Numerical Simulation Of Flame Acceleration And Deflagration To Detonation Transition Of Combustible Gas

The explosion process of combustible gas includes ignition,flame acceleration and deflagration to detonation transition.The physical mechanisms of different stages of flame acceleration are different.Understanding the mechanism of deflagration to detonation transition plays an important role in the prevention and control of gas explosions.Because of the high cost and danger of gas explosion experiment,one of the main research methods is numerical simulation by performance computer.For the physical process of combustion and detonation of active gas,researches of ignition and combustion and detonation process of hydrogen in air and oxygen are simulated by direct numerical simulation code.The followings are description of the main research content and innovative achievements of this paper.(1)Completing the derivation of physical model describing flame propagation of the multicomponent compressible Navier-Stokes equations.Based on the finite difference method,the convection item is discrete by 5th order WENO scheme,and the viscosity item and diffusion item are discrete by 6th order central difference scheme,while time propagation is calculated by 3th order Runge-Kutta format.Adding the 1step model and detail chemical model into physical model,and a large scale high precision parallel code is programmed to simulate flame propagation.The accuracy and convergence of code is confirmed by comparison of laminar flame speed and adiabatic flame temperature between numerical results and experimental data.(2)The effects of different chemical reaction models on the ignition and flame acceleration and detonation process are compared in hydrogen-air mixture,including laminar flame speed,adiabatic flame temperature and ignition delay time in various initial pressure.It is found that 1step model can not correctly reflect the ignition delay time and laminar flame speed,while the results of detail chemical model match to the experimental values.The reason is that parameters of 1step model are calculated by physical parameters in normal pressure,so it can only simulate the corresponding process.Besides,the 1step model do not have the endothermic reaction stage,therefore,the ignition delay time is several orders of magnitude lower than results of detail chemical model because of the longer exothermic stage.(3)The deflagration to detonation transition of hydrogen air mixture is analysed by one dimensional temperature gradient problem.The time and situation of coupling between pressure wave and spontaneous wave is obviously different,because the variety of exothermic reaction of 1step model and detail chemical model leads up to different size of hot pot required for stable detonation.Due to the shorter ignition delay time of 1step model,the velocity of spontaneous wave is faster,and the size of hot spot for stable detonation is shorter than detail chemical model.The calculation results show that 1step model can not correctly simulate ignition and deflagration to detonation transition process.On the other hand,the necessary numerical dissipation is required to maintain stable detonation and convergence of calculation in the temperature gradient model,where the influences of numerical viscosity factor and numerical dissipation on production of detonation are analysed.(4)The flame acceleration and deflagration to detonation transition of hydrogen oxygen mixture in thin tube is simulated with detail chemical model and HWENO format increasing the calculation speed.The development of flame velocity with time is analysed.The pressure and temperature curve along with middle line of tube are plotted to find that the key point of deflagration to detonation transition is local hot spot in the front of flame reaching to detonation.Besides,the influence of numerical oscillation on the shape of flame surface is discussed.