Non-equilibrium condensation modeling of CO₂ nozzle flow under subcritical and supercritical conditions

Turbomachinery is crucial in transcritical CO₂ heat pumps and supercritical CO₂ Brayton cycles. During the internal transcritical expansion process, non-equilibrium condensation can occur, leading to droplet formation, which reduces turbomachinery efficiency and may damage the blades. Currently, non-equilibrium condensation calculations face inaccurate predictions of condensation shock waves and downstream pressures. To investigate the influence of various factors on the accuracy of non-equilibrium condensation numerical simulation, this study examines the effects of nucleation models, droplet growth models, and turbulence models. The Eulerian-Eulerian source term model is employed to compare and study the non-equilibrium condensation within a CO₂ Laval nozzle under subcritical and supercritical inlet conditions. The results indicate that different nucleation models directly affect the numerical accuracy of the nucleation location and the condensation shock wave, with minimal impact on the pressure distribution downstream of the throat. Besides, different droplet growth models have little effect on the numerical accuracy of nucleation location and the downstream pressure distribution. The large eddy simulation has a significant impact on numerical accuracy, with a larger pressure jump and better experimental agreement for downstream pressure distribution. These findings provide guidance for the further development of non-equilibrium condensation models.