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

TL;DR

This study investigates how dilute suspensions of finite-size particles influence the transition to turbulence in channel flow, revealing that even few particles can lower the critical Reynolds number and induce sustained turbulence.

Contribution

It demonstrates that finite-size particles at low volume fractions can trigger and sustain turbulence at lower Reynolds numbers than single-phase flow, highlighting the importance of initial particle arrangement.

Findings

Critical Reynolds number for turbulence decreases with particles.

Initial particle arrangement affects transition to turbulence.

Particles can induce oblique disturbances leading to turbulence.

Abstract

We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e. $\Phi \approx 0.001$. The critical Reynolds number above which turbulence is sustained reduces to $Re \approx 1675$, in the presence of few particles, independently of the initial condition, a value lower than that of the corresponding single-phase flow, i.e. $Re\approx1775$. 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.