ID#: 94
Abstract Title: Auto-Turbulizating Regimes of Gaseous Spherical Flames
Session Title: Flames
Session Date: 7/31/01
Session Start Time: 11:20 AM
Contributing Author: Kidin, N.I.
Organization: Institute For Problems In Mechanics
Country: Russia
Authors: Ya.A. Gostintsev, A.G.I stratov, N.I. Kidin, V.E. Fortov
Short Abstract: ÝÝÝ A spherically propagating flame is a unique object for experimental and theoretical study of the phenomena of spontaneous instability and auto- turbulization of flames formulated more than half a century ago and being actual up to now in accordance with at least two application problems à combustion in turbulent-flow and deflagration to detonation transition. It was experimentally established that hydrodynamical instability of propagating spherical flames results in the limiting self-similar turbulization mode with the time dependence ofÝ radius being 3/2. ÝÝÝ At the conditions of experiments essential effects have the floatingÝ of burning sphere in gravity field when the instability dependence decelerates and burning sphere transforms to thermic. The comparison of characteristic times of burning at the different regimes and floating times allows establishing the area where such influence is not essential in coordinates - flame radius- normal burning velocity; in this case the spontaneous turbulization process is realized completely and there is combustion with the same power time dependence ofÝ radius being the degree 3/2. ÝÝÝ The theoretical treatment allows constructing the most possible scenario of auto-turbulization of free spherical flames with the following space-time stages: development of hydrodynamical instability laminar-flames leading to the curving and fractalization of flame surface, its self- acceleration and turbulization of combustion zone formation of large scale vortex structures due to Taylor instability of the discontinuity surface between cold fresh mixture and hot products in the gravity field. ÝÝÝ The role of combustion heas two circumstances. At first, combustion causes and supports accelerating propagation surface that becomes the fractal with the degree 7/3. The same fractal degree has the flame in turbulent flow with rather large turbulence intensity. Secondly, turbulent energy dissipation at the limiting case of propagation appeared to be the constant value and to be determined via combustion parameters -Ý normal burning velocity in the forth power devided by viscosity. Estimations show that dissipation has the value of several percents of the kinetic energy growth in gaseous flow due to expansion of burning sphere.