2019/09/04 by Yi Hui Tee, Tee, Yi Hui, Diogo Barros +3
Physics and Astronomy · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #physics.flu-dyn
paper · pdf · doi:10.48550/arxiv.1909.02122
10 pages, published in Proceedings of the 13th International Symposium on Particle Image Velocimetry
arxiv created 2019/09/04 · arxiv updated 2019/09/06
The motion of individual magnetic wax spheres with specific gravities of 1.003, 1.050 and 1.150 was investigated in turbulent boundary layers with Reτ=700 and 1300 (d+ = 60 and 120). The spheres were marked with dots all over the surface to monitor their translation and rotation via high-speed stereoscopic imaging. Upon release from rest on a smooth wall, each sphere typically accelerated strongly over a streamwise distance of one boundary layer thickness before approaching an approximate terminal velocity. Spheres with sufficient net upward force lifted off of the wall once released before descending back towards the wall. These spheres mostly translated with the fluid above the wall, undergoing saltation or resuspension, with minimal rotation about all axes. By contrast, spheres that did not lift off after release mainly slid along the wall. As they propagated downstream, they began to roll forward with occasional lift-off events of smaller magnitude. All of the lift-off activities observed were limited to the buffer and logarithmic layers. Both translation and rotation of the spheres were significantly affected by the wall turbulence.