Turbulent swirling flows viewed from the notion of helicity

从螺旋度的概念看湍流旋流

基本信息

批准号：
17540349
负责人：
YOKOI Nobumitsu
金额：
$ 1.86万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

A variational analysis based on the notion of the helicity (correlation between the velocity and the vorticity) was performed. It was shown that the mean-velocity profiles that minimize the enstrophy of the mean flow under the constraint of the constant helicity is realized, whose profiles are in good agreement with the counterpart observed in a turbulent swirling flow. In addition to the helicity constraint, we took the angular-momentum conservation into consideration. This treatment made it possible to reproduce the mean-velocity profiles in an axially rotating turbulent pipe flow in a manner similar to the case in a turbulent swirling flow, whose behaviors appeared to be totally different from each other.The turbulent helicity has been expected to be one of the important turbulent quantities in describing the large-scale structures in tubulent flows. It is, however, true that information on turbulent helicity has been lacking in the study of turbulence. This made it difficult to appropriately simulate turbulent flows with a turbulence model adopting the helicity as a basic statistical quantity. In this research, data of the representative experiment of turbulent swirling flows were re-examined from the viewpoint of the turbulent helicity. The analysis revealed what mechanism is dominant in producing the turbulent helicity.Another improvement is attained in relation to the eccentricity of the turbulent swirling flow in the center region. The highly asymmetric mean-velocity profiles in the center region observed in the experiments were calibrated with the aid of physical arguments such as the symmetry and conservation properties of the swirling flow. It is expected that this calibrated profiles provide a firm basis for the numerical simulation of the turbulent swirling flow.

进行了基于螺旋度（速度和涡度之间的相关性）概念的变分分析。结果表明，实现了在恒定螺旋度约束下最小化平均流熵的平均速度分布，其分布与在湍流旋流中观察到的对应分布非常一致。除了螺旋度约束之外，我们还考虑了角动量守恒。这种处理使得可以以类似于湍流旋流中的情况的方式再现轴向旋转湍流管流中的平均速度分布，其行为似乎彼此完全不同。预计湍流螺旋度是描述湍流中大尺度结构的重要湍流量之一。然而，湍流研究中确实缺乏有关湍流螺旋性的信息。这使得采用螺旋度作为基本统计量的湍流模型难以正确模拟湍流。本研究从湍流螺旋度的角度重新审视了湍流旋流的代表性实验数据。分析揭示了产生湍流螺旋度的主要机制。另一个改进是关于中心区域湍流旋流的偏心率。实验中观察到的中心区域高度不对称的平均速度分布借助旋流的对称性和守恒定律等物理参数进行了校准。预计该校准剖面可为湍流旋流的数值模拟提供坚实的基础。