Fluidisation in artesian flow conditions: Hydromechanically stable granular media

Abstract

In this paper a two-phase continuum theory for fully fluidised, fluid-flowing, granular media is presented. The analysis is restricted to the fluidisation process involving internally stable granular media in artesian conditions. Based on fluidised column test results it is demonstrated that, at the state of incipient fluidisation, the material undergoes a discontinuous transition that can be seen as a phase change. The stationary fluidised state is characterised by the development of particle repulsion and the effect of weak inertia on the resistance of the granular bed to flow. Based on Richardson's expansion law it is demonstrated that the adjustment of porosity to small increases in the fluid flow rate may be approximately described by small-amplitude kinematic porosity rarefaction waves. Linear stability analysis of perturbations out of the stationary state of uniform fluidisation shows that granular inertia plays a destabilising role that leads to mathematical ill-posedeness, which in turn is removed by considering the effect of the mixture's viscosity.