Studied On Hydraulic Characteristics And Body Type Optimization Of Water Conservation Weir

In the middle line of the Project of Transferring Water from South to North in China, the Tianjin section lies from Xiheishan inlet sluice in Xushui County in Hebei, and to the Waihuan River in Tianjin. It is 155.419km long. The Tianjin section transfers water in the way of the free flow following pressure flow. The section of free flow delivers water by the two"U"canals. The section of pressure flow transports water in the means of the stepped low pressure pipes. The main controlled hydraulic structures are the inlet sluice, the stilling pool, the regulating pond, water conservation weir, diversion basin and so on. Water conservation weir is the new-style hydraulic structure that can link the pressure conduits. In the general way, the water conservation weir can be used in the stepped low pressure pipes water conveyance system. It can adjust water level distribution automatically in the pressure pipe. And it can guarantee that the pressure pipe is under pressure all the time. Based on the hydraulic model and numerical simulation, the local head loss coefficient and discharge coefficient are systematically analyzed and the local body type is initially optimized. The achievements fill in the blank of water conservation weir.The main researches made by this paper include several aspects as followings: 1. The local head loss coefficient and the discharge coefficient of the water conservation weir are studied on systematically by the combination of physical model and mathematical model. The influencing factor of the local head loss coefficient variation include water level, height of weir, relative position of weir, difference of elevation between fore and after of the weir, the dimension of water conservation weir,the operating holes and so on. The relation curve of the local head loss coefficient and influencing factors are obtained. The relation curve of the discharge coefficient and weir head has been also gotten in this paper. The work has been done to perfect the stepped low pressure water convey system.2. The local body type of water conservation weir, such as ditching depth behind the weir, top rake at the inlet of downstream pressure pipe and the length fore and after the weir, is optimized by the way of numerical simulation. Through the optimization, the flow pattern over the weir and the velocity distribution in the pipes downstream are adjusted better. The body type after optimization can accord with the flow pattern. The results can be the reference for the designers of water conservation weir.