Academic literature on the topic 'Blow-off Mechanism'
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Journal articles on the topic "Blow-off Mechanism"
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Yamaguchi, Shigeki, Norio Ohiwa, and Tatsuya Hasegawa. "Structure and blow-off mechanism of rod-stabilized premixed flame." Combustion and Flame 62, no. 1 (October 1985): 31–41. http://dx.doi.org/10.1016/0010-2180(85)90091-4.
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Kedia, Kushal S., and Ahmed F. Ghoniem. "The blow-off mechanism of a bluff-body stabilized laminar premixed flame." Combustion and Flame 162, no. 4 (April 2015): 1304–15. http://dx.doi.org/10.1016/j.combustflame.2014.10.017.
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Boopathi, S., P. Maran, V. Caleb Eugene, and S. Prabhu. "Analysis of Lift off Height and Blow-Off Mechanism of Turbulent Flame by V-Gutter Bluff Body." Applied Mechanics and Materials 787 (August 2015): 727–31. http://dx.doi.org/10.4028/www.scientific.net/amm.787.727.
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The experimental investigation has been carried out to study the stabilization and blowout mechanisms of turbulent flame stabilized by V-gutter bluff body in a square duct at reactive and non-reactive conditions. V-shaped bluff bodies made of stainless steel having 1.6 mm thicknessare used for stabilization of the flame.Experiments have been conducted at selective velocities of commercially available methane and oxygen with 60 degree V-gutter as flame holder. It is observed that at stoichiometric conditions, the V-gutter is dominated by shear layer stabilized flames. The flame stability is influenced by bluff body dimensions and mass flow rate which play a major role in combustion instabilities mixing of air fuel ratio and blow off. The lift off decreases at higher blockage ratios.A strong recirculation zone is found in this test rig immediately downstream of the V-Gutter which gradually subsides and disappears far downstream.The lift off height is not much affected by the velocity of the fuel-air mixture.
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Kim, Yu Jeong, Bok Jik Lee, and Hong G. Im. "Dynamics of lean premixed flames stabilized on a meso-scale bluff-body in an unconfined flow field." Mathematical Modelling of Natural Phenomena 13, no. 6 (2018): 48. http://dx.doi.org/10.1051/mmnp/2018051.
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Two-dimensional direct numerical simulations were conducted to investigate the dynamics of lean premixed flames stabilized on a meso-scale bluff-body in hydrogen-air and syngas-air mixtures. To eliminate the flow confinement effect due to the narrow channel, a larger domain size at twenty times the bluff-body dimension was used in the new simulations. Flame/flow dynamics were examined as the mean inflow velocity is incrementally raised until blow-off occurs. As the mean inflow velocity is increased, several distinct modes in the flame shape and fluctuation patterns were observed. In contrast to our previous study with a narrow channel, the onset of local extinction was observed during the asymmetric vortex shedding mode. Consequently, the flame stabilization and blow-off behavior was found to be dictated by the combined effects of the hot product gas pocket entrained into the extinction zone and the ability to auto-ignite the mixture within the given residence time corresponding to the lateral flame fluctuations. A proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic theory of Zukoski and Marble.
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KOCSIS, G., J. S. BAKOS, S. KÁLVIN, L. KÖNEN, G. MANK, and A. POSPIESZCZYK. "Toroidal transport studies in TEXTOR using lithium laser blow-off injection." Journal of Plasma Physics 58, no. 1 (July 1997): 19–30. http://dx.doi.org/10.1017/s0022377897005795.
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The toroidal spread of laser blow-off injected lithium is studied. The temporal variation of the toroidal and radial distributions of the first two ionization stages of cross-field-injected lithium is measured around the injection location by a gated, image-intensified CCD camera. Broad atomic distribution and deep radial penetration of the injected beam is observed. The toroidal delay of the arrival of the Li+ ions is investigated by detecting the intensity of their line radiation at different toroidal positions away from the injection port. Possible explanations for the observations and the possible mechanism for the toroidal spread are discussed in detail. A comparison of the detected distribution of Li ions with a 1D simulation is presented.
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Wan, Jianlong, and Haibo Zhao. "Blow-off mechanism of a holder-stabilized laminar premixed flame in a preheated mesoscale combustor." Combustion and Flame 220 (October 2020): 358–67. http://dx.doi.org/10.1016/j.combustflame.2020.07.012.
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Singh, R. K., Ajai Kumar, V. Prahlad, and H. C. Joshi. "Generation of fast neutrals in a laser-blow-off of LiF–C film: A formation mechanism." Applied Physics Letters 92, no. 17 (April 28, 2008): 171502. http://dx.doi.org/10.1063/1.2906368.
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Lindstedt, R. P. "The modelling of direct chemical kinetic effects in turbulent flames." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 214, no. 3 (March 1, 2000): 177–89. http://dx.doi.org/10.1243/0954410001531999.
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Combustion chemistry-related effects have traditionally been of secondary importance in the design of gas turbine combustors. However, the need to deal with issues such as flame stability, relight and pollutant emissions has served to bring chemical kinetics and the coupling of finite rate chemistry with turbulent flow fields to the centre of combustor design. Indeed, improved cycle efficiency and more stringent environmental legislation, as defined by the ICAO, are current key motivators in combustor design. Furthermore, lean premixed prevaporized (LPP) combustion systems, increasingly used for power generation, often operate close to the lean blow-off limit and are prone to extinction/reignition type phenomena. Thus, current key design issues require that direct chemical kinetic effects be accounted for accurately in any simulation procedure. The transported probability density function (PDF) approach uniquely offers the potential of facilitating the accurate modelling of such effects. The present paper thus assesses the ability of this technique to model kinetically controlled phenomena, such as carbon monoxide emissions and flame blow-off, through the application of a transported PDF method closed at the joint scalar level. The closure for the velocity field is at the second moment level, and a key feature of the present work is the use of comprehensive chemical kinetic mechanisms. The latter are derived from recent work by Lindstedt and co-workers that has resulted in a compact 141 reactions and 28 species mechanism for LNG combustion. The systematically reduced form used here features 14 independent C/H/O scalars, with the remaining species incorporated via steady state approximations. Computations have been performed for hydrogen/carbon dioxide and methane flames. The former (high Reynolds number) flames permit an assessment of the modelling of flame blow-off, and the methane flame has been selected to obtain an indication of the influence of differential diffusion effects among gaseous species. The agreement with experimental data is excellent. The predicted blow-off, velocity is within 10 per cent of the experimental value and it is further shown that experimental levels of major and minor species are well reproduced. Interestingly, comparisons of experimental data with prediction indicate only a modest influence of differential diffusion effects on gaseous species. A comparison with previous modelling efforts, featuring smaller scalar spaces, permits the conclusion that accurate chemistry is a prerequisite for quantitative predications of finite rate chemical kinetic effects.
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Sack, N., and I. Lichtenstadt. "The Effect of General Relativity and Equation of State on the Adiabatic Collapse and Explosion of a Stellar Core." International Astronomical Union Colloquium 108 (1988): 417–19. http://dx.doi.org/10.1017/s0252921100094215.
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The collapse of the iron core of massive stars ( M ≥ 8 MO) is initiated by photodissociation and electron capture. The collapse of the inner core proceeds homologously until it is stopped by the stiffness of the equation of state (hereafter EOS) at nuclear density and it stops or rebounds. A shock forms at the edge of homology. The initial strength of the shock increases with the velocity difference between the inner and outer cores, i.e. it increases with a larger rebound of the inner core. The uniterrupted propagation of this prompt shock through the remainder of the core to the stellar mantle, where it can deliver enough energy to blow off the loosely bound outer layers, has long been proposed as the mechanism of type II supernovae explosions. However most authors did not get an explosion as a result of the prompt mechanism. Recently Baron et al. (1985) reported that the combination of General Relativity (GR) with a relatively soft EOS at nuclear densities leads to a much greater blow off than they got with Newtonian hydrodynamics. In order to see where purely hydrodynamical effects are important, namely for what EOS the GR outburst is greater than the Newtonian, we did a set of pure hydrodynamical adiabatic calculations (complete neutrino trapping) with different EOS above nuclear densities, turning the GR terms on and off. Neutrino leakage, which we do not incorporate, usually leads to harmful energy losses.
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Bykov, V., V. V. Gubernov, and U. Maas. "Mechanisms performance and pressure dependence of hydrogen/air burner-stabilized flames." Mathematical Modelling of Natural Phenomena 13, no. 6 (2018): 51. http://dx.doi.org/10.1051/mmnp/2018046.
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The kinetic mechanism of hydrogen combustion is the most investigated combustion system. This is due to extreme importance of the mechanism for combustion processes, i.e. it is present as a sub-mechanism in all mechanisms for hydrocarbon combustion systems. Therefore, detailed aspects of hydrogen flames are still under active investigations, e.g. under elevated pressure, under conditions of different heat losses intensities and local equivalence ratios etc. For this purpose, the burner stabilized flame configuration is an efficient tool to study different aspects of chemical kinetics by varying the stand-off distance, pressure, temperature of the burner and mixture compositions. In the present work, a flat porous plug burner flame configuration is revisited. A hydrogen/air combustion system is considered with detailed molecular transport including thermo-diffusion and with 8 different chemical reaction mechanisms. Detailed numerical investigations are performed to single out the role of chemical kinetics on the loss of stability and on the dynamics of the flame oscillations. As a main outcome, it was found/demonstrated that the results of critical values, e.g. critical mass flow rate, weighted frequency of oscillations and blow-off velocity, with increasing the pressure scatter almost randomly. Thus, these parameters can be considered as independent and can be used to improve and to validate the mechanisms of chemical kinetics for the unsteady dynamics.
Dissertations / Theses on the topic "Blow-off Mechanism"
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Kedia, Kushal Sharad. "Development of a multi-scale projection method with immersed boundaries for chemically reactive flows and its application to examine flame stabilization and blow-off mechanisms." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85234.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 193-201).
High-fidelity multi-scale simulation tools are critically important for examining energy conversion processes in which the coupling of complex chemical kinetics, molecular transport, continuum mixing and acoustics play important roles. The objectives of this thesis are: (i) to develop a state-of-the-art numerical approach to capture the wide spectra of spatio-temporal scales associated with reacting flows around immersed boundaries, and (ii) to use this tool to investigate the underlying mechanisms of flame stabilization and blow-off in canonical configurations. A second-order immersed boundary method for reacting flow simulations near heat conducting, grid conforming, solid object has been developed. The method is coupled with a block-structured adaptive mesh refinement (SAMR) framework and a semi-implicit operator-split projection algorithm. The immersed boundary approach captures the flame-wall interactions. The SAMR framework and the operator-split algorithm resolve several decades of length and time efficiently. A novel "buffer zone" methodology is introduced to impose the solid-fluid boundary conditions such that symmetric derivatives and interpolation stencils can be used throughout the interior of the domain, thereby maintaining the order of accuracy of the method. Near an immersed solid boundary, single-sided buffer zones are used to resolve the species discontinuities, and dual buffer zones are used to capture the temperature gradient discontinuities. This eliminates the need to utilize artificial flame anchoring boundary conditions used in existing state-of-the-art numerical methods. As such, using this approach, it is possible for the first time to analyze the complex and subtle processes near walls that govern flame stabilization. The approach can resolve the flow around multiple immersed solids using coordinate conforming representation, making it valuable for future research investigating a variety of multi-physics reacting flows while incorporating flame-wall interactions, such as catalytic and plasma interactions. Using the numerical method, limits on flame stabilization in two canonical configurations: bluff-body and perforated-plate, were investigated and the underlying physical mechanisms were elucidated. A significant departure from the conventional two-zone premixed flame-structure was observed in the anchoring region for both configurations. In the bluff-body wake, the location where the flame is initiated, preferential diffusion and conjugate heat exchange furnish conditions for ignition and enable streamwise flame continuation. In the perforated-plate, on the other hand, a combination of conjugate heat exchange and flame curvature is responsible for local anchoring. For both configurations, it was found that a flame was stable when (1) the local flame displacement speed was equal to the flow speed (static stability), and (2) the gradient of the flame displacement speed normal to its surface was higher than the gradient of the flow speed along the same direction (dynamic stability). As the blow-off conditions were approached, the difference between the former and the latter decreased until the dynamic stability condition (2) was violated. The blowoff of flames stabilized in a bluff-body wake start downstream, near the end of the combustion-products dominated recirculation zone, by flame pinching into an upstream and a downstream propagating sections. The blow-off of flames stabilized in flow perforated-plate wake start in the anchoring region, near the end of the preheated reactants-filled recirculation zone, with the entire flame front convecting downstream. These simulations elucidated the thus far unknown physics of the underlying flame stabilization and blow-off mechanisms, understanding which is crucial for designing flame-holders for combustors that support continuous burning. Such an investigation is not possible without the advanced numerical tool developed in this work. Based on the insight gained from the simulations, analytical models were developed to describe the dynamic response of flames to flow perturbations in an acoustically coupled environment. These models are instrumental in optimizing combustor designs and applying active control to guarantee dynamic stability if necessary.
by Kushal Sharad Kedia.
Ph. D.
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Kim, Yu Jeong. "Computational Studies of Stabilization and Blow-off Mechanisms in Bluff-body Stabilized Lean Premixed Flames." Diss., 2021. http://hdl.handle.net/10754/669818.
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A bluff-body has been employed as the flame stabilization scheme for many combustion devices such as gas turbines and aviation engines. Although the bluff-body flame holder has a key advantage of generating a hot gas recirculation zone behind it and assist in stable combustion, it also induces flow field and combustion instabilities such as unstable vortex shedding, which can adversely affect the flame stability and lead to blow-off. The understanding of the physical mechanism of flame stabilization and blow-off processes has been one of the critical subjects in premixed combustion systems under highly turbulent conditions. As considering this, the present dissertation presents insight of flame stabilization and blow-off mechanisms using several series of computational studies and detailed analysis using diagnostic approaches. Two-dimensional direct numerical simulations are conducted to examine flame/flow and blow-off dynamics in lean premixed hydrogen-air and syngas-air flames stabilized on a meso-scale bluff-body in a square channel. Several distinct effects on flame stabilization and blow-off dynamics are investigated, such as reduced confinement, hydrodynamic instability, flame time scale, and differential diffusion effects. For the analysis, a proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic blow-off theory of Zukoski and Marble. The combined approach of computational singular perturbation and tangential stretch rate is applied to examine chemical characteristics in blow-off dynamics. As an extension from Eulerian to Lagrangian viewpoint, Lagrangian particle tracking analysis of post-processing the pre-computed results is performed to examine the local characteristics during the critical transient event of local extinction and recovery.
Book chapters on the topic "Blow-off Mechanism"
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Lovejoy, Shaun. "Macroweather predictions and climate projections." In Weather, Macroweather, and the Climate. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190864217.003.0011.
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“Does the Flapping of a Butterfly’s Wings in Brazil Set off a Tornado in Texas?” This was the provocative title of an address given by Edward Lorenz, the origin for the (nearly) household expression “butterfly effect.” It was December 1972 and it had been nearly ten years since he had discovered it,1 yet its significance was only then being recognized. Lorenz explained: “In more technical language, is the behavior of the atmosphere unstable to small perturbations?” His answer: “Although we cannot claim to have proven that the atmosphere is unstable, the evidence that it is so is overwhelming.” Imagine two planets identical in every way except that on one there is a butterfly that flaps its wings. The butterfly effect means that their future evolutions are “sensitively dependent” on the initial conditions, so that a mere flap of a wing could perturb the atmosphere sufficiently so that, eventually, the weather patterns on the two planets would evolve quite differently. On the planet with the Brazilian butterfly, the number of tornadoes would likely be the same. But on a given day, one might occur in Texas rather than Oklahoma. This sensitive dependence on small perturbations thus limits our ability to predict the weather. For Earth, Lorenz estimated this predictability limit to be about two weeks. From Chapters 4 and 5 and the discussion that follows, we now understand it as the slightly shorter weather– macroweather transition scale. In Chapter 1, we learned that the ratio of the nonlinear to linear terms in the (deterministic) equations governing the atmosphere is typically about a thousand billion. The nonlinear terms are the mathematical expressions of physical mechanisms that can blow up microscopic perturbations into large effects. Therefore, we expect instability. Chapter 4, we examined instability from the point of view of the higher level statistical laws— the fact that, at weather scales, the fluctuation exponents H for all atmospheric fields are positive (in space, up to the size of the planet; in time, up to the weather– macroweather transition scale at five to ten days).
Conference papers on the topic "Blow-off Mechanism"
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Pathania, Rohit S., Aaron Skiba, Jennifer A. Sidey, and Epaminondas Mastorakos. "Blow-off mechanism in a turbulent premixed bluff-body stabilized flame with pre-vaporized fuels." In AIAA Scitech 2019 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2019. http://dx.doi.org/10.2514/6.2019-2238.
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Pathania, Rohit S., Aaron Skiba, Jennifer A. Sidey, and Epaminondas Mastorakos. "Correction: Blow-off mechanism in a turbulent premixed bluff-body stabilized flame with pre-vaporized fuels." In AIAA Scitech 2019 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2019. http://dx.doi.org/10.2514/6.2019-2238.c1.
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Katta, Viswanath R., and W. M. Roquemore. "Studies on Lean-Blowout Characteristics of a Premixed Jet Flame." In ASME 1995 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/95-gt-115.
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The stability characteristics of a fuel-lean premixed jet flame are investigated using a time-dependent, axisymmetric numerical model with a detailed-chemical-kinetics mechanism for H2-O2-N2 combustion. Temperature- and species-dependent transport properties are incorporated. The mathematical model is validated by computing the burning velocities for different equivalence ratios and comparing them with experimentally measured values. Premixed flames that are stably attached to the fuel tube are obtained over a wide range of equivalence ratios. The lower limit for equivalence ratio at which the flame lifts-off from the fuel tube is found to be 0.4. Calculations have also correctly predicted the following scenario: when a premixed flame lifts-off at the base, it becomes unstable and is eventually blown out of the computational domain. The blow-out process is studied by analyzing the stable flame at Φ = 0.4 and the unstable flame at Φ = 0.395. Entrainment of ambient air by the fuel jet upstream of the lifted-flame base reduces the local equivalence ratio which, in turn, is found to be responsible for the blow-out of the flame.
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Ciardiello, Roberto, Rohit S. Pathania, Patton M. Allison, Pedro M. de Oliveira, and Epaminondas Mastorakos. "Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15434.
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Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.
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Kim, Tae-Uk, JeongWoo Shin, and Sang Wook Lee. "Design and Testing of a Crashworthy Landing Gear." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52474.
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The development of a crashworthy landing gear is presented based on the civil regulations and the military specifications. For this, two representative crashworthy requirements are applied to helicopter landing gear design; the nose gear is designed to collapse in a controlled manner so that it does not penetrate the cabin and cause secondary hazards, and the main gear has to absorb energy as much as possible in crash case to decelerate the aircraft. To satisfy the requirements, the collapse mechanism triggered by shear-pin failure and the shock absorber using blow-off valve are implemented in the nose and main gear, respectively. The crash performance of landing gear is demonstrated by drop tests. In the tests, performance data such as ground reaction loads and shock absorber stroke are measured and crash behaviors are recorded by high-speed camera. The test data shows a good agreement with the prediction by simulation model, which proves the validity of the design and analysis.
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Reich, F., F. Otremba, and A. Würsig. "Fail-Safe? A Study About the Integrity of Safety Valves for Tanks for Dangerous Goods." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-62204.
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In Europe, tanks designed on different safety philosophies are used for transporting one and the same liquid dangerous goods (Krautwurst, 2011). Owing to this circumstance, the BAM was commissioned by the BMVBS to conduct a research project designed to analyse and assess the equipment of tanks. Furthermore in these project were researched some failure mechanism of pressure relief devices (PRD). Based on the knowledge gained, possible solutions were worked out under safety-relevant aspects that would benefit tank transport by providing a lower hazard potential. Besides looking at the mode of operation and the construction of PRV, their blow-off characteristics and total flow rate are considered from a safety engineering point of view. Based on in-depth studies, a concept for and the further approach to examinations of the failure limits of PRD, especially of spring loaded relief valves, was developed and comprehensively described in the report “The use of safety devices, particularly safety valves, on transport containers” (Pötzsch, Reich, & Jochems, 2011). The purpose of this study was to investigate failure causes of safety valves by normal modes and accidental fire heat loads. A series of investigations for different influences using safety valves for tanks were obtained. Testing vibration modes and corrosion presents some design limits. Experimental study of a pressure vessel engulfing in fire identify significant design limits. The complete set of results provides direct information of fail-safe modes and discusses the usage.
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Cordier, M., A. Vandel, B. Renou, G. Cabot, M. A. Boukhalfa, and M. Cazalens. "Spark Ignition of Confined Swirled Flames: Experimental and Numerical Investigation." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94384.
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A swirl burner was designed to experimentally study the impact of spark location on ignition efficiency and detailed ignition scenarios until flame stabilization or blow-off were established, following experimental observations. Premixed and non-premixed configurations were investigated for the same turbulent flow, in order to evaluate the fuel heterogeneities on ignition efficiency. Attention was paid to providing accurate data on cold flow velocity field statistics (obtained by stereoscopic PIV) and fuel mole fraction field statistics (obtained by PLIF on acetone). Ignition probability maps were established for all conditions by using laser-induced spark for a constant level of deposited energy. No systematic correlations were observed between local flow properties and ignition probability, which leads to the conclusion that history of the flame kernel inside the combustion chamber, must be taken into account to fully explain the ignition mechanism. From this conclusion, ignition scenarios were built using fast flame visualization and dynamic pressure record. Different steps of the ignition process were identified according to the location of the spark. In order to evaluate ignition probability according to spark location and flow conditions (velocity, turbulence and mixing), we extended the predictive model of Neophytou et al. [1], with some modifications, to examine whether it can be applied to ignition of swirling premixed flames. Flame particles are emitted by the spark and tracked in the flow with a Langevin equation by using non-reactive velocity fields obtained by PIV. Physical criteria are proposed to represent flame particles generation, expansion and extinction. Results indicate a relatively good agreement with the experimental database and the ignition scenarios are also well reproduced.
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Vishnu, R., R. I. Sujith, and Preeti Aghalayam. "Investigation of Flame Dynamics in a V - Flame Combustor During Combustion Instability." In ASME 2014 Gas Turbine India Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gtindia2014-8345.
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Propulsion systems such as gas turbines are susceptible to combustion instability, when operated at lean equivalence ratio [1]. During combustion instability, there is a nonlinear interaction between combustion and acoustics leading to large amplitude acoustic oscillations. These large amplitude oscillations are detrimental to the stability of the combustor and can cause damages to the structural integrity of the combustor, flame flash back or blow off. The main source of nonlinearity is in the heat release rate caused due to the velocity perturbations at the flame holder [2]. The heat release rate fluctuations are due to the variation in the flame surface area. Hence there is a need to understand the flame dynamics that contributes to the heat release rate fluctuations. The present study aims in understanding the stability of a V - flame combustor by varying the flame location inside an acoustic resonator. By varying the flame location the instability regimes of the combustor are identified. At the flame locations where the system exhibits combustion instability, acoustic pressure oscillations are acquired simultaneously with high speed images of the flame front fluctuations so that a correlation can be made between them. Tools from dynamical systems theory are applied to the pressure signal to quantify different dynamical states of the system during combustion instability. Moreover the flame dynamics at each dynamical state are investigated. It is observed that combustion instability is characterized by interesting dynamical states such as frequency locked state, quasi-periodic oscillations, period 3 oscillations and chaotic oscillations. High speed imaging of the flame reveals different interesting patterns of flame behavior during combustion instability. Flame wrinkling, roll up of flame elements, separation as islands of the flame elements and mutual annihilation of flame elements were some of the interesting flame behavior observed. This study helps in understanding the role of nonlinear heat release rate mechanism in establishing different dynamical states during combustion instability.
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Duchaine, Patrick, Quentin Bouyssou, Stéphane Pascaud, Gorka Exilard, and Christophe Viguier. "Soot Emission Optimization of a Helicopter Engine: From Injector Design to Engine Tests Validation." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-16100.
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Abstract Even though no regulation currently exists on helicopter gas turbines, soot production in aeronautic engines is of paramount importance to comply with future rules, as well as to offer environmental-friendly products on the market. Thus, design modifications of the combustion liner and fuel injectors are one way to explore in order to reduce soot emission levels of existing combustors. These design changes are driven both by fundamental knowledge of soot production mechanisms and by advanced combustion and pollutants modelling. The major difficulty is to reduce soot emissions while not deteriorating other combustion performances: NOx and CO emissions, lean blow-off limits and service lifetime. The objective of the present study is to optimize fuel injectors of a recent Safran Helicopter Engines research combustor. The injector design modifications are driven by one main guideline: reducing soot emissions can be achieved by lowering the equivalence ratio downstream of the injector. Detailed designs are achieved thanks to advanced RANS injector and LES combustion computations. Then, in order to mitigate main identified risks — management of soot emissions and lean blow-off limits — engine tests were performed very early in the demonstration process. A combustor is successively equipped with one standard and two modified geometries of fuel injectors on an engine test bench. Experimental results show that the two modified injector geometries reduce smoke numbers by a factor of respectively 2 and 9 and slightly deteriorates lean blow-off limits. These measurements are also compared to CFD computations. Leung et al. model (Combust Flame 1991), relying on phenomenological descriptions of soot formation combined with a LES computation of the combustor, well predicts a significant decrease in smoke level, even if it does not perfectly match engine data. Concerning lean blow-off limits, LES modelling predict a decrease in lean blow-off limits, which do not agree qualitatively with engine test results. As a conclusion, this study identifies a design driving factor for soot reduction, with possibly acceptable impacts on other combustion performances like lean blow-off limits.
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Belardini, Elisabetta, Rajeev Pandit, V. V. N. K. Satish Koyyalamudi, Dante Tommaso Rubino, and Libero Tapinassi. "2nd Quadrant Centrifugal Compressor Performance: Part II." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57124.
Full textAbstract:
The sizing of surge protection devices for both compressor and surrounding system may require the knowledge of performance curves in 2nd quadrant with a certain level of accuracy. In particular two performance curves are usually important: the pressure ratio trend versus flow rate inside the compressor and the work coefficient or power absorption law. The first curve allows estimating mass flow in the compressor given a certain pressure level imposed by system, while the second is important to estimate the time required to system blow down during ESD (emergency shutdown). Experimental data are routinely not available in the early phase of anti-surge protection devices and prediction methods are needed to provide performance curves in 2nd quadrant starting from the geometry of both compressor and system. In this paper two different approaches are presented to estimate performance curves in 2nd quadrant: the first is a simple 1D approach based on velocity triangle and the second is a full unsteady CFD computation. The two different approaches are applied to the experimental data more deeply investigated in part I by Belardini E.[3]. The measurement of compressor behavior in 2nd quadrant was possible thanks to a dedicated test arrangement in which a booster compressor is used forcing stable reverse flow. The 1D method showed good agreement with experiments at design speed. In off-design condition a correlation for deviation angle was tuned on experimental data to maintain an acceptable level of accuracy. With very low reverse flow rates some discrepancies are still present but this region plays a secondary role during the dynamic simulations of ESD or surge events. The unsteady CFD computation allowed a deeper insight into the fluid structures, especially close to very low flow rates when the deviation of the 1D method and the experimental data is higher. An important power absorption mechanism was identified in the pre-rotation effect of impeller as also the higher impact of secondary flows. These two methods are complementary in terms of level of complexity and accuracy and to a certain extent both necessary. 1D methods are fast to be executed and more easily calibrated to match the available experiments, but they have limited capability to help understanding the underlying physics. CFD is a more powerful tool for understanding fluid structures and energy transfer mechanisms but requires computational times not always suitable for a production environment. 1D method can be used for standard compressor and applications for which consolidated experience have been already gathered while CFD is more suitable during the development of new products or up to front projects in general.