Numerical Researches On The Interaction Between Shock Wave And Aluminum Droplet With Evaporation And Combustion

The interaction between shock wave and Aluminum(Al)droplet is a typical issue in the detonation of the thermobaric explosives(TBX),which involves many complex physical and chemical processes including compressible multiphase flow,liquid cavitation,evaporation and combustion.The research on this issue is not only of great help to understand the combustion and heat release mechanism of metal particles in TBX,but also of great value to the research of shock dynamics,multiphase flow and interfacial instability of condensed medium.Nowadays,the necessary research and profound understanding on the complex compressible gas-liquid multi-medium flow,especially with evaporation and combustion,are still scarce.Since the complexity of shock-Al droplet interaction bring considerable difficulties to experimental and theoretical researches,the numerical means become an efficient and economical option.Numerical methods have greatly promoted the development of research on the Al combustion,compressible multiphase flow,and shock-reactive gas interactions.It however still lacks effective numerical tools designed for this complex problem,namely,shock-Al droplet interaction.The main purpose of this thesis is to investigate the interaction between shock wave and a single Al droplet using a suitable numerical method constructed specifically for compressible gas-liquid multi-medium flow combustion.The main contents are as follows:1.Physical and chemical models are established to describe the present complex compressible gas/liquid flow,cavitation,evaporation,combustion,and condensation.On this basis,the numerical method on compressible gas-liquid multi-medium flow combustion is constructed.The double flux model coupling with fifth-order essentially non-oscillatory and third-order Runge-Kutta scheme are employed to solve the unsteady chemical reaction flow.The simulation of gas/liquid flow with evaporation and combustion using the level-set method and real Ghost Fluid Method are conducted.Typical one-dimensional flow and combustion test problems are performed to demonstrate the reliability and accuracy of the constructed numerical method.2.Shock-bubble interaction problems are simulated and analyzed using the present numerical method so that each computation module of the method was tested.First,the numerical simulation of the interaction between a planar shock wave and an elliptic gas column are carried out.Comparisons between the experimental,the theoretical and the current simulation results confirm the reliability of the gas phase multi-medium flow module of the constructed numerical method.The scale effects of the elliptical structure on the evolution of wave system and mixing are analyzed.The numerical simulations of the interaction between shock wave and reactive heavy bubble are conducted.The phenomenon of shock convergence and ignition are investigated.The comparison between the experimental data and the current simulation indicates the good reliability of the gas phase multi-medium flow and combustion module.Finally,the interaction between shock wave and water column is simulated.The evolution of wave system,cavitation,and their relationship are discussed.The comparison of wave system with experimental images verifies the good reliability of the current gas-liquid two-phase coupling method.3.Numerical researches on the interaction between shock wave and Al droplets without evaporation and combustion are carried out.The wave pattern,cavitation phenomenon,Al droplet morphology,and the flowfield establishment after the shock waves impacting are analyzed in detail.The wave system evolution,the formation and collapse of cavitation volume,and the Al droplet deformation caused by different shock intensity are captured.The droplet deformation belongs to the flattening/stripping mode.The unsteady flow in the gas region is mainly dominated by the flow separation and interface deformation.4.The interaction between shock wave and Al droplet with evaporation and combustion is simulated using the constructed numerical method.The numerical results clearly show the evaporation and combustion process of Al droplet impacted by the incident shock wave.The comparisons with the results of steady evaporation theory show that the incident shock wave is found to enhance the droplet surface convection and speed up the Al vapor leaving the Al droplet surface,which is benefit for the droplet evaporation.On the other hand,the pressure near the Al droplet surface increases due to the incident shock hitting,which suppresses the droplet evaporation.With the transportion of convection,evaporation and combustion products on the Al droplet surface are continuously transported downstream,and the combustion mainly occurs on the Al droplet surface and in the downstream vortex region.Moreover,the simulation results also show that combustion can promote the evaporation of Al droplet.In summary,a numerical method designed for simulating compressible gas-liquid multi-medium flow combustion is established in this study,which can be used not only to reproduce the compressible gas,liquid and gas/liquid high-speed flow,but can also be used to dig into the physical and chemical processes including phase change and combustion.On the other hand,the interaction between shock wave and Al droplet are preliminarily investigated using the constructed numerical method in this paper.The evaporation and combustion phenomena of Al droplet under shock impact are obtained and the influence of shock wave on evaporation and combustion of Al droplet are analyzed.These works can be used as the foundation of further researches.