Effect of evaporation on interfacial instabilities of shock-driven droplets

Instability-driven breakup and droplet evaporation play an important role in liquid fuel droplet combustion. In this work, through detailed numerical simulations of a 2D axisymmetric JP-10 fuel droplet, the effect of evaporation rate on surface instabilities were investigated. The Weber number for all the simulations was set at We = 100, representing flow conditions relevant to fuel droplets in detonation engines. The simulations were performed using IMPACT¹, a multiphase shock physics code that employs a 5th order WENO scheme to solve the Euler Equations with Adaptive Mesh Refinement. The interface between the liquid and gaseous phase was tracked using the Level Set method, and a Riemann Ghost Fluid Method integrated with a multi-medium Riemann solver used to couple the two phases. The cases simulated, involved a 10 μm droplet, processed by an impinging shockwave, for different Mach numbers of M=2.0 and M=5.0, with and without evaporation. It was observed that a combination of higher post shock gas density and velocity, obtained at higher Mach numbers, enhanced the growth of thin sheets over the droplet and subsequent droplet breakup. The accumulation of vapor layer near the droplet surface reduced the interfacial shear instabilities.

¹P. Bigdelou, C. Liu, P. Tarey, & P. Ramaprabhu, Comp. & Fluids, 233, 105250, 2021