Numerical study of viscous and rarefaction effects on choked flow in two-dimensional convergent conical nozzle

In this study, a numerical investigation of gas flow through a convergent conical nozzle operating under low-pressure conditions, with an emphasis on choked mass flow behaviour with viscous and rarefaction effects, is conducted. Simulations are performed over a range of pressure ratios spanning the continuum and slip-flow regimes under no-slip, slip, and inviscid wall boundary conditions. At high pressure ratios, all the formulations yield comparable core-flow accelerations, with deviations below 1%, thus indicating near-continuum behaviour. As the pressure ratio decreases, rarefaction effects become increasingly important and lead to discernible differences in flow structure and mass flow rate. Compared with the no-slip model, the slip-flow formulation predicts mass flow rates approximately 3% higher because of reduced wall shear, whereas the inviscid solutions provide deviations of approximately 1% compared with the slip-flow at the lowest pressure ratios. These results highlight the necessity of modelling for accurate prediction of choked flow characteristics in microscale nozzle applications in comparison to the one-dimensional equation.