Numerical Predictions of Cavitating Flow around Model Scale Propellers by CFD and Advanced Model Calibration

The numerical predictions of the cavitating flow around two model scale propellers in uniform inflow are presented and discussed. The simulations are carried out using a commercial CFD solver. The homogeneous model is used and the influence of three widespread mass transfer models, on the accuracy of the numerical predictions, is evaluated. The mass transfer models in question share the common feature of employing empirical coefficients to adjust mass transfer rate from water to vapour and back, which can affect the stability and accuracy of the predictions. Thus, for a fair and congruent comparison, the empirical coefficients of the different mass transfer models are first properly calibrated using an optimization strategy. The numerical results obtained, with the three different calibrated mass transfer models, are very similar to each other for two selected model scale propellers. Nevertheless, a tendency to overestimate the cavity extension is observed, and consequently the thrust, in the most severe operational conditions, is not properly predicted. 1. Introduction In the field of marine applications, and in the particular case of marine propellers, the onset of cavitation is, in general, associated with negative design implications such as thrust reduction, noise, vibration, and erosion. In the last decades, also owing to the steady increasing of the computer performances, in order to improve the design process, several CFD (Computational Fluid Dynamics) methods have been developed for the prediction of the cavitation appearance and the estimation of its effects. In this study, we evaluated the capabilities of the homogeneous, that is, one-fluid model implemented in the ANSYS CFX 12 (for brevity CFX hereafter) commercial CFD solver, for the prediction of cavitating flow around model scale propellers working in uniform inflow. This model treats the cavitating flow as a mixture of two fluids behaving as a single one. The set of the governing equations is composed by the (volume) continuity and momentum equations for the mixture, plus a transport equation for the water volume fraction. The mass transfer rate due to cavitation is regulated by the same source term appearing in the (volume) continuity and volume fraction equations. This source term, in CFX, using the default setting is modelled by employing the mass transfer model originally proposed by Zwart et al. [1] (Zwart for brevity). However, in literature several other mass transfer models are available (see [2]). Thus, in order to improve the reliability of the simulations besides the Zwart