Scour Caused by Three-Dimensional Submerged Square Wall Jet: Sand Deposition in Scour Hole and Ridge

Abstract — Laboratory tests were carried out to assess the local scour by three-dimensional wall jets from a square cross-section nozzle. To this end, three different tailwater depths were used and the jet expansion ratio was held greater than ten. Velocity measurements were conducted using a one component laser Doppler anemometer. The jet exit Reynolds number was maintained to 1x105 and this value can be considered to be high enough for fully turbulent conditions to prevail. It was observed in the present study that the coarser particles are deposited towards the downstream end of the scour. In fact the coarsest particles are located on down slope of the ridge. The velocity measurements were carried out along the plane containing the nozzle axis. It was found that the velocity stays uniform close to the nozzle exit and is similar over the entire test duration. At the sections farther away from the nozzle, negative values of velocity occur at farther distances from the bed indicating the presence of a reverse flow closer to the free surface. One can also note that the volume of scour increases with increase of time. However, for 72 hours test of Test B (H/bo = 4), there is a significant increase in scour volume when compared with t = 48 hours. This is due to the expansion of the scour hole perimeter laterally at H/bo = 4 and at 72 hours. The volume of scour is seen to be increasing with increasing tailwater depth