Numerical Simulation Method And Its Application Of Explosion Flow Field Involving Moving Interface

Explosion flow field of condensed explosives widely exists in the field of defense and economic contribution, there are three forms of moving interface in typical explosion flow field: interface between explosives/detonation products and air; moving boundary between air and movable objects; interface between detonation products/air and water. These three moving interface problems are numerically investigated in this thesis.A numerical simulation algorithm and software for multi-species flow using dynamic hybrid grids is developed, which is the basis of this thesis's research. Integral governing equations in arbitrary Lagrangian Eulerian(ALE) form are solved on dynamic hybrid grid in this software, in which AUSM+-up and HLLC schemes combined with Venkatakrishnan's limiter are used in spatial discretization and multi-stage Runge-Kutta scheme in temporal discretization. The ultimate method has 2-order accuracy both in spatial and temporal direction, and it could hold one/two/three dimensional and spherical/cylindrical/axial symmetry problems. This algorithm is free of characteristic matrix decomposition, accordingly it's suitable for singe/multi-species flows with any form of state equations. The mesh movement strategy combined of deformation and remeshing is used, and a kind of "virtual mesh ventilation method" is used to resolve the problem when multi bodies move from contact to separation and the mesh topology changes.Aimed at the interface between explosive/detonation product and air, a new mixed fluid model of explosive, detonation product and air is proposed within fluid-mixture type algorithm. In this model, JWL and perfect gas state equations are used for explosive/products and air separately, isobaric assumption is made between solid phase(explosives) and gas phase(detonation products and air), and iso-temperature assumption and partial pressure law is used within gas phases. The state equations of mixed fluid in this model can be solved without iteration, so a high computation efficiency is gained. Combined with growth and ignition reaction model, complex flow problems involving moving interface between explosive/detonation products and air can be effectively solved in this model. Detonation of spherical TNT explosives in air is simulated, fluid structure and interface are captured clearly, and the near-field peak overpressure accords well with experimental results. The spread of detonation wave in driven tube is researched, a typical two dimensional detonation wave structure in finite diameter explosives is achieved, and the time history of overpressure on the side and bottom of the driven tube is gained, which affords an important reference to the design of driven tube. Influence of different distribution forms of driven tubes and length of extended section to the performance of shock tube is also analyzed.Aimed at the moving boundary problems between fluid and movable objects, dynamic grid method is used to track moving boundaries, the ALE form of governing equations is derived, and the geometrical conservation law(GCL) is studied. The reason of introducing computation errors when violating GCL is analyzed, and a new volume correction method is proposed, which could eliminate computation errors arised from moving grid. Coupled multi-body dynamics with fluid calculation, a unsteady computation method for the flow field of multi-body with interactional forces is established. Integrated with grid deforming, remeshing, multi-body dynamics and virtual mesh ventilation method, the embedded booster's separation process is simulated, and it's found that pressure oscillation will occur in the inlet and combustor after the open of inlet cover and it's hard to attenuate. When the booster's head passes through the forebody's throat, normal forces on the booster oscillate severely, which may influence the safety of separation. The movement of a truck driven by blast wave is simulated, which validates the simulation ability to the explosion problems involving moving objects.Aimed at the gas-water interface problem in underwater explosion, ALE formulation is used to trace fluid interface, and the modified ghost fluid method is introduced to the interface computation. Through the calculation of several Riemann problems such as gas-gas, gas-water, detonation product-water Riemann problems, this modified ALE method is proved of smaller interface dissipation and higher computation accuracy than Euler and original ALE method. In the simulation of one and two dimensional underwater explosion, interactions between shock wave and gas-water interface is captured, and the maximum radius and first period of air bubble accord well with experimental results. The bubble's interface is clear, without nonphysical spurious oscillations.Finally, a numerical computation software of simulating air blast and underwater explosion is established in this thesis, it could be used to compute detonation of condensed explosives, near-field blast, interaction of blast wave and rigid body and handle multi-fluid interface including gas-gas, gas-solid, gas-liquid interfaces. This software is accuracy, robust and universal, it has been applied in practical engineering problems.