Numerical Simulation And Experimental Study On Body Type Of Discharge Tunnel Based On Different Parabolic Equations

In the hydraulic engineering, when the base plate changes greatly in the water release structure and the elevation has to reduce suddenly, we often use Ogee surface to connect the upstream and downstream to prevent the occurrence of cavitations, such as the spillway tunnel, bottom discharge orifice and so on. Actually, in these circumstances, Ogee surface plays the role as smoothing the water flow. Meanwhile, in Engineering design, Ogee surface is designed as parabolic form usually, but whose coefficient, based on the experience and the importance of selected works, shows great uncertainty. With the influence of Centrifugal force, the shape of Ogee surface affects the pressure of spillway surface and the distribution of velocity in a large degree, which may cause adverse hydraulic phenomenon if designed unreasonably. Thus, it is considered as a significant practical work on developing a reasonable Ogee section.Ogee surface has been widely used in the discharge tunnel, many important data are derived from prototype observation and hydraulic model tests during researches. While, there are many restrictive conditions of prototype observation, hydraulic model test has a number of deficiencies too. However, with the development of computer technology and the theory of computational fluid dynamics, numerical simulation has been applied on the research of discharge tunnel more than before. Compared with model test, numerical simulation not only save much time and fund, but also provides detailed data and information, moreover, numerical simulation can simulate the prototype directly, taking the scale effect out of account.This paper systematically study the Ogee surface, and gives empirical formula, which shows the relationship between head, unit discharge and Ogee coefficient with the help of hydraulic model tests, numerical simulation technology and theoretical analysis. The main contents of this paper include the following aspects:Firstly, it takes model test to research on the discharge tunnel's original body discharge capacity and Ogee surface pressure of one power plant and obtains accurate data. Then, with practical experiment and theoretical analysis it points out the unreasonable designs of the original body and tests body optimization experiment specifically;Secondly, it simulates on the optimal size spillway's flow pattern and wall pressure of the discharge tunnel by means of numerical simulation, the results is well consistent with the measured data obtained from the model experiment, which proves that the methodology of numerical methods is reliable. Next, it calculates the critical Ogee coefficient under different heads and unit discharge condition, and emphasizes the significance of selecting the actual Ogee coefficient according to the critical Ogee coefficient;Finally, using rigid parabolic theory, it analysis the level and diving jet, derives the trajectory equation of free jet, and preliminary identify the factors affecting on the Ogee segment size.It collects many data about discharge tunnel parabolic equation, head, flow rate etc, around our country, combining model tests and the results of numerical simulations, through analysis as well as simulating, getting empirical formula which can be used to select fitted Ogee coefficient. Compared with the selected Ogee coefficient in actual project, it proves this formula is of high accuracy.