Abstract: Flow from the orifice of high dam usually fall with full diffusion in horizontal direction, but in narrow valley it is limited by the width of river. By setting transverse shrinkage baffle plates at the end of the dam orifice, the flow jet becomes narrow and long spreading well in vertical and longitudinal directions, which gives full play to the longitudinal space of river for flood discharge and energy dissipation. However in this case, the pressure on the baffle plate surged due to jet impact, which is detrimental to the structure design of the baffle plate. In this paper, the impact pressure on the baffle plate was researched by changing the shape parameters of baffle plate (contraction ratio β, relative contract length δ and outlet angle γ) as well as water head at the entrance of orifice. Research results revealed that the maximum pressure on the baffle plate was at the beginning point (which is at the joint between suddenly-enlarged side-wall and baffle plate), while no negative pressure was found on the baffle plate which is beneficial to alleviating cavitation of the plate. The maximum impact pressure reduced with the increase of contraction ratio and relative contract length, while increased with the increase of outlet angle and water head at the entrance of orifice.

Key words: high dam project, high-velocity jet flow, flood discharge and energy dissipation, baffle plate, pressure characteristic