Direct Numerical Investigation On Simulation Of Flame Acceleration And Transition From Deflagration To Detonation With Detailed Chemical Kinetics Model

With modern industrial production scale upsized,production intensived,production process complicated and highly automated,the direct and indirect losses and social harmfulness caused by the combustible gas explosion accident increase rapidly,the prevention and control of combustible gas explosion accident have an urgent demand for the research of gas explosion mechanism.Besides,new propulsion technology research with the application of detonation propulsion concept,has becoming the latest improving direction of research work on aircraft propulsion technology.The method to Produce stable transmission detonation wave by deflagration to detonation transition has a strong controllability,has great significance for the research of new aircraft propulsion technology.Therefore,the study of flame acceleration and deflagration to detonation process is very important to the flammable and explosive gas explosion disasters preventionas well as detonation propulsion.This paper has the following main research and innovation points :(1)Based on 6 species7 steps detailed chemical kineticsmodel of hydrogen and oxygen,the multi-species compressible reactive Navier-Stokes equations based on three-dimensional cartesian coordinates and considering viscous diffusion and heat conduction are established.Using fifth-order weighted essentially nonoscillatory(WENO)shemes in spatial discretization,using sixth-order central-difference schemes in viscous terms discretization,and using third-order Additive Runge-Kutta schemes in time discretization.Multidimensional highsolution parallel programs are developed,and the Multidimensional numerical simulation of flame acceleration and deflagration to detonation processin the microscale smooth straight tubes is carried out.the numerical simulation of one dimensional steady laminar flame propagation process is carried out by using the 1D high-solution program and the influence of grid size on the numerical simulation results is studied.The characteristic parameters of different grid size of one dimensional steady laminar flame propagation process are given,and the convergence and accuracy of the program is verified.(2)A 2D direct numerical simulation of the deflagration to detonation Process in microscale tube is carried out,and the whole process from weak ignition,flame acceleration and deflagration to detonation of Hydrogen-oxygen premixed gases in the micro-scale tube.the reasults show that high density area in front of the flame occurs due to the pressure waves superpose and form discontinuity,at the same time the flame heats the unreacted gas ahead of the flame.so when the flame propagate into the high-pressure and high-density preheating zone,the heat release rate of the reaction increase,result in the flame speed growth accelerates.the formation of such kind of temperature related positive feedback mechanism makes the flame speed increase sharply.(3)With the high-solution large-scale parallel program,the 3D numerical simulation of the whole DDT process of Hydrogen-oxygen premixed gases in the micro-scale tube is studied.By analysising the evolution of the characteristic parameters during the process of flame propagation,it is found that the whole process can be divided into th following six stages,the flame instability stage,the laminar flame acceleration stage,the pressure wave in front of flame formation stage,the gradient reaction mechanism formation stage and the detonation wave propagation stage,the flame front structure and characteristics of flow field characteristic parameterfor all six stages are studied.(4)By 2D and 3D numerical simulation,it is found that micro-scale bending detonation caused by the viscous effect could maintain detonation wave continuous propagation without the triple-shock-wave configuration,and determine the detonation wave propagation mode under 3D 0.24 mm tube condition with ambient temperature and pressure and weak ignition is ” galloping mode”.Found that the detonation wave front in the micro-scale tube is weak bending front,the bending front interactions with the wall enables the detonation wave to selfsustain,the viscous effect of wall has a positive feedback effect on detonation self-sustain.At the same time,it is also found that the viscous effect of wall will cause the momentum loss of flame,leading to detonation velocity loss.(5)The 2D and 3D direct numerical simulation of the deflagration to detonation Process with different tube widths is carried out,and found that the flame acceleration rate is significantly negative correlation with the tube widths,the DDT time and the DDT distance is significantly positively correlation with the tube widths.with the increasing of the tube width,three stages of the process of DDT divided by the flame acceleration rate become more obvious.When the channel is 0.24 mm,no obvious blowback phenomenon was observed,and for the several modes with larger width,obvious blowback phenomenon are observed.(6)By studyign the effect of the concentration of inert gas(nitrogen)on DDT process under 3D tube,it is found that with the increasing volume concentration of inert gas(nitrogen),turbulent flame front in the process of flame acceleration becomes long-narrow,thickness of the boundary layer between the flame front and the pipe wall increasing,the energy releasing rate of premixed flame reaction reducing,molecular motion intensity gradually weakening in the reaction zone and reaction intensity decreasing.with the increase of nitrogen concentration,the overdriven detonation wave velocity approximate linear declinesand the DDT time as well as the DDTdistance approximate exponential accelerates.The three-dimensional numerical simulation results reveal that the nitrogen has a certain inhibitory effect to the hydrogen-oxygen premixed gas explosion.