Acceleration Statistics of Neutrally Buoyant Spherical Particles in Intense Turbulence

We measure acceleration statistics of neutrally buoyant spherical particles with a diameter 0.4<d/η<27 in intense turbulence (400<R_λ<815). High speed cameras image polystyrene tracer particles in a flow between counterrotating disks. The measurements of acceleration variance ⟨a²⟩ clearly resolve the transition from the tracer like behavior of small particles to the much smaller accelerations of large particles. Two models of this transition from small to large particle behavior are critically examined. For d>5η, ⟨a²⟩ decreases with the diameter as d^-2/3, in agreement with inertial range scaling arguments. Consistent with earlier work, we find that the scaled acceleration probability density function shows very little dependence on particle size.