Effects of seepage on scour due to submerged jets and resulting flow field

摘要

Scour below two- and three-dimensional outlets were studied by many researchers without seeping flow from the non-cohesive sediment bed. However, investigations on scour in the presence of seepage are relatively sparse. The investigations carried out by the authors are, therefore, a welcomed addition and help to understand better a fairly complex phenomenon that takes place at the interface between the sand-bed and the flowing water. The complexity of the problem can be realized from the fact that the results based on many past investigators are often diametrically opposite. For example, Richardson et al. (1985) found that for the low flow regime the sediment transport rate increased with flow injection. The extent of the increase/decrease depended upon the flow regime. Similarly, Oldenziel and Brink (1974) observed that the injection increased the sediment transport rate. In contrast, Willets and Drossos (1975) concluded that suction near the sand bed enhanced the rate of sediment transport if the extent of the suction zone was limited. Watters and Rao (1971) observed that flow injection inhibits the motion of bed particles, while suction enhances it. They observed the presence of a negative lift force for some bed configurations. This was also reported by Coleman (1967) when the particles were smaller in size as compared to the laminar sub-layer thickness, even in the absence of seepage.