泄洪洞龙落尾段流态控制的试验研究

Experimental investigation of flow regime control for dragon-drop-tail section of the spillway tunnel

龙落尾泄洪洞由于大部分泄洪洞段都处于相对较低的水头,近年来在大型水电工程中有良好的应用。然而,在龙落尾段,坡度大,流速高,为减免空蚀破坏设置掺气设施是必要的。该文以某大型水电工程为对象,运用物理模型试验,通过13个方案,包括底部掺气设施的结构形式,折流器和侧扩两类侧墙掺气方式,以及文中推出的一种后退式侧墙掺气结构,对全断面掺气设施可能导致的水翅危害,水面的局部雍高等不良流态进行了专门研究。结果表明:对于侧墙掺气设施,折流器类掺气比侧扩掺气对流态干扰更大;在满足下游合理的掺气浓度条件下,减小底部挑坎坎高和挑角能够改善水流表面的局部雍高;后退式侧墙掺气设施结构由于上移了侧空腔尾部的位置,可以有效地改善侧掺气设施引起的水翅危害。

The spillway tunnel with dragon-drop-tail section, thanks to low water head acting on most of the tunnel section, is widely used in large-scale hydropower projects. However, it is necessary to place aerator devices avoiding cavitation erosion in the dragon-drop-tail section because of steep slope and high flow velocity in this section. In this paper, taking some hydropower project as an object, the physical model experiments were conducted with thirteen cases, including the structure forms of the bottom aerators, of air entrainment on lateral aerators by either deflector or abrupt enlargement, and a back-type structural form of lateral aerators presented by authors. The flow regimes, especially in the water fins deduced by lateral aerators and the bulge of the flow surface, were investigated. The results showed that, comparing the deflector in lateral walls, the lateral aerator of the abrupt enlargement type could effectively eliminate the water fins, the low ramp height or small angle of the bottom aerator supported avoiding the bulge of the flow surface downstream of the aerator device, and the back-type structural form of lateral aerators could protect the flow from the water fins by means of moving the tail position of the lateral cavity.