壁湍流摩阻时空信号无接触测量实验研究

Experimental study on non-contact measurement of spatio-temporal signals in wall turbulence friction

壁湍流摩擦阻力的产生机理与实验测量是壁湍流基础研究中的重要课题,关系到流动减阻发展和工程技术变革。在壁湍流复杂相干结构迁移演化过程中,会引起内外区强烈的动量交换,使黏性底层速度梯度呈现时空变化,即局部摩擦阻力与相干结构迁移演化呈现时空关联特性。目前鲜有实验测量技术能同时对摩擦阻力时空信号及与其关联的湍流结构发展演化过程进行精准、同步的测量。作为一种无接触的流场测量方法,PIV在摩擦阻力测量方面不断被寄予厚望。本文基于高时空分辨率2D2C TRPIV时序流场的粒子图像数据,开发了一种可调时空分辨率互相关算法(Adjustable Spatio-Temporal Resolution Cross Correlation,ASTRCC)。利用该算法计算了具有高时空分辨率的壁面摩擦阻力,探究了摩擦阻力的空间波动性与时间延迟性,并从时空演化角度探索了壁湍流相干结构与局部流场摩擦阻力的时空关联特性,验证了该算法的正确性。

The generation mechanism and experimental measurement of wall turbulence frictional resistance are critical topics in the fundamental research of wall turbulence,which are related to flow drag reduction and transformative engineering technologies.The migration and evolution of complex coherent structures in wall turbulence cause intense momentum exchange between the inner and outer regions.This leads to spatiotemporal variations in the velocity gradient of the viscous sublayer.Local frictional resistance is correlated with the spatiotemporal changes in these coherent structures.Few experimental measurement techniques currently exist that can accurately and simultaneously measure the spatio-temporal signals of the friction drag and the associated evolution of turbulent structures.As a non-contact flow field measurement method,the Particle Image Velocimetry(PIV)has been increasingly expected to excel in frictional resistance measurement.This paper developed an Adjustable Spatio-Temporal Resolution Cross Correlation(ASTRCC)algorithm,based on high spatiotemporal resolution 2D2C TRPIV time-series flow field particle image data.Wall frictional resistance with high spatiotemporal resolution was calculated using this algorithm.The spatial fluctuations and temporal delays of frictional resistance were investigated.From the perspective of spatiotemporal evolution,the spatiotemporal correlation between coherent structures in wall turbulence and local flow field frictional resistance was explored.The correctness of this method was validated.