ABSTRACT
Modern research has revitalized the non-traditional propulsion concept of oscillating hydrofoils, showing that lifting surfaces may efficiently be used as marine propulsors in specific applications. One promising enhancement of this concept involves in-line tandem flapping foils to mitigate unbalanced forces and potentially increase efficiency by utilizing energy in the wake of the forward foil. This article proposes a 2D semi-empirical model for in-line tandem hydrofoils, based on classical thin-wing theory, complemented to include drag effects using empirical formulations. Results are presented for the 2D case in infinite domain and compared with data from other numerical methods and experiments available in the literature, for single and tandem foil cases. In particular, preliminary dedicated numerical results, obtained with the CFD code ReFRESCO, are introduced. Parametric configuration and optimization are discussed, analysing the effects of geometric and operational parameters on the propulsive performance. The overall results suggest the semi-empirical model has engineering advantages, as its simplicity allows easy exploration of different configurations, capturing the main physics involved, for design optimization and with possible applications on control system development.
