Authors: Razieh Jalalabadi, Norouz Mohammad Nouri
Abstract: Cavitation, usually known as a destructive phenomenon, involves turbulent unsteady two-phase flow. Having such features, cavitating flows have been turned to a challenging topic in numerical studies and many researches are being done for better understanding of bubbly flows and proposing solutions to reduce its consequent destructive effects. Aeration may be regarded as an effective protection against cavitation erosion in many hydraulic structures, like gated tunnels. The paper concerns numerical simulation of flow in discharge gated tunnel of a dam using RNG model coupled with the volume of fluid (VOF) method and the zone which is susceptible of cavitation inception in the tunnel is predicted. Then a vent is considered in the mentioned zone for aeration and the numerical simulation is done again to study the effects of aeration. The results show that aeration is an impressively useful method to exclude cavitation in mentioned tunnels.
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Authors: Xin Hua Wang, Zhi Jie Li, Shu Wen Sun, Gang Zheng
Abstract: The cavitation flow characteristics in jet pipe amplifier with different nozzles were simulated using commercial computational fluid dynamics (CFD) software. The influence of operating parameters and structural parameters of jet nozzles on cavitation jets are the key objective. These parameters mainly include inlet pressure, outlet pressure, temperature of water, nozzle convergence angle, the length of the nozzle cylindrical section, nozzle diameter and nozzle export chamfer angle. The results provide methods to limit the emergence and development of the nozzle jet internal cavitations.
617
Authors: Si Qing Zhang, Guo Hua Ma, Jing Qian
Abstract: The numerical simulation of cavitation flow field in a Francis turbine runner with attached blades was conducted based on the no-slip mixture model in the Euler approach and the Singhal cavitation model. The RNG model after correcting viscosity and the pressure correction algorithm (SIMPLE) were supplemented. The distributions of the water-vapor volume fraction under non-design conditions were obtained. The results show that the method based on two-phase mixture model can be used to simulate the position and degree of cavitation flow in Francis turbine.
637
Authors: Hao Ling Ren, Tian Liang Lin, Cheng Miao, Zhong Shen Li, Sheng Jie Fu
Abstract: Valve orifice is the common place that the cavitation easily occurs in the hydraulic systems. This paper introduces a criteria to estimate the inception of the cavitation of the V-type valve orifice with the stress state. Based on this criteria, a cavitation model which considers the dynamics of the cavity and incompressible gas is proposed to analyze the pressure, stress and the cavitation distribution of the phase in the V-type orifice. The distributions of the cavitation along the axis and the cross section are analyzed. The simulation results show that the cavitation is easily occurred in the downstream just after the orifice and the bubbles are mostly gathered in the top of the cross section which is vertical to the axis of the flow field. The simulation results is reasonable according to the facts. Accordingly, the cavitation of the V-type orifice is predicted reasonably. The research and results of this paper are useful for the design of the hydraulic valves.
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