Dispersed Phase Effects on Boundary Layer Turbulence

Dispersed (i.e. particulate) phases suspended in the turbulent atmospheric boundary layer can take many forms: sea spray, blowing snow, dust, sand, aerosols, etc. While the details regarding the origin and fate of each of these are unique to the environment in which they reside, many common questions arise when trying to predict, interpret, or model their behavior. As complex as these questions may be when trying to quantify dispersed phase transport in the turbulent boundary layer, it becomes significantly more difficult when two-way coupling is considered, where the dispersed phase changes the flow which is responsible for its own transport. This two-way coupling can emerge from direct momentum exchange between the dispersed phase and the surrounding air (i.e. drag), or it can be a result of thermodynamic exchange (i.e. heat transfer or evaporation), and has the potential for modifying surface-atmosphere fluxes in complex ways.

Here we present the results from a series of ongoing numerical simulations which are designed to probe a process-level understanding of the wide variety of coupling mechanisms and large-scale implications of dispersed phases on the atmospheric boundary layer. These simulations are based on direct numerical simulation (DNS) with individually-tracked, Lagrangian particles which are two-way coupled to the surrounding turbulent flow. The influence of two-way momentum exchange, sensible heat exchange, and evaporative thermodynamics on the surrounding air turbulence under various coupling regimes are emphasized, where, for example, particles can carry a significant fraction of the total momentum or heat throughout the boundary layer and potentially change the stability of the flow. Extension to large-scale flows will be discussed.