Study On Impedance Coefficient Of Surge Tank With Manifolds

Surge tank is an important part of hydropower station,it is research focus for experts and design units over the years.In surge tank's design work,it's necessary to select size and type of surge tank,and check via hydraulic transition process calculation.In hydraulic transition process calculation,the selection of impedance coefficient is essential.If the selection of coefficient is imprecise,it will affect the safe operation of hydropower,even lead to failure of whole project and irreparable loss.In conventional hydraulic transition process calculation,impedance coefficient is often selected by referring to relevant norms and calculation manual,selecting the figure based on experience.But to some surge tanks with special structure,such as surge tank with manifolds,there is error in this way.It's necessary to do hydraulic model experiment and CFD analysis,so as to obtain accurate impedance coefficient and hydraulic transition process calculation.For a surge tank with manifolds of a hydropower,in southwest China,this paper researches the impedance coefficient by hydraulic model experiment,PIV test and CFD analysis,it aims to provide reference to other surge tank which have the same structure.The main works and achievements are as follows:(1)Researching the relationship between impedance coefficient and flow ratio,impedance hole area,the number of operation unit by hydraulic model experiment.The result shows: the impedance coefficient of surge tank with manifolds is not a constant figure,it will grows with the flow ratio grows,it will also grows with the impedance hole area decreases.In bypass,the impedance coefficient of two units is larger than the single unit,but in confluence,they're nearly equal.Simultaneously,comparing relevant results via hydraulic experiment and experienced figures,it shows there is a big difference between both side,early experiment result is meaningless to select impedance coefficient of surge tank with manifolds.(2)Researching the relationship between impedance coefficient and the flow field under impedance hole.The result shows: when the impedance coefficient is larger,the flow field is more chaotic,no matter bypass or confluence.The flow-velocity of bypass increase along y axis,but in confluence,the velocity increase along x axis.Finally,this chapter analysis flow distributions of several special conditions.(3)Doing the CFD analysis of impedance coefficient,and comparing impedance coefficient of CFD and the hydraulic experiment.The result shows: their figures are both closed,it indicates that researching impedance coefficient by the CFD is feasible.