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Prevention of Cavitation and Water-Wing for Middle-Piers of Discharge Tunnels

Author(s): Wu Jianhua; Cai Changguang; Ji Wei; Ruan Shiping

Linked Author(s): Jianhua Wu

Keywords: Discharge tunnel; Middle-pier; Cavitation; Water-wing

Abstract: In the construction of high dams, the design of a middle-pier, placed in a discharge tunnel to divide it into two parts, is a better choice that could breakthrough the limits of the manufacture and operation of the gate due to the high head to it. However, cavitation and water-wing, a kind of flow striking the top and side walls of the tunnel, induced by the middle-pier, may take place and bring about bad effects on operation of the tunnel. The experimental models, manufactured with plexiglass material, its geometrical scale λl = 40, of the discharge tunnel with middle-pier for the Sanbanxi Hydropower Station, were designed according to the criteria of gravity and cavitation similarities. The experiments of the six comparing plans were conducted, consisting of atmospheric and vacuum tank models, and the interesting experimental areas included relationships between discharges and reservoir levels, measurement of side wall pressure, comparisons of water-wing states for the various middle- piers, estimations of the incipient cavitation numbers and the flow cavitation numbers and analyses of cavitation characteristics for the tunnel. A kind of new bodily form of middle-pier was developed which has inclined tail with the gradual decrease of height along the flow direction to separate the concentrated forces produced by two flows in the same section of the traditional vertical tail pier. Water-wing states were better improved and non-cavitation conditions were satisfied of incipient cavitation number less than flow cavitation number.


Year: 2005

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