CFD modelling of the condensation inside a Supersonic Nozzle: implementing customized wet-steam model in commercial codes

Non-equilibrium condensation of steam occurs in many jet and turbomachinery devices, such as supersonic nozzles, ejectors and across the last stages of steam turbines. Wet steam models are available in many commercial CFD codes and can represent the metastable behaviour of the flow with reasonable accuracy. Unfortunately, the use of built-in models does not allow freedom in the choice of model parameters and settings. In the present paper, a numerical model for the simulation of wet steam flow has been developed and implemented within a commercial CFD code (ANSYS Fluent) via user defined functions. The scheme is based on a single-fluid approach and solves the transport equation for a homogeneous mixture flow coupled with conservation equations for the number of droplets and liquid mass fraction. The model is compared against a well-known steam nozzle test-case.