Plunging circular jets : Experimental characterization of dynamic pressures near the stagnation zone

Spillways are a requirement for dams' safety, mainly preventing dam over-topping in ood cases. A common spillway solution involves plunging jets which dissipate a considerable energy ow in the plunge pool. Dissipation has to occur in a controlled manner to avoid endangering dam's foundations and the river valley slopes. Indeed, a scouring process in the downstream riverbed will inevitably develop until an equilibrium is reached, or else, a pre-excavated or concrete lined plunge pool has to be provided. The present master thesis explores general actions and scour theory background due to high-velocity jets focusing on experimental studies carried out at LNEC, Lisbon. Special attention is given to the dynamic pressures in the plunge pool oor at the vicinity of the jet stagnation zone. Tests involved a circular plunging jet with velocity ranging from 5 m/s to 18 m/s and plunge pool depth ranging from 4,2 to 12,5 times the jet diameter. Dierences in dynamic pressure measurements are highlighted between transducers located in the inner and in the outer regions of the jet diameter. Results are analyzed, discussed, and compared to previous authors. Several parameters characterizing the dynamic pressures evidence trends tied with the jet velocity that, to the author's knowledge, were not found in previous researches. These can possibly be explained by the recirculating currents in the plunge pool, which intensity increases with jet velocity, and are an inevitable consequence of the xed and limited size of the experimental facility. This aspect deserves further investigation to achieve a better understanding and more complete characterization