Compressible Turbulent Flame Speed of Highly Turbulent Standing Flames PDF Download
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Author: Jonathan Sosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.
Author: Jonathan Sosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.
Author: Jonathan Sosa
Publisher:
ISBN:
Category :
Languages : en
Pages : 117
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Book Description
This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.
Author: Jessica Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 76
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Book Description
One of the fundamental mechanisms for detonation initiation is turbulence induced deflagration-to-detonation transition (tDDT). This research experimentally explores the dynamics of highly turbulent fast flames that are characterized by extremely high turbulent flame speeds, experience increased effects of compressibility, and may develop a runaway acceleration combined with a pressure buildup that leads to tDDT. The flame dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, OH* chemiluminescence, pressure measurements, and schlieren imaging. We study various regimes of fast flame propagation conditions for runaway acceleration of turbulent fast flames and effects of compressibility on the evolution of these flames. When the local measured turbulent flame speed is found to be greater than the Chapman-Jouguet deflagration speed, the flame is categorized to be at the runaway transition regime that eventually leads to a detonation.
Author: Paul A. Libby
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 12
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Book Description
Author: Hardeo Chin
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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Book Description
Propulsion systems are influenced by the efficiency of combustion systems. One approach to substantially improve combustion efficiency is through pressure gain combustion or detonation-based engines. Detonations exhibit attractive features such as increased stagnation pressure and rapid heat release; however, their highly unsteady and three-dimensional nature makes them difficult to characterize. In addition, the deflagration state prior to detonation is not well defined experimentally. Detonations can be achieved via the deflagration-to-detonation transition (DDT), where a deflagration that propagates on the order of 1 - 10 m/s is accelerated to a detonation that propagates on the order of 2000 m/s. The DDT process is highly dynamic and can occur through several mechanisms such as the Zeldovich reactivity-gradient mechanism where hot spots are created by Mach stem reflections, localized vorticial explosions, boundary layer effects, or turbulence. This work focuses on transient compressible flame regimes within the turbulent DDT (tDDT) process which causes a flame to undergo various burning modes. These burning modes can be categorized into four regimes: (1) slow deflagrations, (2) fast deflagrations, (3) shock-flame complex, and (4) detonation. To achieve each burning mode, turbulence levels and propagation velocities are tailored using perforated plates and various fuel-oxidizer compositions. The primary goal of this dissertation is to characterize the relationship between the turbulent flame speed (ST) and Chapman-Jouguet (CJ) deflagration speed (SCJ) using high-speed optical diagnostics in a turbulent shock tube facility. This work will: (1) further validate and classify the turbulence-compressibility characteristics associated with fast flames that lead to detonation onset in a highly turbulent environment, (2) quantify local ST for fast flames, and (3) investigate the flow field conditions of flame modes relating to the SCJ criteria, from slow deflagrations to shock-flame complexes.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 41
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Book Description
Direct numerical simulations of the interaction of a premixed flame with subsonic, high-speed, homogeneous, isotropic, Kolmogorov-type turbulence in an unconfined system show anomalously high turbulent flame speeds, S(T) . Data from these simulations are analyzed to identify the origin of this anomaly. The simulations were performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive-flow code. A simplified reaction-diffusion model represents a stoichiometric H2-air mixture under the assumption of the Lewis number L(e) = 1. Global properties and the internal structure of the flame were analyzed in an earlier paper, which showed that this system represents turbulent combustion in the thin reaction zone regime with the average local flame speed equal to its laminar value, S(L). This paper shows that: (1) Flamelets inside the flame brush have a complex internal structure, in which the isosurfaces of higher fuel mass fractions are folded on progressively smaller scales. (2) Global properties of the turbulent flame are best represented by the structure of the region of peak reaction rate, which defines the flame surface. (3) The observed increase of S(T) relative to S(L) exceeds the corresponding increase of the flame surface area, A(T), relative to the surface area of the planar laminar flame, on average, by 30% and occasionally by as much as 50% in the course of system evolution. This exaggerrated response of S(T) shows that Damkohler's paradigm breaks down for sufficiently high-intensity turbulence, namely at Karlovitz numbers Ka ~ 20, even in the flows characterized by L(e) = 1. (4) The breakdown is the result of tight flame packing by turbulence, which causes frequent flame collisions and formation of regions of high flame curvature 1/ L, or "cusps," where L is the thermal width of the laminar flame.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 31
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Book Description
We study the dynamics and properties of a turbulent flame, formed in the presence of subsonic, high-speed, homogeneous, isotropic Kolmogorovtype turbulence in an unconfined system. Direct numerical simulations are performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive-flow code. A simplified reaction-diffusion model represents a stoichiometric H 2-air mixture. The system being modeled represents turbulent combustion in the well-stirred reactor regime, with Damkoehler number Da = 0.1 and the turbulent velocity at the energy injection scale 30 times larger than the laminar flame speed. The simulations show that flame interaction with high-speed turbulence forms a steadily propagating turbulent flame with a flame width approximately twice the energy injection scale and a speed four times the laminar flame speed. A method for reconstructing the internal flame structure is described and used to show that the turbulent flame consists of tightly folded flamelets. The internal structure of these is virtually identical to that of the planar laminar flame with the preheat zone broadened by approximately a factor of two. The turbulent cascade fails to penetrate the internal flame structure, and so the action of small-scale turbulence is suppressed throughout most of the flame. Finally, our results suggest that for stoichiometric H 2-air mixtures any substantial flame broadening by the action of turbulence cannot be expected in all subsonic regimes.
Author: Jessica Marcella Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 27
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Book Description
One of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, chemiluminescence, and Schlieren measurements. The investigation classifies the fast flame propagation modes at various regimes. The study further examines the conditions for a turbulent fast flame at the boundary of transitioning to quasi-detonation. The evolution of the flame-compressibility interactions for this turbulent fast flame is characterized. The local measured turbulent flame speed is found to be greater than the Chapman–Jouguet deflagration flame speed which categorizes the flame to be at the spontaneous transition regime and within the deflagration-to-detonation transition runaway process.
Author: Albert Ratner
Publisher:
ISBN:
Category :
Languages : en
Pages : 244
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Book Description
Author: Nedunchezhian Swaminathan
Publisher: Cambridge University Press
ISBN: 1139498584
Category : Technology & Engineering
Languages : en
Pages : 447
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Book Description
A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.
