Study On Aeration Characteristics Of Different Flow Structure Areas With Low Froud Numbers

With the rapid development of hydropower enterprise, many large hydro-engineering projects have been built in recent years, characteristics of these projects are high head and large flow, dissipation problems become much more prominent. Many projects that will be built or just under construction have chosen the underflow energy dissipation instead of trajectory energy dissipation because of the poor geological conditions and high environmental requirements.Energy dissipater with step-down floor is a new type energy dissipater for high head, large flow. Because of the step-down, water diffuses along the way when it flows into the stilling pool, vortex and a strong shear turbulent diffusion are formed on both sides of mainstream, high speed of mainstream will keep away from bottom area, and underflow speed has been effectively reduced, therefore, energy dissipater with step-down floor has many advantages such as high energy dissipation rate, steady-state flow, strong adaptability of geological conditions, small water atomization and so on, thus this energy dissipater has a bright future of application. Because of the intense turbulent shear plane formed by the incidence of water and water in the stilling pool, large volumes of air is sucked in water to form water air two-phase flow. The original turbulence structure is bound to change when there are air bubble in it. Obviously, there is a great difference in the flow pattern between air bubbles and water,such as air bubbles following determines the strength of velocity difference of gas-liquid two-phase flow, the existence of the air bubbles make the water swelling and depth increases, and increases the flow pulsation and the instantaneous load of building at the same time, besides it can also cause additional turbulent dissipation. The magnitude and distribution of air concentration will affect bottom velocity, pressure, water depth and energy dissipation and other hydraulic factors of stilling pool. Without any doubt, the study of aerated flow will help people have a better understanding of the relationship between the various hydraulic factors, and it has great significance in optimizing the design of energy dissipation with step-down floor.This article is based on National Natural Science Foundation of China(Item Number:51169008), choosing hydraulic method. Air concentration, velocity,pressure of different flow structure area is measured at Froud number=3.08-5.42under different flow, different depth of the falling-sill and different incident angle. Air concentration rules and mechanism of air bubbles diffusion in this area can be drawn through the comparison analysis of the different hydraulic conditions.