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Gravity‐driven infiltration instability in initially dry nonhorizontal fractures
Author(s) -
Nicholl M. J.,
Glass R. J.,
Wheatcraft S. W.
Publication year - 1994
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/94wr00164
Subject(s) - instability , imbibition , mechanics , geology , geotechnical engineering , infiltration (hvac) , materials science , physics , composite material , botany , germination , biology
Experimental evidence demonstrating gravity‐driven wetting front instability in an initially dry natural fracture is presented. An experimental approach is developed using a transparent analog rough‐walled fracture to explore gravity‐driven instability. Three different boundary conditions were observed to produce unstable fronts in the analog fracture: application of fluid at less than the imbibition capacity, inversion of a density‐stratified system, and redistribution of flow at the cessation of stable infiltration. The redistribution boundary condition (analogous to the cessation of ponded infiltration) is considered in a series of systematic experiments. Gravitational gradient and magnitude of the fluid input were varied during experimentation. Qualitative observations imply that finger development is strongly correlated to the structure of the imbibition front at the onset of flow redistribution. Measurements of fingertip velocity are used to develop a first‐order relationship with fingertip length. Measured finger width is compared to theoretical predictions based on linear stability theory.