Francis Turbine Two-phase Flow Numerical Simulation

Two-phase flow phenomenon widespread in nature and modern industrial production process, and closely relate to the production and life of mankind. At present, in the water conservancy, power, chemical, nuclear power, refrigeration, oil and metallurgical industries, many production facilities are involved in the two-phase flow conditions to start. In the early two-phase flow study, due to the lack of the knowledge of gas-liquid two-phase flow and heat and mass transfer, had a number of industrial accidents.In the early 20th century Two-phase flow problems were clearly put forward in the calculation of the natural cycle of water boiler. In recent years, the two-phase flow was studied in greater depth, applied broader. Therefore numerical simulation of the two-phase flow has become one of the main research directions in the area of CFD.To simulate the two-phase flow, first we must solve is to establish the two-phase flow mathematical models. A complete two-phase flow model should include the modeling of motion equation, the handling of boundary conditions, numerical methods, the preparing program, the results visualization, and so on.In view of this, we first introduced the two-phase flow of domestic and international developments on the mathematical models and methods, and then use CFX to study the whole flow of hydraulic turbine machinery in the two-phase flow, and the part of tail pipes were further study, getting a number of results which with great theoretical and practical significance.A) In hydraulic machinery, the phenomenon of cavitation is very dangerous, it should minimize or avoid as far as possible. From our simulation results found that:in the turbine-wide flow of various places are more obvious signs of cavitation, for example, in fixed guide vanes, free guide vanes, blades and the tail pipes can be seen, which basically achieve the numerical simulation results.B) Cavitation was mainly due to the change of pressure, which is the local pressure of liquid to reduce the saturation vapor pressure. In liquid or liquid-solid internal surface at the junction of the steam or gas cavity of the formation, development and collapse, In turn caused the fluid boundary deformation and material erosion. In the leaves under the surface, easily create negative pressure; cavitation mainly occurred in these parts. The results of simulating and the results of experiments keep basically the same. C) In the tail pipes format a rotating vortex zone which will have a negative impact on the equipment. In order to deal with this problem, we can put the air into the tail pipe. The way by the cross air not only reduce the hazards of cavitaton, but also play a role in the destruction of the vortex.