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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article  
James Scobie, Fabian Hualca, Carl Sangan and Gary Lock
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038458
Engine designers require accurate predictions of ingestion (or ingress) principally caused by circumferential pressure asymmetry in the mainstream annulus. Cooling air systems provide purge flow designed to limit metal temperatures and protect vulnerable components from the hot gases which would otherwise be entrained into disc cavities through clearances between rotating and static discs. Rim seals are fitted at the periphery of these discs to minimise purge. The mixing between the efflux of purge (or egress) and the mainstream gases near the hub end-wall results in a deterioration of aerodynamic performance. This paper presents experimental results using a turbine test rig with wheel-spaces upstream and downstream of a rotor disc. Ingress and egress was quantified using a CO2 concentration probe, with seeding injected into the upstream and downstream sealing flows. The probe measurements have identified an outer region in the wheel-space and confirmed the expected flow structure. For the first time, asymmetric variations of concentration have been shown to penetrate through the seal clearance and the outer portion of the wheel-space between the discs. For a given flow coefficient in the annulus, the concentration profiles were invariant with rotational Reynolds number. The measurements also reveal that the egress provides a film-cooling benefit on the vane and rotor platforms. Further, these measurements provide unprecedented insight into the flow interaction, and provide quantitative data for CFD validation, which should help reduce the use of purge and improve engine efficiency.
TOPICS: Turbines, Disks, Flow (Dynamics), Wheels, Rotors, Annulus, Gases, Engines, Probes, Reynolds number, Sealing (Process), Space, Clearances (Engineering), Computational fluid dynamics, Metals, Temperature, Cooling, Carbon dioxide, Cavities, Pressure, Film cooling
research-article  
Xijia Lu, Scott Martin, Michael McGroddy, Michael Swanson, Joshua Stanislowski and Jason Laumb
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038459
The Allam Cycle is a high performance oxy-fuel, supercritical CO2 power cycle that offers significant benefits over traditional hydrocarbon fuel-based power generation systems. A major benefit arises in the elimination of costly pre-combustion acid gas removal (AGR) for sulfur- (SOX) and nitrogen-based (NOX) impurities by utilizing a novel, embedded cleanup process that utilizes combustion derived NOX as a gas phase catalyst to effect SOX oxidation, followed by NOX removal. The reactions required for this process, which have been well-demonstrated for the cleanup of exhaust gases, convert SOX and NOX species to sulfuric and nitric and nitrous acid for removal from the supercritical CO2 stream. The process results in simplified and significantly lower cost removal of these species and utilizes conditions inherent to the Allam Cycle that are ideally suited to facilitate this process. 8 Rivers Capital and the Energy & Environmental Research Center (EERC) are testing and optimizing this impurity removal process for supercritical CO2 cycles such as the Allam Cycle. Both reaction kinetic modeling and on-site testing have been completed. Initial results show that both SOX and NOX are substantially removed from CO2-rich exhaust gas containing excess oxygen operating under 20 bar utilizing a simple packed spray column. Sensitivity of the removal rate to the concentration of oxygen and NOX was investigated. Follow-on work will focus on system optimization of removal efficiency and removal control, minimization of metallurgy and corrosion risks from handling concentrated acids, and reduction of overall system CAPX/OPEX.
TOPICS: Combustion, Energy / power systems, Cycles, Testing, Nitrogen oxides, Supercritical carbon dioxide, Oxygen, Exhaust systems, Fuels, Corrosion, Gases, Metallurgy, Modeling, Optimization, Sprays, Nitrogen, oxidation, Sulfur, Rivers, Carbon dioxide, Catalysts, Thermodynamic power cycles
research-article  
Alexander Bucknell, Matthew McGilvray, David R.H. Gillespie, Geoffrey B Jones, Alasdair Reed and Dr. David R Buttsworth
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038460
It has been recognised in recent years that high altitude atmospheric ice crystals pose a threat to aircraft engines. It is believed that solid ice particles can accrete inside the core compressor, although the exact mechanism by which this occurs remains poorly understood. Development of analytical and empirical models of the ice crystal icing phenomenon is necessary for both future engine design and this-generation engine certification. A comprehensive model will require the integration of a number of aerodynamic, thermodynamic and mechanical components. This paper studies one such component, specifically the thermodynamic and mechanical processes experienced by ice particles impinging on a warm surface. Results are presented from an experimental campaign using a heated and instrumented flat plate. The plate was installed in the Altitude Icing Wind Tunnel (AIWT) at the National Research Council of Canada (NRC). The heated plate is designed to measure the heat flux from a surface at temperatures representative of the early core compressor, under varying convective and icing heat loads. Heat transfer enhancement was observed to rise approximately linearly with both total water content and particle diameter over the ranges tested. A Stokes number greater than unity proved to be a useful parameter in determining whether heat transfer enhancement would occur. A particle energy parameter was used to estimate the likelihood of fragmentation. Results showed that when particles were both ballistic and likely to fragment, heat transfer enhancement was independent of both Mach and Reynolds numbers over the ranges tested.
TOPICS: Heat transfer, Crystals, Compressors, Ice, Particulate matter, Engines, Reynolds number, Stress, Heat, Temperature, Engine design, Flat plates, Water, Wind tunnels, Aircraft engines, Heat flux
research-article  
Daniele Massini, Tommaso Fondelli, Antonio Andreini, Bruno Facchini, Lorenzo Tarchi and Federico Leonardi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038471
Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished in two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid-dynamics of the environment which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry measurements for investigating the flow-field surrounding the rotating gear. The experiment has been computationally replicated, performing RANS simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.
TOPICS: Gears, Stress, Torque, Pressure, Fluid dynamics, Flow (Dynamics), Temperature, Particulate matter, Eddies (Fluid dynamics), Viscosity, Simulation, Torquemeters, Design, Engineering simulation, Reynolds-averaged Navier–Stokes equations, Spur gears, Turbomachinery, Fuel consumption, Aircraft engines
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  
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  
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  
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
Review Article  
David A. Shifler
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038037
It has been conjectured that if sulfur in fuel is removed, engine materials will cease to experience attack from hot corrosion, since this sulfur has been viewed as the primary cause of hot corrosion and sulfidation. Historically, hot corrosion has been defined as an accelerated degradation process that generally involves deposition of corrosive species (e.g., sulfates) from the surrounding environment (e.g., combustion gas) onto the surface of hot components, resulting in destruction of the protective oxide scale. Most papers in the literature, since the 1970s, consider sodium sulfate salt as the single specie contributing to hot corrosion. Recent Navy standards for Navy F-76 and similar fuels have dropped the sulfur content down to 15 parts per million (ppm). Most observers believe that the removal of sulfur will end hot corrosion events in the Fleet. However, the deposit chemistry influencing hot corrosion is known to be much more complex consisting of multiple sulfates and silicates. Sulfur species may still enter the combustion chamber via ship's air intake, which may include seawater entrained in the air. In addition to sodium sulfate, seawater contains magnesium, calcium and potassium salts, and atmospheric contaminants that may contribute to hot corrosion. This paper will cover some of the revised understanding of hot corrosion and consider other possible contaminants that could further complicate a full understanding of hot corrosion.
TOPICS: Corrosion, Sulfur, Seawater, Sodium, Navy, Fuels, Engines, Combustion gases, Combustion chambers, Potassium, Chemistry, Magnesium (Metal)
research-article  
Klaus Brun, Rainer Kurz and Sarah Simons
J. Eng. Gas Turbines Power   doi: 10.1115/1.4034314
Pressure pulsations into a centrifugal compressor can move its operating point into surge. This is concerning in pipeline stations where centrifugal compressors operate in series/parallel with reciprocating compressors. Sparks (1983), Kurz et al., (2006), and Brun et al., (2014) provided predictions on the impact of periodic pressure pulsation on the behavior of a centrifugal compressor. This interaction is known as the “Compressor Dynamic Response” (CDR) theory. Although the CDR describes the impact of the nearby piping system on the compressor surge and pulsation amplification, it has limited usefulness as a quantitative analysis tool, due to the lack of prediction tools and test data for comparison. Testing of compressor mixed operation was performed in an air loop to quantify the impact of periodic pressure pulsation from a reciprocating compressor on the surge margin of a centrifugal compressor. This data was utilized to validate predictions from Sparks' CDR theory and Brun's numerical approach. A 50 hp single-stage, double-acting reciprocating compressor provided inlet pulsations into a two-stage 700 hp centrifugal compressor. Tests were performed over a range of pulsation excitation amplitudes, frequencies, and pipe geometry variations to determine the impact of piping impedance and resonance responses. Results provided clear evidence that pulsations can reduce the surge margin of centrifugal compressors and that geometry of the piping system immediately upstream and downstream of a centrifugal compressor will have an impact on the surge margin reduction. Surge margin reductions of <30% were observed for high centrifugal compressor inlet suction pulsation.
TOPICS: Compressors, Surges, Pressure, Pipes, Geometry, Piping systems, Testing, Dynamic response, Suction, Pipelines, Excitation, Resonance
research-article  
shilpi agarwal, Puneet Rana and B. S. Bhadauria
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028491
In this paper, we study the effect of local thermal non-equilibrium on the linear thermal instability in a horizontal layer of a Newtonian nanofluid. The nanofluid layer incorporates the effect of Brownian motion along with thermophoresis. A two-temperature model has been used for the effect of local thermal non-equilibrium among the particle and fluid phases. The linear stability is based on normal mode technique and for nonlinear analysis, a minimal representation of the truncated Fourier series analysis involving only two terms has been used. We observe that for linear instability, the value of Rayleigh number can be increased by a substantial amount on considering a bottom heavy suspension of nano particles. The effect of various parameters on Rayleigh number has been presented graphically. A weak nonlinear theory based on the truncated representation of Fourier series method has been used to find the concentration and the thermal Nusselt numbers. The behavior of the concentration and thermal Nusselt numbers is also investigated by solving the finite amplitude equations using a numerical method.
TOPICS: Equilibrium (Physics), Nanofluids, Rayleigh-Benard convection, Fourier series, Rayleigh number, Nanoparticles, Numerical analysis, Stability, Temperature, Fluids, Particulate matter, Brownian motion
research-article  
Corey E. Clifford and Mark Kimber
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028492
Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for free cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this study, a numerical model of a heated horizontal cylinder confined between two, vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the pseudo-unconfined cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.
TOPICS: Heat, Natural convection, Cylinders, Storage, Heat transfer, Rayleigh number, Heat flux, Fuels, Safety, Computer simulation, Cooling, Temperature, Flow (Dynamics), Buoyancy, Spent nuclear fuels, Convection, Boundary-value problems

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