Saffman–Taylor instability

Summary

The Saffman–Taylor instability, or viscous fingering, is an instability of the interface between two fluids. It occurs when a less viscous fluid pushes a more viscous one in a Hele-Shaw cell or a porous medium. A small bulge of the interface forward meets less resistance and so advances faster, and the interface breaks up into fingers. Surface tension damps short wavelengths and sets the scale of the fingers. The instability limits oil recovery by water injection and is a model problem for pattern formation; Saffman and Taylor analysed it in 1958.