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.

涡流是从热交换器中的试管中脱落的，在无数其他通常遇到的实际重要性流中。棚涡流可以激发设备中的振动，这又会导致无效的操作或损坏，这是一种已知现象，通常在设计中占。但是，如果液体流过一个物体，例如管子包含气体或蒸气气泡，则脱落频率可能会移动，因此极端可能出乎意料的频率。脱落频率随着脱落频率的变化而仅部分理解的流量。这项研究的目的是更好地理解遇到虚张声势的身体的多相流的物理机制（即未精简的对象）。这项研究将为解释泡泡流体物理现象的K-12学生提供记录的可视化。这种相互作用将向潜水员的学生群体引入这些流量的相关物理，目的是增加对STEM领域的兴趣。为了更深入地了解多相流中的涡旋脱落，对与泡泡流相关的物理机制进行了精心计划的基础研究，而在名义上是二维流中的圆柱体。该研究将利用最先进的实验技术，理论和数值建模来透彻地了解各种参数的流动。数值模拟将使用具有自适应网格和大型涡流模型的高阶精确流动求解器进行。气泡大小对经过圆柱体的流中边界层和涡流芯的气泡入口的概率和速率具有可预测的影响。小气泡充当被动示踪剂，而对于大气泡，浮力占主导地位。但是，对于中间大小气泡，在气泡尺寸上，涡流中气泡捕获的概率有一个显着的非线性依赖性。气泡以不成比例的速率积聚并增加局部空隙部分，脱落频率的变化有所增加。因此，要研究的问题包括：控制涡流中气体积累的主要机制是什么，分散阶段对基础流的修改会影响浪漫平均密度以外的其他机制来影响涡流的涡流，并且在先前的调查人员的数据及其奖励的范围及其奖励的范围及以前的范围是对涡流的提议？通过使用基金会的智力优点和更广泛影响的评论标准进行评估。