Coherent Structures in Complex Sheared Flows

复杂剪切流中的相干结构

• 批准号: RGPIN-2020-05122
• 负责人: NASIF, GHASSAN(GUS)
• 金额: $ 1.68万
• 依托单位: University of Windsor
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=760495
• 关键词: Coherent; Structures; Complex; Sheared; Flows

Turbulence is a ubiquitous feature of most fluid flows in engineering and industrial applications. The random motion of the fluid particles within the flow provides a major influence on the mixing process and the interaction with the solid surfaces in wall-bounded flows. Turbulent flows can generally be decomposed into coherent and incoherent parts. The existence of the multi-scale coherent (or turbulent) structures in the flow has an important effect on flow dynamics. They act to redistribute the kinetic energy and they are responsible for the transport of mass, heat, and momentum in the mixing layers. Thus, focusing on these structures can be considered as an appropriate and fruitful approach to characterize and understand turbulent flows. It is postulated that the fluid-air interaction in a two-phase flow has a significant effect on the coherent structures, particularly at locations close to the free-surface. Furthermore, the flow dimensions determine the strength and the fluctuation degree of the secondary currents, which also affect the evolution and distribution of the structures. Although researchers have broadly investigated turbulent flows, the internal turbulence mechanism and the influence of the aforementioned effects on the turbulence characteristics are still highly debated. The fact that turbulent flows are strongly three-dimensional creates challenges for identifying the coherent structures using quantitative techniques at moderate and high Reynolds numbers. This is attributed to the inherent limitations and high cost of conventional measurement devices which, contrary to a numerical approach, do not offer quantitative isosurfaces of velocity, pressure, and vorticity With the availability of instrumentation and enhanced computational tools, it is possible to begin a research program to address the above issues and understand their effects on the turbulent structures. An innovative and advanced computational research program will be considered in this research to cope with the limitations in the experimental methods. Available tools in our labs will be used to run a few experiments for validation purposes. To achieve the goals of the current research, different flow fields have been chosen for the study: smooth and rough open-channel flow, flow past a bluff body, and flow over forward and backward-facing steps. In all cases, a two-phase flow model with various aspect ratios will be used to investigate the effect of the flow parameters on the coherent structures. The key objectives of the present research are: (i) to improve our understanding related to the turbulent structures in different flow fields, (ii) provide an enhanced picture of the formation and dynamics of the structures near the free-surface and (iii) investigate the effect of the secondary current on these structures. The study will provide valuable tools that can be used in engineering applications. Over the 5-year cycle, 10 HQP (5 MSc, 5 BSc) will be trained.

湍流是工程和工业应用中大多数流体流动的普遍特征。流体颗粒在流动中的随机运动对壁面流动中的混合过程及其与固体表面的相互作用有着重要的影响。湍流一般可分解为相干部分和非连贯部分。流动中多尺度相干(或湍流)结构的存在对流动动力学有重要影响。它们起到重新分配动能的作用，并负责混合层中的质量、热量和动量的传输。因此，将重点放在这些结构上可以被认为是描述和理解湍流的一种适当和富有成效的方法。假设两相流中的流气相互作用对拟序结构有显著影响，特别是在靠近自由面的位置。此外，水流尺度决定了二次流的强度和起伏程度，也影响了结构物的演化和分布。尽管研究人员对湍流流动进行了广泛的研究，但其内部的湍流机制以及上述效应对湍流特性的影响仍存在较大争议。湍流是强三维的，这给在中雷诺数和高雷诺数下使用定量技术识别相干结构带来了挑战。这归因于传统测量设备的固有局限性和高昂的成本，与数值方法相反，这些设备不能提供速度、压力和涡度的定量等值面，随着仪器和改进的计算工具的可用，有可能开始一个研究计划来解决上述问题并了解它们对湍流结构的影响。这项研究将考虑一种创新的、先进的计算研究方案，以应对实验方法的局限性。我们实验室中的可用工具将用于运行几个实验以进行验证。为了达到本次研究的目的，选择了不同的流场进行研究：平坦和粗糙的明渠水流、钝体绕流以及前后台阶的绕流。在所有情况下，将使用具有不同长宽比的两相流模型来研究流动参数对相干结构的影响。本研究的主要目的是：(I)加深我们对不同流场中湍流结构的理解，(Ii)提供关于自由面附近结构形成和动力学的增强图像，以及(Iii)研究二次流对这些结构的影响。这项研究将为工程应用提供有价值的工具。在5年的周期中，将培训10名HQP(5名硕士，5名理科学士)。