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International audienceIn this work, the main physical characteristics of plane water sheets flowing under gravity andsurrounded by free air are experimentally investigated. By varying the mean flow rate through a 0.8 mm× 100 mm nozzle, water sheets are produced over a range of Reynolds and Weber numbers between210 to 1240 and 0.37 to 13.52, respectively. First, the sensitivity of the sheets shapes to a mass flow ratevariation is evidenced. For a sufficiently high flow rate, a liquid sheet forms with two rims bordering it.These rims join after a certain length L c resulting in a triangle-like shape of the sheet. This characteristiclength is compared with a theoretical prediction given by a model valid for Re >>1. Furthermore,some capillary waves forming a striped pattern are present at the sheet interface near the rims and arepropagating towards the central axis as the sheet falls. These waves are interpreted as the consequenceof the displacement of a high curvature gradient zone at the rim-sheet interface as suggested by theirstationary shape. The critical mass flow rate at which the sheet destabilization is systematically observedis Q c = 0.056 kg.s −1 . It corresponds to a Weber number We ≈2.7, a value in line with the theoreticalone We_th = O(1) which usually indicates a sufficient condition to maintain a stable sheet. Such rupturesare characterized by the appearance of expanding hole(s), predominantly in the lower half of the sheet.The experimentally determined mean expansion velocity proved to be within ±20% of that providedby the well-known Culick expression. As expected, when considering mass flow rates below the abovementioned critical one, an intermittent regime of rupture is obtained characterized by the presence ofsheets, threadlines, jets or drops

EXPERIMENTAL INVESTIGATIONS OF PLANAR WATER SHEETS FLOWING UNDER GRAVITY