Numerical study of the propulsive performance of two-dimensional pitching foils at very high frequencies: scaling laws and turbulence effects

Purpose This paper aims to analyze the propulsive performance of small-amplitude pitching foils at very high frequencies with double objectives: find out scaling laws for time-averaged thrust and efficiency frequencies; characterize Strouhal number above which effect turbulence on mean values cannot be neglected. Design/methodology/approach The force a NACA0012 foil reduced ( k ) Reynolds Re = 16 000 are analyzed using accurate numerical simulations, both assuming laminar flow transition model. results validated available experimental data up about 12 (Strouhal number, St, 0.6). study also compares present predictions theoretical models existing results. For its quarter chord amplitude α 0 8 o , frequency is varied here 30 (St 2), much higher than in any previous or work. Findings this pitch amplitude, effects found negligible St ≲ 0.8, affecting less 10% coefficient CT¯ larger Linear potential theory fails large even small considered, particularly power coefficient, therefore efficiency. It that stretchy="true">¯ ∼ 2 agreement recent models, decays as 1/k, disagreement linear theory. Originality/value Pitching increasingly studied efficient propellers energy harvesting devices. Their has not been sufficiently before. authors provide simulations discern when relevant computation how their affected relation laminar-flow predictions. because some predict over certain ranges structural parameters, only may decide these