Time-resolved sphere and fluid motions in turbulent boundary layers

This paper extends the study by Tee et al. (2020) to investigate effect of large coherent structures on motion spheres with specific gravities 1.006 (P1) and 1.152 (P3) at Reτ = 670 1300 (d+ 56 116). The sphere fluid motions are tracked simultaneously via 3D particle tracking stereoscopic image velocimetry over streamwise-spanwise plane, respectively. With sufficient mean shear, P1 lifts off wall upon release before descending back towards both Reτ. It typically accelerates strongly a streamwise distance less than one boundary layer thickness approaching an approximate terminal velocity. By contrast, denser P3 does not lift but mainly slides along wall. At lower where friction is stronger, this translates unsteady velocity, significantly lagging local fluid. velocities correlate fast- slow-moving zones that approach move them. In most runs, lag travel either or throughout observed trajectories. Vortex shedding, which prevalent for 670, also important. spanwise prompted friction, motion, and/or meandering structures, do appear migrate preferentially into zones.