Distribution Law of Aeration Concentration of Grid-type Underflow Energy Dissipater

The grid can effectively improve effect of underflow energy dissipation and reduce or avoid cavitation damage to bottom of stilling pool.Through hydraulic model tests to study changes of air-entrainment concentration before and after the grid under different opening ratios of circular-hole Γ-shaped grid.Test results were as follows.①Aeration concentration in wall jet zone of stilling pool decreased longitudinally，and there was a sudden change near the grid；in vertical axis direction，aeration concentration was large and small in the middle and two sides were small，and peak position was positively correlated with main flow of incident water stream；in vertical direction，aeration concentration below half the water depth increased significantly along the height，and then change became smaller.②With addition of the grid（opening rate 34%），aeration concentration in front of the grid at position 5 and 30 cm away from entrance of stilling pool increased sharply by 41.11% and 26.82%；grid opening rate decreased from 46% to 22%，aeration concentration on upstream side of the grid（section 6）decreased from 37.75% to 20.32%，and aeration concentration on downstream side of the grid（section 7）decreased from 20.47% to 8.78%.③After the grid was added，the minimum aeration concentration value behind the grid（near the side wall）could reach 6.06%，and flow velocity at measuring point was not large，which meant that stilling pool structure including the grid was not easy to occur cavitation damage.