Pressure field generated in porous medium by air jet injected through the surface

Abstract

Efficient detection of hidden volatile substances in soil requires understanding the mechanisms governing their retention or transport through porous medium. In order to increase the mass transfer rate of the hidden volatile substances, it was suggested in this work to apply forced-convection (filtration) in addition to diffusion by using a gas jet impingement vertically onto the soil (a granular bed; sand). Pressure distribution in the granular bed is studied analytically using the methods from the theory of functions of complex variables. The filtration/granular bed interaction involves the soil permeability, grain size, and jet pressure and impinging velocity. Soil failure due to the filtration-imposed forces is formulated as the Mohr-Coulomb criterion, which involves the angle of internal friction and the cohesion of grains. A comprehensive experimental investigation of the filtration pressure distribution and the jet-driven erosion of granular material is presented here. The experiments were conducted by combining a special pressure-measurement technique allowing for a simultaneous accurate detection of the crater onset and the subsequent evolution of the granular bed. The theoretical predictions are compared to the measured pressure field in the granular bed.