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Air-water flows at hydraulic structures: Experimental investigations of interfacial characteristics and air-water mass transfer

水工结构中的空气-水流动：界面特性和空气-水传质的实验研究

基本信息

批准号：
325271838
负责人：
Dr.-Ing. Matthias Kramer
金额：
--
依托单位：
Hydraulic Engineering and Applied Fluid Mechanics
依托单位国家：
德国
项目类别：
Research Fellowships
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/325271838?language=en
关键词：
Air water flows hydraulic structures

项目摘要

Air-water mass transfer in multiphase flows plays a key role in designing hydraulic structures. Air entrainment processes typically occur in spillways, drop shafts, stilling basins or in the casing of hydraulic impulse turbines. Current knowledge of aerated flows mainly relies on experimental model investigations. For laboratory experiments, dependent scale effects have to be taken into account by ensuring similarity between model and nature, implying geometrical, kinematic and dynamic similarity. In aerated flows, consistent values of Froude-, Reynolds- and Weber-number in model and prototype cannot be fulfilled in geometrical similar models. Experiments results show that some parameters, such as bubble sizes and turbulent scales, are likely to be affected by scale effects, even in 1:2 or 1:3 scale models. Experiments in prototype scale (1:1) are barely available yet. Consequently, future research has to focus on new field measurements, performed in situ at full-scale (Chanson 2013: Hydraulics of aerated flows: qui pro quo? Journal of Hydraulic Research, 51(3), 223-243). The mass transfer of a volatile gas into a liquid mainly depends on interfacial area, diffusion coefficient and the gradient of the gas concentration. In this context, the integration of the mass transfer equation represents an analytical approach determining mass transfer. Preliminary investigations were conducted on a stepped chute with small inclination at the University of Queensland. Direct comparisons between dissolved oxygen measurements and numerical integration of the mass transfer equation showed good agreement between the two methods (Tombees 2005: Air-water mass transfer on a stepped waterway, Journal of Environmental Engineering, 1377-1386). These promising results, the urgent need of large-scale measurements and recent progresses in researching aerated flows, e.g. in signal processing and comparative analyses of different experiments, give reason to conduct new investigations in this field of research. Within the scope of the proposed project, detailed multiphase flow and oxygenation measurements on a stepped chute with steep inclination (1V:0.8H) will be conducted in laboratory and prototype scale. The planned in-situ measurements will contribute to close the existing research gap arising from missing large-scale investigations and the collected data will be used to quantify scaling effects, especially with respect to dissolved oxygen and aeration efficiency. Furthermore, experimental results of air-water flow properties are used for numerical integration of the mass transfer equation and results will be compared with measurements of the oxygen transfer rate. With the simultaneous measurement of oxygen transfer and air-water flow properties, substantial knowledge concerning the description of aerated flows is gained.

多相流中空气-水的传质是水工建筑物设计的关键问题。空气夹带过程通常发生在溢洪道、竖井、消力池或水力冲击式水轮机的壳体中。目前掺气水流的认识主要依赖于实验模型研究。对于实验室实验，必须考虑相关的尺度效应，确保模型和自然之间的相似性，这意味着几何，运动学和动力学相似。在掺气水流中，模型和原型中弗劳德数、雷诺数和韦伯数的一致性在几何相似的模型中是不可能实现的。实验结果表明，即使在1：2或1：3缩尺模型中，气泡尺寸和湍流尺度等参数也可能受到缩尺效应的影响。目前还很少有1：1的原型实验。因此，未来的研究必须集中在新的现场测量，在现场进行全面（香森2013年：加气流水力学：等价？Journal of Hydraulic Research，51（3），223-243）。挥发性气体向液相的传质主要取决于界面面积、扩散系数和气体浓度梯度。在这种情况下，质量传递方程的积分表示确定质量传递的分析方法。初步调查是在昆士兰州大学的一个小倾角的阶梯式溜槽上进行的。溶解氧测量值与传质方程的数值积分之间的直接比较表明两种方法之间具有良好的一致性（Tombees 2005：阶梯水道上的空气-水传质，环境工程杂志，1377-1386）。这些有希望的结果，大规模测量的迫切需要和最近的进展，在研究掺气流动，例如，在信号处理和不同的实验的比较分析，有理由进行新的调查，在这一领域的研究。在拟建项目范围内，将在实验室和原型规模上对陡倾角（1V：0.8H）的阶梯式溜槽进行详细的多相流和充氧测量。计划中的现场测量将有助于填补因缺少大规模调查而造成的现有研究空白，收集的数据将用于量化缩放效应，特别是溶解氧和曝气效率。此外，空气-水的流动特性的实验结果被用于数值积分的传质方程和结果将进行比较与测量的氧传递速率。通过同时测量氧传递和空气-水流动特性，获得了关于掺气流动描述的大量知识。