Analytical and numerical modelling of tandem oscillating foils propulsors

Abstract

The present work investigates theoretical and numerical methods to model oscillating hydrofoils, in single and tandem arrangement. The first part of this work presents a semi-analytical 2D model for a hydrofoil propulsor travelling at constant speed, in infinite domain, undergoing heaving and pitching oscillations, based on the Theodorsen unsteady theory. Following the previous work, the model is developed to estimate the thrust and propulsive efficiency attempting to incorporate the main physical contributions. The second part investigates the same foil arrangements using a high-fidelity CFD approach. In particular, a robust deforming grid method is used, enabling the simulation of cases with large body motions. Results of the semi-analytical model are compared with available published numerical and experimental data, with good agreement. The numerical model results are analysed using verification and validation procedures, allowing accurate physical interpretation of the flow and forces. Additionally, the tandem foil configuration, if properly optimized, is found to increase the single foil thrust by almost three-fold. The overall results suggest that the semi-analytical model may be quite suitable in design studies, and the CFD model showed capable of providing accurate results for the most complex cases and of contributing to a comprehensive understanding of the flow dynamics.