Numerical Investigation of Shock-Wave Load Attenuation by Barriers

Introduction

Major resources have being invested in the last two decades in an effort to find and utilize efficient protective technologies against terror attacks. Most of the resources have been directed to civil and military structures and protection of civil population from explosion induced blast wave loads. Explosive devices exploding inside a bus or an airplane and bombs exploding in the entrance of military bunkers are examples in which a blast wave will be initiated, propagating in a corridor-type structure, causing injuries to human and damage to structures and equipment. Barriers of different sizes and shapes inside a tunnel can cause the incident shock wave to diffract, leaving behind it a complex flow field that changes the impact on the target wall at the end of the tunnel. Several ways to reduce shock-wave loads propagating inside tunnels are based on forcing abrupt changes in the tunnel as in a bent duct [1], passing through particle suspensions [2], or passing through perforated tube walls [3]. In a pioneering experimental work by Dosanjh [4], shadowgraph photography was used to investigate the wave pattern that resulted from the head-on collision of an incident shock wave with a grid like obstacle. Britan et al. [5] investigated the attenuation of a shock wave by grid and orifice plates. In their study, the interaction of shock waves (1.35 < M _s  < 1.7) with porous barriers of different geometries and porosities was examined. The barrier inside the test section of a shock tube initiated the development of a complex wave pattern following the interaction between the incident shock wave and the barrier. They proposed a one-dimensional (1D), inviscid flow model for predicting the flow that results from the collision of an incident shock wave with the barrier. They showed that the over-pressure acting on an endwall protected by a barrier reduces almost linearly with increasing distance between the end-wall and the barrier. Ohtomo et al. [6] investigated the attenuation of a shock wave propagating through arrayed baffle plates. Two baffle plate arrays, oblique and staggered, were tested. In both arrays, the effect of baffle plate arrangements on the shock attenuation was significant. They found that shock attenuation occurs quicker over the oblique one than over the staggered one. This trend was accentuated with increased shock Mach number. The main objective of the present study is to better understand the physical elements governing the induced flow behind the shock wave propagating through a barrier, and optimizing the barrier geometry for better shock wave attenuation. To carry out the overall research plan, a combined (numerical and experimental) approach has been offered: in the first stage, an experimental study was carrying out to check the feasibility of barrier geometry effect on shock wave attenuation. In the second stage, a numerical investigation is being carried out, using experiments to calibrate a reliable numerical code. In the third stage, a comprehensive study will be performed, investigating the physical elements governing the induced flow behind the shock wave while implementing a barrier geometry optimization. This stage will include local experiments to support the numerical findings. The first and second stages of a broader research of shock wave and rigid barrier interaction are presented.