Inertial particle dynamics in the turbulent/non-turbulent interface

This project studies an important problem in particulate systems where turbulence is present in parts of the flow field but not on others. Specifically, the transport, accumulation, settling under gravity and mass transfer of particles or liquid droplets near a turbulent/nonturbulent interface. Such phenomena plays a key role in cloud microphysics as well as in many engineering systems for energy conversion and material processing. The interaction between particles and eddies in turbulence have been studied extensively, although significant gaps still exists, but our understanding is constrained to homogeneous, isotropic turbulence (HIT) or canonical free shear flows like jets and wakes. We will study the dynamics of inertial droplets in a Turbulent/Non-Turbulent Interface. This flow exists at the interface where a highly turbulent flow encounters a quiescent, laminar or weakly turbulent flow. Examples of this are the interface of a turbulent jet where its edge encounters the quiescent ambient fluid, a turbulent boundary layer where it meets with a low turbulent fluctuations freestream, and a buoyant plume where it shears with the quiescent fluid. Although shear between the turbulent and the non-turbulent streams can generate turbulence, the conditions right at the interface where the high turbulent fluctuations encounter the laminar flow are very different from the canonical shear-generated mixing between two already turbulent flows. The dynamics of inertial particles as they cross this interface and jump from interacting with highly energetic eddies on one side of the interface to the weakly turbulent of laminar flow on the other side of the interface have been scarcely studied.

We will used two wind tunnels, at LEGI and at the University of Washington, where conditions can be created to study droplets interacting at a gradient of turbulence intensity, with and without mean shear, and normal or parallel to gravity. Different parameter regimes are accessible in both wind tunnels so this study can produce the most comprehensive characterization of this complex physics problem.

The understanding from this project will be applied to understanding mixing, supersaturation and droplet growth in cumulus clouds and in vapor deposition in round jets and flames.