Viscous fingering with imposed uniaxial anisotropy

We study viscous fingering in the radial Hele-Shaw cell with a set of parallel grooves on one of the plates in order to obtain the morphological phase diagram of a system with imposed uniaxial anisotropy. Varying the pressure of air injected into glycerin and the distance between the plates, a rich variety of phases can be obtained corresponding to all of the possible combinations of stable or splitting tips in directions parallel and perpendicular to the grooves. We demonstrate that the effective anisotropy governing the stability of the tips is a result of a complex interplay between the local anisotropy and the driving force.