Inertial Particle Acceleration Statistics in near-Wall Turbulence

The motion of water droplets over a flat plate mounted in a wind tunnel with high levels of free stream turbulence is measured using high-speed particle tracking. The accelerations are calculated by convolution of the measured particle trajectories with a Gaussian smoothing and differentiating filter. The longitudinal acceleration mean and variance are found to increase with increasing particle inertia, contrary to what had been found for inertial particles in homogeneous isotropic turbulence. To further investigate this trend, we use direct numerical simulations of channel flow laden with particles. By comparing results with and without gravity, we see that the puzzling reversal in the trend is due to the complex interaction of the particles with turbulence, the mean shear and gravity.