A Lagrangian Analysis of the Surface Flow in a Jet Dissipation Basin at Equilibrium

A jet impinging on a loose bed stilling basin will induce a scour hole, thus changing the bed geometry, which will also affect the flow field in the stilling basin. The erosion caused by the jet will create a scour hole and a deposition bar. Both will evolve in time until, hopefully, they reach an equilibrium. As the bed reaches the equilibrium, it is also expected, if the flow rate stays constant, that the flow in the stilling basin will become steady and can be easily analyzed by imaging methods. In this paper, an analysis of the surface velocity field in the stilling basin at the equilibrium is made with emphasis on the flow above the deposition bar. Two techniques are used: Particle Image Velocimetry for an overall analysis of the flow, allowing to characterize the recirculation areas in terms of size and intensity and Particle Tracking Velocimetry allowing for a Lagrangian analysis of the flow, and therefore allowing to directly compute the trajectories of individual particles. Particle Tracking Velocimetry allows also to compute the velocity field in regions of the flow where the seeding concentration is low.