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国外五十年代开始采用的窄缝式挑流消能,为解决狭谷河段建坝的消能防冲问题开辟了一条新途径,国内是从七十年代中期开始这方面的介绍、研究与应用的。实践与研究都说明,窄缝挑流是适于狭谷河段枢纽泄水建筑物的消能措施。由于窄缝挑流的挑坎出口断面急剧收缩,其水流条件比较复杂,所以这种消能工有待于进一步探讨。本文仅就收缩段的水流特性及挑距计算问题作一些研究。(一)窄缝挑坎收缩段的水流特性1.窄缝挑坎的起挑水头窄缝挑坎的水舌流态是随上游水头的升高而变化的。底孔上采用窄缝挑坎,水流首先由强迫水跃转化为过渡流态,即水舌主体形成挑流,挑坎内水流表面仍有漩滚存在(图1—a)随水头增高表面漩滚的挑出,且当收
The narrow-slot stream-type energy dissipation adopted in foreign countries in the 1950s opened up a new way for solving the energy-dissipation and anti-scouring problems in the construction of the Daxue reach. The domestic introduction, research and application started from the mid-1970s of. Both practice and research show that the narrow-gap pick-off is an energy dissipation measure suitable for the drainage structures in the hub of the valley. Due to the sudden narrowing of the outlet section of the picket with narrow slits and the complicated flow conditions, the energy dissipater needs to be further explored. In this paper, only the shrinkage of the flow characteristics and the calculation of the distance to make some research. (A) Narrow slit Tug contraction section of the water flow characteristics 1. Narrow slit pick ridge from the water head narrow slit Tug tongue water flow is with the upstream head changes. Bottom hole with narrow slit pick ridge, the water flow from the first forced transition into a transitional flow state, that is, forming the body of water picks picks, picks up the surface of the water flow there is still a spiral existence (Figure 1-a) with the head increased surface swirl Rolling singled out, and when closed