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Diffusive–thermal Instability
Diffusive–thermal instability or thermo–diffusive instability is an instrinsic flame instability that occurs both in premixed flames and in diffusion flames and arises because of the difference in the diffusion coefficient values for the fuel and heat transport, characterized by non-unity values of Lewis numbers. The instability mechanism that arises here is the same as in Turing instability explaining chemical morphogenesis, although the mechanism was first discovered in the context of combustion by Yakov Zeldovich in 1944 to explain the cellular structures appearing in lean hydrogen flames. Quantitative stability theory for premixed flames were developed by Gregory Sivashinsky (1977), Guy Joulin and Paul Clavin (1979) and for diffusion flames by Jong S. Kim (1997). Dispersion relation for premixed flames To neglect the influences by hydrodynamic instabilities such as Darrieus–Landau instability, Rayleigh–Taylor instability etc., the analysis usually neglects effects due ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Combustion Instability
Combustion instabilities are physical phenomena occurring in a reacting flow (e.g., a flame) in which some perturbations, even very small ones, grow and then become large enough to alter the features of the flow in some particular way. In many practical cases, the appearance of combustion instabilities is undesirable. For instance, thermoacoustic instabilities are a major hazard to gas turbines and rocket engines. Moreover, flame blowoff of an aero-gas-turbine engine in mid-flight is clearly dangerous (see flameout). Because of these hazards, the engineering design process of engines involves the determination of a stability map (see figure). This process identifies a combustion-instability region and attempts to either eliminate this region or moved the operating region away from it. This is a very costly iterative process. For example, the numerous tests required to develop rocket engines are largely in part due to the need to eliminate or reduce the impact of thermoacous ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffusive Thermal Instability
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules. The result of diffusion is a gradual mixing of material such that the distribution of molecules is uniform. Since the molecules are still in motion, but an equilibrium has been established, the result of molecular diffusion is called a "dynamic equilibrium". In a phase with uniform temperature, absent external net forces acting on the particles, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluid Dynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including '' aerodynamics'' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation. Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kuramoto–Sivashinsky Equation
In mathematics, the Kuramoto–Sivashinsky equation (also called the KS equation or flame equation) is a fourth-order nonlinear partial differential equation. It is named after Yoshiki Kuramoto and Gregory Sivashinsky, who derived the equation in the late 1970s to model the diffusive–thermal instabilities in a laminar flame front. The Kuramoto–Sivashinsky equation is known for its chaotic behavior. Definition The 1d version of the Kuramoto–Sivashinsky equation is :u_t + u_ + u_ + \fracu_x^2 = 0 An alternate form is :v_t + v_ + v_ + v v_x = 0 obtained by differentiating with respect to x and substituting v = u_x. This is the form used in fluid dynamics applications. The Kuramoto–Sivashinsky equation can also be generalized to higher dimensions. In spatially periodic domains, one possibility is :u_t + \Delta u + \Delta^2 u + \frac , \nabla u, ^2 = 0, where \Delta is the Laplace operator, and \Delta^2 is the biharmonic operator. Properties The Cauchy problem for the 1d K ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Number
The Zel'dovich number is a dimensionless number which provides a quantitative measure for the activation energy of a chemical reaction which appears in the Arrhenius exponent, named after the Russian scientist Yakov Borisovich Zel'dovich, who along with David A. Frank-Kamenetskii, first introduced in their paper in 1938. In 1983 ICDERS meeting at Poitiers, it was decided to name after Zel'dovich.Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59. It is defined as :\beta = \frac \cdot \frac where *E_a is the activation energy of the reaction *R is the universal gas constant *T_b is the burnt gas temperature *T_u is the unburnt mixture temperature. In terms of heat release parameter \alpha, it is given by :\beta = \frac \alpha For typical combustion phenomena, the value for Zel'dovich number lies in the range \beta\approx 8-20. Activation energy asymptotics Activation energy asy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grigory Barenblatt
Grigory Isaakovich Barenblatt (russian: Григо́рий Исаа́кович Баренблат; 10 July 1927 – 22 June 2018) was a Russian mathematician. Education Barenblatt graduated in 1950 from Moscow State University, Department of Mechanics and Mathematics. He received his Ph.D. in 1953 from Moscow State University under the supervision of A. N. Kolmogorov. Career and research Barenblatt also received a D.Sc. from Moscow State University in 1957. He was an emeritus Professor in Residence at the Department of Mathematics of the University of California, Berkeley and Mathematician at Department of Mathematics, Lawrence Berkeley National Laboratory. He was G. I. Taylor Professor of Fluid Mechanics at the University of Cambridge from 1992 to 1994 and he was Emeritus G. I. Taylor Professor of Fluid Mechanics. His areas of research were: # Fracture mechanics # The theory of fluid and gas flows in porous media # The mechanics of a non-classical deformable solids # Turbule ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rayleigh–Taylor Instability
The Rayleigh–Taylor instability, or RT instability (after Lord Rayleigh and G. I. Taylor), is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Drazin (2002) pp. 50–51. Examples include the behavior of water suspended above oil in the gravity of Earth, mushroom clouds like those from volcanic eruptions and atmospheric nuclear explosions, supernova explosions in which expanding core gas is accelerated into denser shell gas, instabilities in plasma fusion reactors and inertial confinement fusion. Water suspended atop oil is an everyday example of Rayleigh–Taylor instability, and it may be modeled by two completely plane-parallel layers of immiscible fluid, the denser fluid on top of the less dense one and both subject to the Earth's gravity. The equilibrium here is unstable to any perturbations or disturbances of the interface: if a parcel of heavier fluid is displaced downw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Darrieus–Landau Instability
The Darrieus–Landau instability or hydrodynamic instability is an instrinsic flame instability that occurs in premixed flames, caused by the density variation due to the thermal expansion of the gas produced by the combustion process. In simple terms, the stability inquires whether a steadily propagating plane sheet with a discontinuous jump in density is stable or not. It was predicted independently by Georges Jean Marie Darrieus and Lev Landau. The instability analysis behind the Darrieus–Landau instability considers a planar, premixed flame front subjected to very small perturbations. It is useful to think of this arrangement as one in which the unperturbed flame is stationary, with the reactants (fuel and oxidizer) directed towards the flame and perpendicular to it with a velocity u1, and the burnt gases leaving the flame also in a perpendicular way but with velocity u2. The analysis assumes that the flow is an incompressible flow, and that the perturbations are governed by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paul Clavin
Paul Clavin is a French scientist at Aix-Marseille University, working in the field of combustion and statistical mechanics. He is the founder of Institute for Research on Nonequilibrium Phenomena (IRPHE). Biography Clavin served as the chair of the Physical Mechanics at Institut Universitaire de France from 1993 to 2004. He received Ya.B. Zeldovich Gold Medal from The Combustion Institute in 2014 and a fellow of The Combustion Institute. A workshop titled ''Out-of-Equilibrium Dynamics'' was conducted in 2012 in honor of Clavin's 70th birthday. He is the recipient of Grand Prix award from French Academy of Sciences in 1998 and received Plumey award from Société Française de Physique in 1988. He was elected membre correspondant at the French Academy of sciences The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV of France, Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Premixed Flame
A premixed flame is a flame formed under certain conditions during the combustion of a premixed charge (also called pre-mixture) of fuel and oxidiser. Since the fuel and oxidiser—the key chemical reactants of combustion—are available throughout a homogeneous stoichiometric premixed charge, the combustion process once initiated sustains itself by way of its own heat release. The majority of the chemical transformation in such a combustion process occurs primarily in a thin interfacial region which separates the unburned and the burned gases. The premixed flame interface propagates through the mixture until the entire charge is depleted. The propagation speed of a premixed flame is known as the flame speed (or burning velocity) which depends on the convection-diffusion-reaction balance within the flame, i.e. on its inner chemical structure. The premixed flame is characterised as laminar or turbulent depending on the velocity distribution in the unburned pre-mixture (which provid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gregory Sivashinsky
Gregory I. Sivashinsky (also known as Grisha) is a professor at Tel Aviv University, working in the field of combustion and theoretical physics. Biography Sivashinsky was born in Moscow to Israel and Tatiana Sivashinsky. He is married to Terry Sivashinsky. He finished his master's degree at Moscow State University in 1967 and worked as a research assistant there until 1971. He emigrated to Israel in 1971. He was a pupil of Grigory Barenblatt and Yakov Borisovich Zel'dovich. He completed his PhD at Technion – Israel Institute of Technology in 1973 and worked as a lecturer there for two years. He joined Tel Aviv University in 1974 and settled there. He is the recipient of Ya.B. Zeldovich Gold Medal from The Combustion Institute and a fellow of The Combustion Institute. See also References External links * {{DEFAULTSORT:Sivashinsky, Gregory Fluid dynamicists 1945 births Living people Fellows of The Combustion Institute ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter.However, most of the universe's mass is not in the form of baryons or chemical elements. See dark matter and dark energy. Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds. For the most common isotope of hydrogen (symbol 1H) each atom has one proton, one electron, and no neutrons. In the early universe, the formation of protons, the nuclei of hydrogen, occurred during the first second after the Big Bang. The emergence of neutral hydrogen atoms throughout the universe occurre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
