泄洪洞内具有阻塞与扩散段的水平旋流消能方式水力特性的试验与数值模拟(1)

Model tests and numerical simulation on hydraulic characteristics of level rotary flow in spillway tunnel with blocking and diffuser. I

本文采用Realizable k-ε双方程紊流模型和VOF法,并结合模型试验,对一种新型的水平旋流复合式内消能泄洪洞的流态及水力特性进行了分析。结果表明:旋流洞段为空腔直径沿程变化的旋流,扩散段为气水混掺的旋转两相流;空腔直径沿程表现出分段变化的特点,在起旋室内与阻塞扩散段变化较大,在旋流洞段变化较平缓;旋流洞段壁面压强整体较大,但在旋流阻塞段迅速降低;旋流空腔负压沿程增大并在旋流阻塞起始点达到最大;旋流洞段发生空化空蚀可能性较小,而扩散段末端有出现空化空蚀的可能性,需加强结构设计或采用超空化体型。旋流阻塞的设置增大了旋流洞壁面压强,减小了空化空蚀的可能性。

Numerical simulation was conducted for spiral-flow in a composite spillway tunnel of internal energy dissipation with a realizable k-e turbulence model and a VOF model, and hydraulic characteristics of the tunnel were analyzed based on physical model tests. By the simulation, the flow changed its regime from a spiral flow with a cavity core of variable diameter in the level vortex section into a rotational two-phase flow of water-air mixture in the expansion section. The diameter of cavity core took different variation trends in different sections along the tunnel, and it varied faster in a greater extent in the sections of vortex generator and blocking-expansion device but slower in the level vortex section. Tunnel wall pressure in the level vortex tunnel, quite high overall, showed a sharp drop in the blocking section, and the core pressure of rotary cavity that keeps negative, was slowly dropping along the tunnel until its minimum at the inlet of blocking section. The outlet of expansion section, where flow cavitation could not be ruled out, needs a special attention in structure design. Application of the blocking to flow rotation, however, can raise the wall pressure in the vortex tunnel and hence suppress the possibility of flow cavitation.