Power Extraction Performance of a Semi-activated Flapping Foil in Gusty Flow

A numerical investigation on the power extraction performance of a semi-activated flapping foil in gusty flow is conducted by using the commercial software FLUENT. The foil is forced to pitch around the axis at one-third chord and heave in the vertical direction due to the period lift force. Different from previous work with uniform flow, an unsteady flow with cosinusoidal velocity profile is considered in this work. At a Reynolds number of 1100, the influences of the mechanical parameters (spring constant and damping coefficient), the amplitude and frequency of the pitching motion, the amplitude of the gust fluctuation and the phase difference between the pitching motion and the gusty flow on the power extraction performance are systematically investigated. Compared with the case of uniform flow, the capability energy harvesting of the system is enhanced by the introduction of the gusty flow. For a given pitching amplitude and frequency, the power extraction efficiency increases with the gust fluctuation amplitude. Moreover, with an optimal phase difference between pitch and gust (phi = 180), the efficiency can be further enhanced due to the generation of high lift force.