Title: Evaporation of dilute droplets in a turbulent jet: clustering and entrainment effects,
Abstract: Droplet evaporation in turbulent sprays involves unsteady, multiscale and
multiphase processes which make its comprehension and model capabilities still
limited. The present work aims to investigate droplet vaporization dynamics
within a turbulent spatial developing jet in dilute, non-reacting conditions.
We address the problem using a Direct Numerical Simulation of jet laden with
acetone droplets using an hybrid Eulerian/Lagrangian approach based on the
point droplet approximation. A detailed statistical analysis of both phases is
presented. In particular, we show how crucial is the preferential sampling of
the vapour phase induced by the inhomogeneous localization of the droplets
through the flow. The preferential segregation of droplets develops suddenly
downstream the inlet both within the turbulent core and in the mixing layer.
Two distinct mechanisms have been found to drive these phenomena, the inertial
small-scale clustering in the jet core and the intermittent dynamics of
droplets across the turbulent/non-turbulent interface in the mixing layer where
dry air entrainment occurs. These phenomenologies strongly affect the overall
vaporization process and lead to a spectacular widening of droplets size and
vaporization rate distributions in the downstream evolution of the turbulent
spray.