Study Of The Mechanism On Flame Propagati,on And Deflagration To Detonation Transition With Fluidic Obstacle

In the field of detonative propulsion,the fluidic obstacle has been a novel short-distance and low-loss detonation initiation device.It is used to accelerate the flame in detonation chamber and shorten the DDT(deflagration to detonation transition)distance and time.In this paper,experiments and numerical simulations are conducted to study the effect and mechanism of fluidic obstacle on flame acceleration and DDT process.The experimental system for detonation test is built to investigate the differences of flame propagation processes in smooth duct,duct with solid obstacle and duct with fluidic obstacle,respectively.The results show that the fluidic obstacle with the same concentration as the mainstream can shorten the ignition delay time,enhance the combustion intensity at the initial stage,and induce the self-ignition in the boundary layer downstream.The fluidic obstacle has a better influence on the flame acceleration compared with solid obstacle case,which can shorten the DDT distance by 50.2%and the DDT time by 57.6%compared with the case in smooth duct.The block-structured mesh adaptive refinement program AMROC is used to simulate the flame acceleration and DDT process in duct with fluidic obstacle.The two-dimensional viscid unsteady reactive Navier-Stokes equations with the multi-step chemical reaction model are used as the governing equations for the simulations.The results show that the fluidic obstacle producing compression wave,which mo'ves upstream and influence the instability of the initial flame.The fluidic obstacle also interact with the mainstream and strengthen the turbulence of the flow field.The mushroom vortices induced by the fluidic obstacle are pushed by the mainstream,which form a long disturbance zone along the propagation direction.The interaction between the flame and these vortices change the flame front shape.The entrained and distorted flame increases the area of the reaction front and the local heat release rate increases.Compared with solid obstacle,fluidic obstacle can induce more vortices in the unburned zone.In these cases,obstacle composed by reactive premixed gas has the best influence on flame acceleration,and the DDT distance decreases by 41.6%as well as the DDT time decreases 42.2%compared to case in smooth duct.The fluidic obstacle composed by oxygen or inert gas will reduce the local concentration of free radicals,resulting in less flame acceleration.In addition,the effects of different fluidic obstacle arrangements on flame acceleration and DDT process are studied and the different mechanisms are analyzed from the perspective of flame-vortex interaction.Finally,the effects of initial parameters of fluidic obstacle,such as initial stagnation temperature,initial total pressure and injection nozzle width,on the DDT process are investigated by numerical simulations.The results show that with the increase of initial temperature,the DDT distance and time increase first and then decrease.With the increase of initial pressure and nozzle width,the DDT distance and time decrease monotonically.