Stilling basins are critical energy-dissipating structures in high-head hydraulic projects, yet conventional stilling basins often face challenges of insufficient energy dissipation and excessive bottom pressure under high water head and large unit discharge conditions. The integration of sudden expansion and drop sill into stilling basin design has emerged as a potential solution, but its hydraulic characteristics and the specific impact of sudden expansion remain inadequately quantified and understood. To address this research gap, this study experimentally investigates the hydraulic performance of stilling basins with sudden expansion and drop sill, conducting physical model tests on nine design schemes that contrast basins with and without sudden expansion. The tests measure time-averaged pressure, fluctuating pressure, and aeration concentration at key positions of the basin floor. The results demonstrate that the drop sill stilling basin with sudden expansion is technically feasible for application under conditions of high water head and large unit discharge. In the direction perpendicular to the flow, the distributions of time-averaged pressure, fluctuating pressure, and aeration concentration are non-uniform, generally exhibiting a decreasing trend in the order of the 1/4 centerline, chute extension line, 1/2 centerline, and near-sidewall line. Specifically, the time-averaged pressure, fluctuating pressure, and aeration concentration at the bottom of the sudden-expansion basin are, respectively, lower than those of the non-sudden-expansion basin. Notably, the primary protection zones of the sudden-expansion and drop sill stilling basin are situated between the chute extension line and the 1/4 centerline, as well as in the region ranging from the drop sill to 0.4l (with l denoting the stilling basin length). These findings verify that sudden expansion significantly modifies the hydraulic characteristics of stilling basins by reducing pressure and aeration concentration in key areas, and further provide quantitative design parameters and theoretical support for the optimization of sudden-expansion and drop sill stilling basins in high-head hydraulic engineering projects.
Li et al. (Fri,) studied this question.