Investigation On Detonation Initiation And Propagation In Supersonic Flows

In order to get a better unsderstanding on detonation-based ramjet,the phenomenon of detonation initiation and propagation in supersonic flows were taken into account.The hot jet initiation in supersonic combustible mixtures and the irregular detonation propagation were investigated with the high-precision adaptive mesh numerical simulation,experimental observation and theoretical analysis.In order to understand the mechanism of the hot jet detonation in the supersonic premixed gas under the influence of the boundary layer,the modified adaptive mesh refinement program AMROC were used to simulate the hot jet initiation in the straight channel.When only considered the influence of single boundary layer,the jet initiation process can be divided into three stages: the interaction between the hot jet induced bow shock and the boundary layer,the detonation initiation,and the development of the initiated detonation front.The hot jet initiation mechanism is controlled by the interaction between the bow shock and the boundary layer.Shock-induced combustion is formed behind the interaction region.And the combustion surface is coupled with the shock surface to form the partial detonation.There exists a Mach number range to achieve the hot jet initiation,which is smaller than the Mach number range of the previous Euler research.The separation zone before the hot jet on the upper wall has a great influence on the shape of the bow shock.When the separation zone is large enough,the hot jet cannot initiate the premixed gas.The initiation process of hot jet induced bow shock reflection is simplified to the initiation process of the slope induced oblique shock reflection.It is found that there are two mechanisms for the initiation process of the oblique shock reflection on the wall surface: the regular reflection shock induced detonation and the Mach reflection induced detonation.The initiation mechanism between oblique shock waves interaction is more complicated,and the regular intersection induced detonation combustion mechanism dominates the initiationprocess.Under the influence of the boundary layer,the hot jet initiaiton experiments in supersonic premixed gas found that when the jet intensity is large,the hot jet initiation in supersonic premixed flow is mainly caused by the interaction bwtween the jet-induced bow shock and the separation shock.When the jet intensity is weak,the separation zone before the jet has a great influence on the detonation initiation,and the interaction between separation shocks dominate the initiaiton process.The flow field can only form "<" shaped two separate shock waves induced combustion structure.The simulations of irregular detonation in supersonic flows were carried out.It is found that there are four types of triple-wave structure on the irregular detonation wave front,two types of unburned gas pockets,and three kinds of shock surface.The structure of the irregular detonation wave surface is complex,the length of the induced zone varies greatly,and the simulation requires high grid accuracy.Grid accuracy has a large impact on the simulation results of irregular detonation.When the activation energy is low,the physical viscosity has a limited influence on the regular detonation wavefront.When the activation energy is increased,the physical viscosity has a significant influence on the irregular detonation wavefront,and the vortex structure of the wavefront is seriously dissipated by the physical viscosity.A large-scale three-dimensional detonation initiation simulation via a hot jet was carried out.Research found that the focusing effect of the wall surface of three-dimensional circular tube promotes the detonation initiation.When a single hot jet is used,the detonation occurs on the lower wall surface,and when the colliding hot jets were used,the detonation occurs on side wall surfaces.In the square tube,the hot jet initiation occurs at the corners of the tube wall,and the initiated detonation front has a superposition of diagonal mode and rectangular mode.