no definite statistical preference for spin ratio linked to the effect of bulk swirl. In some cases, however, the CCR configuration promotes a broader distribution of spin ratios centered around the standing mode (s = 0) while the CR setup favors azimuthal modes spinning in the counterclockwise direction. An attempt is made to interpret the occurrence of instabilities by making use of flame describing functions (FDFs) measured in a single-injector combustor. It is found that the FDFs corresponding to the two swirler categories (lower swirl and higher swirl) are relatively distinct. The observed behavior is tentatively interpreted using an instability analysis in which the injector and upstream plenum are represented by an impedance which shifts the band of instability. The unstable behavior is then linked to the relative position of the FDF phase with respect to the instability band in the frequency range corresponding to the expected azimuthal mode frequency. The phase and gain of the FDF notably depend on the swirl number and it is possible to distinguish, for the present configuration, a category of low swirl number injectors inducing stable operation and another category of high swirl number units leading to oscillations.
Predicting Emissions Across Design Variations of an Aero-Engine Combustor Using FGM and PISO
Authors: Karalus Megan , Brandt Dustin , McManus Liam , Munktell Erik 
Published: October 2022

Abstract
A modeling approach for quickly predicting Carbon Monoxide (CO) and Unburned Hydrocarbon (UHC) emissions is assessed in Simcenter STAR-CCM+ version 2021.3. Both magnitude and trends are evaluated across design variations of an aero-engine test combustor operating at an idle condition. Large Eddy Simulation (LES) is used with the non-iterative Pressure Implicit by Splitting of Operators (PISO) scheme, and the Flamelet Generated Manifold (FGM) combustion model. There are four geometric design variations of the same test combustor where changes are made to the dome effusion cooling, main swirler, and downstream orifices. These four geometries are chosen for this study because they yield distinctly different CO and UHC emissions, thus reducing signal to noise in assessing the predictive capability of the modeling approach. Sensitivity of the results to a key parameter in the liquid fuel spray breakup model is provided. By varying the breakup rate, the prediction of the CO emissions is shown to compare very favorably both in magnitude and trend to the experimentally measured values. The UHC emissions are shown to compare well for three of the four designs. Results are also generated using the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) scheme; these show the same behavior as PISO. However, the results with PISO can be obtained between 2.5 and 3.5X faster than the more traditional approach. Combining the computational efficiency of FGM and PISO allows for fast and accurate predictions of regulated emissions, and therefore down-selection of designs earlier in the design process.
Heat Transfer and Pressure Loss of Additively Manufactured Internal Cooling Channels With Various Shapes
Authors: Wildgoose Alexander J. , Thole Karen A. 
Published: October 2022

Abstract
Additive manufacturing (AM) provides the ability to fabricate highly customized internal cooling passages that are relevant to gas turbine components. This experimental study examines the pressure loss and heat transfer performance of a range of fundamental channel shapes that were produced using direct metal laser sintering. Circular, hexagonal, pentagonal, elliptical, diamond, square, rectangular, trapezoidal, and triangular channel cross-sections were investigated. To maintain the same convective surface area between shapes, the wetted perimeters of the channel cross-sections were kept constant. Parallel computational fluid dynamic simulations were performed to understand the relationships in cooling performance between several channel shapes. Several characteristic length scales were evaluated to scale the pressure loss and heat transfer measurements. Among the channel shapes investigated, the diamond channel showed the lowest Nusselt number and friction factor. The pentagon exhibited a similar Nusselt number as the circular channel despite having a lower friction factor. There was no difference in scaling the friction factor or Nusselt number results of the different channels shapes between using the square root of cross-sectional area compared to hydraulic diameter as the characteristic length scale.
The Ignition of C1–C7 Natural Gas Blends and the Effect of Hydrogen Addition in the Low and High Temperature Regimes
Authors: Mohamed A. Abd El-Sabor , Bikram Sahu Amrit , Panigrahy Snehasish , Bourque Gilles , Curran Henry 
Published: October 2022

Abstract
New ignition delay time (IDT) measurements for two natural gas (NG) blends composed of C1 – C7 n-alkanes, NG6 (C1:60.625%, C2:20%, C3:10%, C4:5%, nC5:2.5%, nC6:1.25%, nC7:0.625%) and NG7 (C1:72.635%, C2:10%, C3:6.667%, C4:4.444%, nC5:2.965%, nC6:1.976%, nC7:1.317%) by volume with methane as the major component are presented. The measurements were recorded using a high-pressure shock tube (HPST) for stoichiometric fuel in air mixtures at reflected shock pressures (p5) of 20–30 bar and at temperatures (T5) of 987–1420 K. The current results together with rapid compression machine (RCM) measurements in the literature show that higher concentrations of the higher n-alkanes (C4 – C7) ∼1.327% in the NG7 blend compared to the NG6 blend result in the ignition for NG7 being almost a factor of two faster than NG6 at compressed temperatures of (TC) ≤ 1000 K. This is due to the low temperature chain branching reactions that occur for higher alkane oxidation kinetics in this temperature range. On the contrary, at TC &gt; 1000 K, NG6 exhibits ∼20% faster ignition than NG7 primarily because about 12% of the methane in the NG7 blend is primarily replaced by ethane (∼10%) in NG6, which is significantly more reactive than methane at these higher temperatures. The performance of NUIGMech1.2 in simulating these data is assessed and it can reproduce the experiments within 20% for all the conditions considered in the study. We also investigate the effect of hydrogen addition to the auto-ignition of these NG blends using NUIGMech1.2 which has been validated against the existing literature for natural gas/hydrogen blends. The results demonstrate that hydrogen addition has both an inhibiting and promoting effect in the low- and high-temperatures regime, respectively. Sensitivity analyses of the hydrogen/NG mixtures are performed to understand the underlying kinetics controlling these opposite ignition effects. At low temperatures, H-atom abstraction by ȮH radicals from C3 and larger fuels are the key chain-branching reactions consuming the fuel and providing the necessary fuel radicals which undergo low temperature chemistry (LTC) leading to ignition. However, with the addition of hydrogen to the fuel mixture, the competition for ȮH radicals by H2 via the reaction H2+ȮH↔Ḣ+H2O reduces the progress of the LTC of the higher hydrocarbon fuels thereby inhibiting ignition. At higher temperatures, since Ḣ+O2↔Ö+ȮH is the most sensitive reaction promoting reactivity, the higher concentrations of H2 in the fuel mixture leads to higher Ḣ atom concentrations leading to faster ignition due to an enhanced rate of the Ḣ+O2↔Ö+ȮH reaction.