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The Separating Shear Layer Development with the Artificial Disturbances

人工扰动下分离剪切层的发育

基本信息

批准号：
01550159
负责人：
HONAMI Shinji
金额：
$ 1.22万
依托单位：
The Science University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

The separation and reattachment phenomena of turbulent shear layers have been an important subject in the engineering application. A backward-facing step flow has been investigated as a model of separated flows with the reattachment process. The perturbed shear layers can be obtained, when an artificial disturbance is provided upstream of the step edge in the backward facing step flow. For example, a fence installation upstream of the backward-facing step corresponds to the multi-step concept to enhance the turbulent mixing as in a combustor design. The aim of the present project is to understand the reattachment process by using a fence installed upstream of the separation point or by providing the step wall vibrations with a particular frequency and amplitude. Therefore, a local turbulence structure is changed drastically at the step and there might be the possibilities to control the separation and reattachment process.The following fruitful results and conclusions were obtained. The reattachment length has a strong correlation with a fence height or the vibration frequency and the amplitude. The reattachment process can be effectively controlled by changing the disturbance strength. The strong perturbation occures even in the case of a smaller disturbance, in particular, in the turbulence quantities, while the flow with a stronger disturbance involves overwhelming perturbation. The structures in the inner shear layer are strongly affected by the inherent mechanism of the turbulent mixing downstream of the step, although those of the outer shear layer are not altered even in the downstream location.

湍流剪切层的分离和再附现象一直是工程应用中的重要课题。本文研究了后台阶流作为有再附着过程的分离流模型。在后向台阶流动中，在台阶边缘上游施加人工扰动，可以得到扰动剪切层。例如，在后向台阶的上游安装一个挡板，就相当于在燃烧室设计中采用多台阶概念来增强湍流混合。本项目的目的是通过使用安装在分离点上游的栅栏或通过提供具有特定频率和振幅的台阶壁振动来理解再附着过程。因此，局部湍流结构在台阶处发生了剧烈的变化，可能存在控制分离和再附着过程的可能性。再附着长度与栅栏高度或振动频率和振幅有很强的相关性。通过改变扰动强度可以有效地控制再附着过程。即使在较小扰动的情况下，特别是在湍流量中，也会发生强扰动，而具有较强扰动的流动涉及压倒性扰动。内剪切层中的结构强烈地受到步骤下游的湍流混合的固有机制的影响，尽管外剪切层的结构即使在下游位置也没有改变。