Numerical investigation of shock wave attenuation

2018-12-16Research interest on shock wave attenuation arises from the potential serious damage caused by shock and blast waves. For example, during an explosion occurring in an underground mine or subway tunnel, the shock front is forced to propagate in the direction of the channels. Therefore, an effective strategy needs to be implemented inside the channel to prevent the shock wave from propagating through, while simultaneously mitigating the part that could be reflected back. Here, varying approaches to attenuate shock waves in channels are explored using numerical models. The motion of the shock wave and the corresponding flow features are studied, and the shock attenuation effectiveness of the different approaches is compared. ❧ One approach to mitigate an incident shock wave is by partially blocking the channel with solid obstacles of various geometries and arranging them in different patterns. Cylindrical, square and triangular shaped solid obstacles are placed in staggered and non-staggered subsequent columns to attenuate a planar incident shock wave. Besides the matrix obstacle formation, an arrangement of obstacles placed along a logarithmic spiral curve is investigated, which is motivated by previous work on the shock focusing properties of such geometry. Results from numerical simulations show that obstacles placed along a logarithmic spiral curve delay the arrival of the transmitted and reflected shock waves. In addition, it is shown that the attenuation effectiveness depends on the obstacle shape and effective flow area. ❧ An alternative shock attenuation approach involves water instead of solid obstacles. Water is attractive because of its high impedance and large heat capacity, where a large amount of energy can be absorbed by water when mitigating the shock wave. On the other hand, unlike solid obstacles, which may block the path used for safe escape of affected population if collapsed by the shock wave, water will not obstruct the channel due to its fluid properties. In the current study, a numerical two-phase flow model is used to characterize the difference between the shock wave reflection off straight solid and water surfaces, and the results are compared with analytical and numerical solutions of the solid wedge cases. The wave patterns are quantitatively studied through measurement of the transition angles and triple point trajectories. ❧ Furthermore, propagation of a normal shock wave through water droplet matrices is simulated for four different droplet configurations, i.e., placing the droplets in 1×1, 2×2, 3×3, and 4×4 matrix formations. The total volume of water is kept constant throughout all the cases. The physical motion of the water droplets, such as the center-of-mass drift and velocity, is quantitatively studied. Also, the motion is analyzed from an energy perspective, where the kinetic energy transferred from the shock induced flow to the water droplets is traced. Results show that up to 23.4% of the kinetic energy input from the shock induced flow converts to the kinetic energy of the water droplets. At last, the pressure and impulse upstream and downstream of the water droplet matrices are tracked to evaluate shock attenuation, and the results are compared against the solid obstacle cases