Analysis of the pressure buildup behind rigid porous media impinged by shock waves in time and frequency domains

Abstract

The transformation of a time-dependent pressure pulse imposed on the front face of a rigid porous medium sample, mounted in a tunnel, through the sample and a fixed-volume air gap between the rear face of the sample and the end wall of a tunnel is studied both experimentally and analytically. In the experiments, rigid porous samples that are placed at various distances from a shock tube end wall are subjected to the impingement of shock waves. The pressure buildup behind the porous sample is monitored and compared with the pressure imposed at the front face of the porous sample. The shock tube is fitted with a short driver section in order to generate blast-like decaying pressure profiles, which continue to decay after the initial shock impingement. In this scenario, the measured pressure profile at the end wall, which is affected by the properties of the porous medium and the size of the air gap separating its rear face and the shock tube end wall, is significantly different from the pressure profile imposed on the front face of the porous sample. The mechanism governing the pressure transformation provided by the porous medium is attributed to a selective filtration process that attenuates the pressure changes associated with high frequencies. The results of the present study are also analysed in conjunction with previously published analytical and numerical models to achieve a broader understanding of the physical mechanisms affecting the pressure buildup.