Impact Hydraulic Jump

The hydraulic jump occuring close to a gate‐type structure is analyzed both by theoretical and experimental means. The transition phenomenon between a classical‐hydraulic jump and the supercritical sluice gate underflow may be modeled with the jump‐position parameter. This ratio $\lambda$ is equal to the distance between the toe of jump and the gate, and the roller length of a classical jump. For $\lambda >2$, the hydraulic jump is almost classical, whereas blowout of the jump occurs for $\lambda >1$. Typical‐impact jumps are found for $\lambda =1.2$. For impact jumps, the average tailwater depth is always smaller than the sequent depth. However, significant tailwater oscillations, eventually under resonance conditions, are set up, which increase as $\lambda$ decreases. The mechanisms of both resonance and blowout are explained, and frequency is also correlated to $\lambda$ and found to decrease with increasing $\lambda$. Finally, a relation between the relative‐gate opening and the approach Froude number is introduced for which incipient blowout was noted.