On the applicability of Chapman-Jouguet theory for the determination of detonation velocity in heterogeneous explosive system

 

 

报告人:  Hoi Dick Ng

      Concordia University

 

 

时间：2016年6月21日(周二)上午9:30

 

地点：中国科学院力学研究所1号楼312会议室

 

报告摘要：

For more than a century, the Chapman-Jouguet (CJ) criterion has been well accepted and used for the determination of detonation velocity of homogenous explosives such as gaseous combustible mixtures. The CJ criterion is a thermodynamic condition that gives a unique solution of the one-dimensional conservation equations with the Rayleigh line tangent to the equilibrium Hugoniot curve. The steady velocity is purely determined by the energetics of the reactive system. Recently, there is a growing interest in studying detonation dynamics in heterogeneous mixtures, such as condensed-phase explosives. The heterogeneity of the reactive medium resulting in localized explosion centers or discrete “hot spots” can influence the dynamics of the detonation propagation. Whether the CJ model originally derived for a uniform medium provides a suitable condition to determine detonation velocities in heterogeneous energetic media is the focus of this research.

The applicability of the Chapman-Jouguet (CJ) criterion is tested computationally here for heterogeneous explosive media using a simple detonation analog based on the reactive Burgers’ equation and the ideal detonation model using the reactive Euler’s equations with single-step Arrhenius kinetics in both one- and two-dimension. In all cases, the heterogeneity of the explosive media is mimicked using a discrete energy source approach. The reactive medium is spatially discretized by concentrating the reactant into regions and point-like sources separated by inert gaps. The average wave speeds resulting from different test scenarios and simulations performed in this study will be examined. The presence of the highly discrete reactive layerswhere the process of heat release is completed before reaching flow equilibrium, and how naturally-evolved and heterogeneity-induced wave irregularities might be a mechanism of thermalization which enhances the flow’s ability to reach an equilibrium state resulting in a propagation speed closer to the CJ velocity, will be discussed. These simple simulations have implications for whether the CJ criterion is valid to predict the detonation velocity in heterogeneous explosive media based on purely thermodynamics consideration using the overall energy release of the reactive medium.

 

报告人简介：

Hoi Dick Ng, 吳凱廸, is an associate professor at Concordia University, Montreal, Canada. He received his Bachelors, Masters and PhD in Mechanical Engineering all from McGill University, Canada in 1999, 2001 and 2005, respectively. Prior to joining Concordia, he worked as a NSERC post-doctoral fellow at Princeton University, USA and at the University of Cambridge, UK. He is currently a Tier-II Concordia University Research Chair in applied combustion and fuels, and a fellow of the Canadian Society for Mechanical Engineering (CSME). He is a recipient of the Petro-Canada Young Innovators Award, the CSME I.W. Smith Award for outstanding achievement of young engineer in mechanical engineering and two times the Milton van Dyke Award from the APS DFD at the annual Gallery of Fluid Motion. He has been awarded this year the Chinese Academy of Sciences (CAS) President's International Fellowship Initiative (PIFI) for Visiting Scientists. His research lies in the area of chemically reacting and unsteady fluid dynamics, and detonation phenomenon in particular.