Experimental study of drag reduction in flumes and spillway tunnels

Experiments in an open flume model and spillway tunnel model were carried out using drag reduction techniques. Two drag reduction techniques were adopted in the experiments： polymer addition and coating. The drag reduction effect of a polyacrylamide （PAM） solution and dimethyl silicone oil coating were studied in the flume model experiments, and the results were analyzed. Experiments were then carded out with a model of the Xilnodu Hydropower Station, the second largest dam in China. In order to reduce the resistance, the spillway tunnels were internally coated with dimethyl silicone oil. This is the first time that these drag reduction techniques have been applied to so large a hydraulic model. The experimental results show that the coating technique can effectively increase flood discharge. The outlet velocity and the jet trajectory distance are also increased, which enhances the energy dissipation of the spillway tunnel.

Research on the optimal design of spillway tunnel

In order to meet the needs of various tasks of water conservancy project, tunnel excavation under the ground, called hydraulic tunnel. Hydraulic tunnel according to the functions of flood discharge, water diversion, irrigation, water supply, and the construction diversion tunnel of desilting emptying. Nowadays, water conservancy project on flood discharge runnel design requirements more and more high, so the factors taken into account the amount of spillway tunnel engineering, engineering cost, structure design and other factors to evaluate nature of the spillway tunnel is very important. Therefore, in actual construction, of spillway tunnel of optimization design, whether from the economic point of view, or from the point of view of safety and applicability are necessary. This article mainly from the overall layout of flood discharge tunnel, structure design and so on, and then discuss the optimization scheme.

3-D NUMERICAL SIMULATION OF FLOW THROUGH AN ORIFICE SPILLWAY TUNNEL

A Large Eddy Simulation (LES) approach based on the weakly compressible hydrodynamic equation with a single plase fluid model for the cavitation flow has been developed and employed in simulating 3 D unsteady viscous flow through an orifice type spillwy tunnel. The finite volume approach in space and the predictor corrector method in time have been used to the numerical discretization, and the 'Law of wall' is applied at the solid boundary. The velocity, pressure fields and the cavitation phenomenon are obtained, the computational results show that 3 D LES approach can give more realistic flow field prediction of the orifice type spillway tunnel.

HYDRAULIC RESEARCH OF AERATORS ON TUNNEL SPILLWAYS

The selection of the configuration and size of an aerator was of importance for a tunnel spillway under the conditions of high speed flows. Experimental investigations were conducted on the effects of entrained air on the tunnel spillway in the Goupitan Project, based on the criterion of gravity similarity and the condition of aerated flow velocity of over 6 m/s, with physical models. The configurations of the aerators were presented of a larger bottom air concentration, to protect the tunnel spillway from cavitation as well as to see no water fills in the grooves.

Cavity filling water control below aerator devices

With the rapid development of high dam projects within China, the dragon-drop-tail spillway tunnel is introduced and widely used. In view of the high water head and the large flow velocity on the dragon-drop-tail section, aerator devices are usually placed for the cavitation damage control. For the device placed in its initial position, it is a serious concern to design a suitable flow regime of the cavity and to control the cavity filling water due to the large flow depth and the low Froude number through this aerator. In this study, the relationships between the geometries of the aerator device and the jet impact angle of the lower trajectory of the flow are theoretically analyzed with/without a local slope. Nine test cases with different geometries are designed, the effectiveness of the filling water control is experimentally investigated under different operation conditions, and two criteria of the local slope design are proposed. It is concluded that the cavity flow regime and the filling water can be improved if a small impact angle and some suitable geometries of the local slope are designed.

Technology improvements and management innovations in construction of Xiluodu hydropower station on Jinsha River

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