EXPERIMENTS IN A ROTATING HELE-SHAW CELL

We introduce a modification to Hele-Shaw hows consisting of a rotating cell. A viscous fluid (oil) is injected at the rotation axis of the c ell, which is open to air. The morphological instability of the oil-ai r interface is thus driven by centrifugal force and is controlled by t he density (not viscosity) difference. We derive the linear dispersion relation and verify the maximum growth rate selection of initial patt erns within experimental uncertainty. The nonlinear growth regime is s tudied in the case of vanishing injection rate. Several characteristic lengths are studied to quantify the patterns obtained. Experimental d ata exhibit good collapse for two characteristic lengths, namely, the radius of gyration and the radial finger length, which in the nonlinea r regime appear to grow linearly in time.