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Vortical Mode Interactions and Bypass Transition Delay in Two-Fluid Boundary Layers

二流体边界层中的涡旋模式相互作用和旁路跃迁延迟

基本信息

批准号：
EP/F034997/1
负责人：
Tamer Zaki
金额：
$ 32.52万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FF034997%2F1
关键词：
Vortical Mode Interactions Bypass Transition

项目摘要

Two-fluid shear flows are ubiquitous in engineering and environmental fluid mechanics. Examples include the boundary layer above deicing agents in aerodynamics, surface cooling using a liquid film sheared by an external gas flow, and the interaction the atmospheric boundary layer with ocean waves. The instability of these two-fluid flows is clearly significant: the aerodynamic lift and drag depend on the state of the boundary layer around the airfoil, the cooling rate of sheared films depends on the disturbance level in the flow, and the instability of ocean waves leads to breakdown and sea sprays.In this proposal, the canonical problem of a boundary layer above a film of different viscosity and density is studied. The flow is subjected to free-stream turbulence, similar to what is observed in engineering and environmental flows. This interaction causes a laminar boundary layer to breakdown to a chaotic, or turbulent, state in a manner known as bypass transition. In the proposed research, the stability of the boundary layer is compared in the presence and absence of an underlying film. It is expected that, depending on the properties of the film, the breakdown to turbulence can be accelerated or delayed. Since turbulence enhances mixing and, as a result, viscous drag, our interest is in transition delay which can lead to significant cost savings via drag reduction. The research will include two components: perturbation analysis and numerical simulations. The analysis will focus on fundamental aspects of the interaction between flow disturbances and the two-fluid boundary layer, for example how a vortical perturbation is affected by the presence of the interface between the two fluids. The simulations will provide a numerical laboratory where the full non-linear breakdown process from laminar to turbulence is simulated, and the role of the underlying film quantified. The combination of the analytical and numerical approaches will provide a comprehensive view of the interaction of free-stream perturbations with the two-fluid boundary layer. Despite the focus on the canonical boundary layer problem, the proposed framework is general and is applicable to a host of other engineering and environmental two-fluid shear flows.

双流体剪切流动在工程和环境流体力学中普遍存在。例子包括空气动力学中除冰剂上方的边界层，利用外部气流剪切的液膜进行表面冷却，以及大气边界层与海浪的相互作用。这些两种流体流动的不稳定性显然是显着的：气动升力和阻力取决于翼型周围的边界层的状态，剪切膜的冷却速率取决于在流动中的扰动水平，和海浪的不稳定性导致崩溃和海sprais.In这个建议，在不同的粘度和密度的膜上方的边界层的正则问题进行了研究。流动受到自由流湍流的影响，类似于在工程和环境流动中观察到的情况。这种相互作用导致层流边界层以一种称为旁路过渡的方式分解为混沌或湍流状态。在拟议的研究中，边界层的稳定性进行了比较，在存在和不存在下伏膜。根据薄膜的性质，可以预期湍流的分解可以加速或延迟。由于湍流增强了混合，因此，粘性阻力，我们的兴趣是在过渡延迟，这可以导致显着的成本节省通过减阻。研究将包括两个部分：扰动分析和数值模拟。分析将集中在流动扰动和两种流体边界层之间的相互作用的基本方面，例如，如何涡扰动是由两种流体之间的界面的存在下的影响。这些模拟将提供一个数值实验室，模拟从层流到湍流的完整非线性击穿过程，并量化底层薄膜的作用。分析和数值方法的结合将提供自由流扰动与双流体边界层的相互作用的全面视图。尽管集中在典型的边界层问题，所提出的框架是通用的，适用于其他工程和环境的双流体剪切流的主机。