拉格朗日剖面法在拖曳水槽涡系演化中的应用

Application of Lagrangian section method in vortex evolution experiments of a towing tank

传统研究方法对于拖曳水槽中的旋涡涡系演化实验,通常水槽的横流面使用激光片光,并对CCD相机拍摄的时间序列下的旋涡运动图像进行分析,但此类研究方法只局限于研究涡系的平面运动.为能从三维空间对于复杂旋涡的演化过程形成进一步的认识,文中提出了一种提取、重构三维复杂涡系的新方法:拉格朗日剖面法,即在基于流场描述的拉格朗日方法下,利用拍摄到的旋涡运动照片,结合伽利略变换和Matlab软件的图像处理技术,编写代码,确定颜色阈值,将流显图片转化为相应数字图像,并提取拖车运动速度与相机拍摄间隔时间重构涡系在时间维度上的相对位置,将二维平面图像转换到三维尺度中,刻画出旋涡的空间演变形态.本方法对直观认识复杂三维涡系演化现象,分析涡系干扰、演变机理具有一定价值,与常规研究尾涡空间演变的方法相比,具有性价比高的特点.

For common methods of investigating the vortex motion evolution experiment in a towing tank,a cross-flow plane is usually illuminated by the laser sheet,and vortex motion photos taken by the CCD camera which is placed on one side of the end face of the towing tank are usually analyzed.However,this method only contributes to investigating vortex planar motion.For offering further insight into its spatial evolution process,a new method named Lagrangian section method is developed to extract and restructure the three-dimensional complex vortex system structure.The method is based on the Lagrangian theory to depict the flow field,combined with the image processing technology of Matlab software to transform vortex motion photos into digital ones.Owing to Galilean transformation,their spatial relative locations are determined by considering the trailer speed and the camera shooting interval.After they are arranged logically,the three-dimensional spatial structure of the vortex system is restructured well to depict the real physical structure.The new method can help people cognize the evolution phenomenon on three-dimensional complex vortex system directly and comprehend vortex interaction mechanism better.Compared to common research technique,it has the characteristics of high cost performance.