Flow structure at a confluence: experimental data and the bluff body analogy

An experimental characterization of the hydrodynamics of a mixing interface at an open channel confluence is presented. In the laboratory experiments, both a confluence and a cylinder set-up were studied in order to validate the bluff body analogy, which has been proposed to characterize the mixing interface. The experimental characterization included flow visualization and the computation of the mean flow field, time scales of the coherent structures, and turbulent kinetic energy. The comparison among the two configurations confirms the validity of the analogy as similar features were found for the mean flow field and time scales of the coherent structures. However, differences in the length of the stagnation zone, the flow velocity deficit, and the turbulence intensity were observed. These differences should be taken into account when the bluff body analogy is used to characterize the confluence hydrodynamics and to quantify the mixing at the confluence interface.