Abstract: The heavy rainfall and mist flow induced by flood discharge atomization of high dam projects may have negative effect on the hydropower project and its surrounding environment. Researchers have done much work on its influence region and rainfall intensity distribution on the downstream banks. Because of the complexity of this phenomenon, the formation mechanism of the flood discharge atomization is still not well revealed. Using high speed video technique in simplified hydraulic model tests, we observed the formation process of flood discharge atomization when a deflecting flow nappe drops into the downstream pool in different hydraulic conditions. We especially focused on the movement of the flow nappe and surface water around the drop area, and then analysed the components of different sources and their features. We obtain that the flood discharge atomization source could be divided into two types: dropping caused by the instability and aeration of nappe, and splashing caused by the collision between nappe and downstream water. Specially, the formation of the splashing atomization source is closely related with the periodical formation and dissipation of water surface bulges in the nappe drop area.

Key words: flood discharge atomization, atomization source caused by nappe drop, jet nappe, drop area, nappe splash