bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aero-Thermal Coupled Design Optimization of a Turbine Vane and the Effect on Heat Load of Endwall
Authors: Liu Zhansheng , Yang Kefeng , Feng Zhenping 
Published: January 2021

Abstract
The 3D aerodynamic design optimization has been applied in the generation of modern turbine blade profile. However, the traditional design method paid little attention to the decrease of heat transfer coefficients on the blade external surface. In the present work, a typical high load turbine vane, VKI LS89 cascade, was optimized with the decrease of aerodynamic loss and heat load chosen as the optimization objective functions. Numerical simulation methods were validated by the experiment data, and simulations results agreed well with the measured values. Both 2D profiles and stagger curves of the vane were parameterized by no-uniform B-Spline. There were totally seven movable control points for the 2D profiles, and four movable control points for the corresponding stagger curves. And the locations of the B-Spline control points and stagger angles were taken as the design variables. Multi-objective genetic algorithm coupled with surrogate model was adopted to acquire the optimal cases with better aero-thermal performance. The profiles of the vane were firstly optimized in a linear cascade model, and then the stagger curves and sections stagger angle were modified for better overall performance. Mass flow rate of the mainstream and exit flow angle at outlet were constrained by the comprehensive objective functions during the 3D optimization process. The results showed that profiles with high aerodynamic efficiency and low heat load can be obtained by the 2D profiles optimization design. Additionally, the heat load could be decreased by the 3D optimization design. Furthermore, the effects of optimization on the heat load distributions of the endwall were studied, and it can be observed that the 3D optimization obviously modified the heat transfer patterns of the endwall.
Blades and Vanes Platform Laser Rebuilding
Authors: Gabrielli A. , Moretto M. 
Published: January 2021

Abstract
The evolution of industrial gas turbines towards increased efficiency and performance requires ever higher operating temperatures for the engines. In order to remain competitive in the market, OEM companies continuously need to develop maintenance programs and reconditioning technologies able to extend the life of these components as much as possible. During the operation, turbine blades and vanes are prone to deterioration due to the high temperature of the gas passing along the platform surface, causing hot corrosion and thermomechanical fatigue. In particular, this results in deterioration and crack formation at platform edges. If oxidized, cracked or otherwise deteriorated locations are found during service inspections, the component platform has to be rebuilt. The standard method for rebuilding the platform is to remove the deteriorated material volume and rebuild it by welding. In particular, the most common welding method for rotor blades and stator vanes restoration today is the tungsten inert gas welding (GTAW). However, tungsten inert gas welding has a large heat affected zone, which can later lead to major distortion, due the elevated thermal input, and loss of structural integrity of the reconditioned part. In particular, for single crystal material high thermal input can promote recrystallization issues and this phenomenon compromises the mechanical properties and considerably reduces the life of the component. The most recent reconditioning techniques developed by Ansaldo Energia involves the use of laser metal deposition technology to rebuild the damaged areas and restore the platform to the original shape. Prior to the automated process the area, on which the clad will be laid, requires precise preparation. This paper describes a customized, automatic process to restore the deteriorated blade or vane area by the laser metal deposition technique for equiaxial or single crystal material, minimizing the thermal input and resulting in high resistance rebuilding.
Development and Validation of a Continuous Random Walk Model for Particle Tracking in Accelerating Flows
Authors: Vadgama Nikul , Kapsis Marios , Forsyth Peter , McGilvray Matthew , Gillespie David R. H. 
Published: January 2021

Abstract
Stochastic particle tracking models coupled to RANS fluid simulations are frequently used to simulate particulate transport and hence predict component damage in gas turbines. In simple flows the Continuous Random Walk (CRW) model has been shown to model particulate motion in the diffusion-impaction regime significantly more accurately than Discrete Random Walk implementations. To date, the CRW model has used turbulent flow statistics determined from DNS in channels and experiments in pipes. Robust extension of the CRW model to accelerating flows modelled using RANS is important to enable its use in design studies of rotating engine-realistic geometries of complex curvature.
This paper builds on previous work by the authors to use turbulent statistics in the CRW model directly from Reynolds Stress Models (RSM) in RANS simulations. Further improvements are made to this technique to account for strong gradients in Reynolds Stresses in all directions; improve the robustness of the model to the chosen time-step; and to eliminate the need for DNS/experimentally derived statistical flow properties. The effect of these changes were studied using a commercial CFD solver for a simple pipe flow, for which integral deposition prediction accuracy equal to that using the original CRW was achieved. These changes enable the CRW to be applied to more complex flow cases.
To demonstrate why this development is important, in a more complex flow case with acceleration, deposition in a turbulent 90° bend was investigated. Critical differences in the predicted deposition are apparent when the results are compared to the alternative tracking models suitable for RANS solutions. The modified CRW model was the only model which captured the more complex deposition distribution, as predicted by published LES studies. Particle tracking models need to be accurate in the spatial distribution of deposition they predict in order to enable more sophisticated engineering design studies.
Experimental Investigations of Superheated and Supercritical Injections of Liquid Fuels
Authors: Yin Zhiyao , Kutne Peter , Eichhorn Jochen , Meier Wolfgang 
Published: January 2021

Abstract
Single- and multi-component liquid fuels are injected in a jet-in-coflow configuration at elevated temperatures and pressures with both a custom plain orifice nozzle and a commercial pressure-swirl atomizer. The transitions in spray morphology from mechanical breakup to superheated/supercritical regimes are characterized qualitatively by laser shadowgraphy and evaluated based on quantitative measures of superheat. Although fuel preheating exhibits no discernible effect in the mechanical breakup regime, dramatic jet-to-plume transition as well as build up of fuel vapor in the spray chamber are observed with increasing level of superheat. The difference between two different atomizers in terms of spray behavior diminishes at high levels of superheat, suggesting the predominant role of thermal effect on spray morphology in superheated/supercritical regimes. For a mutli-component fuel such as Jet A-1, the transition into a fully flashing spray occurs at temperatures lower than expected values, which are calculated by treating Jet A-1 as a single-component fuel. Additionally, pressure drop is shown as a sensitive indicator for the departure from mechanical breakup and the onset of thermal effect on the spray. Comparisons between measured and estimated pressure drop also reveal the differences in susceptibility to thermal effects between the plain orifice and the pressure-swirl atomizers.
Effect of Hydrogen on Steady-State and Transient Combustion Instability Characteristics
Authors: Strollo John , Peluso Stephen , O’Connor Jacqueline 
Published: January 2021

Abstract
This paper examines the effects of steady-state and transient hydrogen enrichment on thermoacoustic instability in a model gas turbine combustor. Combustion instability, a feedback loop between flame heat release rate oscillations and combustor acoustics, is characterized in a swirl-stabilized flame operated at a range of hydrogen-natural gas fuel blends and heat rates. Measurements of combustor chamber pressure fluctuations and CH* chemiluminescence imaging are used to characterize instability at a range of operating conditions. Steady-state tests show that both mixture heat rate and hydrogen content affect system stability. At a given heat rate, higher levels of hydrogen result in unstable combustion. As heat rate increases, instability occurs at lower concentrations of hydrogen in the fuel. Transient operation was tested in two directions — instability onset and decay — and two hydrogen-addition times — a short time of 1 millisecond and a longer time of 4 seconds. Results show that instability onset processes, through the transient addition of hydrogen, are highly repeatable regardless of the timescale of hydrogen addition. Certain instability decay processes are less repeatable, resulting in cases that do not fully transition from unstable to stable combustion despite similar changes in hydrogen fuel flow rate. Flame behavior before, during, and after the transient is characterized using high-speed CH* chemiluminescence imaging. Analysis of the high-speed images show changes in flame stabilization and dynamics during the onset and decay processes. The results of this study can have implications for systems that experience variations in fuel composition, particularly in light of growing interest in hydrogen as a renewable fuel.
Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures
Authors: Kumar Rajesh S. 
Published: January 2021

Abstract
Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is that formed via Polymer Impregnation and Pyrolysis (PIP). As this process involves pyrolysis process to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage leads to significant defects in the final material in the forms of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.
Unsteady Flow Simulation of an Axial Fan for Dry Cooling in a CSP Plant Using the Variational Multiscale Method
Authors: Barnabei Valerio Francesco , Castorrini Alessio , Corsini Alessandro , Van der Spuy Johan , Rispoli Franco 
Published: January 2021

Abstract
We present an unsteady simulation of an axial fan with low pressure and high flow rate, developed during the MinWaterCSP EU project, specifically designed and optimized for Concentrating Solar Power (CSP) plants with the aim of reducing water consumption at the condenser stage. An earlier version of the fan, referred as M-fan, was initially developed to serve the hybrid cooling system, to boost the overall heat transfer performance with dry cooling. In this work, we will performing a Computational Fluid Dynamics (CFD) analysis of the unsteady flow on a redesigned and scaled version of the M-fan, referred as T-fan, by The T-fan was designed and optimized to reduce noise emissions and improve efficiency with respect to the M-fan. We perform the simulation using an in-house built C++ parallel code for CFD analysis using Finite Elements (FE). We model the flow dynamics using the Residual Based Variational MultiScale method (RBVMS) to obtain a stabilized solution of the Navier-Stokes equation using FE discretization. We will discuss the simulation results of the RBVMS model by comparing our simulation of the T-fan with experimental results on the same fan.
A Numerical Investigation Into Secondary Flows at the Inlet to a Low-Pressure Compressor Transition Duct
Authors: Tsakmakidou Dimitra , Walker A. Duncan , Hall Chris 
Published: January 2021

Abstract
To reduce fuel-burn and CO2 emissions from aero gas turbines there is a drive towards very-high bypass ratio and smaller ultra-high-pressure ratio core engine technologies. However, this makes the design of the ducts connecting various compressor spools more challenging as the larger required radius change increases their aerodynamic loading. This is exacerbated for the duct which feeds the engine core as it must accept the relatively low-quality flow produced by the fan root. This is characterised by a hub-low pressure profile and large secondary flow structures which will inevitably increase loss and the likelihood of flow separation. This paper presents a numerical design study aimed at modifying an existing fully annular, low-speed test facility to produce larger, more representative rotor loss cores. The CFD domain comprises a single stage axial compressor and transition duct representative of the low-pressure spool in a high bypass ratio turbofan. The rotating and stationary frames were coupled using a sliding mesh and a uRANS approach with Reynolds Stress closure for the turbulence modelling. The methodology was first validated using existing experimental data before examining a number of parameters such as inlet boundary layer thickness, inlet swirl, tip gap, blade solidity, thickness, lean. It was found that a combination of an increased inlet hub boundary layer and a reduction in solidity sufficiently increased the hub loading and encouraged the development of significantly large loss cores. Preliminary CFD results also showed that the increased rotor loss cores promoted better mixing through the outlet guide which subsequently reduced hub boundary layer thickness and secondary flows. Despite incurring a larger total pressure loss this suggested that the transition duct moved further from stall and could therefore potentially be made shorter.
CMSX-4® Plus (SLS): An Improved 3rd Generation Single Crystal Alloy
Authors: Wahl Jacqueline , Harris Ken 
Published: January 2021

Abstract
Ongoing demand for advanced aero gas turbine engines with lower fuel burn and commensurate reduced CO2 emissions require single crystal (SX) superalloys capable of operating at higher gas and metal temperatures beyond the capability of 2nd generation, 3% rhenium (Re)-containing SX alloys, currently used extensively in commercial and military flight engines. These complex cooled turbine blades and vane castings must have an excellent balance of high temperature mechanical properties, producibility, oxidation/hot corrosion resistance, coating compatibility including TBC performance and phase stability.
The highest strength nickel-base SX superalloys currently in production (3rd generation CMSX-10K® and CMSX-10N® alloys) contain 6–7% Re. These highly alloyed, specialty alloys have some application drawbacks including some secondary reaction zone (SRZ) phase instability in the base alloy adjacent to the coatings, low temperature internal oxidation/hot corrosion attack requiring sophisticated dual role internal and external coatings and difficulty in production solution heat treatment. In addition, current 3rd generation SX alloys have relatively higher density which is a disadvantage in terms of weight and inertia in rotating part applications, and high cost due to the elevated Re content.
An improved, lower Re content (4.8%), 3rd generation SX superalloy, CMSX-4® Plus (SLS) has been developed with improved properties and performance over current 3rd generation SX alloys, while lacking the drawbacks. Coatings have been successfully developed which are compatible with the base alloy and suitable bond coats for TBC application. This paper presents the characterization of CMSX-4 Plus (SLS) alloy, including composition, mechanical and physical properties, oxidation properties and phase stability, along with production status.
Experimental and Kinetic Evaluation of Pressurized Lean Premixed Hydrogen-Air Flame Stability With Carbon Dioxide and Steam Dilution
Authors: Runyon Jon , Pugh Daniel , Giles Anthony , Goktepe Burak , Bowen Philip , Marsh Richard , Morris Steven 
Published: January 2021

Abstract
A study has been undertaken to experimentally and numerically evaluate the use of carbon dioxide or steam as premixed fuel additive in hydrogen-air flames to aid in the development of lean premixed (LPM) swirl burner technology for low NOx operation. Chemical kinetics modelling indicates that the use of CO2 or steam in the premixed reactants reduces H2-air laminar flame speed and adiabatic flame temperature within the well-characterized range of preheated LPM methane-air flames, albeit in markedly different proportions; for example, nearly 65 %vol CO2 as a proportion of the fuel is required for a reduction in laminar flame speed to equivalent CH4-air values, while approximately 30 %vol CO2 in the fuel is required for an equivalent reduction in adiabatic flame temperature, significantly impacted by the increased heat capacity of CO2. The 2nd generation high-pressure generic swirl burner, designed for use with LPM CH4-air, was therefore utilized to experimentally investigate the influence of CO2 and steam dilution on pressurized (up to 250 kW/MPa), preheated (up to 573 K), LPM H2-air flame stability using high-speed OH* chemiluminescence. In addition, exhaust gas emissions, such as NOx and CO, have been measured in comparison with equivalent thermal power conditions for CH4-air flames, showing that low NOx operation can be achieved. Furthermore, pure LPM H2-air flames are characterized for the first time in this burner, stabilized at low equivalence ratio (approximately 0.24) and increased Reynolds number at atmospheric pressure compared to the stable CH4-air flame (equivalence ratio of 0.55). The influence of extinction strain rate is suggested to characterize, both experimentally and numerically, the observed lean flame behavior, in particular as extinction strain rate has been shown to be non-monotonic with pressure for highly-reactive and diffuse fuels such as hydrogen.
Effect of Different Fuels on Combustion Instabilities in an Annular Combustor
Authors: Soundararajan Preethi Rajendram , Vignat Guillaume , Durox Daniel , Renaud Antoine , Candel Sébastien 
Published: January 2021

Abstract
Combustion instabilities in annular combustors of jet engines is a recurring issue. In the present study, the characteristics of instabilities for different fuels are investigated by combining the instability maps obtained in an annular combustor equipped with multiple swirling spray injectors (MICCA-Spray) and flame describing functions (FDFs) from a single sector configuration (SICCA-Spray). Two types of liquid fuels are injected as hollow cone sprays: heptane, which is fairly volatile, and dodecane, which is less volatile. Experiments are also conducted with gaseous propane, perfectly premixed with air, which serves as a reference. An instability map is systematically drawn by varying the global equivalence ratio and thermal power. The data indicate that the amplitude and frequency of instabilities depend, for the same operating point, on the fuel injection conditions (premixed or spray) and fuel type. Overall trends show that premixed propane is unstable in a broad operating domain. Injection of liquid fuels induces changes in time lag that modify the unstable regions. For heptane the instability map is closer to the propane reference map whereas dodecane exhibits wider stable regions. Variations can also be observed in the behavior of spin ratio that characterizes the azimuthal structure of the coupling mode. An attempt is made to understand these features by examining the FDF, which gives the ratio of relative fluctuations in heat release rate to the relative fluctuations in velocity. The FDFs measured in a single sector configuration gives access to gain and phase information that can be used to determine unstable bands. It is found that based on whether the MICCA-Spray instability frequency is within these bands, the instability amplitude can be high or low. This indicates that the difference in instabilities between the three fuels can be linked to the variations in FDFs.
Multi-Jet Impingement Heat Transfer With a Dimple-Pimple Patterned Jet Plate
Authors: Zawati Husam , Gupta Gaurav , Khlyapov Yakym , Fernandez Erik , Kapat Jayanta , Schaenzer Megan , Rodriguez Jose 
Published: January 2021

Abstract
The objective of the present study is the evaluation of the heat transfer difference between a novel jet plate configuration and a conventional flat jet orifice plate. Physical mechanisms that lead to a change in Nusselt number when comparing both configurations are discussed in two regions: impingement and crossflow. In the presented work, both plates with identical inline arrays of (20 × 26) circular air jets impinging orthogonally on a flat target comprised of 20 segments parallel to the jet orifice plates, are studied. The first is a staggered configuration of a pimple-dimple (convex-concave) plate. This plate features two jet diameters: (a) 4.63 mm emanating from negative sphere of 14.63 mm in radius inward imprint; (b) 2.19 mm emanating from a positive sphere of 17.07 mm in radius, protruding from the base of the plate. The second jet plate is flat, which serves as a baseline for the heat transfer study. This plate has a constant jet orifice diameters of 3.49 mm, found based on the definition of total average open area of the first plate (NPR configuration).
Heat transfer characteristics and turbulent flow structures are investigated over jet-averaged Reynolds numbers (Reav,j) of 5,000, 7,000, and 9,000. Jet-to-plate distance (Z/Dj) is varied between (2.4 – 6.0) jet diameters. A numerical study is carried out to compare various turbulence models (κε-EB, κε-Lag EB, κε-v2f, κω-SST, RST). Numerical simulations are analyzed in detail to explain the underlying mechanism of heat transfer enhancement, related to such geometries.
The convex-concaved plate yields lower globally-averaged heat transfer coefficients when compared to a flat jet plate in the impingement region. However, enhancement up to 23% is seen in the crossflow region, where the crossflow effects are dominant in a maximum-crossflow configuration.