Investigations on the use of a KFm-4 profile to improve the energy extraction performance of a fully-activated flapping foil

Numerical simulations are performed to evaluate the effects of KFm-4 profile geometry, reduced frequency, and Reynolds number on the energy extraction performance of a fully-activated flapping foil. First, assuming that the flow is laminar, the governing equations are solved at a Reynolds number of Re = 1 100 to investigate the effects of step position, step thickness, step angle, trailing edge shape, and reduced frequency on the performances of the flapping foil. Then, the performances of the flapping foil are computed for Reynolds numbers up to 5.0105, assuming that the flow is fully turbulent for Re higher than 104. The obtained results show that the performance of the KFm-4 flapping foil is higher than that of the baseline profiles and that the maximum energy extraction efficiency is obtained when the step is located at the position Xm/c = 0.5 and the step thickness is equal to em = 0.06c, while the step angle has a negligible effect. Moreover, higher efficiency is obtained when the KFm-4 profile is built with a flat trailing edge. The results also show that the optimum reduced frequency is f* = 0.14 and that the efficiency of the KFm-4 flapping foil increases slightly with increasing Reynolds number.