HYDRAULIC JUMP IN AERATED FLOW

Abstract

The hydraulic jump is one of the most interesting phenomena in the field of hydraulic engineering. It constitutes the rapid transition from supercritical flow to subcritical flow. The jump has been studied by both the scientist and the engineer, each attaches a different significance to the same phenomenon. In high velocity open channel flow like those over spillways or chutes the flow turbulence gives rise to surface disturbances which lead to air entrainment. Air is also introduced artifically into the flow by devices called aerators to prevent cavitation erosion of spillway surfaces. The aerated water is further carried downstream and in this way the flow upstream of the hydraulic jump may get aerated either due to self-aeration or forced-aeration. This entrained air can strongly influence the performance of hydraulic structure. The present study was, therefore, aimed at obtaining the variation of air concentration in hydraulic jump with non-aerated and aerated approaching flow. The approaching flow was aerated using both self-aeration and forced-aeration. Based on this study the sequent depth ratio in hydraulic jumps with aerated prejump flow condition is obtained as 1 1/2 y2 = f (1+2F~)2—ll y 1.42 l 1 Further, the air concentration within a hydraulic jump is observed to increase due to aeration of the approaching flow. A predictor has been developed to estimate the mean air concentration within a hydraulic jump with non-aerated and aerated prejump flow conditions.