Wetting front instability: 2. Experimental determination of relationships between system parameters and two‐dimensional unstable flow field behavior in initially dry porous media

This paper describes and interprets experimental studies of wetting front instability guided by the dimensional analysis presented in paper 1 (R.J. Glass et al., this issue). When a wetting front passes from a fine‐textured layer of initially dry sand into an underlying coarse layer, the front breaks into fingers. A specially developed vertical slablike chamber and associated techniques were developed for the study of such fingering. The flow rate through the system is systematically varied by using different mean grain size separates for the upper layer (the same coarse separate being used for the bottom layer). Relationships between finger width, propagation velocity, moisture content, and flow rate through individual fingers are experimentally determined and related to the properties of the bottom layer and the flow rate through the system. The results are different than those found in a previous experimental study which used different techniques for sample preparation. Results obtained here agree with a formulation derived earlier by J‐Y. Parlange and D.E. Hill (1976) through linear stability analysis.