Author(s): Jin Feng; Jiang Bole; Chen Jian
Linked Author(s):
Keywords: Valve stand; Lateral offsets; Drop step; Side deflectors; Topslope; Small bucket; Cavitation damage; Areation concentration; Underwaternoise; Irregularities
Abstract: Practice shows that when working head is over 80m, common valve sealing cannot function normally. For this reason, tainter valve with eccentric hinge or hydraulic sealing is adopted. In this case, the both sidewalls of valve stand laterally broaden, and the bottom vertically drops. By means of physical modeling, numerical modeling and prototype survey, cavitation characteristics of valve stand with drop step and lateral offsets was studied. Physical models consisted of a 1:30 vacuum tank model of the bottom outlet at the Longyangxia Power Station, a 1:30 vacuum tank model of the deep outlet at the Three Gorges Project (TGP), and a 1:20 open flume model of the deep outlet of TGP. Weakly compressible method and large vortex modeling were applied in three dimensional numerical modeling. The equations of conservation of mass and conservation of momentum were dispersed in finite-volume method on the bound grid of hexahedron, so as to satisfy the computation in complicated flow channel. The research indicates that, for the valve stand with drop step and lateral offsets, the characteristics of areation and pressure at bottom of chute is similar to that for areator only with drop step, but broadening water jet produces high pressure gradient and intensive pressure fluctuation on the sidewalls, where areation concentration is low, so that cavitation is liable to happen. To eliminate cavitation on the sidewalls, application of side deflectors should be avoided. When width of lateral offsets is not large enough, it is recommended to reduce the top slope at the outlet and to shorten the horizontal length of lateral offsets. Cavitation, produced by the lateral offsets, can be eliminated through configuration optimization. Nevertheless, as areation concentration is low and velocity of water jet is high, it is necessary to control the irregularity of wall surface strictly within 20m downstream of the valve stand, to prevent irregularity cavitation damage.
Year: 2001