Inertial particle dynamics in a turbulent/non-turbulent interface*

Turbulent/non-turbulent interfaces are ubiquitous in nature and represent the physics of many important canonical flows (wakes, jets, mixing layers). Two separate flow regions with different turbulent intensities share a sharp interface, where we study the dynamics of inertial particles. The transport of inertial particles across T/NT interfaces plays a role in the description of cloud boundaries, where the droplet-laden turbulent cloud interior mixes with the unladen laminar outer flow. This experimental study focuses on the entrainment of inertial particles across a turbulent/non-turbulent interface.

Spanwise profiles of particle vertical and horizontal velocities were measured by laser interferometry in a wind tunnel. Turbulence is generated by a passive grid combined with gas/liquid atomizers that introduce the inertial particles. These atomizers, at the entrance of the test section, contribute significantly to the carrier phase turbulence and sheared velocity profile. Selecting the atomizer injection profile enables us to control the gradient of turbulent intensity through the tunnel cross-sectional area. Particle velocity distributions are not Gaussian across the interface, as opposed to on the turbulent side where the statistics are canonically normal. Conditional statistics on particle velocities confirm that the transport of droplets from the turbulent to the non-turbulent side is dominated by the integral-scale turbulent eddies.