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Satoshi Hada - One of the best experts on this subject based on the ideXlab platform.
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Impact of the Combustor-Turbine Interface Slot Orientation on the Durability of a Nozzle Guide Vane Endwall
Journal of Turbomachinery, 2013Co-Authors: A. A. Thrift, Karen A. Thole, Satoshi HadaAbstract:The combustor-turbine interface is an essential component in a gas turbine engine as it allows for thermal expansion between the first stage turbine vanes and combustor section. Although not considered as part of the external cooling scheme, leakage flow from the combustor-turbine interface can be utilized as coolant. This paper reports on the effects of orientation of a two-dimensional leakage slot, simulating the combustor-turbine interface, on the net heat flux reduction to a nozzle guide vane endwall. In addition to adiabatic effectiveness and heat transfer measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed in the vane Stagnation Plane. Four interface slot orientations of 90°, 65°, 45°, and 30° located at 17% axial chord upstream of a first vane in a linear cascade were studied. Results indicate that reducing the slot angle to 45° can provide as much as a 137% reduction to the average heat load experienced by the endwall. Velocity measurements indicate the formation of a large leading edge vortex for coolant injected at 90° and 65° while coolant injected at 45° and 30° flows along the endwall and washes up the vane surface at the endwall junction.© 2012 ASME
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Effects of Orientation and Position of the Combustor-Turbine Interface on the Cooling of a Vane Endwall
Journal of Turbomachinery, 2012Co-Authors: A. A. Thrift, Karen A. Thole, Satoshi HadaAbstract:First stage, nozzle guide vanes and accompanying endwalls are extensively cooled by the use of film cooling through discrete holes and leakage flow from the combustor-turbine interface gap. While there are cooling benefits from the interface gap, it is generally not considered as part of the cooling scheme. This paper reports on the effects of the position and orientation of a two-dimensional slot on the cooling performance of a nozzle guide vane endwall. In addition to surface thermal measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed at the vane Stagnation Plane. Two slot orientations, 90° and 45°, and three streamwise positions were studied. Effectiveness results indicate a significant increase in area averaged effectiveness for the 45° slot relative to the 90° orientation. Flowfield measurements show dramatic differences in the horseshoe vortex formation.Copyright © 2011 by ASME
Forman A. Williams - One of the best experts on this subject based on the ideXlab platform.
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Rate-ratio asymptotic analysis of the structure and mechanisms of extinction of nonpremixed CH4/N-2-O-2/N2O/N-2 flames
Proceedings of the Combustion Institute, 2015Co-Authors: Kalyanasundaram Seshadri, Xue-song Bai, Forman A. WilliamsAbstract:Rate-ratio asymptotic analysis is carried out to elucidate the influence of nitrous oxide on the structure and critical conditions for extinction of nonpremixed methane flames. Steady, axisymmetric, laminar flow of two counterflowing streams toward a Stagnation Plane is considered. One stream is made up of a mixture of methane and nitrogen. The other stream is a mixture of oxygen, nitrous oxide, and nitrogen. A reduced mechanism of five global steps is employed in the analysis. Chemical reactions are presumed to take place in a thin reaction zone that is established in the vicinity of the Stagnation Plane. On either side of this thin reaction zone, the flow field is inert. These inert regions are called outer zones. Methane and nitrous oxide are completely consumed in the reaction zone, while oxygen is presumed to leak through the reaction zone. In the reaction zone, chemical reactions are presumed to take place in two layers-the inner layer and the oxidation layer. In the inner layer fuel (methane) is consumed and the intermediate species hydrogen and carbon monoxide are formed. These intermediate species are oxidized in the oxidation layer to water vapor and carbon dioxide. Radicals are produced in the oxidation layer from chain-branching reactions that consume hydrogen. Asymptotic analysis gives the scalar dissipation rate at extinction. Critical conditions for extinction predicted by the analysis agree well with previous experimental data. Nitrous oxide is found to have an inhibiting effect on the flame, promoting extinction. The inhibiting effect is attributed to the competition between the net reaction of nitrous oxide with hydrogen to form water vapor and nitrogen and the chain-branching reaction between oxygen and hydrogen that produces radicals. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)
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effects of diluents on nox formation in hydrogen counterflow flames
Combustion and Flame, 2002Co-Authors: Geir J Rortveit, Johan E Hustad, Shuichi Li, Forman A. WilliamsAbstract:Abstract Laminar diluted hydrogen flames have been studied in a counterflow burner. Measurements were made of profiles of temperature and of [NO], which are compared with predictions from numerical computations. A constant strain rate of 100 s −1 was used in every experiment. The hydrogen stream was diluted with the inerts N 2 , CO 2 , and He. Besides diffusion flames, the fuel streams were partially premixed to equivalence ratios from 2.7 to 3.9. There is evidence that, for these degrees of premixing, attached to the exit of the fuel duct there is a rich premixed flame, whose hot products burn in a diffusion flame close to the Stagnation Plane. Differences between the influences of the various diluents are discussed in terms of differences in heat capacities, thermal-radiative properties, and effects on chemical reactions. Maximum measured flame temperatures varied from 1830 to 2170 K, and measured [NO] ranged from 3.6 to 21.5 ppm. Numerical predictions show good agreement with experiments for both temperatures and [NO] at the lower temperatures. At higher temperatures, the predicted [NO] exceeds its measured value, the difference being attributed to probe effects.
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Spray structure in counterflowing streams with and without a flame
Combustion and Flame, 1993Co-Authors: Paul A. Libby, Forman A. WilliamsAbstract:An experimental and theoretical study is performed on two-phase counterflowing streams with and without flames in which methanol sprays, transported in nitrogen from a lower circular duct, flow upward to meet a pure oxygen stream that flows downward from the upper circular duct. The spray structure and entire flowfield are measured by a two-component phase doppler particle analyzer. The relative motion of droplets as a function of droplet diameter and the effect of the flame on the counterflow field are determined. The influences of the flowfield and the flame sheet on spray structure are measured. A theoretical analysis of droplet behavior in counterflowing streams is also performed on the basis of the spray equation applied away from the Stagnation Plane. Comparisons between measured and predicted number density as a function of axial position are made. These experimental and theoretical results help in understanding the fundamental mechanisms of spray combustion.
Kaoru Maruta - One of the best experts on this subject based on the ideXlab platform.
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extinction characteristics of ch4 o2 xe radiative counterflow planar premixed flames and their transition to ball like flames
Combustion and Flame, 2013Co-Authors: Koichi Takase, Xing Li, Masato Katsuta, Takuya Tezuka, Masao Kikuchi, Susumu Hasegawa, Hisashi Nakamura, Kaoru MarutaAbstract:Abstract Extinction characteristics of CH4/O2/Xe radiative counterflow premixed flames and their transition to ball-like flames were examined by computations and microgravity experiments. First, the flammability limit of flame ball for the mixture was estimated to be leaner than that of counterflow premixed flame by one-dimensional computations with detailed chemistry. Extinction experiments under microgravity showed that there was a ball-like flame prior to total extinction in the vicinity of the Stagnation-Plane in the low-speed counterflow field at stretch rate of 1.6–3.2 s−1. Formation of such a ball-like flame occurred subsequent to the extinction of counterflow flames and the ball-like flame was finally extinguished when the equivalence ratio was further decreased. Two-dimensional computations indicated that the temperature of the ball-like flame increased with the decrease of equivalence ratio in the near-limit condition when it approached extinction. The temperature distribution of the computational ball-like flame was in qualitative agreement with that of the flame ball. The ball-like flame in the counterflow field was considered to be stable based on steady-state two-dimensional computation at an equivalence ratio slightly richer than the limit of a transient ball-like flame. Such a stable computational ball-like flame is not perfectly spherical. The ball-like flame observed in this study is thought to have a close correlation with the ideal flame ball which is generally established in a quiescent mixture.
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Extinction characteristics of CH4/O2/Xe radiative counterflow planar premixed flames and their transition to ball-like flames
Combustion and Flame, 2013Co-Authors: Koichi Takase, Masato Katsuta, Takuya Tezuka, Masao Kikuchi, Susumu Hasegawa, Hisashi Nakamura, Kaoru MarutaAbstract:Abstract Extinction characteristics of CH4/O2/Xe radiative counterflow premixed flames and their transition to ball-like flames were examined by computations and microgravity experiments. First, the flammability limit of flame ball for the mixture was estimated to be leaner than that of counterflow premixed flame by one-dimensional computations with detailed chemistry. Extinction experiments under microgravity showed that there was a ball-like flame prior to total extinction in the vicinity of the Stagnation-Plane in the low-speed counterflow field at stretch rate of 1.6–3.2 s−1. Formation of such a ball-like flame occurred subsequent to the extinction of counterflow flames and the ball-like flame was finally extinguished when the equivalence ratio was further decreased. Two-dimensional computations indicated that the temperature of the ball-like flame increased with the decrease of equivalence ratio in the near-limit condition when it approached extinction. The temperature distribution of the computational ball-like flame was in qualitative agreement with that of the flame ball. The ball-like flame in the counterflow field was considered to be stable based on steady-state two-dimensional computation at an equivalence ratio slightly richer than the limit of a transient ball-like flame. Such a stable computational ball-like flame is not perfectly spherical. The ball-like flame observed in this study is thought to have a close correlation with the ideal flame ball which is generally established in a quiescent mixture.
Alessandro Gomez - One of the best experts on this subject based on the ideXlab platform.
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Pressure and temperature dependence of soot in highly controlled counterflow ethylene diffusion flames
Proceedings of the Combustion Institute, 2019Co-Authors: Kevin Gleason, Francesco Carbone, Alessandro GomezAbstract:Abstract Soot volume fraction and dispersion index were measured by pyrometry in a series of highly controlled counterflow diffusion flames, with peak temperatures, Tmax, spanning a few hundred degrees and pressure covering the 0.1–0.8 MPa range. An unprecedented level of control was implemented by selecting flames with a self-similar structure to ensure that the normalized temperature-time history experienced by the reactants was the same, regardless of pressure. The self-similarity was verified by suitably rescaling the transverse coordinate with respect to a characteristic diffusion length. At constant Tmax, the soot volume fraction increases approximately by two orders of magnitude as the pressure is raised from 1 atm to 4 atm, and by one to two additional orders of magnitude with an additional doubling of the pressure to 8 atm. At constant pressure, the soot load spans two to three orders of magnitude and soot formation exhibits increased sensitivity to temperature as the pressure is raised. Soot inception occurs near the flame, with an increase in soot concentration that becomes steeper at higher Tmax. The increase is accompanied by a decrease in the dispersion exponent that is suggestive of dehydrogenation and aging of the particles and is sharper at higher Tmax. Soot experiences continuous growth in a monotonically decreasing temperature field until it is convected away radially at the Stagnation Plane, with essentially no opportunity for oxidation. Evidence of two distinct mechanisms for soot formation was found: the classic high temperature, high activation energy process affecting soot formed in the vicinity of the flame and followed by dehydrogenation; and a relatively low-temperature, zero activation energy process, associated with the increase in volume fraction at low-temperatures in proximity of the Stagnation Plane. The latter is tentatively attributed to dimerization of aromatics, as revealed by the concurrent increase in the dispersion index corresponding to an increase in the particle hydrogen content.
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EXTINCTION AND REIGNITION IN COUNTERFLOW SPRAY DIFFUSION FLAMES INTERACTING WITH LAMINAR VORTICES
Proceedings of the Combustion Institute, 2002Co-Authors: Vito S. Santoro, Alessandro GomezAbstract:The interaction of laminar vortices with a methanol spray counterflow diffusion flame was studied experimentally with vortices generated from either the fuel side or the oxidizer side. The overall stoichiometry was such that the flame resided on the fuel side of the gas-Stagnation Plane. Local extinction and subsequent reignition were investigated as the circulation of the vortex was varied. It was found that extinction required vortices of larger circulation if generated from the oxidizer side. The effect was attributed to stretching and possibly, partial dissipation of the vortex, as it approached the Stagnation Plane before interacting with the flame. The robustness of the spray flame to vortex-induced extinction was compared with that of a similar gaseous flame. The spray flame was found to be comparatively weaker. Of the two potential culprits for such a difference, namely, the energetic handicap of spray flames due to the latent heat of vaporization of the liquid fuel and droplet inertia, the former was found to be the dominant factor. After extinction occurred, a hole was created in the diffusion flame, confining the combustion process to an annular region. The flame was then able to propagate back toward the centerline, re-establishing itself as a flat diffusion flame. The time interval for this reignition process was investigated as a function of the vortex circulation. It was found that, if the vortex approached the flame from the fuel side, the reignition time was much shorter than when the vortex was injected from the oxidizer side, and decreased for increasing values of the vortex circulation. In contrast, the reignition time increased with the circulation, if the vortex approached the flame from the oxidizer side. Only in the latter case, droplet inertia played a role in the reignition process.
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Thermophoretic Effects on Particles in Counterflow Laminar Diffusion Flames
Combustion Science and Technology, 1993Co-Authors: Alessandro Gomez, Daniel E. RosnerAbstract:Abstract Thermophoresis, meaning particle drift down a local gas temperature gradient, is now known to be important to many combustion-related technologies. Until now, however, no direct experimental determinations of primary and aggregated particle thermophoretic diffusivities, αT D, in high temperature combustion environments have been reported. To perform such measurements, we selected a seeded laminar counterflow diffusion flame (CDF) operated at low strain-rate as a well-defined combustion system, offering at the same time a low velocity and high temperature gradient environment. We established a CH4/ O2Inert opposed jet diffusion flame in which the gaseous fuel/oxygen ratio, and the diluent flow rates were adjusted to obtain a flat, stable flame, approximately coincident with the gas Stagnation Plane (GSP). Particles fed to or formed on either or both sides of the GSP move toward this Plane until the local axial velocity is exactly counterbalanced by the thermophoretic velocity. As a result of this ...
A. A. Thrift - One of the best experts on this subject based on the ideXlab platform.
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Impact of the Combustor-Turbine Interface Slot Orientation on the Durability of a Nozzle Guide Vane Endwall
Journal of Turbomachinery, 2013Co-Authors: A. A. Thrift, Karen A. Thole, Satoshi HadaAbstract:The combustor-turbine interface is an essential component in a gas turbine engine as it allows for thermal expansion between the first stage turbine vanes and combustor section. Although not considered as part of the external cooling scheme, leakage flow from the combustor-turbine interface can be utilized as coolant. This paper reports on the effects of orientation of a two-dimensional leakage slot, simulating the combustor-turbine interface, on the net heat flux reduction to a nozzle guide vane endwall. In addition to adiabatic effectiveness and heat transfer measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed in the vane Stagnation Plane. Four interface slot orientations of 90°, 65°, 45°, and 30° located at 17% axial chord upstream of a first vane in a linear cascade were studied. Results indicate that reducing the slot angle to 45° can provide as much as a 137% reduction to the average heat load experienced by the endwall. Velocity measurements indicate the formation of a large leading edge vortex for coolant injected at 90° and 65° while coolant injected at 45° and 30° flows along the endwall and washes up the vane surface at the endwall junction.© 2012 ASME
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Effects of Orientation and Position of the Combustor-Turbine Interface on the Cooling of a Vane Endwall
Journal of Turbomachinery, 2012Co-Authors: A. A. Thrift, Karen A. Thole, Satoshi HadaAbstract:First stage, nozzle guide vanes and accompanying endwalls are extensively cooled by the use of film cooling through discrete holes and leakage flow from the combustor-turbine interface gap. While there are cooling benefits from the interface gap, it is generally not considered as part of the cooling scheme. This paper reports on the effects of the position and orientation of a two-dimensional slot on the cooling performance of a nozzle guide vane endwall. In addition to surface thermal measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed at the vane Stagnation Plane. Two slot orientations, 90° and 45°, and three streamwise positions were studied. Effectiveness results indicate a significant increase in area averaged effectiveness for the 45° slot relative to the 90° orientation. Flowfield measurements show dramatic differences in the horseshoe vortex formation.Copyright © 2011 by ASME
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influence of flow injection angle on a leading edge horseshoe vortex
International Journal of Heat and Mass Transfer, 2012Co-Authors: A. A. Thrift, Karen A. TholeAbstract:Abstract Junction flows that develop at the base of protruding obstructions occur in many applications. An unsteady horseshoe vortex is formed as a component of these junction flows, which increases the local heat transfer on the associated endwall. Augmenting this junction flow can be achieved through the injection of fluid upstream of the obstruction. This experimental study evaluated the effects of injection angle for a two-dimensional slot placed upstream of a vane leading-edge with four injection angles of 90°, 65°, 45°, and 30°. Results showed that high momentum injection increased the endwall heat transfer at each slot angle while low momentum injection resulted in a relatively lower augmentation of endwall heat transfer. A leading-edge vortex turning into the endwall was formed at the junction in the Stagnation Plane for high momentum injection at 90° and 65° while a leading-edge vortex turning away from the wall was formed for 45° and 30° injection. For low momentum injection, a vortex turning into the endwall was formed at all injection angles.