| This thesis has included two main parts:(1) Experimental study on interaction between aeration bubbles and cavitation bubbles of cavitation region;(2) Numerical simulation and experimental study on turbulence cavitation characteristics of hydrodynamic cavitation advice with multi-orifice plates.High-velocity flow can not be analyzed according to the general hydraulics problems because of its specificity, involving many aspects such as fluctuation of flow, aeration, cavitation, energy dissipation and atomization etc. Cavitation is the focus and difficulty which concerned by hydraulics experts at home and abroad. When the flow velocity reaches a certain value and flow pressure is lower than the relevant saturated vapor pressure, the hole, hollow or cavity will occur inside of the flow, which is the phenomenon of cavitation. Cavitation erosion arises from the cavity flow from low-pressure to higher pressure. It is necessary to reveal the mechanism law of cavitation on microscopic, because of the complexity phenomenon of the fluid internal. On the one hand, cavitation has a negative impact, such as destruction of the surface of the discharge structures, damage of hydraulic machinery, etc. On the other hand, it has a positive impact, such as treating hard-biodegradable pollutants, cutting steel plates, etc. Therefore, it can be enhance the integrity of the research to study to prevent or strengthen the cavitation in particular situation.In the first part, the relation between aeration bubbles and cavitation bubbles are experimental studied based on reducing cavitation erosion as a starting point. With the development of hydropower and hydraulic, the increase of discharge structure from high dams, the cavitation cause by high-velocity flow can not be ignored. In order to prevent the problem of cavitation damage because of high-velocity flow, an economic and effective measure is to set up aerators for generating forced aeration in the low-pressure cavitation regions or upper locations liable to cavitation erosion. It is necessary to study the mechanism of aeration to prevent the cavitation damage. So far, the research only on the interaction between cavitation bubbles mainly, but there is little study of interactions between aeration bubble and cavitation bubble in the cavitation region on the condition of aeration. The interaction between aeration bubbles and cavitation bubbles of cavitation region of the semi-cylindrical and cylindrical irregularities were observed in details by using three-dimensional Particle Image Velocimetry, high speed photography, and the pressure data acquisition system of Sinocera-YE6263in the Hydraulics Laboratory at Zhe Jiang University of Technology. The effects of interaction between aeration bubbles and cavitation bubbles at different gas concentrations and different flow velocities were considered. The experimental results showed that the particle images and high-speed photographs captured were consistent with velocity vector handling by the manage system. The effects of velocity and gas concentration to the interaction between aeration bubbles and cavitation bubbles were not independent through high-speed photographs. The range of cavitation cloud reduced on aeration. The empirical formula of the effective gas concentration and velocity was given, which shown that the effective gas concentration decreasing with increasing of velocity.The second part is based on using the positive effects of cavitation as a starting point. Turbulence cavitation characteristics of hydrodynamic cavitation advice with multi-orifice plates were numerical simulated and experimental studied. With the process of industrialization, it is a serious threat to human’s health with wastewater which contains large amounts of hard-biodegradable pollutants. Hydrodynamic cavitation is a new method to treat hard-biodegradable pollutants in recent years, which of great significance to solve the global water pollution problem. This paper was based on the hydrodynamic software FLOW-3D, the turbulence characteristics of multi-orifice plates with different shapes (rectangular, triangle, circle) were numerical simulated, such as turbulent kinetic energy, turbulence intensity and Reynolds stress. The effect of different velocities, multi-orifice plates with different size, number and arrangement were considered. The pressure characteristics behind multi-orifice plates were experimental studied by the pressure data acquisition system of SINOCERA-YE6263. The effect of multi-orifice plates with different size, number and arrangement to the time average pressure and frequency spectrum were considered. The multi-orifice plate which is most conducive to cavitation was obtained by optimization. |
PDF Full Text Request