SUMMARYThis study examines theoretically the development of early transients for axisymmetric ow of a thin ÿlm over a stationary cylindrical substrate of arbitrary shape. The uid is assumed to emerge from an annular tube as it is driven by a pressure gradient maintained inside the annulus, and/or by gravity in the axial direction. The interplay between inertia, annulus aspect ratio, substrate topography and gravity is particularly emphasized. Initial conditions are found to have a drastic e ect on the ensuing ow. The ow is governed by the thin-ÿlm equations of the 'boundary-layer' type, which are solved by expanding the ow ÿeld in terms of orthonormal modes in the radial direction. The formulation is validated upon comparison with the similarity solution of Watson (J. Fluid Mech 1964; 20:481) leading to an excellent agreement when only 2-3 modes are included. The wave and ow structure are examined for high and low inertia. It is found that low-inertia uids tend to accumulate near the annulus exit, exhibiting a standing wave that grows with time. This behaviour clearly illustrates the di culty faced with coating high-viscosity uids. The annulus aspect is found to be in uential only when inertia is signiÿcant; there is less ow resistance for a ÿlm over a cylinder of smaller diameter. For high inertia, the free surface evolves similarly to two-dimensional ow. The substrate topography is found to have a signiÿcant e ect on transient behaviour, but this e ect depends strongly on inertia. It is observed that the ow of a high-inertia uid over a step-down exhibits the formation of a secondary wave that moves upstream of the primary wave. Gravity is found to help the ÿlm (coating) ow by halting or prohibiting the wave growth. The initial ÿlm proÿle and velocity distribution dictate whether the uid will ow downstream or accumulate near the annulus exit.