Study On Hydraulic Characteristics Of Flat-bottomed Bottom Outlets

Analysing the investigations on the hydraulic characteristics of flood tunnels in recent years, the hydraulic research of flat-bottomed bottom outlets was carried out by means of physical model and theoretical analysis.Based on 1/30 scale physical model, hydraulic characteristics of air entrainment of the flat-bottomed tunnel for seven plans were investigated and a new type of aerator with good aerated performence was presented in the paper. And then, whether an aerator was needed was demonstrated.Theoretically, the characteristics of backtracking flow of three types of aerators were analysed. Compared with flat-bottomed aerator, the impact angle of the aerator with a downstream baffler was smaller and it has better aerated effects than the one without downstream bafflers.Dimension analysis showed that the cavity length and air demands of the aerator with downstream baffler was affected by the Froude number and the geometry of its downstream baffler.Physical model experiments showed that under the conditions of partical opening of the gate for the bottom outlet, surface profile of free-flow section and sidewall pressure distribution of curve section increased with the opening of the gate, but the cavity length of the aerator decreased with the opening of the gate. The discharge coefficients of big or small gate opening were bigger than the ones of the medium opening.