Experimental And Numerical Simulation Of Water Fall And Aeration In Overflow Weir Of Siphon Well In Power Plant

There are a large number of fire/nuclear power plants in China's coastal areas,and seawater is widely used as a direct water supply system for cooling water.Because the tide level of sea water is constantly changing under the influence of season and tide,the water fall height of the overflow weir of drainage siphon well will also change accordingly.When the offshore tide level is low,the larger drop height causes more entrainment and aeration of the discharge water under the overflow weir of siphon well.Some of the bubbles drift to the open sea with the flow,forming foam under certain conditions,causing visual and olfactory pollution.With the vigorous development of China's nuclear power construction and increasing attention to environmental protection,the siphon well drainage defoaming problem in nuclear power plants is becoming more and more important and widely concerned.Physical model test is usually used to study the defoaming problem of siphon wells in power plants.Although the model test can directly reflect the aeration situation,it is difficult to obtain the numerical value which can accurately reflect the actual engineering because of the scale effect and the limitation of aeration concentration measurement methods.Compared with this,the numerical simulation method is more intuitive and effective in theory,which can remedy the above shortcomings.However,at present,there is no relevant research and Practice on the numerical simulation of Siphon Well defoaming problem.There are still great difficulties and limitations in understanding complex gas-water two-phase flow problems and simulation methods.Based on engineering practice,this paper studies and explores the law of water fall and aeration change of Siphon Well overflow weir under different control conditions by combining physical model test with numerical simulation method.The main research results are as follows:(1)It is clearly put forward that the core of the problem of flow aeration in siphon wells(the focus of attention)should be the aeration effect caused by water entrainment in the process of swirling energy dissipation in the 'back section of the weir.Through the combination of physical model test and numerical simulation analysis,the effects of different weir types,different single width discharge,different drop height and different water depth behind the weir on the variation law of aeration in the back section of Siphon Well weir is summarized and analyzed.The results of simulation study better reflect the actual situation of the project than before,and lay a foundation for the formulation of anti-foaming and anti-foaming design principles of siphon wells.(2)The VOF model in FLUENT and the standard k-? model are used for the first time to carry out the simulation calculation of water fall and aeration of Siphon Well overflow weir.The numerical simulation calculation is close to the variation law of water aeration along the course of model test,that is,the numerical simulation can approximately reflect the basic variation law of water fall and aeration effect of Siphon Well overflow weir.The simulation results can provide a reference for the preliminary optimization of defoaming measures in drainage Siphon Well.(3)Based on the comprehensive analysis results of physical model test and numerical model calculation and combined with similar engineering practice experience,the basic principles or requirements of Siphon Well overflow weir type,single width overflow,drop height,water depth behind weir and length of back section of weir are preliminarily summarized and put forward from the viewpoint of Siphon Well anti-foaming,defoaming requirement and engineering economy and practicability.It provides a reference for the defoaming design of drainage Siphon Well and the smooth development of corresponding research work,and also lays a foundation for the compilation of design guidelines or regulations for drainage siphon wells in power plants in the future.