Droplet breakup under impulsive acceleration using moving particle semi-implicit method

This paper presents the numerical simulations of droplet breakup under an impulsive acceleration in another immiscible fluid by the Moving Particle Semi-implicit (MPS) method, and the effect of the density ratio between droplet and ambient fluid on a critical Weber number. The MPS method is based on the fully Lagrangian description. Governing equations of fluid flows are transformed into equivalent particle interactions by moving particles and their interactions. Our simulation results of droplet breakup are consistent with experimental observations. Time-dependent dynamic behaviors of droplet are analyzed based on disruptive hydrodynamic force and resistive force. The investigated range of density ratio is from 1 to 9, and the other parameters are chosen as follows: the Reynolds number from 600 to 700, and the Ohnesorge number from 1.0x10-5 to 5.0x10-5, which are typical in accidents occurring in sodium-cooled fast reactors and light water reactors: water leak to sodium and fuel coolant interactions. It is shown that the critical Weber number is inversely proportional to density ratio, and especially is strongly dominated as the density ratio is less than 3. The normal mode analyses of the Kelvi-Helmholz and Rayleigh-Taylor instabilities also verify this trend. It is also consistent with the Tan and Bankoff experimental value. Furthermore, the Weber number on the onset of breakup is investigated, which is approximately 0.4 for the above density ratios. (author)