DISTRIBUTION AND MOTION OF PARTICLES IN THE TURBULENTBOUNDARY LAYER OF CHANNEL FLOW

This paper numerically investigates particles immersed in the turbulent boundary layer of channel flow. The methodology is a combination of three cutting-edge numerical technologies, i.e., the direct numerical simulation of turbulent flow, the point-particle immersed boundary method and the discrete particle method. We quantify the motion and distribution of near-wall particles by means of Voronoi analysis based on a set of instantaneous particle positions. It was found that the motion of particles have strong effects on flow velocity profiles and turbulence intensities, is closely related to the dynamics of the near wall coherent flow structures, i.e., the ejections of low-speed fluid carry particles towards the outer flow and the sweeps of high-speed fluid as well as gravitational settling bring particles back towards the wall. Most of particles in the turbulent boundary layer reside preferentially in low speed fluid regions and streamwise-aligned streaky structures. Particles keep in "clusters" over substantial time scales and sometimes they jump into "voids", after which those particles relatively quickly migrate back to a neighbouring low speed region.