Numerical approaches for moist air condensing flows modelling in the transonic regime

•CFD study of the moist air transonic flow in Laval nozzles by means of single- and two-fluid models.•Mathematical models of condensation processes, homogeneous and heterogeneous.•The study of the effect of air relative humidity value on the condensation process and flow in nozzles.•The numerical studies of pollution importance on condensation phenomenon.•Losses estimations in the moist airflow in nozzles. The paper presents mathematical modelling of water vapour condensation process in the moist air transonic internal flows. The condensation model based on the classical theory of nucleation and molecular-kinetic droplet growth model is implemented into a commercial software ANSYS Fluent. Two approaches are shown in the paper, one in which the air with water droplets is treated as a fluid mixture and second where the water droplets and humid air are computed as separate phases. Both models are validated against in-house and literature experimental studies of internal flow in nozzles. The impact of air humidity and contamination on the condensation process in internal flows for different conditions is examined. The latent heat release in the condensation process influences the flow structure, thus the analysis of condensation wave and shock wave position change with the change of relative air humidity is presented. Moreover, the importance of inertia force and the resulting velocity difference between phases is highlighted. The paper shows that the impact of the condensation in transonic flow is non-negligible and should be taken under consideration in high-velocity flow simulations.