HYDRAULIC JUMP IN CHANNEL CONTRACTION

The hydraulic jump in a linearly contracting channel is studied in rel ation to choking flow. For a contraction intended to perform under sup ercritical flow, choking is an important design consideration because of the increase of flow depth and modified upstream conditions. Based on the momentum equation, a relation for the sequent depths ratio is d etermined and verified with extended experiments. Further, the mechani sms of both hydraulic jump and the choking flow are described. The wal l surface profile is shown to be similar and equal to the profile of t he classical hydraulic jump for a relatively small contraction rate. T he lengths of roller and jump are determined, and substantial agreemen t with the classical jump is again found. The choking of a channel con traction is discussed as the limit condition of the hydraulic jump. A simplified model is shown to agree with observations. A design equatio n for choking is proposed.