CHAPTER 5

HYDRAULLIC JUMP

Hydraulic Jump and its Usefulness in the Design

General Hydraulic jump is the jump of water that takes place when a super-

critical flow changes into a sub-critical flow. When a stream of watermoving with a high velocity and low depth (i.e. supercritical flow) strikesanother stream of water moving wit a low depth (i.e. sub-critical flow), asudden raise n the surface of the former takes place. This phenomenonis called Hydraulic jump, and is generally accompanied by a large scaleturbulence, dissipating most of the kinetic energy of super-critical flow,such a phenomenon may occur in a canal below a regulating sluice, atthe bottom of a spillway, or at a place where a steep channel slopesuddenly turns flat.

When water falls over a spillway or a vertical or a glacis fall, it acquires alot of momentum and velocity. This high velocity, if allowed to persist,shall cause large scale erosion and scouring of the downstream soil ofthe work, and hence, it must be checked or controlled. In suchsituations, the phenomenon of hydraulic jump can b4e user with greatadvantage for dissipating the kinetic energy of the water.

Hydraulic Jump and its Usefulness in the Design

General If the jump is low, i.e. the change in the depth is small, the water

shall not rise abruptly but will pass through a number of aundulations. Such a low jump is called an undelay jump. IN thiscase, the energy dissipation shall be low and incomplete.

But on the other hand, if the jump is high, i.e. when the change indepth is large, the jump shall occur abruptly and is called a directjump. Such a in the design of hydraulic-cum-irrigation structures.

It may be noted that the depth before the jump is always less thanthe depth after the jump. The depth before the jump is calle4d theinitial depth (Y1) and the depth after the jump is called thesequent depth (Y2). These depths are shown on specific energycurve (Fig. 10.1)

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Hydraulic Jump and its Usefulness in the Design

And must be differentiated form al-ternate depths Y1 and Y2 ‘ . Y2 ‘ isthe depth that shall occur in a sub-critical flow if there was no loss ofenergy in the jump formation; while Y2 is the actual depth that occursafter depth that occurs after the jump, involving the energy loss HL.

The Use of Hydraulic Jump

Occurrence of Hydraulic Jump

MOMENTUM EQUATION

MATHEMATICAL ANALYSIS

Consider a channel reach and point 1 and 2 on the same in a length of Lj i.e, between two

sections 1-1 and 2-2

Jump Analysis in Rectangular Channel

BASIC CHARACTERISTICS OF TH JUMPLoss of energy in jumpLoss of energy in jump

Which gives the Loss of energy in jump in rectangular channel

Relative loss of energy in Hydraulic Jump

Which gives the relative energy loss equation. E1 is the energy before the jump.

Relative loss of energy in hydraulic Jump

Efficiency of the jump

Height of jump (hj) and relative height (hj/E)

Jump Analysis in non Rectangular Channel

TYPES OF HYDRAULIC JUMP

Various types of jump based on Fr1

JUMP IN EXPONENTIAL CHANNEL

JUMP IN EXPONENTIAL CHANNEL

EXAMPLE

EXAMPLE

Solution :

EXAMPLE

Solution :