Ecology, Environment and Conservation Paper

Vol 23, Sept. Suppl. Issue 2017; Page No.(321-327)

COMPARISON OF VELOCITY PROFILES FOR FREE AND SUBMERGED HYDRAULIC JUMP

Nisha Khanam and Mudgal B.V.

Abstract

Sudden transition of the flow from supercritical to the subcritical regime is accompanied by the formation of hydraulic jump. The geometric elements like the supercritical depth y1 and the subcritical depth y2 are related by the Belanger¬ís equation and the length of the jump Lj is related to the subcritical depth y2. Also many investigators have studied the velocity field in the body of the jump and have established that the flow profile in the forward direction is akin to that of the wall jets. In this study the velocity profiles in the body of the hydraulic jump, both free and submerged, is revisited. Experiments have been carried out on free and submerged hydraulic jumps in a rectangular channel. The velocity profiles are measured using an Acoustic Doppler Velocimeter (ADV). The ADV data are de-spiked using the Velocity Signal Analyser (VSA). Velocity profiles thus obtained are analysed for the rate of decay of maximum velocity (Um/Uj vs x/ y2) and growth of the half width of the wall jets (b/y2 vs x/y2). Also, the flow profiles thus measured are compared with the shape factor (H = δ*/θ) (ratio of displacement thickness to the momentum thickness). The length of the jump is defined as the length over which the value of the shape factor changes from that of wall jet to boundary layer type. This concept is used in defining the length of the jump for submerged hydraulic jumps. A modified submergence factor (Sm) is defined to account for the depth at downstream of the sluice gate.

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