The Study On Hydraulic Characteristics Of Long Distance And High Drop Water Supply Pipeline By Gravity

In recent years, with the rapid process of urbanization in China, the mountain town construction has obtained rapid development, as one of the life-line engineering, the water supply project developments has lagged behind. The mountainous terrain has special terrain of fluctuation in height difference, steep in slope potential, less in flat terrain etc, based on the above especially, the water delivery systems in mountainous city are also long distance and high head gravity water delivery systems. However, due to the long distance, terrain elevation, complex hydraulic conditions inside the pipeline and other factors, the system supply water to the town under gravity, on one hand, the excess pressure that locates in low-lying nodes of the pipeline leads to pipe burst; on the other hand, when the pipe valves is suddenly closed, rapid change in flow velocity, the pressure inside the pipeline largely fluctuates, and causes water hammer accident, leads to pipe burst, the water delivery pipe burst poses a serious threat to the safety of water supply in mountain town. Therefore, studying the hydraulic characteristics of long distance and high head gravity flow conduit and proposing the control measures of water hammer pressure have important theoretical and practical significance to ensure the safety of water supply in mountain towns.First of all, based on the field investigation and literature, summarizes the macro hydraulic characteristics of long distance and high head gravity flow water transfer, on this basis, establishes the calculation model of water hammer pressure by the fluid mechanics theory of steady flow, transient flow and bubble motion etc. And the model is used to write Matlab program, carry out numerical calculation, analyses the impact of distance and height to the hydraulic characteristics of gravity flow pipeline that under steady-state and transient conditions, the numerical results show that: ①when the pipeline is operating under steady state, the pressure in bottom pipe joint is very high, bubbles easily gather at convex points, and can lead to flow decreases or disconnection in pipeline; ②when the pipeline length increases, the maximum pressure in the valve at the end of pipeline increase first and then decrease, the increase in frictional head loss caused by increase in pipeline length is the main reason of decrease in the maximum water hammer pressure;③when the pipeline height difference gradually increases, the maximum pressure in the valve at the end of pipeline increases gradually, on the basis of height difference,the steady-state pressure changes a little; ④when the height and length increase with linear correlation at the same time, the pipeline length and height difference has reduction and increase effect on the maximum pressure in valve, but as a whole, with the increase of height difference and the length of pipeline, the maximum pressure in valve gradually increases;⑤when the gas containing the pipeline, the calculation should consider the impact of water hammer with gas, if there gas transients occurrence in pipeline, the maximum pressure of valve-closing hammer can occur at any node of the pipeline.Secondly, based on the study on hydraulic characteristics of long distance and high drop water delivery pipes with gravity flow, research the protective measures of water hammer pressure, analysis the causes and pressure change characteristics of long distance and high drop gravity water hammer. The pressure regulating principle of the protecting devices is described, such as air valve, over-pressure relief valve, hydraulic-control butterfly valve, two-way surge tank. Different water hammer protection schemes are took to calculate a county water diversion project in Ganzi and a county-level city water diversion project in Inner Mongolia. In the county water diversion project in Ganzi, the scheme of installing double-acting air valve, over-pressure relief valve, hydraulic-control butterfly valve and common two-way surge tank in designated position can meet the requirements of water hammer protection target. In the county-level city water diversion project in Inner Mongolia, the scheme of installing double-acting air valve, hydraulic-control butterfly valve, box-way surge tower in designated position can meet the requirements of water hammer protection target.In summary, the project puts forward modeling method and numerical calculation model of water hammer pressure calculation theory, studies the hydraulic characteristics of mountain towns, long distance and high gravity conduit with gap length and gap, and the water hammer pressure protection equipment pressure principle were analyzed, finally, combined with the engineering practice verified. The safety of water supply has certain theoretical guidance and practical reference value of the research results of the mountain town of long distance and high gravity drop water pipeline. Studies the hydraulic characteristics variation rules of long distance and high gravity conduit in mountain towns with the length and gap changes, and pressure regulating principle of the water hammer protective equipment is analyzed, finally, verified the principle with the engineering practice. The research results have some theoretical guidance and practical reference value for the safety of long distance and high drop gravity water supply pipeline.