Abstract: Considering gas phase unsteadiness and droplet internal recirculation,we developed an unsteady evaporation and combustion model for moving droplets.It adopts dynamic grid method tracking droplet interface location and conservation equations updating interface boundary conditions.Based on one step global chemical reaction,flame shape and combustion characteristics of n-heptance droplets at different convective velocity are simulated and analyzed.It shows that internal recirculation of moving droplet promotes low temperature area moving to the center of recirculation.Envelop flame translates into wake flame as convective velocity exceeding a critical value.Area of fuel rich and high temperature region and combustion rate at envelop flame are higher than those of wake flames remarkably.Droplet surface temperature and evaporation rate distribution at an envelop flame are different from those of wake flame obviously as well.

Key words: moving droplet, internal recirculation, dynamic mesh, flame shape, combustion rate