Numerical Simulation Of Strong Shear Two-phase Flow In Horizontal Vortex Spillway Tunnel With Blocking

Adding the obstruction at the end of swirling tunnel could not only largely improve the situation of negative pressure and high velocity, but also can increase the rate of energy dissipation. However, for the horizontal vortex spillway tunnel with blocking,the study on two-phase flow in the blocking and diffusion section is not mature.Based on the project of The Natural Science Foundation of China——Study on Hydraulic Characters of Two-phase Intense Shear Flow in A Compound Inner Dissipation with Rotary-obstruction and Rotary-diffusion, this paper adopt numerical simulation, with the Realizable k-? model and the Mixture model, to study the two-phase flow in the blocking and diffusion section. The main research results are as follows:(1) The theory and method about numerical simulation of water-air two-phase flow are studied and discussed in detail and a set of suitable conditions for the simulation of strongly swirling water-air two-phase flow has been chosen.(2 ) The change regulations of the basic two-phase hydraulic characteristics in the blocking and diffusion section are described and analysed, including the flow pattern, the swirl cavity diameter, the pressure, the flow velocity, the turblent kinetic energy and the turblent disipation rate.(3) The total energy dissipation in the horizontal vortex spillway tunnel with blocking can reach up to 80%, and the energy dissipation in the blocking and diffusion sections and the front part of diversion tunnel, is about half of the total, which has a good effect of energy dissipation.(4) In the diffusion section and the front part of diversion tunnel, cavitation number is low, which could lead to the risk of cavitation. But, the flow near the end of diffusion is water-air two-phase flow, fully and equably, which could reduce the possibility of cavitation destruction.(5) By analyzing the flow pattern and the distribution of the flow velocity, it's considered that the main inducement of the mixing in the blocking and diffusion section is the hydraulic jump. The aeration mechanism is mainly similar to that of the free-surface air entrainment in the hydraulic jump flow, as well as the effect of rotating centrifugal force, so the new concept of the air entrainment in the vortex hydraulic jump flow was proposed.