How Motion Trajectory Affects the Energy Extraction Performance of an Oscillating Foil

Abstract

The energy extraction from oscillating plunging/pitching hydrofoils with sinusoidal or non-sinusoidal pitching motions is investigated numerically. The study encompasses the Strouhal number St from 0.05 to 0.35 and the maximum effective angle of attack (AOA) max α from 10 to 20 degree. Two types of non- sinusoidal pitching profiles are imposed to examine the effect of motion trajectory on the energy extraction performance of oscillating foils. The first type is derived from a cosine effective AOA and the second type is the trapezoidal-like pitching motion with several adjustable parameters. Computation was conducted by solving unsteady Navier-Stokes equations for laminar flows. For both the sinusoidal and non-sinusoidal pitching, a larger max α results in a higher extraction power ( ) and total efficiency ( p C T η ). For the pitching motion derived from the cosine effective AOA, the time-mean C and p T η is much beyond those for the sinusoidal one at relatively high . With the trapezoidal-like motions, the significant increase of C and St p T η can be observed over a certain range of St depending on the adjustable parameters. The study shows that an optimum trapezoidal-like profile may increase the output power coefficient and total output efficiency as high as 50% over a wide range of St.