Journal of Engineering for Gas Turbines and Power Newest Issue
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en-usWed, 17 Jan 2018 00:00:00 GMTWed, 17 Jan 2018 11:43:37 GMTSilverchaireditor@gasturbinespower.asmedigitalcollection.asme.orgwebmaster@gasturbinespower.asmedigitalcollection.asme.orgMethods for the Calculation of Thermoacoustic Stability Boundaries and Monte Carlo-Free Uncertainty Quantification
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2657493
Wed, 17 Jan 2018 00:00:00 GMTMensah GA, Magri L, Moeck JP. <span class="paragraphSection">Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain-based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible flow computations. They result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial for safe gas turbine operation. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. One general challenge regarding uncertainty quantification is the sheer number of uncertain parameter combinations to be quantified. For instance, uncertain parameters in an annular combustor might be the equivalence ratio, convection times, geometrical parameters, boundary impedances, flame response model parameters, etc. A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the problem is using adjoint perturbation theory. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo (MC) simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz, it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental data are available.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2657493Catalytic Influence of Water Vapor on Lean Blow-Off and NO x Reduction for Pressurized Swirling Syngas Flames
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2663693
Wed, 17 Jan 2018 00:00:00 GMTPugh D, Bowen P, Crayford A, et al. <span class="paragraphSection">It has become increasingly cost-effective for the steel industry to invest in the capture of heavily carbonaceous basic oxygen furnace or converter gas, and use it to support the intensive energy demands of the integrated facility, or for surplus energy conversion in power plants. As industry strives for greater efficiency via ever more complex technologies, increased attention is being paid to investigate the complex behavior of by-product syngases. Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H<sub>2</sub>O on heavily carbonaceous syngas mixtures. Direct formation of CO<sub>2</sub> from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species (such as OH), changing the dominant path for oxidation. The observed catalytic effect is nonmonotonic, with the reduction in flame temperature eventually prevailing, and overall reaction rate quenched. The potential benefits of changes in water loading are explored in terms of delayed lean blow-off (LBO), and primary emission reduction in a premixed turbulent swirling flame, scaled for practical relevance at conditions of elevated temperature (423 K) and pressure (0.1–0.3 MPa). Chemical kinetic models are used initially to characterize the influence that H<sub>2</sub>O has on the burning characteristics of the fuel blend employed, modeling laminar flame speed and extinction strain rate across an experimental range with H<sub>2</sub>O vapor fraction increased to eventually diminish the catalytic effect. These modeled predictions are used as a foundation to investigate the experimental flame. OH* chemiluminescence and OH planar laser-induced fluorescence (PLIF) are employed as optical diagnostic techniques to analyze changes in heat release structure resulting from the experimental variation in water loading. A comparison is made with a CH<sub>4</sub>/air flame and changes in LBO stability limits are quantified, measuring the incremental increase in air flow and again compared against chemical models. The compound benefit of CO and NO<sub>x</sub> reduction is quantified also, with production first decreasing due to the thermal effect of H<sub>2</sub>O addition from a reduction in flame temperature, coupled with the potential for further reduction from the change in lean stability limit. Power law correlations have been derived for change in pressure, and equivalent water loading. Hence, the catalytic effect of H<sub>2</sub>O on reaction pathways and reaction rate predicted and observed for laminar flames are appraised within the challenging environment of turbulent, swirl-stabilized flames at elevated temperature and pressure, characteristic of practical systems.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2663693Impact of Precessing Vortex Core Dynamics on Shear Layer Response in a Swirling Jet
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661630
Wed, 17 Jan 2018 00:00:00 GMTFrederick M, Manoharan K, Dudash J, et al. <span class="paragraphSection">Combustion instability, the coupling between flame heat release rate oscillations and combustor acoustics, is a significant issue in the operation of gas turbine combustors. This coupling is often driven by oscillations in the flow field. Shear layer roll-up, in particular, has been shown to drive longitudinal combustion instability in a number of systems, including 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. In this paper, we couple experiment with linear stability analysis to determine whether a PVC can suppress shear layer receptivity to longitudinal acoustic modes in a nonreacting swirling flow at a range of swirl numbers. The shear layer response to the longitudinal acoustic forcing manifests as an m = 0 mode since the acoustic field is axisymmetric. 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 companion 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.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661630Flame Dynamics Intermittency in the Bistable Region Near a Subcritical Hopf Bifurcation
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661748
Wed, 17 Jan 2018 00:00:00 GMTEbi DD, Denisov AA, Bonciolini GG, et al. <span class="paragraphSection">We report experimental evidence of thermoacoustic bistability 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 (PDFs) of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bistable 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 bistability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the nonconstant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661748Toward Investigation of External Oil Flow From a Journal Bearing in an Epicyclic Gearbox
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661035
Wed, 17 Jan 2018 00:00:00 GMTBerthold M, Morvan H, Young C, et al. <span class="paragraphSection">High loads and bearing life requirements make journal bearings the preferred choice for use in high-power, planetary gearboxes in jet engines. With the planet gears rotating about their own axis and orbiting around the sun gear, centrifugal forces generated by both motions interact with each other and create complex kinematic conditions. This paper presents a literature and state-of-the-art knowledge review to identify existing work performed on cases similar to external journal bearing oil flow. In order to numerically investigate external journal bearing oil flow, an approach to decompose an actual journal bearing into simplified models is proposed. Preliminary modeling considerations are discussed. The findings and conclusions are used to create a three-dimensional (3D), two-component computational fluid dynamics (CFD) sector model with rotationally periodic boundaries of the most simplistic approximation of an actual journal bearing: a nonorbiting representation, rotating about its own axis, with a circumferentially constant, i.e., concentric, lubricating gap. In order to track the phase interface between the oil and the air, the volume of fluid (VoF) method is used. External journal bearing oil flow is simulated with a number of different mesh densities. Two different operating temperatures, representing low and high viscosity oil, are used to assess the effect on the external flow field behavior. In order to achieve the future objective of creating a design tool for routine use, key areas are identified in which further progress is required.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2661035Experimental and Analytical Assessment of Cavity Modes in a Gas Turbine Wheelspace
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664166
Wed, 17 Jan 2018 00:00:00 GMTBerg RA, Tan CS, Ding Z, et al. <span class="paragraphSection">Fast response pressure data acquired in a high-speed 1.5-stage turbine hot gas ingestion rig (HGIR) show 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 (AR), 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.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664166Surface Roughness Impact on Low-Pressure Turbine Performance Due to Operational Deterioration
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2659630
Wed, 17 Jan 2018 00:00:00 GMTKellersmann A, Weiler S, Bode C, et al. <span class="paragraphSection">The overall efficiency and operational behavior of aircraft engines are influenced by the surface finish of the airfoils. During operation, the surface roughness significantly increases due to erosion and deposition processes. The aim of this study is to analyze the influence of roughness on the aerodynamics of the low-pressure turbine (LPT) of a midsized high bypass turbofan. In order to gain a better insight into the operational roughness structures, a sample of new, used, cleaned, and reworked turbine blades and vanes are measured using the confocal laser scanning microscopy technique. The measurement results show local inhomogeneities. The roughness distributions measured are then converted into their equivalent sand grain roughness ks,eq to permit an evaluation of the impact on aerodynamic losses. The numerical study is performed using the computational fluid dynamics (CFD)-solver turbomachinery research aerodynamics computational environment (TRACE) which was validated before with the existing data from rig experiments. It is observed that the influence of the surface roughness on the turbine efficiency is significant at take-off but negligible at cruise. A detailed analysis on the aerodynamics at take-off shows that very rough airfoils lead to higher profile and secondary loss. Due to the higher disturbances present in flows circulating over rough walls, the transition occurs earlier, and the momentum thickness increases in the turbulent boundary layer. The service-induced roughness structures cause an efficiency drop in the LPT of ηT=−0.16% compared to new parts. A gas path analysis showed that this results in an increased fuel flow of Δm˙f=+0.06% and an exhaust gas temperature (EGT) rise of ΔEGT=+1.2K for fixed engine pressure ratio which is equivalent to roughly 4% of the typical EGT margin of a fully refurbished engine. This result stresses the importance of roughness-induced loss in LPTs.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2659630Lateral Equilibrium Position Analysis Program With Applications to Electric Submersible Pumps
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664234
Wed, 17 Jan 2018 00:00:00 GMTNorrbin CS, Childs DW. <span class="paragraphSection">The long length of subsea electric submersible pumps (ESPs) requires a large amount of annular seals. Loading caused by gravity and housing curvature changes the static equilibrium position (SEP) of the rotor in these seals. This analysis predicts the SEP due to gravity and/or well curvature loading. The analysis also displays the rotordynamics around the SEP. A static and rotordynamic analysis is presented for a previously studied ESP model. This study differs by first finding the SEP and then performing a rotordynamic analysis about the SEP. Predictions are shown in a horizontal and a vertical orientation. In these two configurations, viscosities and clearances are varied through four cases: 1X 1cP, 3X 1cP, 1X 30cP, and 3X 30cP. In a horizontal, straight-housing position, the model includes gravity and buoyancy on the shaft. At 1cP-1X and 1cP-3X, the horizontal statics, show a moderate eccentricity ratio for the shaft with respect to the housing. With 30cP-1X, the predicted static eccentricity ratio is low at 0.08. With 30cP-3X, the predicted eccentricity ratio increases to 0.33. Predictions for a vertical case of the same model are also presented. The curvature of the housing is varied in the Y–Z plane until rub or close-to-wall rub is expected. The curvature needed for a rub with a 1X 1cP fluid is 7.5 deg of curvature. Curvature has little impact on stability. With both 1X 30cP and 3X 30cP, the maximum curvature for a static rub is over 25 deg of curvature. Both 1X 30cP and 3X 30cP remain unstable with increasing curvature.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664234A Detailed Study of the Effects of Biodiesel Addition and Exhaust Gas Recirculation on Diesel Engine PCCI Combustion, Performance and Emission Characteristics by KIVA–CHEMKIN Coupling
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664157
Wed, 17 Jan 2018 00:00:00 GMTZehni A, Saray R, Neshat E. <span class="paragraphSection">In this study, a numerical study is performed by KIVA–CHEMKIN code to investigate the effects of biodiesel addition and exhaust gas recirculation (EGR) on diesel engine premixed charge compression ignition (PCCI) combustion, performance, and emission characteristics. The studies are performed for neat diesel fuel and mixture of 10–40% biodiesel addition at 67%, 50%, and 40% EGR. For this purpose, a multichemistry surrogate mechanism using methyl decanoate (MD) and methyl-9-decenoate (MD9D) is used. The main innovation of this work is analyzing the chemical, thermodynamic, and dilution effects of biodiesel addition as well as different EGR ratios on PCCI combustion behavior. The results show that the main effect of EGR on PCCI combustion of biodiesel blend is related to the high temperature heat release (HTHR), and its effect on low temperature heat release (LTHR) is low. With increasing biodiesel addition, the role of the chemical effect is increased compared to the thermodynamic and dilution effects. Rate of production analysis (ROPA) indicate that for the different biodiesel ratios, the effect of reaction nC<sub>7</sub>H<sub>16</sub> + HO<sub>2</sub> = C<sub>7</sub>H<sub>15-2</sub> + H<sub>2</sub>O<sub>2</sub> is more effective on the start of combustion (SOC) compared to the other reactions. For a defined biodiesel addition, with decreasing EGR, total (unburned) hydrocarbon (THC) and CO are decreased, while NO<sub>x</sub> and indicated specific fuel consumption (ISFC) are increased.</span>http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2664157