Transition and self-sustained turbulence in dilute suspensions of finite-size particles

We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e., Phi approximate to 0 0.001. The critical Reynolds number above which turbulence is sustained reduces to Re approximate to 1675, in the presence of few particles, independently of the initial condition, a value lower than that of the corresponding single-phase flow, i.e., Re approximate to 1775. In the dilute suspension, the initial arrangement of the particles is important to trigger the transition at a fixed Reynolds number and particle volume fraction. As in single phase flows, streamwise elongated disturbances are initially induced in the flow. If particles can induce oblique disturbances with high enough energy within a certain time, the streaks breakdown, flow experiences the transition to turbulence and the particle trajectories become chaotic. Otherwise, the streaks decay in time and the particles immigrate towards the channel core in a laminar flow. (C) 2015 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.