| Water hammer is an inevitable and having certain harm unsteady flow phenomenon in hydropower station and pumping station. Hydraulic changing sharply will impact on dynamic characteristics of the units seriously, even making security threats. The mathematical model of current water hammer calculation has a long history and the computational methods are varied. This model is widely used in aerodynamics,fluid mechanics and etc,but about the improvement of water hammer theoretical model and the more reasonable calculating methods have not yet been more seen.Firstly, this paper introduces the current mathematical model and the computational methods of water hammer calculation, pointing out that the continuity equation of current water hammer computation being used in the mathematical model can't satisfy condition of steady flow. Furthermore it does not match the momentum principle that the rule of change of water body between two fixed cross-sections in the pipeline is considered when water hammer motion equation is derived from momentum theorem, the research object cannot be changed.Then this paper builds a more rational research model, which avoids those unreasonable problems of the current water hammer equation, and using momentum theorem and law of conservation mass derive a new mathematical model. According to the new mathematical model derives the calculation formula of water hammer wave speed. More, this paper obtains a new system of equations of water hammer calculation associating elasticity equation of conduit, elasticity equation of water and 1-d unsteady flow basic differential equations. Using the system in simple pipe water pressure numerical, the result indicates that it's more accurate and reasonable with the fact. So this paper associates this system of equations of water hammer with the water hammer wave speed to study the change rule of wave speed in the pipeline, the results indicate that wave speed is changing in the pipe, which are accurate with the fact. |
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