水門から噴出するWallJetによる洗掘限界について

Abstract

In order to establish the mechanics of scour downstream of a culvert and anoutlet and to discuss the method for preventing from scour, it is necessary, firstof all, to analyze the characters of flow close to a bed, especially the boundarylayer developing there. The first part of this paper, therefore, presents an analysisof the boundary layer growth in a wall jet issuing from a submerged outlet, basedon the momentum equation for a boundary layer connecting with two-dimensionalfree turbulent jets. Characters of diffusion of a wall jet, boundary layer growthand resistance laws are discussed on the basis of the experimental results of walljets, and it is cleared that comparisons between the experimental results and thetheoretical ones are satisfactory for practical purpose.The main purpose of the paper is to obtain some fundamental data for estimat-ing the length of apron of a submerged outlet under the condition that the sedi-ment bed downstream of aprons is not scoured absolutely by action of flow. In thesecond part, the criterion for scour from the wall jet in the region having a con-stant maximum volocity is discussed by using the results obtained in the first part.The experimental results of the criterion are compared with the theoretical re-lationships, and an empirical formula for the criterion is proposed on the basis ofthe both results. In addition, some considerations on the design of the length ofapron are briefly described.