Viscous fingering with adverse anisotropy: A new Saffman-Taylor finger

Viscous fingering in a linear channel is investigated in the presence of anisotropy, when the directions of easy growth are at 45^∘{} to the direction of the cell axis. Experimentally, when the velocity is increased, the stable fingers and the averaged unstable ones tend to occupy an increasing fraction of the cell width, in contrast with the standard situation. The numerical simulation and the analytical investigation reveal the existence of a new solution for the Saffman-Taylor finger which does not belong to the standard manifold.