Saffman-Taylor instability — DLA morphology via capillary number
Cells filled: 0 | Fractal dim ≈ — | Ca: 0.50
The Saffman-Taylor instability occurs when a less-viscous fluid (e.g. air) displaces a more-viscous fluid (e.g. oil) in a porous medium or Hele-Shaw cell. Surface tension stabilizes at small capillary number Ca = μU/γ (compact finger), while Ca → ∞ (zero surface tension) gives fractal DLA-like branching. The finger width λ/W → 0.5 at high Ca, and the fractal dimension crosses over from d_f = 2 to d_f ≈ 1.71 (DLA universality class).