DIRECT NUMERICAL-SIMULATION OF PARTICLE ENTRAINMENT IN TURBULENT CHANNEL FLOW

Particle entrainment process in a turbulent channel flow is studied. The time history of the instantaneous turbulent velocity vector field is generated by the direct numerical simulation of the Navier-Stokes equation with the aid of a pseudospectral code. The equation of motion of submicrometer particles including Stokes drag and Brownian diffusion is used, and typical entrained particle trajectories are evaluated and statistically analyzed. It is shown that the wall coherent structure plays a dominant role on the particle entrainment process. Particles are removed from the wall region by being captured in the high speed streams moving away from the wall, which are formed by the flow structure. Furthermore, single streamwise vortices are shown to be more frequent than pairs of counter-rotating ones at every instance of time. Temporal average of the vorticity field, however, shows roughly periodic sequence of counter-rotating vortices in the wall region. © 1995 American Institute of Physics.