518 / 2018-12-31 22:57:25

Energy harvesting of a semi-active flapping hydrofoil in shear flow

Energy conversion; Hydrofoil; Shear flow; Semi-active; Flow-induced motion

全体主题 > 节能、联产、热泵

Tidal energy has drawn more and more attention for renewable energy research. The most widely used energy collecting devices in this area are turbine-based energy converters. Compared with the traditional turbine-based energy converters, the flapping hydrofoil systems are receiving considerable interest in recent years for its high structural reliability and friendliness to environment. The flapping hydrofoil utilizes oscillatory motion to harvest energy. Different mechanical parameters are applied in uniform flow to improve the energy harvesting efficiency of flapping hydrofoil, while the shear flow is common in ocean and rivers. The reduced pitching frequency and pitching amplitude for energy harvesting by semi-active flapping hydrofoil are studied in this work. For semi-active flapping hydrofoil, the rigid hydrofoil is forced to pitching and then induced the oscillation in the direction of perpendicular to incoming flow. The effects of reduced pitching frequency and pitching amplitude on power extraction are investigated numerically. The reduced pitching frequency f* is varied from 0.08 to 0.26 and the interest pitching amplitude range is 5°≤θm≤85°. The reduced velocity range in this study is 2≤U*≤14. The numerical results are compared with that of uniform flow. The objective of this work is to optimize the energy harvesting by the semi-active flapping in shear flow. The two-dimensional Unsteady Reynolds-Averaged Navier-Stokes with k-ω SST turbulence model is applied to simulate the flow-induced vibration of the semi-active flapping hydrofoil. For plunging motion, the oscillator is model as a mass-spring-damping system. The plunging motion equation of the foil is discretizated by fourth-order Runge–Kutta method. The results show that for given pitching amplitude and reduced velocity, the energy convert efficiency increases first and then decrease with the increasing of reduced pitching frequency. The highest energy convert efficiency is close to 30% when f*=0.18. For reduced pitching frequency and reduced velocity, high energy convert efficiency is obtained in the range of 60°≤θm≤80°. For optimal mechanical parameters of f*and θm, the harvesting of energy by semi-active flapping hydrofoil and the amplitude of oscillation in the direction of cross flow increase with the rising of reduced velocity. The energy convert efficiency of semi-active flapping hydrofoil increases first and then drops with the rising of reduced velocity, the highest energy convert efficiency is observed when U*=5.