Numerical Study of Pulsation-Controlled Droplet Generation in a Microfluidic T-Junction

Droplet generation in microfluidic T-junctions is a key process in various chemical and biomedical applications requiring precise size and frequency control. This study presents a numerical investigation of pulsation-controlled droplet formation using a two-phase incompressible laminar flow model with constant surface tension and defined wettability. Simulations were conducted in COMSOL Multiphysics employing the Level Set method, and the model was validated against the benchmark data of Bashir et al., accurately reproducing droplet pinch-off time and morphology under steady co-flow conditions. Pulsatile inlet velocity was then introduced to analyze its influence on droplet dynamics. Results show that at frequencies between 35 and 60 Hz, droplet generation becomes synchronized with the pulsation cycle, producing one droplet per period. Beyond 60 Hz, synchronization is lost, leading to irregular breakup and loss of droplet size control. The droplet length exhibited an approximately linear dependence on pulsation frequency, indicating predictable and tunable droplet formation. These findings demonstrate that simple modulation of the dispersed-phase velocity enables droplet-on-demand operation and robust control of droplet size and generation rate in standard microfluidic T-junctions.