Shift In Shedding Frequency In Multiphase Flow Past A Cylinder

经过圆柱体的多相流中脱落频率的变化

• 批准号: 2024672
• 负责人: Simo Makiharju
• 金额: $ 39.72万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2024672&HistoricalAwards=false
• 关键词: Shift; Shedding; Frequency; Multiphase; Flow

Vortices are shed from tubes in heat exchangers and in countless other commonly encountered flows of practical importance. The shed vortices can excite vibration in the equipment, which in turn can lead to inefficient operation or damage, which is a known phenomenon and usually accounted for in the design. However, if the liquid flow past an object like a tube contains gas or vapor bubbles, the shedding frequency can shift and hence excite potentially unexpected frequencies. The flows with a shift in the shedding frequency remain only partially understood. The goal of this research is to better understand the physical mechanisms of multiphase flows encountering a bluff body (i.e. an object that is not streamlined). This research will provide recorded visualizations for K-12 students explaining the bubbly-fluid physical phenomena. This interaction will introduce a diverse student population to the relevant physics of these flows with the goal of increasing interest in the STEM field. To gain a deeper understanding of vortex shedding in multiphase flows, a carefully planned fundamental study is undertaken on the physical mechanisms relevant to a bubbly flow past a cylinder in a nominally two-dimensional flow. The research will utilize state-of-art experimental techniques, theory, and numerical modelling to gain a thorough understanding of the flow over a wide range of parameters. The numerical simulations will be carried out using high-order accurate flow solvers with adaptive meshes and large eddy simulation models. The bubble size has a predictable effect on the probability and rate of bubble entrainment to boundary layers and vortex cores in a flow past a cylinder. Small bubbles act as passive tracers, whereas for large bubbles buoyancy dominates. However, for intermediate size bubbles there is a notable nonlinear dependence on probability of bubble capture in the vortices on bubble size. For conditions where bubbles accumulate in the vortices at disproportionate rate and increasing local void fraction, there is an enhanced shift in shedding frequency. Hence, the questions to be studied include: what are the dominant mechanisms controlling gas accumulation in the vortex cores, does the modification of the underlying flow by the dispersed phase affect vortex shedding by mechanisms other than modification of average density in wake, and does the vortex shedding frequency bifurcate as suggested by previous investigators’ data?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

涡流从热交换器中的管道以及无数其他常见的具有实际重要性的流动中脱落，脱落的涡流会激发设备振动，进而导致运行效率低下或损坏，这是一种已知的现象，通常会在设备中产生这种现象。然而，如果液体流过含有气体或蒸汽气泡的物体，脱落频率可能会发生变化，从而激发出潜在的意外频率。这项研究是为了更好地理解多相流遇到钝体（即非流线型物体）的物理机制，这项研究将为 K-12 学生提供记录的可视化，解释气泡流体的物理现象。为了更深入地了解多相流中的涡旋脱落，我们对与气泡相关的物理机制进行了精心策划的基础研究。该研究将利用最先进的实验技术、理论和数值模拟来深入了解各种参数下的流动。使用具有自适应网格和大涡模拟模型的高阶精确流动求解器，气泡尺寸对经过圆柱体的流动中气泡夹带到边界层和涡核的概率和速率具有可预测的影响。示踪剂，而对于然而，对于中等尺寸的气泡，涡流中的气泡捕获概率对气泡尺寸具有显着的非线性依赖性。因此，需要研究的问题包括：控制涡核中气体聚集的主要机制是什么，分散相对底层流动的改变是否会影响其他机制的涡流脱落。与尾流平均密度的修改相比，涡旋脱落频率是否如先前研究人员的数据所建议的那样分叉？该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。