Hydraulic Jump Control Using Stilling Basin with Abruptly Expanding and Negative Step

The present research describes a laboratory study of a hydraulic jump in an abruptly expanding channel and a negative step. The Froude numbers were chosen between 4.5 and 9. This steady hydraulic jump is insensitive to downstream conditions (i.e., tailwater depth). It has an energy dissipation of 45–70%, and therefore it is a good economical design. Four physical models with the expansion ratios of B = 1, 1.33, 1.6, and 2, and two different heights of negative steps (s = 3 and 6 cm) were considered. The results showed that the S-jumps were asymmetric, and the abrupt expansion caused an increase of the jump length and energy loss, while the sequent depth was decreased. By using the negative step, the hydraulic jump was changed to a symmetric shape; also, the hydraulic jump length was significantly reduced when compared to the sudden expansion channel without it; the sequent depth was increased, while the energy loss was decreased. In order to estimate the hydraulic jump characteristics, empirical relations associated with the expansion ratio of basin walls, the relative height of negative steps, and inflow Froude number were proposed based on the experimental data.