2C-2D PIV/PTV measurements of high Reynolds number turbulent channel flow with sub-viscous-length wall-normal resolution

This study presents a high spatial resolution hybrid particle image velocimetry/particle tracking velocimetry (PIV/PTV) methodology for investigating high Reynolds number turbulent channel flow. Utilising two 103-megapixel cameras, the experiment captures the entire channel height with a spatial resolution finer than the viscous length scale. To ensure accurate mapping of the PIV image pairs to a common coordinate system, a novel holography-based pixel-to-pixel imaging sensor registration technique is developed, which achieves an uncertainty of better than 0.5μm. At the same time, an efficient second calibration process accounts for lens distortion. The hybrid PIV/PTV analysis leverages PIV velocity vectors as predictors to identify particle pairs for PTV, with velocity vectors sorted into bins of 0.6 viscous length height in the wall-normal direction for statistical velocity analysis. The resulting first- and second-order velocity statistics and the streamwise velocity spectra agree with the equivalent results obtained from direct numerical simulations (DNS) of turbulent channel flow at similar friction Reynolds number, validating the effectiveness of the proposed methodology in capturing the structure of turbulent channel flow with resolution equivalent to DNS resolution.