Study On Methods Of Controlling Water-hammer Wave Velocity In Model Tests For Fluid Transients

The study on water-hammer phenomena plays an important role in both the design of water conveyance system and the operation of a hydroelectric station. It's an indispensable component of the study on the water-hammer wave propagation theory. Model tests are always of great importance to the study, and the simulation of water-hammer wave velocity is one of the key techniques in model tests.In order to control water-hammer wave velocity, some methods are usually used, i.e. making model pipelines of the wall material with lower Young's modulus of elasticity, air entrainment in model pipelines, and making use of various structures and transversal sections. The theory of water-hammer with gas and the approach to simulate the wave velocity by employing split pipe have been analyzed.The method of placing a small pipe with high elasticity full of air inside the model pipeline has been proposed in this thesis, based on the analysis of water-hammer wave velocity, their affecting factors, and the study of methods used previously.Through model tests, the following aspects have been analyzed:1. A small pipe makes the water-hammer wave velocity decreasing obviously. The effect is different because of different material, diameter, and air pressure.2. The increscent friction coefficient shows the affecting on head losses in the model pipeline with a small pipe. Also, the values are various due to affecting factors.3. The temperature in the testing laboratory affects values mentioned above.On the basis of a series of test results, the method of placing a small pipe with high elasticity foil of air in the model pipeline to decrease water-hammer wave velocity is proved to be feasible. Problems to be studied further have been proposed.