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.,Φ≈ 0.001.The critical Reynolds number above which turbulence is sustained reduces to Re ≈ 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 ≈ 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.