EXPERIMENTAL-STUDY OF COATING FLOWS IN A PARTIALLY-FILLED HORIZONTALLY ROTATING CYLINDER

We describe a number of different phenomena seen in the free-surface f low inside a partially filled circular cylinder which is rotated about its horizontal axis of symmetry. At low angular velocities the flow s ettles into a steady two-dimensional flow with a front where the coati ng him coalesces with the pool at the bottom of the cylinder. This mod e becomes unstable at higher angular velocities, initially to a sloshi ng mode on the rising side of the coating film and then to an axial in stability on the front. The undulations that appear on the front grow into large-amplitude stationary patterns with cusp-like features for s ome parameter values. At still higher angular velocities and volume fr actions, a number of different inertial instabilities and patterns app ear. We present a phase diagram of the various transitions and charact erize some of the more prominent instabilities and patterns in detail, along with some possible mechanisms for the observed behaviour.