Numerical Investigation of Shock Wave Attenuation by Geometrical Means: Double Barrier Configuration

Abstract

Due to the increase in global terror threats, many resources are being invested in efforts to find and utilize efficient protective means and technologies against blast waves induced by conventional and nonconventional weapons. Bombs exploding in the entrance of military underground bunkers initiate a blast wave that propagates in a corridor-type structure causing injuries to human and damage both to the structures and the equipment. Rigid barriers of different geometries inside a tunnel can cause the blast wave to diffract and attenuate, leaving behind it a complex flow field that changes the impact on the target downstream of the barrier. In our earlier phase of the research that dealt with a single barrier configuration, it was shown that the opening ratio (i.e., the cross section that is open to the flow divided by the total cross section of the tunnel) is the most dominant parameter in attenuating the shock wave. Additionally, it was found that when the opening ratio was fixed at 0.375, the barrier inclination angle was significantly more effective than the barrier width in attenuating the shock wave. The present phase of the research focuses on the dependence of the shock wave attenuation on a double barrier configuration, while keeping the opening ratio fixed at 0.375. The methodology is a numerical approach that has been validated by experimental results. The experiments were conducted in a shock tube using a high-speed camera. The numerical simulations were carried out using a commercial code based on an MSC-DYTRAN solver under initial conditions similar to those in the experiments. A wide span of the barrier geometrical parameters was used to map in a continues manner the effect of the barrier geometry on the shock wave attenuation. By analyzing the geometrical parameters characterizing the double barrier configuration, better understanding of the physical mechanisms of shock wave attenuation is achieved. It was shown that for a double barrier configuration, the first barrier inclination angle was very dominant in attenuating the shock wave, as expected, while the efficiency of the second barrier inclination angle depended on the distance between the two barriers. Only when the distance between the two barriers was increased and the second barrier was far enough from the first barrier, it affected the attenuation regardless of the first barrier.