相干结构的尺度相似性与尺度相似亚格子模型

Scale similarity of coherent structures and scale-similar sub-grid model

为了对多尺度相干结构在湍流大涡模拟尺度相似亚格子模型中的作用进行实验测量研究,分析尺度相似亚格子模型的适用尺度范围以及尺度相似亚格子模型沿平板湍流边界层法向的变化规律.用热线风速仪以高于对应最小湍流时间尺度的分辨率精细测量了风洞中平板湍流边界层不同法向位置流向速度分量的时间序列信号,用局部平均速度结构函数检测湍流多尺度相干结构的条件采样方法将壁湍流信号中的多尺度相干结构成份与非相干成份分离,比较去除多尺度相干结构成份前后尺度互相关系数的变化规律,研究多尺度相干结构在湍流不同尺度间动量、能量传递的机理.研究表明,不同尺度的湍流结构相似特性存在一个尺度范围,大涡模拟的尺度相似亚格子尺度不能大于能量最大尺度.

The research sought an investigation of the effect of multi-scale coherent eddy structures on scalesimilar LES （large eddy simulation） sub-grid model of turbulence flow. The main focus of the study examined the valid scale range of LES scale-similar sub-grid model, as well as its evolution in normal-wall direction across turbulent boundary layer. Time sequence signals of longitudinal velocity component at different normal-wall positions in turbulent boundary layer are measured by IFA300 constant temperature anemometer and hot-wire probe with sampling resolution higher than the frequency that corresponds to the smallest time scale of turbulence. Multi-scale coherent eddy structures are extracted from turbulent fluctuating velocity signals by locally-averaged velocity structure function and conditional sampling method. Velocity fluctuating signals, including or excluding coherent eddy structures, are separated respectively. A comparsion of scale-correlation factors with and without multi-scale coherent eddy structures was performed. The mechanism of kinetic and momentum transfer in turbulence was revealed utilizing the concept of multi-scale coherent eddy structure. There is a scale range where scale similarity is valid. The scale where LES scale-similar sub-grid model is valid must be smaller than the maximum energetic scale.