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Accepted Manuscripts

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research-article  
Tine Seljak, Klemen Pavalec, Marco Buffi, Agustin Valera Medina, David Chiaramonti and Tomaz Katrasnik
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041312
Increased public concerns and stricter regulatory frameworks promote the role of bioliquids (liquid fuel for energy purposes other than for transport, including electricity and heating and cooling, produced from biomass). This is a driving force for development and employment of micro-gas-turbines (MGTs) due to their ability to combust bioliquids with less favorable properties in a decentralized manner. Gas turbines are characterized by relatively high combustion efficiency at relatively low concentrations of harmful emissions, relatively high effective efficiency and durability when utilizing a common portfolio of gas turbine approved fuels. It is thus desired to preserve these advantages of gas turbines also while burning bioliquids and further relying on their scalability that is crucial to efficient support of decentralized energy production at small scales. To support these objectives, MGT technology needs to allow for utilization of bioliquids with much wider spectrum of physical and chemical properties compared to common commercially available MGTs in a single MGT based plant. In this view, the present study is providing the first thorough overview of challenges and solutions encountered by researchers across the wide area of bioliquids in MGTs.
TOPICS: Combustion, Fuels, Chemical properties, Biomass, Durability, Gas turbines, Heating and cooling, Microturbines, Distributed power generation, Emissions, Micro gas turbines
research-article  
Jeffrey Brown, Joseph Beck, Alex Kaszynski and John Clark
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041314
This effort develops a surrogate modeling approach for predicting the effects of manufacturing variations on performance and unsteady loading of a transonic turbine. Computational fluid dynamics (CFD) results from a set of 105 as-manufactured turbine blade geometries are used to train and validate the surrogate models. Blade geometry variation is characterized with point clouds gathered from a structured light, optical measurement system and as-measured CFD grids are generated through mesh morphing of the nominal design grid data. Principal component analysis (PCA) of the measured airfoil geometry variations is used to create a reduced basis of independent surrogate model parameters. It is shown that the surrogate model typically captures between 60% and 80% of the CFD predicted variance. Three new approaches are introduced to improve surrogate effectiveness. First, a zonal PCA approach is defined which investigates surrogate accuracy when limiting analysis to key regions of the airfoil. Second, a training point reduction strategy is proposed that is based on the k-d tree nearest neighbor search algorithm and reduces the required training points up to 38% while only having a small impact on accuracy. Finally, a alternate reduction approach uses k-means clustering to effectively select training points and reduces the required training points up to 66% with a small impact on accuracy.
TOPICS: Manufacturing, Modeling, Turbines, Computational fluid dynamics, Geometry, Airfoils, Optical measurement, Principal component analysis, Trains, Blades, Design, Turbine blades, Algorithms
research-article  
Wenliang Qi, Pingjian Ming, Jia Ming, Ye Peng and Chen Liu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041283
Injection flow dynamics plays a significant role in fuel spray, this process control the fuel-air mixing, which in turn is critical for the combustion and emissions process in diesel engine. In the current study, an integrated spray, combustion and emission numerical model is developed for diesel engine computations based on the General Transport Equation Analysis (GTEA) code. The model is first applied to predict the effect of turbulence inside the nozzle which is considered by the submodel of hybrid breakup model on diesel spray process. The results indicate that turbulence term enhances the rate of breakup, resulting in more new droplets and smaller droplet sizes, leading to high evaporation rate with more evaporated mass. The model is also applied to simulate combustion and soot formation process of diesel. The effects of ambient density, ambient temperature, oxygen concentration and reaction mechanism on ignition delay, flame lift-off length and soot formation are analyzed and discussed. The results show that although higher ambient density and temperature reduce the ignition delay and causes the flame stabilization location to move upstream, this is not helpful for fuel-air mixing because it increases the soot level in the fuel jet. While higher oxygen concentration has negative effects on soot formation. In addition, the model is employed to simulate the combustion and emission characteristics of a low-temperature combustion (LTC) engine. The overall agreement between the measurements and predictions of in-cylinder pressure, heat release and emission characteristics are satisfactory.
TOPICS: Fuels, Combustion, Diesel, Emissions, Soot, Sprays, Drops, Turbulence, Density, Temperature, Ignition delay, Diesel engines, Flames, Oxygen, Pressure, Flow (Dynamics), Heat, Computer simulation, Engines, Evaporation, Low temperature, Nozzles, Computation, Cylinders, Process control
research-article  
Prithwish Kundu, Muhsin Ameen, Chao Xu, Umesh Unnikrishnan, Tianfeng Lu and Sibendu Som
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041281
Stiffness of large chemistry mechanisms is a major hurdle towards predictive engine simulations. Detailed mechanisms with thousands of species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The cost of simulations typically increase super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets (Tabulated Flamelet Model) and fast chemistry solvers. The flamelet solver consists of the traditional operator-splitting scheme with Variable coefficient ODE solver; and a numerical Jacobian. A new framework with LSODES chemistry solver and an analytical Jacobian was implemented. Results show that the computational cost is linearly proportional to the number of species in a given chemistry mechanism and 2-3 orders of magnitude faster than the traditional solvers. This framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2,755 species and 11,173 reactions. The Engine Combustion Network experiments are modeled using large eddy simulations (LES) coupled with detailed mechanisms. The model is validated across a range of ambient temperatures. Qualitative results from the simulations were validated against experimental OH and CH2O PLIF data. The study demonstrates that detailed reaction mechanisms (~1000 species) can be used in engine simulations with a linear increase in computation cost with number of species during the tabulation process and a small increase in the 3D simulation cost.
TOPICS: Engines, Simulation, Chemistry, Computation, Stiffness, Large eddy simulation, Temperature, Combustion
research-article  
Alessio Suman, Nicola Casari, Elettra Fabbri, Michele Pinelli, Luca di Mare and Francesco Montomoli
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041282
Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. Experimental tests have been carried out on (i) a full scale gas turbine unit, (ii) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (iii) wind tunnel testing or hot gas facilities using a coupon as the target. In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. The historical data of particle deposition obtained over thirty years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.
TOPICS: Particle collisions, Gas turbines, Particulate matter, Temperature, Testing, Wind tunnels, Aircraft engines, Fuels, Viscosity, Kinetic energy, Nozzles, Performance, Erosion
research-article  
Francesca De Domenico, Steven M. Lowe, Luming Fan, Simone Hochgreb, Priyav Shah, Benjamin A.O. Williams and Paul Ewart
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041275
Temperature and composition spots in a turbulent flow are detected and time-resolved using Laser Induced Thermal Grating Spectroscopy (LITGS). A 355 nm wavelength PIV laser is operated at 0.5 -1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In a open laminar jet, a feasibility study shows that small (~ 3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, travelling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access.
TOPICS: Density, Flow (Dynamics), Temperature, Wavelength, Lasers, Temperature measurement, Diffraction gratings, Spectroscopy, Turbulence, Entropy, Fluctuations (Physics), Jets, Combustion chambers, Calibration, Quartz
research-article  
Rodrigo Rodriguez Erdmenger, Katya Menter, Rogier Giepman, Aneesh Vadvadgi, Thomas Lavertu, Thomas Leonard and Stephen W T Spence
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041279
The air handling system for large diesel/gas engines such as those used on locomotive, marine, and power generation applications require turbochargers with a high reliability and with turbomachinery capable to adjust to different operating conditions and transient requirements. The usage of variable geometry turbocharging (VGT) provides flexibility to the air handling system but adds complexity, cost and reduces the reliability of the turbocharger in exchange for improved engine performance and transient response. For this reason, it was desirable to explore designs that could provide the variability required by the air handling system, without the efficiency penalty of a conventional waste gate and with as little added complexity as possible. The current work describes a new low-cost variable geometry turbine design to address these requirements. The new tandem nozzle concept proposed is applicable to both axial and radial turbines, and has been designed using conventional 1D models and 2D/3D CFD methods. The concept has furthermore been validated experimentally on two different test rigs. In order to avoid the long lead times of procuring castings, the nozzle for the axial turbine was manufactured using new additive manufacturing techniques. Both the axial turbine and the radial turbine designs showed that the concept is capable to achieve a mass flow variability of more than 15% and provide a robust and cost-effective alternative to conventional VGT designs by significantly reducing the number of moveable parts.
TOPICS: Turbochargers, Turbines, Nozzles, Geometry, Transients (Dynamics), Reliability, Gates (Closures), Flow (Dynamics), Engines, Computational fluid dynamics, Design, Energy generation, Locomotives, Turbomachinery, Gas engines, Additive manufacturing, Diesel
research-article  
Xueliang Lu and Luis San Andres
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041270
In subsea environments, multiphase pumps add pressure to the process fluid thus enabling long distance tie back systems that eliminate topside oil and gas separation stations. One challenge to construct a reliable multiphase pump is that they must handle a mixture whose gas volume fraction (GVF) changes suddenly. The mixture GVF affects the static and dynamic forced performance of seals, and which could lead to an increase in rotor lateral or axial vibrations. This paper extends prior work with uniform clearance seals and presents the static and dynamic performance of a three-wave surface annular seal designed to deliver a significant centering stiffness. The test element has length L=43.4 mm, diameter D=127 mm, and mean radial clearance cm=0.191 mm. At a shaft speed of 3.5 krpm (23 m/s surface speed), an air in ISO VG 10 oil mixture with an inlet GVF, 0 to 0.9, feeds the seal at 2.5 bara pressure and 37 °C temperature. The mixture mass flow rate decreases continuously with an increase in inlet GVF. The liquid seal (GVF=0) shows frequency independent force coefficients. However, operation with a mixture produces stiffnesses that vary greatly with excitation frequency. The direct damping coefficients are not functions of frequency albeit dropping rapidly in magnitude as the GVF increases. The extensive test campaign reveals a wavy-surface seal offers a centering stiffness ability, a much desired feature in vertical submersible pumps that suffer from persistent static and dynamic stability issues.
TOPICS: Waves, Leakage, Pumps, Stiffness, Clearances (Engineering), Pressure, Flow (Dynamics), Temperature, Separation (Technology), Fluids, Damping, Ocean engineering, Submersibles, Excitation, Rotors, Vibration, Dynamic stability
research-article  
Yogesh Singh, Michael Presby, Manigandan Kannan and Gregory Morscher
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041271
The method of direct current potential drop (DCPD) can be utilized as an effective, and convenient approach for in-situ damage detection, and as a non-destructive evaluation technique. We present the results from use of a multiprobe DCPD technique for in-situ damage detection in loading of a SiC/SiC composite. It is shown that in three different modes of loading (monotonic, fatigue, and cyclic load-unload), the sensing capabilities of DCPD technique compares well to the techniques of modal acoustic emission (AE) and digital image correlation (DIC). It was also found that DCPD technique provides a far earlier warning of failure under fatigue loading than the other two methods. In addition, we show that strategically placed multiple voltage leads on the specimen surface provides a promising way of qualitatively determining the crack initiation site. Therefore, the use of multiple lead DCPD method, together with other techniques, provides a viable option for sensing damage in ceramic matrix composites (CMCs) with complex geometries, and for applications at higher temperatures.
TOPICS: Ceramic matrix composites, Damage, Fatigue, Temperature, Composite materials, Nondestructive evaluation, Stress, Fracture (Materials), Acoustic emissions, Failure
research-article  
Mauricio Gutierrez, Paul Petrie-Repar, Robert Kielb and Nicole L. Key
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041280
Accuracy when assessing mistuned forced response analyses is still a mayor concern. Since a full coupled analysis is still very computational expensive, several simplifications and reduced order models are carried out. The use of a reduction method, the assumptions and simplifications, generate different uncertainties that challenge the accuracy in the results. Experimental data are needed for validation and also to understand the propagation of these uncertainties. This paper shows a detailed mistuned forced response analysis of a compressor blisk. The blisk belongs to the Purdue Three-Stage(P3S) Compressor Research Facility. Two different stator-rotor-stator configurations of 38 and 44 upstream stator vanes are taken into consideration. Several loading conditions are analyzed at three different speed lines. A reduced order model known as subset nominal mode (SNM), has been used for all the analyses. This reduction takes as a basis a set of modes within a selected frequency spectrum. It can consider a complete family of modes to study the disk-blade modal interaction. A detailed comparison between the predicted and measured results have been performed, showing a good agreement for the high loading conditions.
TOPICS: Compressors, Stators, Uncertainty, Rotors, Disks, Blades
research-article  
Cao Chen, Xiaojun Yan, Xiaoyong Zhang, Yingsong Zhang, Min Gui and Min Tao
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041252
Some cracks were detected on the fir-tree root of turbine blade in an in-service aero-engine, and the aluminized coating was considered to be the main cause of these cracks. To study the effect of aluminized coating on fatigue life of turbine blade, the combined low and high cycle fatigue (CCF) tests are carried out at elevated temperature on both aluminized and untreated turbine blades. Probability analysis of test data is conducted and the result indicates that the median life is decreased by 62.2% due to the effect of the aluminized coating. Further study on the mechanism of crack initiation and propagation has been conducted based on fractography and cross-section morphology analysis by using scanning electron microscope (SEM), and the results indicate: 1) The aluminized coating consists of two layers, of which the inner layer is considered to contain the s phase and it reduces the resistance to fatigue of blade. 2) Many cavities are found in the inner layer of aluminized coating, which lead to the initiation of cracks and result in the reduction of crack initiation life. 3) The marker band widths of aluminized and untreated blade are very close, which indicated the aluminized coating may have no effect on the crack propagation life of the blade.
TOPICS: Turbine blades, Temperature, Coating processes, Coatings, High cycle fatigue, Fracture (Materials), Blades, Cavities, Crack propagation, Fatigue life, Fractography, Probability, Aircraft engines, Fatigue, Scanning electron microscopes
research-article  
Clemens Bernhard Domnick and Dieter Brillert
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041253
Steam turbine inlet valves are used to control the power output of steam turbines for power generation. These valves may be subject to vibration under certain operating conditions, especially in part-load operation. Several research papers and reports show that elevated valve vibrations can result in damage to parts of a steam turbine installation. A comprehensive literature review considering 43 different valves investigated in 51 studies reveals the effects causing vibrations. The physics of these effects are explained and methods for reducing flow-induced dynamic forces are presented based on the findings published in the literature. A classification scheme for typical valve designs is developed and the design features are evaluated in terms of valve vibration. Numerical methods for analyzing the fluid dynamics of valves are also presented.
TOPICS: Flow (Dynamics), Valves, Vibration, Steam, Design, Excitation, Steam turbines, Damage, Stress, Physics, Fluid dynamics, Energy generation, Numerical analysis
research-article  
Daniel A. Nelson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041244
This paper presents the design and development of a non-contacting dry-gas mechanical seal for high performance automotive turbocharger applications. Turbochargers are increasingly being incorporated into high performance automobile engines to improve fuel efficiency, enhance energy recovery, and increase horsepower as compared with similar sized naturally aspirated engines. Minimizing the wear rate of tribological surfaces in the turbomachinery is critical to maximizing the reliability and durability of the turbocharger. A dry-gas seal for turbochargers and related technologies with 2 to 4 cm shafts has been developed. The seal provides a complete barrier between the bearing oil and compressor flow path and is capable of reverse pressure and high speed. The seal performance was evaluated for speeds between 60,000 to 80,000 RPM, pressure differentials between -0.8 (reverse pressure) to 6 bar, and temperatures between 20 to 200 $^{\circ}$C. Structural and thermal response of the seal components to the operating conditions are analyzed using finite element methods and the tribological behavior of the seal rings are analyzed using computational fluid dynamics. The design is experimentally validated in a seal test stand. This novel approach reduces turbocharger blowby and shows no measurable wear when compared with piston ring seals.
TOPICS: Turbochargers, Pressure, Design, Tribology, Wear, Temperature, Compressors, Horsepower, Reliability, Piston rings, Finite element methods, Bearings, Computational fluid dynamics, Durability, Energy recovery, Turbomachinery, Automotive engines, Naturally aspirated engines, Fuel efficiency, Flow (Dynamics)
research-article  
Pedro Rodrigues, Olivier Gicquel, Nasser Darabiha, Klaus Peter Geigle and Ronan Vicquelin
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041242
Many laboratory-scale combustors are equipped with viewing windows to allow for characterization of the reactive flow. Additionally, pressure housing is used in this configuration to study confined pressurized flames. Since the flame characteristics are influenced by heat losses, the prediction of wall temperature fields becomes increasingly necessary to account for conjugate heat transfer in simulations of reactive flows. For configurations similar to this one, the pressure housing makes the use of such computations difficult in the whole system. It is therefore more appropriate to model the external heat transfer beyond the first set of quartz windows. The present study deals with the derivation of such a model which accounts for convective heat transfer from quartz windows external face cooling system, free convection on the quartz windows 2, quartz windows radiative properties, radiative transfer inside the pressure housing and heat conduction through the quartz window. The presence of semi-transparent viewing windows demands additional care in describing its effects in combustor heat transfers. Because this presence is not an issue in industrial-scale combustors with opaque enclosures, it remains hitherto unaddressed in laboratory-scale combustors. After validating the model for the selected setup, the sensitivity of several modeling choices is computed. This enables a simpler expression of the external heat transfer model that can be easily implemented in coupled simulations.
TOPICS: Pressure, Heat transfer, Combustion chambers, Modeling, Quartz, Flames, Chemically reactive flow, Simulation, Engineering simulation, Convection, Radiative heat transfer, Cooling systems, Heat conduction, Computation, Natural convection, Heat losses, Transparency, Wall temperature
research-article  
Markus Weilenmann, Yuan Xiong, Mirko R. Bothien and Nicolas Noiray
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041240
This study deals with thermoacoustic instabilities in a generic sequential combustor. The thermoacoustic feedback involves two flames: the perfectly premixed swirled flame anchored in the first stage and the sequential flame established downstream of the mixing section, into which secondary fuel is injected in the vitiated stream from the first stage. It is shown that the large amplitude flapping of the secondary fuel jet in the mixing section plays a key role in the thermoacoustic feedback. This evidence is brought using high-speed Background Oriented Schlieren (BOS). The fuel jet flapping is induced by the intense acoustic field at the fuel injection point. It has two consequences: first, it leads to the advection of equivalence ratio oscillations toward the sequential flame; second, it modulates the residence time of the ignitable mixture in the mixing section, which periodically triggers autoignition kernels developing upstream of the chamber. In addition, the BOS images are processed to quantify the flow velocity in the mixing section and these results are validated using PIV. This study presents a new type of thermoacoustic feedback mechanism which is peculiar to sequential combustion systems. In addition, it demonstrates how BOS can effectively complement other diagnostic techniques that are routinely used for the study of thermoacoustic instabilities.
TOPICS: Oscillations, Fuels, Combustion chambers, Flames, Feedback, Combustion systems, Acoustics, Flow (Dynamics)
research-article  
Enrico Munari, Mirko Morini, Michele Pinelli, Klaus Brun, Sarah Simons and Rainer Kurz
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041255
Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge can be classified as mild, classic or deep, but operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. To fill this gap, this paper proposes a formulation of a surge severity index. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of the application of the Buckingham's Pi-theorem and a careful analysis of the causative and restorative factors of surge. Finally, some practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.
TOPICS: Surges, Damage, Compressors, Machinery, Inspection, Maintenance, Theorems (Mathematics), Flow (Dynamics), Vibration, Industrial plants, Sensitivity analysis, Simulation results, Mechanical structures
research-article  
Nicola Aldi, Nicola Casari, Mirko Morini, Michele Pinelli, Pier Ruggero Spina and Alessio Suman
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041249
Over recent decades, the variability and high costs of the traditional gas turbine fuels (e.g. natural gas), have pushed operators to consider low-grade fuels for running heavy-duty frames. Synfuels, obtained from coal, petroleum or biomass gasification, could represent valid alternatives in this sense. Synfuels are filtered before the combustor stage, but the contaminants are not removed completely. This fact leads to a considerable amount of deposition on the nozzle vanes due to the high temperature value. Particle deposition can increase surface roughness, modify the airfoil shape and clog the coolant passages. At the same time, land based power units experience compressor fouling. Hot sections and compressor fouling work together to determine performance degradation. This paper proposes an analysis of the contaminant deposition on hot gas turbine sections based on machine nameplate data. The combination of gas turbine net power, efficiency and turbine inlet temperature with different types of synfuel contaminants highlights how each gas turbine is subjected to particle deposition. The simulation of particle deposition on one hundred gas turbines ranging from 1.2 MW to 420 MW was conducted following the fouling susceptibility criterion. Low-efficiency frames (characterized by lower values of TIT) show the best compromise in order to reduce the effects of particle deposition in the presence of high-temperature melting contaminants. A high-efficiency frame is suitable when the contaminants are characterized by a low-melting point thanks to their lower fuel consumption.
TOPICS: Gas turbines, Particulate matter, Synthetic fuels, Fuels, Compressors, Melting, High temperature, Airfoils, Combustion chambers, Energy efficiency, Biomass, Coal, Temperature, Machinery, Simulation, Surface roughness, Coolants, Natural gas, Nozzles, Turbines, Fuel gasification, Petroleum, Shapes, Fuel consumption
research-article  
Martin Schulz, Fritz Klocke, Jan Riepe, Nils Klingbeil and Kristian Arntz
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041167
Titanium alloys are used instead of steel and nickel-based alloys to lower the weight of turbines whenever it is applicable. Due to the high manufacturing costs of titanium, near-net-shape processes like laser metal deposition (LMD) processes are an approach to improve the production of new turbomachinery components. Additionally, these processes are also suitable for repair. LMD uses wire or powder as additional material. When highly reactive materials like titanium grade 5 (Ti6Al4V) are processed, wire-based laser metal deposition (LMD-W) processes are superior to powder-based processes due to the smaller reactive surface. Nowadays, three main challenges exist when titanium grade 5 (Ti6Al4V) is processed by additive manufacturing (AM): First of all the high affinity to oxygen combined with the increased brittleness of the material in case of a contamination with already low amounts of oxygen has to be faced. Secondly, the material is prone to distortion induced by thermal stress during the manufacturing process. Finally, the material has a complex bimodal microstructure, which has to be adjusted properly to generate optimal strength. The following publication will present how these technical challenges are faced. The heat input into the workpiece and thereby the area that has to be covered with shielding gas is minimized. This is done by minimizing the laser spot size as well as adjusting the travel speed. Thereby a local shielding of the process was realized. With this optimized process, it was possible to generate several specimens for metallurgical analysis.
TOPICS: Metals, Lasers, Wire, Optimization, Titanium, Manufacturing, Oxygen, Shapes, Turbines, Brittleness, Metallurgical analysis, Titanium alloys, Thermal stresses, Contamination, Alloys, Steel, Maintenance, Nickel, Weight (Mass), Heat, Turbomachinery, Additive manufacturing
research-article  
Artur Figueiredo, Robin Jones, Oliver J Pountney, James Scobie, Gary Lock, Carl Sangan and David Cleaver
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041206
This paper presents Volumetric Velocimetry (VV) measurements for a jet in crossflow that is representative of film cooling. Volumetric velocimetry employs particle tracking to non-intrusively extract all three components of velocity in a three-dimensional volume. This is its first use in a film-cooling context. The primary research objective was to develop this novel measurement technique for turbomachinery applications, whilst collecting a high-quality data set that can improve the understanding of the flow structure of the cooling jet. A new facility was designed and manufactured for this study with emphasis on optical access and controlled boundary conditions. For a range of momentum flux ratios from 0.65 to 6.5 the measurements clearly show the penetration of the cooling jet into the freestream, the formation of kidney-shaped vortices and entrainment of main flow into the jet. The results are compared to published studies using different experimental techniques, with good agreement. Further quantitative analysis of the location of the kidney vortices demonstrates their lift off from the wall and increasing lateral separation with increasing momentum flux ratio. The lateral divergence correlates very well with the self-induced velocity created by the wall-vortex interaction. Circulation measurements quantify the initial roll up and decay of the kidney vortices and show that the point of maximum circulation moves downstream with increasing momentum flux ratio. The potential for non-intrusive volumetric velocimetry measurements in turbomachinery flow has been clearly demonstrated.
TOPICS: Jets, Film cooling, Vortices, Kidney, Momentum, Flow (Dynamics), Cooling, Turbomachinery, Boundary-value problems, Separation (Technology), Particulate matter
research-article  
Eric Kurstak, Ryan Wilber and Kiran D'Souza
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041204
A considerable amount of research has been conducted to develop reduced order models of bladed disks that can be constructed using single sector calculations when there is mistuning present. A variety of methods have been developed to efficiently handle different types of mistuning ranging from small frequency mistuning, which can be modeled using a variety of methods including component mode mistuning (CMM), to large geometric mistuning, which can be modeled using multiple techniques including pristine rogue interface modal expansion (PRIME). Research has also been conducted on developing reduced order models that can accommodate the variation of specific parameters in the reduced space; these models are referred to as parametric reduced order models (PROMs). This work introduces a PROM for bladed disks that allows for the variation of rotational speed in the reduced space. These PROMs are created by extracting information from sector models at three rotational speeds, and then the appropriate reduced order model is efficiently constructed in the reduced space at any other desired speed. This work integrates these new PROMs for bladed disks with two existing mistuning methods, CMM and PRIME, to illustrate how the method can be readily applied for a variety of mistuning methods. Frequencies and forced response calculations using these new PROMs are compared to the full order finite element calculations to demonstrate the effectiveness of the method.
TOPICS: Disks, Coordinate measuring machines, Finite element analysis

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