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BOTTOM AIR CONCENTRATION OF AERATED CHUTES

机译:底部空气浓度的充气滑槽

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High-speed flows on dams have a potential for cavitation damage of the concrete surface. Air introduced by so-called aerators is known to reduce those damages. These aerators are placed in regions where flow velocities are high and local pressures are low. Free surface aeration is normally not taken into account when positioning aerators. Moreover the air detrainment process downstream of the aerator is not yet fully understood. However, if the spacing between two aerators is too large, the air detrainment process reduces the bottom air concentration below the critical value required for chute protection. If the distance between two aerators is too short, super-saturation may occur, requiring uneconomically high sidewalls and increasing flow velocity due to reduced friction. An improved design guideline for aerator spacing is thus required. To understand the influence of various hydraulic parameters, an experimental approach is presented in this paper. A 14 m long hydraulic chute model with variable bottom slope built at the Laboratory of Hydraulics, Hydrology and Glaciology VAW, ETH Zurich, using remote controlled fiber-optical instrumentation was employed. Pre-aerated discharge was supplied to focus the air detrainment gradients det(C) and the bottom air concentration C_b, which is most important for cavitation protection. Results from selected measurements with a variable bottom slope between 10 % and 50 % and inflow Froude numbers up to 11 are discussed.
机译:坝上的高速流动具有混凝土表面的空化损坏的可能性。已知通过所谓的曝气器引入的空气来减少这些损坏。这些曝气器放置在流速高,局部压力低的区域中。在定位曝气器时通常不会考虑自由表面通气。此外,曝气器下游的空气剥离过程尚不完全理解。然而,如果两个曝气器之间的间距太大,则空气碎屑过程将底部空气浓度降低低于滑槽保护所需的临界值。如果两个曝气器之间的距离太短,则可能发生超饱和度,需要不经济上的高侧壁和由于摩擦力而增加的流速。因此需要一种改进的曝气间隔设计指南。为了了解各种液压参数的影响,本文提出了一种实验方法。采用了一种14米长的液压斜槽模型,采用了液压,水文和冰川术VAW,Eth苏黎世实验室内置的可变底部斜坡,使用远程控制光纤仪表。供应预曝气的排放以聚焦空气碎屑梯度DET(C)和底部空气浓度C_B,这对于空化保护最重要。从10%至5​​0%的可变底部坡度的选择测量结果,讨论了高达11的流入弗劳德数。

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