The atomization mechanism of the gas-liquid multiphase flow through an internally mixing twin-fluid Y-jet atomizer has been studied by examining both the internal and external flow patterns. Superheated steam and light fuel oil (LFO) are used as working fluids. The flow is numerically modeled using the compressible Navier-Stokes equations; the hybrid large eddy simulation approach through wall-modeled large eddy simulations (WMLES) is used to resolve the turbulence with the large eddy simulations, whereas the Prandtl mixing length model is used for modeling the subgrid-scale structures, which are affected by operational parameters. A volume-of-fluid to discrete phase model (VOF-to-DPM) transition mechanism is utilized along with dynamic solution-adaptive mesh refinement to predict the initial development and fragmentation of the gas-liquid interface through VOF formulations on a sufficiently fine mesh, while DPM is used to predict the dispersed part of the spray on the coarser grid. Two operational parameters, namely, gas-to-liquid mass flow rate ratio (GLR) and liquid-to-gas momentum ratio, are compared; the latter is found to be an appropriate operational parameter to describe both the internal flow and atomization characteristics. It is confirmed that the variation in the flow patterns within the mixing port of the atomizer coincides with the variation of the spatial distribution of the spray drops
