bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bayesian Calibration of Kinetic Parameters in the CH Chemistry Towards Accurate Prompt-NO Modelling
Authors: Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M. 
Published: October 2022

Abstract
Significant efforts made by the gas turbine industry have helped reduce nitrogen oxides (NOx) emissions considerably. To meet and surpass the increasingly stringent regulations, accurate and robust thermochemical mechanisms are needed to help design future sub-10 ppm combustion systems. Uncertainty in kinetic modelling, however, can result in large prediction uncertainty and significant discrepancy between models that hinder the identification of promising combustors with confidence. Direct reaction rate measurements are seldom available for some reactions, especially when involving short-lived radicals like methylidyne, CH. As the main precursor to the prompt-NO formation pathway, its large parametric uncertainty directly propagates through the nitrogen chemistry preventing accurate and precise emissions predictions. Recent independent CH concentration measurements obtained at various operating conditions are used as indirect rate measurements to perform statistical, or Bayesian, calibration. A subset of important reactions in the CH chemistry affecting peak-CH concentration is identified through uncertainty-weighted sensitivity analysis to first constrain the parametric space of this prompt-NO precursor. Spectral expansion provides the surrogate model used in the Markov-Chain Monte Carlo method to evaluate the posterior kinetic distribution. The resulting constrained CH-chemistry better captures experimental measurements while providing smaller prediction uncertainty of a similar order as the uncertainty of the measurements, which can increase the confidence in simulation results to identify promising future low-emissions configurations. For the quasi-steady state species CH, fuel decomposition reactions leading to CH production are constrained while little impact is observed for intermediate reactions within the CH-chemistry. The reduction in prediction uncertainty results mainly from the constrained correlations between parameters which greatly limit the set of feasible reaction rate combinations. Additional independent direct and indirect measurements would be necessary to further constrain rate parameters in the CH chemistry, but this calibration demonstrates that predictions of radical species can be improved by assimilating enough data.
Development of an Open-Source Autonomous CFD Meta-Modeling Environment for Small-Scale Combustor Optimization – Part I
Authors: Briones Alejandro M. , Rankin Brent A. 
Published: October 2022

Abstract
This work presents an open-source autonomous CFD meta-modeling environment (OpenACME) for small-scale combustor design optimization in a deterministic and continuous design space. OpenACME couples several object-oriented programming open-source codes for conjugate-heat transfer, steady-state, multiphase incompressible RANS CFD-assisted engineering design meta-modeling. There are fifteen design variables. Non-parametric rank regression (NPRR), global sensitivity analyses (GSA), and single-objective (SOO) optimization strategies are evaluated. The Euclidean distance (single-objective criterion) between a design point and the utopic point is based on the multi-objective criteria: combustion efficiency (η) maximization and pattern factor (PF), critical liner area factor (Acriticol), and total pressure loss (TPL) minimization. The SOO approach conducts Latin Hypercube Sampling for reacting flow CFD for subsequent local constraint optimization by linear interpolation. The local optimization successfully improves the initial design condition. The SOO approach is useful for guiding the design and development of future gas turbine combustors. NPRR and GSA indicate that there are no leading-order design variables controlling η, PF, Acritical, and TPL. Therefore, interactions between design variables control these output metrics because the output design space is inherently non-smooth and nonlinear. In summary, OpenACME is developed and demonstrated to be a viable tool for combustor design meta-modeling and optimization studies.
Effect of Strong Azimuthal Swirl on Ignition and Light-Around in an Annular Combustor
Authors: Kwah Yi Hao , Agostinelli Pasquale Walter , Richard Stéphane , Exilard Gorka , Pascaud Stéphane , Gicquel Laurent , Dawson James R. 
Published: October 2022

Abstract
In this paper we investigate the effect of strong azimuthal swirl on ignition dynamics in a laboratory-scale annular combustor. Bulk azimuthal swirl was produced by a novel angled injector configuration, producing swirling jet flames oriented downwards towards the combustor backplane and in the azimuthal direction, replicating a simplified version of the SAFRAN spinning combustor concept. To provide more realistic flow conditions, the design included Rich-Quench-Lean (RQL) staging via a circumferential distribution of dilution ports and an effusion cooled combustor backplane. High-speed imaging and an azimuthal array of photomultipliers to measure OH* chemiluminescence were used to characterise the ignition dynamics for different injector velocities and global equivalence ratios. The mass flows through the injectors, dilution ports, and effusion cooled backplane were independently metered so that the injector equivalence ratio and global equivalence ratio could be separately controlled. The light-around times were found to have no clear correlation with the injector velocity since the rich injector equivalence ratio meant the flame burned in a non-premixed mode even though the global equivalence ratio was lean due to the RQL staging. However, it was found that lower injector velocities extended the lean ignition limit based on the global equivalence ratio. The ignition sequence during light-around (order in which the injectors are ignited) was found to be highly repeatable, igniting each consecutive injector in the anticlockwise direction (the direction of bulk swirl). In rare cases, the ignition sequence was observed to branch in both directions. Finally, in an effort to extend the lean ignition limit, the effect of azimuthal staging was investigated. Two configurations were tested. In the first configuration, the injectors on one half of the annulus were operated at a fixed equivalence ratio whereas the other half of the annulus was operated at a different equivalence ratio. In the second configuration, every second injector had the same equivalence ratio. Both configurations extended the lean extinction limit but the first configuration was the most effective.
Low Mach Preconditioning for Turbomachinery Flow Simulations With Cavities and Variable Gas Compositions
Authors: Sivel Pierre , Frey Christian , Kügeler Edmund , Keil Markus 
Published: October 2022

Abstract
The optimization of turbomachines increasingly relies on highly accurate numerical performance predictions. Loss predictions require the cavities of the machine to be included in numerical simulations. Commonly, in cavities, the velocity of the simulated fluid is small. For density-based solvers, this results in slow convergence and inaccurate computations. Further, the fluid in cavities is often composed of several gases. This paper presents the low Mach preconditioning method for multi-component thermally perfect gas of DLR’s inhouse solver TRACE.
Two low Mach academic test cases, a lid driven cavity and an air and exhaust gas mixing layer, are computed to validate the preconditioner. Both test cases show an accelarated convergence and an improved accuracy, when preconditioning is used.
A 1.5 stage low-pressure turbine rig with a labyrinth seal is computed with thermally perfect air. The result shows a good agreement with the experimental reference. The fluid is then changed to exhaust gas, and two air inflows are added in the labyrinth seal, to analyze the effect of low Mach preconditioning on the mixing of the two gases. The preconditioned computation shows an improved convergence in the cavity. Moreover, the wall temperature and the gas distribution in the cavity differ, when preconditioning is applied.
A Nonlinear Rotordynamics Model for Automotive Turbochargers Coupled to a Physical Model for a (Semi) Floating Ring Bearing System
Authors: Jung Wonbae , San Andrés Luis , Kim Jungbae 
Published: October 2022

Abstract
Automotive turbochargers (TCs) use an engine oil lubricated bearing system to produce acceptable performance (as per the engine volumetric efficiency) and proven reliability. However, the bearings also cause TC rotordynamic responses that are rich in subsynchronous whirl motions through reaching stable limit cycles. The paper describes the lubrication model for a finite length semi-floating ring bearing (SFRB) system and its coupling to the rotor and ring structure models for prediction of both linear and nonlinear system responses and their characterization in terms of motion amplitudes and whirl frequency content. The SFRB model includes a thermal energy transport network for the inner and outer films in both radial bearings and the thrust bearings located on the end sides of the ring. The large temperature difference between the hot shaft and a cold housing induces a three-dimensional thermal gradient in the fluid films and the floating ring, further exacerbated by the heat generated from drag power losses in the inner films adjacent to the rotor. The temperature gradients affect the lubricant viscosity and the bearing system operating clearances. The integration of the rotor and bearing system (RBS) equations of motion accounts for the SFRB nonlinear forces and starts from a static equilibrium position, if existing. Analysis of the start-up speed response of a commercial TC, from 500 Hz (30 krpm) to 4,000 Hz (240 krpm), and for particular mass imbalance conditions, shows dominant subsynchronous vibrations (SSV) with frequencies ranging from approximately ¼ to ∼ ½ of shaft speed and a transition from conical to cylindrical-bending rotor mode shapes. The model predictions of nonlinear behavior are accurate when benchmarked to a set of measurements procured in a gas stand test rig. The analysis also investigates the influence of the bearing inner clearance and rotor mass imbalance distribution on the onset, persistence and severity of SSV.
Economizer Location Optimization for a Centrifugal Compressor With Refrigerant as Working Fluid
Authors: Urcia Jose , Yan Jin , Fagundes Tadeu 
Published: October 2022

Abstract
In a typical HVAC chiller, centrifugal compressors are used to compress the refrigerant. These compressors are of single or multi-stage cycles that can be configured for a reinjection between cycles. This reinjection introduces cascade cycle options while improving the Coefficient of Performance (COP). One cascade cycle option that has become industry standard is an economizer cycle. During this process, the goal becomes to reinject flow back into the compressor between stages while the remaining flow continues through the cycle. The exact location of the economizer where its benefit would be at a maximum has yet to be determined. This paper develops a high-fidelity full compressor model where an economizer may be simply added into any location. A thermodynamic cycle analysis is used to highlight the locations where an economizer may be most beneficial thus limiting the number of locations to investigate. Initially, three different full compressor models are developed with increased model complexity for model validation. The most complex agreed with experimental results with high-accuracy and was used for further economizer testing. The most complex compressor model is investigated under 100% the design speed without the added economizer where a baseline is achieved. The thermodynamic cycle analysis is then implemented to identify the optimal economizer location based on the interstage pressure. Four locations are determined to fit the criteria. Two economizer locations were found to exhibit improved performance when compared to the remaining locations, increasing the aerodynamic efficiency of the base model by 10%.
Jet Entrance Configurations and Swirl Motion Effects on Heat Transfer Characteristics Inside Blade Leading Edge of the Gas Turbine
Authors: Elwekeel Fifi , Abdala Antar , Zheng Qun 
Published: October 2022

Abstract
In the present work a simulation is conducted by CFD to predict the cooling performance in a chamber with a swirl motion using nine shapes of injection entrances. The injection entrances are with different cross sections; rectangular (case A), circular (case B), half circular (case C), square (case D), elliptical (case E), equilateral triangular (case F) and three configurations of convergent shapes (case G, H, I). The simulation is performed at constant hydraulic diameter for all shapes and at varied Reynolds number. The investigation parameters are temperature distribution in swirl chamber, circumferential and total velocities, circumferential and axially averaged Nusselt numbers, friction factor and thermal performance parameter. The results show that the temperature increases in all cases compared to the rectangular entrance shape. The convergent shapes give high performance in the heat transfer as well as high friction. Circular entrance shape has a higher circumferential and total velocity compared to all cases.
Study on the Vibration Characteristics of Bladed Disks With Damping Mistuning
Authors: Kaneko Yasutomo , Watanabe Toshio , Furukawa Tatsuya 
Published: October 2022

Abstract
Bladed disks with slight blade variations are referred to as a mistuned system. Many researchers have suggested that while mistuning induces an undesirable effect on the forced response, it provides a beneficial (stabilizing) effect on the blade flutter (self-excited vibration). However, almost all studies have focused on the deviation in the blade frequency, and few studies have investigated damping mistuning. In a blisk (integrally manufactured bladed disk), damping mistuning appears to be negligible because material damping is dominant and its deviation is small. However, in a bladed disk where the blade root is inserted into the disk groove, damping mistuning caused by partial contact between the root and groove during rotation cannot be neglected in predicting the resonant response of a bladed disk. Some works suggest that the structural damping of a root-type bladed disk measured using the half-power method during rotation tests largely fluctuates in each individual blade. Damping mistuning may also affect the stability of the blade flutter. Therefore, in predicting the stability of a blade flutter, the effect of damping and frequency mistuning should be considered. From these backgrounds, in the current study, by incorporating the damping mistuning into a reduced-order model, namely, fundamental mistuning model, frequency response and stability analyses of bladed disks are systematically performed. From the calculated results, the effect of damping mistuning on the forced and self-excited vibrations of bladed disks is clarified. In addition, although the authors proposed a simultaneous optimization method for mistuned bladed disks for forced vibration and amount of unbalance in a previous work, damping mistuning was not considered. In the present study, the robustness of an optimal mistuned system for damping mistuning is also evaluated.
Effect of Counter- and Co-Swirl on Low-Frequency Combustion Instabilities of Jet A-1 Spray Flames
Authors: Ahn Byeonguk , Kim Kyu Tae 
Published: October 2022

Abstract
The present article experimentally investigates the influence of pilot swirling directions on low-frequency combustion instabilities of pilot diffusion flames in a laboratory-scale combustor with Jet A-1 fuel and air at atmospheric pressure. Airblast atomization nozzles with either counter-rotating (CTR) or co-rotating (COR) pilot swirl flows were examined using nonlinear time-series analyses and high-speed flame imaging measurements under idle and sub-idle operating conditions. We show that while the amplitude and frequency of limit cycle oscillations are observed to be similar for both cases, detailed examinations of measured experimental data reveal marked differences in stabilization mechanisms and pressure-heat release coupling processes. The spray flame dynamics subjected to counter-rotating swirl flows are governed by large-amplitude pressure oscillations, even under the influence of destructive pressure-heat release rate interference. The mechanism of destructive interference is closely related to the interactions between a spiral diffusion flame and a periodically-detached reaction zone. Non-premixed liquid-fueled flames involving co-rotating swirl, on the other hand, feature a more compact and intense reaction zone.
Particle Rebound/Deposition Modelling in Engine Hot Sections
Authors: Jiang Lei-Yong , Trembath Patrick , Patnaik Prakash , Capurro Michele 
Published: October 2022

Abstract
The current state of the art in experimental and analytical research on environmental particle ingestion related to engine hot sections was reviewed, with greater emphasis focussed on sand particles. From these efforts, the available experimental data for model calibration were identified, and a particle rebound/deposition model has been developed. A semi-empirical approach is selected to model sand particles bouncing off metal surfaces, where the coefficients of restitution measured in a temperature range of 297–1323 K from Delimont et al are used to calculate particle bounce-back velocity components. The developed deposition model is based on non-dimensional parameters and the analysis over more than seventy experimental datasets related to particle deposition in engine hot sections carried out by Suman et al. Moreover, the metal surface temperature, one of two critical parameters in particle deposition, is also included in the model. The developed rebound/deposition model was successfully implemented into the ANSYS CFD Premium solver and checked step by step. The model is calibrated by two cases: sand [or Arizona road dust (ARD)] particle impingement on a circular plate and Mt. St. Helens volcanic ash (comparable with ARD particles in terms of chemical composition) impinging on a first-stage air-cooled nozzle guide vane (NGV). For the former case, the calibrated model predicts fairly well the variation of particle capture efficiencies with flow/particle temperatures. The latter case indicates that the particle capture efficiency at engine operating conditions can be assessed by the developed model. Due to the lack of experimental data that would permit a full calibration/validation, for the time being it could be only used under limited conditions. Certainly, the model will be continuously improved as the relevant experimental data appears.
Effects of Bleed Slot Size on the Shock-Wave/Boundary-Layer Interactions in a Transonic Compressor Stator
Authors: Li Bai , Zhou Xun , Luo Lei , Du Wei 
Published: October 2022

Abstract
A numerical investigation of shock-wave/boundary-layer interaction in a transonic compressor stator with different slot widths is presented in the current work. The fluid in boundary layer is bled through the suction slot into a plenum to control the separation. Three different slot widths at inlet Mach number of 1.0 are studied. Numerical results show that all sizes of slot are capable of reducing the total pressure loss coefficient. The maximum amplitude of decline in pressure loss is 75.7% compared to the cascade without bleed. The optimum bleed pressure and corresponding optimum bleed mass in terms of minimizing pressure loss appear in three different slots. The wider slot leads to a lower pressure loss at the optimum bleed pressure. The shock wave on the suction surface is reorganized by the slot bleed. At the same bleed pressure, the wider slot causes the modified shock wave closer to the downstream. The expansion in front of modified shock wave could change the flow direction over slot. The tangential momentum of boundary layer at slot downstream edge is increased by the slot bleed. This enhances the ability of the boundary layer to withstand the adverse pressure gradient.
Investigation of Adaptive Mesh Refinement on an Industrial Gas Turbine Combustor
Authors: McManus Liam , Karalus Megan , Munktell Erik , Rogerson Jim 
Published: October 2022

Abstract
An adaptive mesh refinement (AMR) method is demonstrated for Large Eddy Simulations (LES) of an industrial gas turbine combustor, the SGT-100 provided by Siemens Energy Industrial Turbomachinery Ltd.
In this paper, the Simcenter STAR-CCM+® solver is used to dynamically refine a series of Large Eddy Simulations with a Flamelet Generated Manifold (FGM) combustion model as applied to the SGT-100. Mesh refinement criteria are defined using second gradients of mixture fraction and reaction progress.
Two meshes are assessed with and without AMR. The results are then compared to a refined static mesh and experimental data. The accuracy and computational cost of the static and adaptively refined meshes are discussed. It is shown that AMR can provide close to 2x speed up compared to a refined static mesh with similar predictions of mean and RMS quantities of the flow field, flame temperature and major species.
Numerical Study on the Performance of Hybrid Darrieus-Savonius Vertical Axis Wind Turbines Having Twisted Blades
Authors: Saad Ahmed S. , Ahmed Mahmoud 
Published: October 2022

Abstract
Darrieus and Savonius rotors are the main types of vertical axis wind turbines. Darrieus rotors exhibit high power coefficient but suffer from lower self-starting capabilities. On the other hand, Savonius rotors demonstrate relatively high self-starting capabilities but with an inferior power coefficient. Therefore, the current study proposes three hybrid Darrieus-Savonius designs with different angles of twisting aiming at having a compact turbine with high coefficient of power and easy to self-start. The Savonius turbine is placed inside the Darrieus turbine in the three proposed hybrid designs. Accordingly, the trends of coefficient of power against ratio of rotor tip speed in addition to coefficient of torque over a whole cycle (360 degrees) are computed. The coefficient of static torque during a whole cycle is also calculated. Therefore, three dimensional, incompressible, and unsteady Reynolds-Average Navier-Stokes equations in conjunction with the turbulence model of k-ω shear-stress transport is developed and numerically simulated utilizing ANSYS Fluent. The devolved numerical model is validated using the available measurements from literature. The predicted characteristics of flow field over the three suggested hybrid designs are analyzed and presented.
Accordingly, results illustrated that a significant enhancement of the coefficient of power is attained by suggested hybrid designs with twisting blades in comparison with the straight-bladed design. The model with twisted-bladed Darrieus and Savonius turbines with angles of twisting of 90° and 45°, respectively attains the largest peak of coefficient of power of 0.353. This hybrid configuration exhibits lower static torque fluctuations with positive values during the whole cycle. Consequently, using the suggested hybrid turbine with twisting blades improves both coefficient of power and the self-starting capability of the turbine.