Mesures de turbulence dans le ressaut hydraulique

The research reported on in this paper constitutes a continuation of previous work in the course of which certain unsuspected features of the hydraulic jump were deduced from mean flow characteristics. The present study was aimed at verifying these deductions and thereby provided the necessary stimulus for undertaking perhaps one of the first explorations of turbulent quantities in a genuine hydraulic jump. The measurements of turbulent mean flow properties and turbulence intensities in streamwise direction which are dealt with at length in the body of the paper confirm conclusively that the flow structure of the hydraulic jump is strongly dependent upon the conditions of supercritical inflow. In particu1ar, existence of fully developed flow at the upstream end of the jump leads to a state of turbulence which, not unlike that of a turbulent wall jet, is the consequence of simultaneous occurance of both free turbulence and wall turbulence. On the other hand, if the inflow into the jump is undeveloped, wall turbulence is practically absent since it is now known that the entering supercritical sheet will tend to separate from the channel bottom with increasing Froude number. As a likely result of this both the intensity of turbulence and the longitudinal extent of the turbulent region of a jump with undeveloped inflow are up to four-times less than that of an equivalent, fully-developed jump of the same Froude-number rating. The measurements of the present study agree weir with comparable data which were obtained by Rouse et al in their classical investigation of an air model of the hydraulic jump. However, the present results clearly identify the air-model case as a jump with undeveloped inflow and, hence, restrict the utility of these widely known data to jumps such as are encountered immediately downstream of sluice gates