GRAVITY INVASION PERCOLATION IN 2 DIMENSIONS - EXPERIMENT AND SIMULATION

We present experiments and computer simulations of slow drainage in a two-dimensional porous medium. The effect of gravity is systematically varied by tilting the system from the horizontal position. The width a of the front between the fluids is found to scale with the dimensionless Bond number Bo (ratio between gravitational and capillary forces) as sigma approximately Bo-0.57, as predicted by theory. The external perimeter of the invaded structure is shown to be fractal with the fractal dimension D(e) congruent-to 1.34 for length scales smaller than the front width.