While I know (and can observe) that solids don't settle easily in a turbulent flow, I struggle with understanding why exactly this is the case. Here' my problem:
Conceptually, turbulence means high Re-number (or vice ersa), and that means the inertail forces are far stronger than friction/viscous forces. But friction keeps the particle suspended, and I would see bouyancy and gravity as inertial forces.
In a non-moving fluid, the only forces acting on a particle are friction (pointing upwards with a sinking particle) and gravity/buoancy, with a net force pointing up or down and/or movement of the particle.
In a perfect turbulent flow, I would expect no dominant direction of flow. So, the fluid 'tugs' at my particle in one direction one moment and somwhere else the next moment - the net force from the friction over a long enough time will be zero, but bouyancy has a preferred direction.
Here's how I would explain why solids don't settle in turbulent flows and I ask you to poke holes into this explanation:
In turbulent conditions, friction is generally proportional to $v^2$, with $v$ beeing the velocity of the particle relative to the fluid. So compared to the same particle in the same fluid but in laminar conditions, the friction resulting from a specific downward (or upward) velocity is higher. This is compunded by the fact that for a particle sinking, any surrounding upward flow will have a stronger effect than a surrounding downward flow with the same speed relative to the particle. Hence, solids settle far slower in turbulent flows.