Mechanism Of Free Jets' Scour On Rocky River Beds

As high dams of large discharges in narrow valleys increase, the investigation for downstream energy dissipation and scour problems of high dams is more and more important. To solve downstream energy dissipation and scour problems of the Three-Gorges spillway (Yangtze River) and Xiaowan arch dams (Lancang River), this thesis has investigated some mechanism problems of free jets' scour on rocky river beds in detail. The main results obtained are given as follows.According to laboratory tests and previous investigated results, a general model for the scour process on rocky river beds by free jets has been proposed. This process may be divided into three sub-processes, which are the disintegration of the rockbed, rock blocks' pulling out of the rock matrix and the ball milling and formation of the scour pit. The formation and development of the scour pit, in fact, are the result of interaction of these three sub-processes. Finally, as the equilibrium of the available energy of the submerged jet (dissipated by the scour pool) and the rockbed erosion resistance is approached, no further erosion occurs and the scour pit reaches the state of equilibrium.According to fundamental behaviors of the submerged jet within a plunge pool, the study results of free impinging jets have been used to analyze the diffusive characteristics of oblique submerged impinging jets and variations of basic physical variables in the different jet sub-regions in detail. Then, different discriminations of lifting conditions for rock blocks within the impacting zone and the region of the submerged wall jet in a...