Experiments and Modeling of Bubbly Surface Jets

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)提供资金的。这项研究项目将评估气泡的存在对湍流结构、速度分布以及最终由表面射流引起的水卷吸的影响，以及由此产生的气相分布。有充分的实验证据表明，与含有气泡的自由表面平行的水平表面喷流比单相喷流携带更多的周围水。除了进一步加深关于两相表面射流的基本知识外，该项目还旨在检验气泡的存在将增加表面射流携带的水的假设，并为评估处理两相表面射流的两相流动模型提供完整的数据集。这些实验将复制沃克等人的实验。(1995)，但将增加一个文丘里型气泡喷射器，气体体积分数从0到30%。速度和雷诺应力将使用条件平均技术用热膜探头测量。用多尖端玻璃光学位相探测探头测量气体体积分数、气泡速度和尺寸分布。根据平均速度测量，将进行质量和动量平衡计算，以推断水的夹带程度。模拟的目的是测试现有两相流模型捕捉实验观测结果的能力，并确定需要改进模拟的领域。这项工作将是第一次研究气泡对表面射流的影响。这个项目是为博士论文而开发的，也是研究和教育的重点融合。如果成功，该项目将促进关于射流/自由表面相互作用以及气泡对湍流特性和水夹带的影响的基本知识。该项目将有助于理解和改进溢洪道下游流动的模拟，在溢洪道下游，高度通风的表面射流的存在导致大多数数值模型严重低于对卷吸，从而对流型的预测。更好的建模能力可以设计出缓解措施，以减少气泡夹带和向高深度输送，最终导致大量总溶解气体浓度和泡沫鱼疾病，这是非常令人关注的环境问题。气泡表面射流还出现在许多工程应用中，特别是在对国家安全具有重要意义的舷尾船舶和喷水动力船舶上。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Carrica0853286This research project will evaluate the effect of the presence of bubbles on the turbulence structure, velocity distribution and ultimately the water entrainment caused by surface jets, as well as the resulting gas phase distribution. There is ample experimental evidence that a surface jet issued horizontally, parallel to a free surface containing bubbles entrains more surrounding water than that of a single-phase. Besides furthering basic knowledge on two-phase surface jets, the project is designed to test the hypothesis that the presence of bubbles will increase the water entrained by the surface jet, and to provide a complete data set to evaluate two-phase flow models dealing with two-phase surface jets. The experiments will replicate those of Walker et al. (1995), but will add a Venturi-type bubble injector with gas volume fractions ranging from 0 to 30%. Velocities and Reynolds stresses will be measured with hot film probes using conditional averaging techniques. Gas volume fraction, bubble velocity and size distribution will be measured with a multiple tip glass optical phase detection probe. From the averaged velocity measurements mass and momentum balance calculations will be performed to infer the degree of water entrainment. The simulations are intended to test the ability of the available two-phase flow models to capture the experimental observations, and to identify the areas that need modeling improvements. This work will be the first study of the effects of bubbles on surface jets. This project has been developed for a doctoral thesis and so is a focused confluence of research and education. If successful, the project will advance the basic knowledge of jet/free surface interaction and the effects of bubbles on turbulence characterization and water entrainment. This project will help understand and improve modeling of flows downstream of spillways, where the presence of highly ventilated surface jets causes most numerical models to grossly under predict entrainment and thus the flow pattern. Better modeling capabilities can devise mitigation measures to reduce the bubble entrainment and transport to high depths that ultimately causes large total dissolved gas concentrations and bubble fish disease, which is of great environmental concern. Bubbly surface jets also appear in many engineering applications, notably on transom stern ships and in waterjet powered ships, of importance to national security.