High Resolution Numerical Computational Methods And Simulation Of Condensed Explosives Detonation

High resolution numerical simulation of condensed explosives detonation has important theoretical values and application prospects in many aspects,such as the safety of the explosive charge,the reliability of the weapon,and so on.In the present dissertation,benefited from investigating systemly the important achievements and current research status with the intimate connection to this field at home and abroad,the high resolution numerical algorithm was presented to deeply investigate a series of the condensed explosive detonation phenomena,which commonly contains multi-stage development,multi-medium interaction and multi-scale coupling in the process of explosives initiation,detonation formation and its propagation inside the intricate channel.The main contributions of this dissertation are listed as follows:(1)Based on the specific characteristics of condensed explosives corresponding to each stages from initiation to the steady detonation,the reactive flow Euler governing equation,elastic-plastic governing equation with the simplified elementary reactive model and two-phase flow governing equation derived from the BN model for describing detonation process were established,respectively.Reactive flow Euler equations including phenomenological reactive model has the highly effective advantage in simulating shock to detonation transition,corner diffraction and shaped effect of condensed explosives.As to the second governing equations,due to introduce simplified elementary reactive model,it can be utilized to investigate the micro-scale hotspot formation and its evolution mechanism.The two-phase governing equations with BN model can be used to analyze the influence of the ignition temperature,temperature gradient,porosity,particle size on explosive combustion to detonation transition.(2)Solving the partial derivative of the pressure term on the conserved quantity in the mixed reaction zone of condensed phase explosives was presented.The mixed reaction zone usually includes both of solid explosives and gas product and each component always changes with time elapse,which causes that the state of equation of the mixture can not be given by an explicit formulation throught coupling the equations of state of both components.In this dissertation,the JWL equation of state was regarded as an example to construct an equation system in the chemical reaction zone,in which the unknown quantities are set to derivatives of the specific volume with respect to conserved quantities.Then chain rule was used to obtain the pressure expression based on independent conservative partial derivatives at any instant.Thus,the characteristic space transformation in the three regions,i.e.,the unreacted explosive,the completed reacted product and the mixed reaction zone can be implemented successfully when discreting the governing equations in space with high order WENO scheme.(3)Combining the Grüneisen and stiff-gas equations of state with the double shock approximation theory,the Riemann solver for explosive and air interface was established which can offer the pressure,velocity at the interface and the densities on both sides.The local Level Set method also was developed for tracking interface evolution according to the strong discontinuity nature of condensed explosives detonation front.The velocity field close to the moving interface was modified by Riemann solution,which effectively avoids the error caused by velocity discontinuity when solves the interface position.Based on MPI,constructing enclosed type parallel module realized the data bidirectional communication between the current arbitrary processor and all adjacent processors,which satisfies the special requirements of local Riemann problem in the RGFM method.With the aid of the proposed enclosed parallel method,large-scale parallel computation with 3D RGFM method was performed.(4)Based on the model and computing method mentioned above,choosing the high evolution WENO(Weighted Essentially Non-Oscillatory)scheme for the spatial discretization of governing equations in alliance with TVD Runge-Kutta(Total Variation Diminishing Runge-Kutta)for time discretization,the high order numerical code of condensed explosive detonation was developed.(5)Used the propagation,the corresponding simulations and investigations of shock to detonation transition,micro-scale hotspot formation and thermal initiation were realized.The propagating process of the condensed explosive detonation wave through complex channel was executed.The corner-turning effect,sharped effect and cavity collapse due to detonation wave compression also were simulated.The numerical results obtained were compared with that finished numerically and experimentally in the available references,which further validates the reliability of the self-developed high resolution code.