Flow observations at a vertical drop structure

Abstract

Results from an experimental study conducted to investigate the characteristics of the velocity field along the jet trajectory of a drop structure are presented. Constant temperature anemometry is used for detailed quantitative measurements of the air-water flow characteristics. The measurements indicate the occurrence of four different velocity profiles along the jet path. At the brink, a non-uniform velocity profile is observed while at the free falling jet a uniform one. On the sliding jet, the profiles resemble those of a submerged turbulent jet and at the drop base, the shape of the profile is fairly uniform. Moreover, in the cases of a fully aerated an non-aerated drop structure, it is found that there is no significant difference in the velocity profile of the sliding jet. In addition, measurements of local void fraction indicate the presence of air bubbles inside the recirculating pool area only. These bubbles are likely brought into this area by a mechanism similar to that of a plunging jet.