Experimental Investigation of Scour by Turbulent Wall Jets in Flowing Water

In the present study, scour development by wall jets in flowing water in a 90o bend was investigated. To study the secondary flows effect, two different locations for the jet on the outer wall of the bend were considered (1) the beginning of the bend (0o) and (2) the end of the bend (90o). The studied parameters are the flume Froude number (Ff), the jet Reynolds number (Rj), and the jet submergence rate (H/do). The results showed that under the influence of the flume flow, the jet trajectory and the scour profile are deflected to the flume flow direction. With increasing Rj, mound height (hm) and the max scour depth (ds) increase. Due to the secondary currents effect, ds at the end of the bend is as much as the nozzle diameter (1do) greater than ds for the jet at the beginning of the bend. Also, for Rj > 36000, the scour development in the jet direction (ys/B) can make a choking in the flume that for Ff < 0.121, the flume choking is more likely. The findings show that with increasing the ratio of the flume flow velocity to the jet velocity (r), the scour profile development in the flume flow direction (xs/do) increases and can reach 100do. For r < 0.06, with decreasing the flume velocity, ys/B increases and for r > 0.06, increase in the Flume velocity causes an increase in the scour development in the width of the flume. Furthermore, r = 0.06, was introduced as a point with the minimum effect of the jet on the flume, which can be utilized in the design of wastewaters discharge. Finally, some equations with acceptable accuracy were developed to estimate the scour profile development in the length and width of the flume.