鉛直噴流による洗掘限界について

Abstract

In order to prevent the scour resulting from water falls, such as a vertical waterjet impinging normally on a sediment bed, it is necessary to make clear the hydraulicmechanism of the beginning of motion of sand gravels, that is the criterion for scour, due to the flows caused by a vertical jet.The first part of this paper deals with the theoretical approach to solve the char-acter of flows close to a boundary which is caused by impingement of jets on a normalboundary. A theoretical consideration for the boundary layer growth on the normalboundary in the various cases of two and three dimensional jets, at submerged and non-submerged conditions is described with the aid of the results of some experiments. Inthe above considerations, the boundary layer growth in the vicinity of impingement ofjets is disclosed.In the second part, the criterion for scour from a vertical submerged water jet isanalyzed by the same procedure as done by the author in the previous paper entitled"Basic Studies on the Criterion for Scour from Flows Downstream of an Outlet". It isconcluded from the comparison between the theoretical and experimental results that thefundamental relationships in the criterion for scour, which are reduced by the theory, are in good agreement with the experimental results. Based on both results of the theoryand the experiments, an empirical formula for the criterion for scour from a verticalsubmerged water jet is proposed, and moreover, some considerations on the method pre-venting the bed from scour are described.