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首页> 外文会议>ASME/JSME Fluids Engineering and Laser Anemometry Conference and Exgibition >EFFECTS OF UNSTEADINESS IN TRANSITIONAL SHEAR-FLOWS: APPLICATION TO A WAKE FLOW
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EFFECTS OF UNSTEADINESS IN TRANSITIONAL SHEAR-FLOWS: APPLICATION TO A WAKE FLOW

机译：不稳定在过渡剪切流动中的影响：唤醒流动的应用

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摘要

In recent years, results from experimental and numerical investigations suggest that large scale dynamics plays a dominating role in transitional shear-flows. Many authors (Karniadakis et Al.,1992, Williamson et Al.,1993) have clearly shown that large scale structures can result from the instability of the mean velocity profile. These structures undergo a deterministic evolution strongly affected by reciprocal nonlinear interactions. In this context a dynamical system approach is a suitable tool to model large scale dynamics in transitional shear-flows because it is able to encode these deterministic processes. A dynamical system is presented, describing the local time evolution of large scale motions for a general three-dimensional disturbance superimposed to the basic velocity field. In this paper the model was applied to a two-dimensional cylinder wake in an unsteady mean flow. At this purpose an extension of the mathematical model was performed in order to achieve information on the effects of unsteadiness of the basic flow in transitional wake dynamics. Row visualisations and velocity measurements were also carried out in a hydraulic tunnel. This produced useful information to select the main features of the large scale motion in the cylinder wake. A low dimensional system, obtained as a truncated form of the proposed model, was used to describe the dynamical behaviour of the wake. A good agreement was found between the experimental and numerical results. The role of a low frequency basic flow noise in the wake dynamics was described, thus confirming other authors findings (Miksad et Al., 1992).
机译：近年来，实验和数值调查的结果表明，大规模动态在过渡剪切流动中起着主导作用。许多作者（Karniadakis等，1992，Williamson等，1993）清楚地表明，大规模结构可能是由于平均速度概况的不稳定性。这些结构经历了受互易非线性相互作用的强烈影响的确定性演化。在这种情况下，动态系统方法是一种适合于过渡剪切流模型的大规模动态的合适工具，因为它能够编码这些确定性过程。提出了一种动态系统，描述了叠加到基本速度场的一般三维干扰的大规模运动的局部时间演变。在本文中，模型应用于不稳定的平均流动的二维气缸醒来。此时，执行数学模型的延伸，以实现关于过渡唤醒动态中基本流量不稳定的效果的信息。在液压隧道中也进行了行性等值和速度测量。这产生了有用的信息，以选择气缸唤醒中大规模运动的主要特征。使用作为所提出的模型的截短形式获得的低尺寸系统来描述唤醒的动态行为。在实验和数值结果之间发现了一个良好的一致性。描述了唤醒动力学中低频基本流噪声的作用，从而确认了其他作者调查结果（Miksad等，1992）。

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