圆柱绕流尾涡图像的灰度特征和纹理特征

Grayscale histogram and texture features of wake vortex image behind circular cylinder

图像技术是流体力学研究的重要手段,在流动显示和流动测量中应用广泛;随着信息技术的发展,图像技术在流动规律研究的应用不断深入。论文以圆柱绕流为对象,分析雷诺数Re=50~1725时尾涡图像的分布特征,解析图像的灰度特征参数和纹理特征参数随雷诺数的变化规律,并开展流动特性解释。研究发现,圆柱绕流的紊动扩散速率、分离点位置、尾涡空间分布的变化导致了图像灰度与纹理呈现出不同的识别特征:当Re<600时,尾涡的灰度直方图的均值随雷诺数的增加线性递减;当Re=148~642时,基于尾涡图像的纹理对比度推导出的尾涡脱落周期长度与经验取值吻合良好;当Re>170时,灰度歪斜度随雷诺数递增且表现为明显的线性关系。

Image technology is an important approach to fluid mechanics research widely used in flow visualization and flow measurement,and its application in such research is continuously deepening with the development of information technology.By taking the flow past a circular cylinder as an example,this paper analyzes the image characteristics of wake vortices in the Reynolds number(Re)range of 50 to 1725.We examine variations in the image feature parameters of grayscale histogram and texture with Re,and give an interpretation related to flow characteristics.The results show three factors,the turbulent diffusion rate of the wake flow,separation point locations,and the spatial distribution of wake vortices,are responsible for different characteristics of the grayscale histogram and texture.At Re<600,the mean value of gray level decreases linearly with Re;at Re=148~642,the vortex shedding period based on texture analysis agrees well with its empirical calculation;at Re>170,the skewness of grayscale histogram increases with Re and follows a linear correlation.