Abstract: The unsteady bubbly flows through converging–diverging nozzle are studied numerically using Lagrangian finite volume scheme and homogeneous bubbly mixture model. The model accounts for bubble dynamics by Rayleigh-Plesset equation. Calculations of critical bubbly flows are performed and reasonable agreements with experiment results are observed. The critical bubbly flow fields with different boundary conditions are simulated, and the influences of initial bubble radius, inlet pressure and initial void fraction on the critical inlet velocity are discussed. The results show the critical inlet velocity increases with the increasing inlet pressure, initial bubble radius, and the decreasing initial void fraction.