Free-surface vortex of crest outlets induced by flow rounding side pier.

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Fei Ma, Jian-hua Wu, Yu Wang

Tuesday 30 june 2015

17:00 - 17:15h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 7F. Engineering - Instrumentation

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The crest outlet is a usual element for discharge flood in hydropower engineering, and the operating gates are often equipped to control discharge. In fact, several crest outlets usually are designed to share discharge task together. It was observed in physical model tests that, in operating gate partly opening conditions, single free-surface vertex may occur near the emergency gate slot only at the left or right side crest outlet, but not at the middle crest outlets, and it was only adjacent to side pier, but not adjacent to middle pier. In addition, the vertex may entrain air and correspondingly flow downstream. The purpose of this paper is to reveal the behaver of this kind of vertex, including the details of its influencing factors and effect on engineering security. In this study, the crest outlet physical model tests were conducted. The model comprises of a WES spillway, a slope chute and a flip bucket. Three crest outlets are used and each crest outlet width is 16.25 cm, and the maximum head is 33.8 cm, and the maximum distance from reservoir bank to side pier is 35 cm. Present research systematically investigated the effect of operating gate opening, water head and the distance from reservoir bank to side pier on vertex. The tests results indicated that, the flow rounding side pier is major influencing factor for generating single side vertex with air-core; the air-core diameter of vertex decreased with increasing gate opening and water head, and increased with increasing distance from reservoir bank to side pier; nevertheless, the location of vertex nearly didn’t change in any case; moreover, the vertex flowed along crest outlet affected the dynamic pressure head of sidewall, the pressure head may decreased, even down to a negative value, and it is dangerous to project security.