A model of evaporating spray droplet dispersion

Abstract

A model with a discrete droplet size distribution has been built in order to investigate the fate and influence of marine spray droplets dispersed by atmospheric turbulence as they evaporate. In its present state the Couche Limite Unidimensionelle Stationnaire d'Embruns (CLUSE) model considers freshwater droplets between 5 and 105 μm in radius that are ejected from a water surface by bursting air bubbles. The droplets are then diffused in a fully developed atmospheric surface layer. The droplet population is separated into 10 categories according to their size. The mass concentration of each category is treated as a scalar field, like sensible heat and water vapor concentration. Diffusion by air turbulence is modeled by K diffusivities. In addition, specific droplet surface processes (i.e., ejection and deposition) and the effects of inertia and gravity are explicitly modelled. The effects of evaporation (i.e., droplet shrinking, production of water vapor, and absorption of sensible heat) are modeled by local source‐sink functions that couple all 12 budget equations. The model is adjusted for comparison with measurements of turbulence statistics and droplet distributions taken in the Institut de Mécanique Statistique de la Turbulence air‐water tunnel. The influence of evaporating droplets on the humidity and sensible heat fields and fluxes, as well as the coupling of turbulent diffusion and evaporation is demonstrated.