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

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.