Acceleration statistics of heavy particles in turbulence

We present the results of direct numerical simulations of heavy particle transport in homogeneous, isotropic, fully developed turbulence, up to resolution 512³ ( R_λ≈ 185 ). Following the trajectories of up to 120 million particles with Stokes numbers, St , in the range from 0.16 to 3.5 we are able to characterize in full detail the statistics of particle acceleration. We show that: (i) the root-mean-squared acceleration aᵣₘₛ sharply falls off from the fluid tracer value at quite small Stokes numbers; (ii) at a given St the normalized acceleration aᵣₘₛ/(ε³/ν)1/4 increases with R_λ consistently with the trend observed for fluid tracers; (iii) the tails of the probability density function of the normalized acceleration a/aᵣₘₛ decrease with St . Two concurrent mechanisms lead to the above results: preferential concentration of particles, very effective at small St , and filtering induced by the particle response time, that takes over at larger St .