Supercritical Exchange Flow Down a Sill

Abstract

A detailed experimental study was conducted to investigate the hydraulics, interfacial instability, and mixing in the supercritical region of exchange flows downstream of a sill crest. Measurements of the velocity field and the interface position were obtained using flow visualization and particle image velocimetry. Large periodic fluctuations in the measurements of the flow rate and interface position were caused by the Kelvin–Helmholtz (KH) instabilities at the interface as well as the internal seiche. These KH instabilities caused entrainment of fluid from the upper layer into the lower layer, with the entrainment coefficient considerably larger than the values for gravity currents.