Measurements of free-surface profile in transient flow with a simple light-slicing method.

A simple light-slicing technique for the direct measurement of the free-surface shape h(x) in onedirectional transient liquid flows is studied. The method is used to determine h(x) with a precision of the order of 10(-2) mm along a line several centimeters long, allowing for height differences of some millimeters. It is useful for transient flows in rectangular channels in which capillarity and liquid adhesion at walls perturb lateral observations; the method can also be used for nondiffusive fluids in cases in which it is not advisable to add diffusive particles.