arXiv subjects

Leonid Kagan

Publications and source records attributed to Leonid Kagan.

7 recordsLinked to original sources

arXiv2026

On initiation of detonation in large fuel-air clouds

The proposed study is motivated by experimental evidence, dating back to 1985, demonstrating the possibility of deflagration-to-detonation transition (DDT) in a fuel-air cloud. The detonation is initiated by a flame jet developed in a thin open-ended tube inserted into the cloud. Despite the experimental data, a first-principle understanding of the mechanism controlling the transition is still missing. The current research is aimed at resolution of this issue through a simple 2D formulation involving minimum physical ingredients.

physics.flu-dyn↗

arXiv2024

On disintegration of lean hydrogen flames in narrow gaps

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front are interpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, size, heat losses and Lewis numbers at which the self-drifting flamelets may exist.

physics.flu-dyn↗

arXiv2024

On dynamics of gasless combustion in slowly varying periodic media: periodic fronts, their stability and propagation-extinction-diffusion-reignition pattern

In this paper we consider a classical model of gasless combustion in a one dimensional formulation under the assumption of ignition temperature kinetics. We study the propagation of flame fronts in this model when the initial distribution of the solid fuel is a spatially periodic function that varies on a large scale. It is shown that in certain parametric regimes the model supports periodic traveling fronts. An accurate asymptotic formula for the velocity of the flame front is derived and studied. The stability of periodic fronts is also explored, and a critical condition in terms of parameters of the problem is derived. It is also shown that the instability of periodic fronts, in a certain parametric regimes, results in a propagation-extinction-diffusion-reignition pattern which is studied numerically.

nlin.PS↗

arXiv2023

Modeling of 2D self-drifting flame-balls in Hele-Shaw cells

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front a reinterpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists.

physics.flu-dyn↗

arXiv2021

Modeling of thermonuclear fusion flames : transition to detonation

The paper is concerned with identification of the key mechanisms controlling deflagration-to-detonation transition in stellar medium. The issue of thermal runaway triggered by positive feedback between the advancing flame and the flame-driven precompression is discussed in the framework of a one-dimensional flame-folding model. The paper is an extension of the authors' previous study dealing with the non-stoichiometric fusion, $fuel \to products$, kinetics (Phys.Rev.E, 103(2021)) over physically more relevant, $fuel+fuel \to products$, kinetics. Despite this change the runaway effect endures. The transition occurs prior to merging of the flame with the flame-supported precursor shock, i.e. the pretransition flame does not reach the threshold of Chapman-Jouguet deflagration.

physics.flu-dyn↗

arXiv2019

Deflagration-to-detonation transition in an unconfined space: II. Expanding hydrogen-oxygen flames

The problem of deflagration-to-detonation transition in an unconfined environment is revisited. With a freely expanding self-accelerating hydrogen-oxygen flame as an example, it is shown that deflagration-to-detonation transition is indeed possible provided the flame is large enough. The transition occurs prior to merging of the flame with the flame-supported precursor shock. The pre-transition flame does not reach the threshold of CJ-deflagration. Numerical simulations employed are based on the recently developed pseudo-spectral method with time and space adaptation.

physics.flu-dyn↗

arXiv2017

Strongly nonlinear asymptotic model of cellular instabilities in premixed flames with stepwise ignition temperature kinetics

In this paper we consider ignition-temperature, first-order reaction model of thermo-diffusive combustion that describes dynamics of thick flames arising in a theory of combustion of hydrogen-oxygen and ethylene-oxygen mixtures. These flames often assume the shape of propagating curved interfaces that correspond to level sets of constant temperature. We derive a fully nonlinear equation that governs dynamics of these level sets under a single assumption of small curvature. We study this equation for various asymptotic parameter regimes and discuss the ranges of validity of the corresponding simplified models. Our theoretical findings are supported by numerical simulations.

nlin.CD↗