Biomedical subjects

Vitaly Bychkov

Publications and source records attributed to Vitaly Bychkov.

5 recordsLinked to original sources

PubMed2006

Violent folding of a flame front in a flame-acoustic resonance.

The first direct numerical simulations of violent flame folding because of the flame-acoustic resonance are performed. Flame propagates in a tube from an open end to a closed one. Acoustic amplitude becomes extremely large when the acoustic mode between the flame and the closed tube end comes in resonance with intrinsic flame oscillations. The acoustic oscillations produce an effective acceleration field at the flame front leading to a strong Rayleigh-Taylor instability during every second half period of the oscillations. The Rayleigh-Taylor instability makes the flame front strongly corrugated with elongated jets of heavy fuel mixture penetrating the burnt gas and even with pockets of unburned matter separated from the flame front.

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PubMed2006

Explosion triggering by an accelerating flame.

The analytical theory of explosion triggering by an accelerating flame is developed. The theory describes the structure of a one-dimensional isentropic compression wave pushed by the flame front. The condition of explosion in the gas mixture ahead of the flame front is derived; the instant of the explosion is determined provided that a mechanism of chemical kinetics is known. As an example, it is demonstrated how the problem is solved in the case of a single reaction of Arrhenius type, controlling combustion both inside the flame front and ahead of the flame. The model of an Arrhenius reaction with a cutoff temperature is also considered. The limitations of the theory due to the shock formation in the compression wave are found. Comparison of the theoretical results to the previous numerical simulations shows good agreement.

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PubMed2005

Theory and modeling of accelerating flames in tubes.

The analytical theory of premixed laminar flames accelerating in tubes is developed, which is an important part of the fundamental problem of flame transition to detonation. According to the theory, flames with realistically large density drop at the front accelerate exponentially from a closed end of a tube with nonslip at the walls. The acceleration is unlimited in time; it may go on until flame triggers detonation. The analytical formulas for the acceleration rate, for the flame shape and the velocity profile in the flow pushed by the flame are obtained. The theory is validated by extensive numerical simulations. The numerical simulations are performed for the complete set of hydrodynamic combustion equations including thermal conduction, viscosity, diffusion, and chemical kinetics. The theoretical predictions are in a good agreement with the numerical results. It is also shown how the developed theory can be used to understand acceleration of turbulent flames.

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PubMed2003

Importance of the Darrieus-Landau instability for strongly corrugated turbulent flames.

The renormalization ideas of self-similar dynamics of a strongly turbulent flame front are applied to the case of a flame with realistically large thermal expansion of the burning matter. In that case a flame front is corrugated both by the external turbulence and by the intrinsic flame instability (the Darrieus-Landau instability). The analytical formulas for the velocity of flame propagation are obtained. It is demonstrated that the flame instability is of principal importance when the maximal hydrodynamic length scale is much larger than the cutoff wavelength of the instability, provided the turbulent intensity is not too high.

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PubMed2003

Coordinate-free description of corrugated flames with realistic density drop at the front.

The complete set of hydrodynamic equations for a corrugated flame front is reduced to a system of coordinate-free equations at the front using the fact that the vorticity effects remain relatively weak even for corrugated flames. It is demonstrated how small but finite flame thickness may be taken into account in the equations. Similar equations are obtained for turbulent burning in the flamelet regime. The equations for a turbulent corrugated flame are consistent with the Taylor hypothesis of "stationary" external turbulence.

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