RÉSUMÉ

In wall-bounded turbulent flows laden with small heavy particles, the turbulence pushes the particles towards the wall, where the particles tend to cluster into streamwise-elongated streaks. We study the process of formation of the particle-streaks, and its relation with the near-wall turbulence, using point-particle Eulerian-Lagrangian large-eddy simulations in a fully-developed turbulent channel flow laden with small heavy particles. In the literature, the formation of the particle-streaks has been generally attributed to the sweeps and ejections associated with the passage of streamwise vortices further away from the wall. However, we show that the sweeps and ejections associated with the passage of the streamwise vortices are not directly associated with the formation of the particle-streaks. We show that the formation of the particle-streaks is closely related with the fluid streaky-pattern close to the wall. We present a new characterization of the fluid-streaky pattern in terms of its streamlines, and show that the formation of the particle-streaks is slow process of collection associated with the convergence of these streamlines into a few "baselines". These "baselines" have a very good correlation with the particle-streaks. They both have an extremely-long life, and once formed they remain roughly in the same position for a long time.