Calculable Research On Fluid Transients Of Air Cushion Surge Chamber

Air cushion surge chamber can also be named pneumatic surge chamber. The first air cushion surge chamber in the world was built in Driva water power plant in Norway in 1973. In our country, the proper application and research on the subject of air cushion surge chamber started at the end of last century or the beginning of this country. In view of the application of air cushion surge chamber being in cradle in our country, many questions need to be researched. It is impossible to involve all the problems. The purpose of this paper is only to discuss several questions involved in the calculation on fluid transients of air cushion surge chamber.(1) Calculation on water level surge of air cushion surge chamberHydraulic calculation of conventional surge chamber needs to calculate the maximum and minimum pressure of the chamber, namely the highest upsurge and lowest surge, and adds safety coefficient to the result of the highest and lowest surge to determine the size of surge chamber. The computing method of the size of air cushion surge chamber is the same as conventional surge chamber. To constant flow, the varying rule between gaseous volume and pressure meets Boyle Gas Law. But, in transient process of water diversion system, kinetic characteristic of the gas in air cushion surge chamber has certain complexity when there is great fluctuation in surge chamber. Therefore, when computing surge of air cushion surge chamber, firstly, it is necessary that gaseous volume and pressure meet actual rule and important to establish correct mathematic model. Secondly, initial height and pressure of the chamber should be confirmed correctly. Then the computing method of water level surge of air cushion surge chamber is acquired.(2) Water hammer calculation of water diversion system of air cushion surge chamber.Water hammer calculation adopts method of characteristics. Besides applying equation of continuity and momentum equation, it is greatly important to sufficiently consider the operating characteristics of air cushion surge chamber and correctly deal with any impossible boundary conditions of water diversion system of hydropower station. The attention of this paper is to establish boundary condition equation of air cushion surge chamber and consider the effects of varying of speed of rotation of the sets on heightening of water hammer pressure when handling the boundary of water turbine.(3) Defining the steady section of air cushion surge chamber.Research on steady section is one of the most important parts in studying air cushion surge chamber. To meat the water level fluctuation of air cushion surge chamber, quite large control section is necessary, which is several times even dozens of times to conventional surge chamber. That is not only diseconomy, but also goes against structural stability. The computing formula of steady section of air cushion surge chamber, put forward by the author, is more important to reasonably reduce steady section and save investment of project.(4) Calculating example of air cushion surge chamber.To an actual hydropower station, firstly, calculation on fluid transients of conventional surge chamber; secondly, choosing air cushion surge chamber and applying the investigative achievement to count analyze its fluid transients, and then, illuminating the advantages and disadvantages of air cushion surge chamber through further comparison, the further in-depth study of researching fluid transients of air cushion surge chamber will be put forward.The research results of the above have preferably solved the hot point problems discussed and studied in the process of the calculation of water diversion system unsteady flow of air cushion surge chamber, offer theoretical basis to accuracy calculation and reasonable design of air cushion surge chamber, and are helpful to make air cushion surge chamber more popularized in our country.