Study On Numerical Simulation Of Aerated Water Flow With A Two-fluid Model

Aerated water flow is a very important flow phenomena in hydraulic engineering, and is also one of the emphases of study on high-speed hydraulics. Air entrainment changes the flow characteristic largely, which, subsequently, have varies advantaged or unadvantaged effects on hydraulic structures. However, most of studies on aerated water flows, a typical air-water two-phase flows, were carried out by experiments and only a little has been achieved in theory and numerical simulation because of its complexity. Air entrained flows have been studied mainly in numerical simulation field by using of two-fluid model in this dissertation.The development of study on two-phase flows, especially on air entrained flows are brief reviewed, the basic ways to construct mathematical model of two-phase flows are discussed. The two-fluid model is adopted. The local instantaneous equations of mass and momentum of two-phase flow are derived together with the corresponding Inter-phase jump conditions. Averaged equations and jump conditions are derived using a general averaging operator, and weighting procedure is applied to obtain the general governing equations ofintwo-fluid model for two-phase flow. The closure problems of the basic equations of two-fluid models are discussed. A summary and critical assessment of research achievements on the interfacial momentum transfer term and the turbulence models are presented. A standard k-e model is developed to predict air-water two-phase flow turbulence and RNG k - s model is also applied to compare with the standard k-s model.Starting from the basic equations of two-phase flows, two-fluid model for aerated water flows is established according to the characteristics of air-water flows in hydraulic engineering. The general convection-diffuse form of the governing equations has been established for the convenience for numerical computation.The above governing partial differential equations are discretized by the finite-volume method. Colocated grid arrangement in the Catision coordinate system is applied. A corrected method is presented for equations of void fraction. The partial elimination algorithm (PEA) is implemented for momentum equations. Referring to InterPhase Slip Algorithm (IPSA), an approach is presented for the solution of the problems in the air-water two-phase flow.Aerated water flow in open channel is simulated for a given boundary condition, and the computational results of air concentration distribution are in reasonable agreement with the experimental data.The study in this dissertation has provided a good basis for numerical simulation of air-water two-phase flow in future.