Pressure Fluctuations on the Bed of Submerged Hydraulic Jump

The hydraulic jump has many usages in transport and treatment of water and wastewater. It may be considered macroscopically as a rapidly varied flow with strong vortices those generate macro turbulent fluctuations. The pressure fluctuation due to turbulence must be carefully considered in designation of hydraulic structures. In addition; cavitation, abrasion, and vibration due to the intense turbulence and pressure fluctuation may also contribute significantly to damage of a stilling basin. This paper discusses the characteristics of pressure fluctuation in submerged hydraulic jump downstream of spillways and also the effects of submergence ratio on the pressure fluctuation.

The experiments were carried out in a rectangular conduit (constituted from a30ospillway by 1.8m height and a horizontal flume by 0.3m width and 3m length), for the Froude number of 7.07 and also different ratios of submergence. Pressure data were recorded by pressure transducers having sampling rate of 100 Hz.

Experiments show that intensity of pressure fluctuation on the hydraulic jump bed is a function of Froude number, relative distance from basin’s beginning and submergence ratio. Increasing of submergence ratio, decreases the coefficients of pressure fluctuation ( , , ) so that increasing the s. r. from 1 to 2, the decreases %89. Also the coefficient of standard deviation  and the extreme coefficients of pressure fluctuation  and decrease by increasing the s. r., and maximum value of  and occur in the range of X/Y1£20.

Therefore, this range has more importance from the structural designation of view and the higher ratio of submergence supports the higher confidence for designation.