Extreme accelerations in turbulent flows

Even in weakly turbulent flows, fluid tracers routinely undergo strong accelerations tens of standard deviations in excess of the mean. These extreme events are thought to influence everyday phenomena such as rain formation in wet clouds or the turbulent combustion of fuel in engines. We report results on high resolution particle tracking experiments in a vigorously stirred turbulent flow between $R_\lambda = 130$ and $450$. These are matched with high resolution direct numerical simulations of isotropic turbulence. By acquiring very large datasets we quantify the distribution of rare, strong acceleration events (as infrequent as one in $10^8$ and in excess of 30 standard deviations) and their scaling with Reynolds number. We present back-to-back comparisons between the two to quantify the statistics of accelerations at unprecedented accuracy and discuss their consequences for turbulent flows.