Hydraulic jump and its practical applications.

Hydraulic jump

Hydraulic jump formed on a spillway model

Rapid flow and hydraulic jump on a dam


 
 
 
 
Hydraulics Jump or Standing Wave
 

Hydraulics jump is local non-uniform flow phenomenon resulting from the change in flow from super critical to sub critical. In such as case, the water level passes through the critical depth and according to the theory dy/dx=infinity or water surface profile should be vertical. This off course physically cannot happen and the result is discontinuity in the surface characterized by a steep upward slope of the profile accompanied by lot of turbulence and eddies. The eddies cause energy loss and depth after the jump is slightly less than the corresponding alternate depth. The depth before and after the hydraulic jump are known as conjugate depths or sequent depths.

y1 & y2 are called


conjugate depths

 
 
 
Classification of Hydraulic jump

 

• Fr1 <1.0: Jump impossible, violates second law of thermodynamics.

• Fr1=1.0 to 1.7: Standing-wave, or undular, jump about 4y2 long; low dissipation, less than 5 percent.

• Fr1=1.7 to 2.5: Smooth surface rise with small rollers, known as a weak jump; dissipation 5 to 15 percent.

• Fr1=2.5 to 4.5: Unstable, oscillating jump; each irregular pulsation creates a large wave which can travel downstream for miles, damaging earth banks and other structures. Not recommended for design conditions. Dissipation 15 to 45 percent.

• Fr1=4.5 to 9.0: Stable, well-balanced, steady jump; best performance and action, insensitive to downstream conditions. Best design range. Dissipation 45 to 70 percent.

• Fr1>9.0: Rough, somewhat intermittent strong jump, but good performance. Dissipation 70 to 85 percent.

Uses of Hydraulic Jump
 

• Hydraulic jump is used to dissipate or destroy the energy of water where it is not needed otherwise it may cause damage to hydraulic structures.

• It may be used for mixing of certain chemicals like in case of water treatment plants.

• It may also be used as a discharge measuring device.

Equation for Conjugate Depths
 

Location of Hydraulic Jumps  
Flow Under a Sluice Gate:
 
 

Location of hydraulic jump where it starts is


L=(Es-E1)/(S-So)

Condition for Hydraulic Jump to occur

ys

Flow becomes uniform at a distance L+Lj from sluice gate where

Length of Hydraulic jump = Lj = 5y2 or 7(y2-y1)