Abstract:Abstract:【Objective】In order to optimize the size and layout of discharge structure, explore the relevance between flow field distribution and local scour of the river bed.【method】Physical experiments in a large-scale hydropower station surface and bottom joint flood discharge facilities based, used standard turbulence model and VOF free surface capture technology, three dimensional flow field of the combined flood was numerical simulated , obtained the flow velocity ,water line and pressure hydraulic characteristics of the surface orifice spillway, bottom outlet and the pond. By comparing with the experimental results of hydraulic model, the correlation mechanism between the flow field structure and the downstream channel scour pattern was analyzed.【Result】Results show that: the original design of the stilling pool water fluctuation, flow disorder, pool water secondary sag and mainstream dive riverbed, lateral diffusion is not sufficient. The corresponding physical model, which occurs serious erosion in the downstream. Erosion is the most serious on the right bank and behind the left guide wall of surface hole, is just on the right bank of the mainstream posted shore and left back pressure area. Through improved the shape of the plunge pool with the methods of retaining the construction diversion wall between low porosity and surface hole stilling pools and so on, significantly improved the flow regime of stilling basin, the pool water secondary drop decreases, dive is weakened, a pool level of the mainstream diffusion more fully, lateral extrusion can be suppressed sufficiently. Accordingly, the scope and depth of the riverbed erosion are greatly reduced, especially on the right bank side corresponds to the original proposal prepared hole area almost no erosion occurs.【Conclusion】Obviously, in the simulation of local scour is still not mature , based on flow field analysis method for trend analysis of riverbed scouring, layout and shape optimization and direct discharge structure is feasible.