Gravity-driven flow of Herschel-Bulkley fluid in a fracture and in a 2D porous medium

New analytical models are introduced to describe the motion of a Herschel-Bulkley fluid slumping under gravity in a narrow fracture and in a porous medium. A useful self{similar solution can be derived for a fluid injection rate that scales as t; an expansion technique is adopted for a generic injection rate which is power{law in time. Experiments in a Hele-Shaw cell and in a narrow channel filled with glass ballotini confirm the theoretical model within the experimental uncertainty.