The Experimental And Theory Research On Flame Instabilities Induced By Shock-Flame Interactions

As a part of a project "enhancement mechanism of focusing shock-flame interactions on deflagration-to-detonation transition", the experimental investigations, theoretical analysis and numerical simulations are carried out to study the flame instabilities induced by shock-flame interactions.Shock-flame interactions experiments are conducted in a horizontal shock tube with 9.4 m long, 32 mm inner diameters. A series of photographs are successfully obtained using a YA-16 high speed camera. The photographs display the flame's instability, distortion and breakup.The Rayleigh-Taylor and Kelvin-Helmholtz instabilities induced by small disturb in the two unmixed fluids interface are discussed, and the influences by fluids physics properties such as viscidity are also discussed by means of the established mathematical model. And five phases of instabilities development are introduced, especially, the nonlinearity process of the instabilities is analyzed.Based on the Navier-Stokes equations coupled with the chemical reaction terms and some relevant thermodynamic and kinetic data, the interaction between shock wave and flame is investigated numerically using modified Van Leer splitting scheme, flame instability and mechanism of vortex formation are discussed. The calculated results indicate that a bifurcated A. wave can be formed when the shock passes through the flame, and pre-induced shock transmission in the flame leads to the formation of Mach stem, followed by spheral shock wave. The Rayleigh-Taylor and Kelvin-Helmholtz instabilities occurred in the flame induced by shock wave lead to the flame distortion and breakup. The consequent distortion and enlargement of flame surfaces lead to substantial enhancement of the burning rate. The influences of the shock Mach number and initial mass percentage of premixed gas on the interface instabilities are different, the former dominates the enhancement of the flame distortion and enlargement -of flame surfaces, while the latter is contributed to the trend of deflagration to detonation transition.The experimental and calculated results are in good agreement.