ABSTRACT
It is shown that the appearance of dry patches on a wetted wall may be explained as being a consequence of a hydrodynamic instability which only occurs at very low Reynolds numbers. A steady disturbance, periodic in the cross-stream direction but allowed to grow or decay in the downstream direction is imposed on the steady constant film thickness flow. This corresponds to the “roping” disturbance observed experimentally. A critical Reynolds number is found below which the flow is unstable.
