Experimental study of inclined film flow along periodic corrugations: The effect of wall steepness

Gravity-driven film flow along an inclined periodic wall with transverse rectangular corrugations is studied experimentally. The effect of corrugation steepness (=height/length) is considered in detail and an interesting contrast emerges between properties of the flow that are apparently independent of corrugation steepness and properties that are strongly affected by it. The steady interaction between the wall and the flow leads to a statically deformed free surface, whose amplitude is independent of the corrugation heights tested. Beyond the maximum steady free-surface amplitude, a three-dimensional pattern is established (consisting of transverse arrays of depressions along corrugation valleys), again at conditions independent of corrugation height. On the contrary, steep corrugations expand significantly the stable region of steady flow. Also, fully developed traveling waves (emerging from ambient noise under unsteady conditions) are significantly larger and more regular than under the same conditions along a flat wall. This difference is attributed to the continuous interaction of traveling pulses with the steadily deformed substrate.