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research-article  
Michael A Rohmer, Luis San Andres and Scott M Wilkinson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038472
This paper details a water lubricated test rig for measurement of the performance of hydrostatic thrust bearings (HTBs). The rig contains two water lubricated HTBs (105 mm outer diameter), one is the test bearing and the other a slave bearing. Both bearings face the outer side of thrust collars of a rotor. The paper shows measurements of HTB axial clearance, flow rate, and recess pressure for operation with increasing static load (max. 1.4 bar) and supply pressure (max. 4.14 bar) at a rotor speed of 3 krpm (12 m/s OD speed). Severe angular misalignment, static and dynamic, of the bearing surface against its collar persisted and affected all measurements. The HTB axial clearance increases as the supply pressure increases and decreases quickly as the applied load increases. The reduction in clearance increases the flow resistance across the film lands thus reducing the through flow rate with an increase in recess pressure. In addition, an estimated bearing axial stiffness increases as the operating clearance decreases and as the supply pressure increases. Predictions from a bulk flow model qualitatively agree with the measurements. Alas they are not accurate enough. The differences likely stem from the inordinate tilts (static and dynamic) as well as the flow condition. The test HTB operates in a flow regime that spans from laminar to incipient turbulent. Quantification of misalignment at all operating conditions is presently a routine practice during operation of the test rig.
TOPICS: Hydrostatics, Stress, Thrust bearings, Water, Flow (Dynamics), Pressure, Bearings, Clearances (Engineering), Rotors, Stiffness, Turbulence, Arches, Thrust
research-article  
Maxime Huet
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038473
The noise generated by the passage of acoustic and entropy perturbations through subsonic and choked nozzle flows is investigated numerically using an energetic approach. Low-order models are used to reproduce the experimental results of the Hot Acoustic Test rig (HAT) of DLR and energy budgets are performed to characterize the reflection, transmission and dissipation of the fluctuations. Because acoustic and entropy perturbations are present in the flow in the general case, classical acoustic energy budgets cannot be used and the disturbances energy budgets proposed by Myers (J. Fluid Mech. 226 (1991) 383-400) are used instead. Numerical results are in very good agreement with the experiments in terms of acoustic transmission and reflection coefficients. The normal shock present in the diffuser for choked regimes is shown to attenuate the scattered acoustic fluctuations, either by pure dissipation effect or by converting a part of the acoustic energy into entropy fluctuations.
TOPICS: Flow (Dynamics), Nozzles, Acoustics, Fluctuations (Physics), Energy budget (Physics), Entropy, Energy dissipation, Reflectance, Diffusers, Shock (Mechanics), Noise (Sound), Reflection, Fluids
research-article  
Rachel A Berg, Choon S. Tan, Zhongman Ding, Gregory M. Laskowski, Pepe Palafox and Rinaldo Miorini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038474
Fast response pressure data acquired in a high-speed 1.5-stage turbine Hot Gas Ingestion Rig shows the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio, purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.
TOPICS: Gas turbines, Cavities, Pressure, Flow (Dynamics), Turbines, Oscillations, Resonance, High pressure (Physics), Design
research-article  
Nicolai Stadlmair, Tobias Hummel and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038475
In this paper, we present a method to determine the quantitative stability level of a lean-premixed combustor from dynamic pressure data. Specifically, we make use of the autocorrelation function of the dynamic pressure signal acquired in a combustor where a turbulent flame acts as a thermoacoustic driver. The unfiltered pressure signal including several modes is analyzed by an algorithm based on Bayesian statistics. For this purpose, a Gibbs sampler is used to calculate parameters like damping rates and eigenfrequencies by a Markov-Chain Monte-Carlo (MCMC) method. The method provides a robust solution algorithm for fitting problems without requiring initial values. First, a simulation of a stochastically forced van-der-Pol oscillator with pre-set input values is carried out to demonstrate accuracy and robustness of the method. In this context it is shown that, despite of a large amount of uncorrelated background noise, the identified damping rates are in a good agreement with the simulated parameters. Secondly, this technique is applied to measured pressure data. By doing so, the combustor is initially operated under stable conditions before the thermal power is gradually increased by adjusting the fuel mass flow rate until a limit-cycle oscillation is established. It is found that the obtained damping rates are qualitatively in line with the amplitude levels observed during operation of the combustor.
TOPICS: Combustion, Damping, Noise (Sound), Statistics as topic, Pressure, Combustion chambers, Algorithms, Signals, Limit cycles, Chain, Fittings, Flames, Robustness, Oscillations, Stability, Flow (Dynamics), Fuels, Turbulence, Thermal energy, Simulation
research-article  
Philippe Versailles, Graeme M.G. Watson, Antoine Durocher, Gilles Bourque and Jeffrey M. Bergthorson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038416
Increasingly stringent regulations on NOx emissions are enforced by governments owing to their contribution in the formation of pollutants affecting human health and the environment. The design of low-emission combustors requires thermochemical mechanisms of sufficiently high accuracy. Recently, a comprehensive set of experimental data, collected through laser-based diagnostics in atmospheric, stagnation, premixed flames, was published for all isomers of C1-C4 alkane and alcohol fuels [1-3]. The formation of NO through the flame front via the prompt route was shown to be strongly coupled to the maximum concentration of the methylidyne radical, [CH]peak, and the flow residence time within the CH layer. A proper description of CH formation is then a prerequisite for accurate predictions of NO concentrations in hydrocarbon-air flames. However, a comparison against the experimental data of [3] revealed that modern mechanisms are unable to capture the stoichiometric dependence of [CH]peak and, for a given equivalence ratio, the predictions of different mechanisms span over more than one order of magnitude. This paper presents an optimization of the specific rate of nine elementary reactions included in the San Diego mechanism. A quasi-Newton algorithm is used to minimize an objective function defined as the sum of squares of the relative difference between the numerical and experimental data of [3]. A mechanism properly describing CH formation for lean to rich, C1-C3 alkane-air flames is obtained, which enables accurate predictions of prompt-NO formation over a wide range of equivalence ratios and fuels.
TOPICS: Fuels, Optimization, Flames, Emissions, Governments, Regulations, Pollution, Nitrogen oxides, Ethanol, Flow (Dynamics), Lasers, Combustion chambers, Algorithms, Design
research-article  
Daniel Pugh, Philip Bowen, Andrew Crayford, Richard Marsh, Jon P Runyon, Steven Morris and Anthony Giles
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038417
Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O on heavily carbonaceous syngas mixtures. Direct formation of CO2 from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species, changing the dominant path for oxidation. The observed catalytic effect is nonmonotonic, with the reduction in flame temperature eventually prevailing, and reaction rate quenched. The potential benefits of changes in water loading are explored in terms of lean blowoff, and emissions reduction in a premixed turbulent swirling flame at conditions of elevated temperature (423K) and pressure (0.1-0.3MPa). Kinetic models are used initially to characterize the influence that H2O has on the burning characteristics of the fuel blend employed, modelling flame speed and extinction strain rate. These modeled predictions are used as a foundation to investigate the experimental flame. OH* chemiluminescence and OH PLIF are employed as optical diagnostic techniques to analyze changes in heat release structure resulting from H2O addition. A comparison is made with a CH4/air flame and changes in lean blow off stability limits are quantified. The compound benefit of CO/NOx reduction are quantified also, with production first decreasing due to the thermal effect of H2O addition from a lowering of flame temperature, coupled with the potential for further reduction from the change in lean stability limit. Power law correlations have also been derived for the change in pressure.
TOPICS: Water vapor, Syngas, Flames, Swirling flow, Nitrogen oxides, Water, Temperature, Pressure, Stability, Combustion, Fuels, Turbulence, Chemiluminescence, Temperature effects, Chain, Modeling, Heat, Carbon dioxide, Hydrogen, Methane, oxidation, Emissions
research-article  
James A. Scobie, Fabian P. Hualca, Marios Patinios, Carl M. Sangan, J Michael Owen and Gary D. Lock
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038361
In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimise the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly-stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages. This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space.
TOPICS: Gas turbines, Flow (Dynamics), Sealing (Process), Wheels, Disks, Rotors, Fluids, Gases, Heat, Mass transfer, Service life (Equipment), Space, Boundary layers, Turbines, Fluid dynamics, Annulus, Blades, Carbon dioxide, Enthalpy, Stators, Test facilities
research-article  
Christina Salpingidou, Dimitrios Misirlis, Zinon Vlahostergios, Stefan Donnerhack, Michael Flouros, Apostolos Goulas and Kyros Yakinthos
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038362
This work presents an exergy analysis and performance assessment of three recuperative thermodynamic cycles for gas turbine applications. The first configuration is the conventional recuperative cycle in which a heat exchanger is placed after the power turbine. In the second configuration, referred as alternative recuperative cycle, a heat exchanger is placed between the high pressure and the power turbine, while in the third configuration, referred as staged heat recovery cycle, two heat exchangers are employed, the primary one between the high and power turbines and the secondary at the exhaust, downstream the power turbine. The first part of this work is focused on a detailed exergetic analysis on conceptual gas turbine cycles for a wide range of heat exchanger performance parameters. The second part focuses on the implementation of recuperative cycles in aero engines, focused on the MTU-developed Intercooled Recuperative Aero (IRA) engine concept, which is based on a conventional recuperation approach. Exergy analysis is applied on specifically developed IRA engine derivatives using both alternative and staged heat recovery recuperation concepts to quantify energy exploitation and exergy destruction per cycle and component, showing the amount of exergy that is left unexploited, which should be targeted in future optimization actions.
TOPICS: Thermodynamic cycles, Gas turbines, Exergy analysis, Cycles, Turbines, Heat exchangers, Exergy, Engines, Heat recovery, High pressure (Physics), Optimization, Exhaust systems, Aircraft engines
research-article  
Bradley R. Nichols, Roger L. Fittro and Christopher P. Goyne
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038363
Reduced oil supply flow rates in fluid film bearings can cause cavitation, or lack of a fully developed hydrodynamic film layer, at the leading edge of the bearing pads. Reduced oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses; however, little experimental data of its effects on system stability and performance can be found in the literature. This study looks at overall system performance through observed subsynchronous vibration patterns of a test rig operating under reduced oil supply flow rates. The test rig was designed to be dynamically similar to a high-speed industrial compressor. It consists of a flexible rotor supported by two tilting pad bearings in vintage, flooded bearing housings. Tests were conducted over a number of supercritical operating speeds and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings. A low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain. During supercritical operation, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. Under lightly loaded conditions, the amplitude of the subsynchronous peak increased dramatically with decreasing oil supply flow rate and increasing operating speed. Under an increased load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results.
TOPICS: Flow (Dynamics), Vibration, Bearings, Stress, Cavitation, Flutter (Aerodynamics), Compressors, Modeling, Rotors, Fluid films, Operating temperature, Stability
research-article  
Oskar Thulin, Olivier Petit, Carlos Xisto, Xin Zhao and Tomas Gronstedt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038364
An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (intercooler) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g. a secondary cycle, moving with the aircraft. Afterwards the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e. nacelle surfaces, to reject the core heat and contribute to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a heat exchanger in the bypass duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered heat exchangers and the secondary cycle major components is made. A striking strength of the present analysis is the assessment of the component irreversibility rate and its contribution to the overall aero-engine losses.
TOPICS: Heat, Engines, Exergy, Heat exchangers, Aircraft, Cycles, Drag reduction, Ducts, Turbofans, Aircraft engines, Organic Rankine cycle
research-article  
Ward De Paepe, Marina Montero Carrero, Svend Bram, Alessandro Parente and Francesco Contino
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038365
Micro Gas Turbines (mGTs) offer several advantages for small-scale Combined Heat and Power (CHP) production compared to their main competitors, the Internal Combustion Engines (ICEs), such as low vibration level, cleaner exhaust and less maintenance. The major drawback is their lower electrical efficiency, which makes them economically less attractive and explains their low market penetration. Shifting towards more innovative cycles may help enhancing the performance and the flexibility of mGTs. One interesting solution is the introduction of water ¬either as auto-raised steam or hot liquid¬, in the mGT cycle. The so-called humidification of the mGT cycle has the potential of increasing the electrical performance and flexibility of the mGT, resulting in a higher profitability. However, despite the proven advantages of mGT humidification, only few of these engines have been experimentally tested and up to now, no cycle is commercially available. With this paper, we give a comprehensive review of the literature on research and development of humidified mGTs: we examine the effect of humidification both on the improvement of the cycle efficiency and flexibility and on the performance of the specific mGT components. Additionally, we will present the different possible layouts, both focusing on the numerical and experimental work. Finally, we pinpoint the technological challenges that need to be overcome for humidified mGTs to be viable. In conclusion, humidification of mGT cycles offers great potential for enhancing the cycle's electrical efficiency and flexibility, but further research is necessary to make the technology commercially available.
TOPICS: Micro gas turbines, Cycles, Internal combustion engines, Electrical efficiency, Combined heat and power, Vibration, Maintenance, Engines, Industrial research, Exhaust systems, Profitability, Steam, Water
research-article  
Erik E. Swanson and P. Shawn O'Meara
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038366
To meet the challenging demands for high performance, affordable compliant foil bearings, a novel compliant support element has been developed. This recently patented, novel support element uses a multidimensional array of multiple, formed, cantilever “wing foil” tabs. The wing foil bearing has all the features required to achieve state of the art performance (Gen III for radial bearings). This paper describes two radial foil beings using the wing foil and the unique design features. Test data for a 31.75 mm diameter bearing operating in air and in steam up to 42 krpm are presented to demonstrate the performance of this bearing. It is shown to have low subsynchronous vibration and reasonable damping through rigid shaft critical speeds.
TOPICS: Design, Wings, Foil bearings, Bearings, Damping, Vibration, Cantilevers, Steam
research-article  
Giuseppe Battiato, Christian M. Firrone, Teresa Berruti and Bogdan I. Epureanu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038348
Most aircraft turbojet engines consist of multiple stages coupled by means of bolted flange joints which potentially represent source of nonlinearities due to friction phenomena. Methods aimed at predicting the forced response of multi-stage bladed disks have to take into account such nonlinear behavior and its effect in damping blades vibration. In this paper a novel reduced order model is proposed for studying nonlinear vibration due to contacts in multi-stage bladed disks. The methodology exploits the shape of the single-stage normal modes at the inter-stage boundary being mathematically described by spatial Fourier coefficients. Most of the Fourier coefficients represent the dominant kinematics in terms of the well-known nodal diameters (standard harmonics), while the others, which are detectable at the inter-stage boundary, correspond to new spatial small wavelength phenomena named as extra harmonics. The number of Fourier coefficients describing the displacement field at the inter-stage boundary only depends on the specific engine order excitation acting on the multi-stage system. This reduced set of coefficients allows the reconstruction of the physical relative displacement field at the interface between stages and, under the hypothesis of the Single Harmonic Balance Method, the evaluation of the contact forces by employing the classic Jenkins contact element. The methodology is here applied to a simple multi-stage bladed disk and its performance is tested using as a benchmark the Craig-Bampton reduced order models of each single-stage. GT2017-64814
TOPICS: Friction, Flanges, Modeling, Disks, Displacement, Engines, Kinematics, Wavelength, Nonlinear vibration, Vibration, Damping, Shapes, Turbojets, Excitation, Aircraft, Blades, Bolted flanges
research-article  
Zheng Min, Sarwesh Narayan Parbat, Li Yang, Bruce Kang and Minking K. Chyu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038351
Increasingly high thermal load causes severe oxidation and corrosion for base alloy in turbine airfoils. To survive in this extreme high temperature and harsh oxidation environment, development of structural bond coating layers consequently becomes one of the key technologies for extremely efficient cooling. Present study proposed a method to fabricate structural coating layers on top of turbine blades with the aid of additive manufacturing and oxide dispersion strengthened (ODS) nickel based alloy. ODS powder comprised of evenly distributed host composite particles (Ni, Al, Cr) with oxide coating layer (Y2O3) was subjected to a direct metal laser sintering process to fabricate a desirable structural coating layer above Nickel based superalloy substrates. Systematic experimental tests were carried out focusing on the effect of laser power on interface adhesion, microstructure and surface finish of the ODS coating layer. Based on characterization results from indentation tests and microscopy observations, an optimal coating quality was obtained under 250W laser power. The selected samples were then characterized under isothermal conditions of 1200 ? for 2000 hours. SEM observations and EDAX analysis were conducted in different stages of the oxidation process. Results indicated a formation of protective Al2O3 scale on top of the ODS coating layer at early stage, which showed long term stability throughout the oxidation test. In addition, the observed adhesion between ODS coating layer and substrate was tight and stable throughout the entire oxidation test. Present study has proved that additive manufacturing has the capability to fabricate structural and protective coating layers for turbine airfoils.
TOPICS: Nickel, Coating processes, Coatings, Manufacturing, High temperature, oxidation, Lasers, Adhesion, Alloys, Turbines, Additive manufacturing, Airfoils, Protective coatings, Microscopy, Particulate matter, Superalloys, Sintering, Oxide coatings, Stress, Finishes, Turbine blades, Corrosion, Metals, Stability, Cooling, Composite materials
research-article  
Dominik Ebi, Alexey Denisov, Giacomo Bonciolini, Edouard Boujo and Nicolas Noiray
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038326
We report experimental evidence of thermoacoustic bi-stability in a lab-scale turbulent combustor over a well-defined range of fuel-air equivalence ratios. Pressure oscillations are characterized by an intermittent behavior with "bursts", i.e. sudden jumps between low and high amplitudes occurring at random time instants. The corresponding probability density functions of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bi-stable region. The gain and phase between acoustic pressure and heat release rate fluctuations are evaluated at the modal frequency from simultaneously recorded flame chemiluminescence and acoustic pressure. The representation of the corresponding statistics is new and particularly informative. It shows that the system is characterized, in average, by a nearly constant gain and by a drift of the phase as function of the oscillation amplitude. This finding may suggest that the bi-stability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the non-constant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.
TOPICS: Dynamics (Mechanics), Bifurcation, Flames, Sound pressure, Fluctuations (Physics), Oscillations, Stability, Heat, Fuels, Turbulence, Acoustics, Chemiluminescence, Density, Pressure, Combustion chambers, Damping, Probability, Signals, Statistics as topic
research-article  
Iacopo Rossi, Valentina Zaccaria and Alberto Traverso
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038321
The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/ gas turbine (SOFC/GT) hybrids are an example where advanced control techniques can be effectively applied. For example, to manage load distribution among several identical generation units characterized by different temperature distributions due to different degradation paths of the fuel cell stacks. When implementing a MPC, a critical aspect is the trade-off between model accuracy and simplicity, the latter related to a fast computational time. In this work, a hybrid physical and numerical approach was used to reduce the number of states necessary to describe such complex target system. The reduced number of states in the model and the simple framework allow real-time performance and potential extension to a wide range of power plants for industrial application, at the expense of accuracy losses, discussed in the paper.
TOPICS: Solid oxide fuel cells, Predictive control, Temperature distribution, Tradeoffs, Power systems (Machinery), Stress, Fuel cells, Gas turbines, Power stations
research-article  
Sheng Wei, Brandon Sforzo and Jerry M. Seitzman
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038322
This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates non-uniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel-air flow, with a matched velocity and an equivalence ratio near 0.75. Differences in early ignition kernel development are explored using three, synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel-air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time.
TOPICS: Jet fuels, Ignition, Imaging, Fuels, Emissions, Flow (Dynamics), Heat, Cooling, Fluids, Lasers, Combustion chambers, Gas turbines, Cavities, Flames, Chemical reactions, Air flow, Chemiluminescence, Fluorescence
research-article  
Michael Woehr, Markus Müller and Johannes Leweux
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038323
This paper presents the development approach, design and evaluation of three turbocharger compressors with variable geometry for heavy duty engines. The main goal is the improvement of fuel economy without sacrifices regarding any other performance criteria. In a first step, a vaned diffuser parameter study shows that efficiency improvements in the relevant operating areas are possible at the cost of reduced map width. Concluding from the results three variable geometries with varying complexity based on vaned diffusers are designed. Results from the hot gas test stand and engine test rig show that all systems are capable of increasing compressor efficiency and thus improving fuel economy in the main driving range of heavy duty engines. The most significant differences can be seen regarding the engine brake performance. Only one system meets all engine demands while improving fuel economy.
TOPICS: Engines, Compressors, Turbochargers, Geometry, Trucks, Fuel efficiency, Corporate average fuel economy, Diffusers, Design, Brakes
research-article  
Mark Frederick, Kiran Manoharan, Joshua Dudash, Brian Brubaker, Santosh Hemchandra and Jacqueline O'Connor
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038324
Combustion instability is a significant issue in the operation of gas turbine combustors. Shear layer roll-up, in particular, has been shown to drive longitudinal combustion instability in both laboratory and industrial combustors. One method for suppressing combustion instability would be to suppress the receptivity of the shear layer to acoustic oscillations, severing the coupling mechanism between the acoustics and the flame. Previous work suggested that the existence of a precessing vortex core (PVC) may suppress the receptivity of the shear layer, and the goal of this study is to first, confirm that this suppression is occurring, and second, understand the mechanism by which the PVC suppresses the shear layer receptivity. We couple experiment with linear stability analysis to determine whether a PVC can suppress shear layer receptivity to longitudinal acoustic modes in a non-reacting swirling flow at a range of swirl numbers. The shear layer response to the longitudinal acoustic forcing manifests as an m=0 mode. The PVC has been shown both in experiment and linear stability analysis to have m=1 and m=-1 modal content. By comparing the relative magnitude of the m=0 and m=-1,1 modes, we quantify the impact that the PVC has on the shear layer response. The mechanism for shear layer response is determined using forced response analysis, where the shear layer disturbance growth rates mirror the experimental results. Differences in shear layer thickness and azimuthal velocity profiles drive the suppression of the shear layer receptivity to acoustic forcing.
TOPICS: Dynamics (Mechanics), Shear (Mechanics), Swirling flow, Acoustics, Combustion, Stability, Combustion chambers, Gas turbines, Vortices, Flames, Mirrors, Oscillations
research-article  
Tomomi Nakajima, Kiyoshi Segawa, Hiromichi Kitahara, Akimitsu Seo, Yutaka Yamashita and Takeshi Kudo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038282
All turbine blades have mistuned structures caused by manufacturing variations within the manufacturing tolerance, such as the geometrical deviations and variance of material properties. The mistuning effect has a known tendency to increase the dynamic stress, but it is also known to be difficult to predict the maximum vibration response before the operation. This paper studies the blade vibration of grouped blades in a low-pressure steam turbine. The study objectives are to characterize the vibration behavior of the grouped blade structure and to evaluate the maximum response of all blades in a stage. An experimental investigation is carried out in a vacuum chamber, and blades are excited by an air jet during start-up and shut-down. The circumferential blade amplitude distribution is measured by non-contact sensors and strain gauges. The circumferential blade amplitude distribution is found to differ depending on vibration modes and nodal diameters, but the relative tendency is almost the same for all types of operation at each mode and all nodal diameters. Therefore, the median of all experimental results obtained with the non-contact sensors is used in a comparison with calculation results and results of two theoretical curves obtained using equations from the literature. In comparing the measurement results and the calculation results, the circumferential blade amplitude distribution is not the same with all modes and nodal diameters. However, the maximum amplitude magnification is about 1.5-1.8, and all measurement results are lower than the results for the two theoretical equations.
TOPICS: Vibration, Blades, Steam turbines, Sensors, Manufacturing, Stress, Turbine blades, Air jets, Materials properties, Magnification, Strain gages, Vacuum, Pressure

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