Computation Method On Cavitation Number For Spillway

This study introduces the methods and the present development of cavatation research. Form the points of half-experiential and half-theoretical method and numerical simulation, this study computes the influential factors of hydraulic cavitation , such as velocity and pressure, based on this, cavitation number can be calculated. The half-experiential and half-theoretical method is to derive the velocity distribution function on the experimental data, and it found this formula can calculate the velocity on both steep and slight slop , ogee section . The pressure of ogee section is determined by solving the differential equation which reflects the kinematic process of water on ooge section. These hydro-parameters combined with the characters of protrusion can be used to calculate the caviattion number .Numerical simulation is also be used to calculate cavitation parameters, this study attributes to the development of computer technique. The flow field is simulated by k-e turbulence equation, structure grids is employed, some particular parts are separated by some refined grids so as to get exacter results. The water surface is defined by the VOF, velocity and pressure are coupled by PISO . the simulation results is compared with the experimental data, and it fits well. Is shows this modeling can be used to compute flow field as well as cavitation number like above.Furthermore, another cavitation calculation method is proposed. The critical pressure in the center of the vortex behind the protrusion, so as to predict cavitation. The basic theory is that the water flow over the protrusion and is separated, a vortex occurring behind the protrusion, within the vortex the low pressure exists in the center part, cavitation happens here firstly, this study derives a formula which using the velocity and the pressure near the protrusion to judge cavitation, if the pressure in the center of vortex is lower than the saturated water vapor pressures with corresponding temperature , it defines cavitation occurs,beside, some parameters are corrected with experimental data. This paper employs CFD and half-experiential and half-theoretical methods to analyze the cavitation ,in addition, the incipient cavitation number is calculated in this way.