Numerical Simulation And Application Of Frazil Ice Evolution In Diversion Channel In High Attitude And Cold Regions

Ice dam age is the key problem hi ndering norm al operation of hydropower stations especially the diversion hydropower stations in high altitude and cold regions. The ice damage to diversion channel is clos ely related to the frazil ice evolution. At present, less attention is pa id to numerical simulation of frazil ice evolution, and the numerical models have mainly been one or two dimensional models. Therefore, it is of great significance to investigate the mechanism of fr azil ice evolution, and systematically analyze the key factors which influence the thermal balance.A 3-D unsteady Euler-Euler two-phase k-εturbulence model is developed. The interaction between ic e and water is f ully considered in mom entum transfer term, which includes the drag, virtual m ass, lift forces, buoyancy force caused by density and temperature difference. Solar radiation, effective radiation, evaporative heat loss and convective heat loss on water surface are considered in thermal transfer term, and the heat transfer between ice and water is also considered. The prediction by the present model for ice evolution is confir med by the em pirical quantity of ice and simulated results of ice evolution in the upper Yellow River reported by Wu Jianjiang. Diversion channel of a hydropower station in Northwest of China is taken as a case. The impact of key influence factors on thermal balance (temperature, diversion water flux, and wind velocity) on the frazil ice evolution is simulated, and the velocity, temperature, ice volum e fraction along the channel are analyzed. The results show that:(1) The water velocity is higher in the center of channel than it near the bank. It increases gradually in the transition secti on of tunnel inlet, wh ile decreases in the transition section of tunnel outlet. T he water velocity decreases in the bend channel. The regulation of ice velocity is similar to the water velocity.(2) Ice temperature increas es sh arply along the chann el, while the water temperature recovers from a m inimum va lue. There is a sudden point of ice concentration distribution along the diversion channel. The location of the sudden point and the lowest water temperature is almost the same.(3) The ice quantity and ice concentrati on increases along the channel. The ice concentration in the center of channel is h igher than it near the bank of channel. It is decreased gradually along the water depth direction. (4) By analyzing the ef fect of temperature, water flux, and wind velocity on ice quantity, it is concluded that the m ain factors of a ffecting ice quantity in diversion channel are in order of temperature, wind velocity, and water flux.