Numerical study on the power extraction performance of a flapping foil with a flexible tail

Abstract

The numerical study on the power extraction performance of a flapping foil with a flexible tail is performed in this work. A NACA0015 airfoil is arranged in a two-dimensional laminar flow and imposed with a synchronous harmonic plunge and pitch rotary motion. A flat plate that is attached to the trailing edge of the foil is utilized to model a tail, and so they are viewed as a whole for the purpose of power extraction. In addition, the tail either is rigid or can deform due to the exerted hydrodynamic forces. To implement numerical simulations, an immersed boundary-lattice Boltzmann method is employed. At a Reynolds number of 1100 and the position of the pitching axis at third chord, the influences of the mass and flexibility of the tail as well as the frequency of motion on the power extraction are systematically examined. It is found that compared to the foil with a rigid tail, the efficiency of power extraction for the foil with a deformable tail can be improved. Based on the numerical analysis, it is indicated that the enhanced plunging component of the power extraction, which is caused by the increased lift force, directly contributes to the efficiency improvement. Since a flexible tail with medium and high masses is not beneficial to the efficiency improvement, a flexible tail with low mass together with high flexibility is recommended in the flapping foil based power extraction system.

Energy harvesting of a heaving and forward pitching wing with a passively actuated trailing edge

“…However, to help evaluate the performance for the rigid wing to the more standard pitching the following comparisons can be made. At a similar Strouhal number, 0.033 in this study versus 0.050 by Wu et al (2015), the mean value of the power coefficient, C p , is 0.144 in this study versus 0.032 for Wu et al This indicates the advantage of the added component due to angular motion induced by the present study. Similarly, at a reduced frequency of 0.048 in the present study versus 0.05 used by Liu et al (2013), the mean value of the power coefficient in the present study is 0.12, compared with that of Liu et al of 0.0625.…”

Passive heaving of elliptical cylinders with active pitching – From cylinders towards flapping foils

“…They also suggested the possibility of having the aerofoil flex passively. Using an immersed boundary-lattice Boltzmann method, Wu, Shu, Zhao, , and Tian (2015a) and Wu, Wu, Tian, Zhao, and Li (2015b) investigated energy harvesting from a flapping aerofoil with either a rigid or flexible plate attached to the trailing edge, with prescribed pitching and heaving and with prescribed pitching and flow-induced heaving, finding that whether a rigid or flexible tail was used could significantly affect the Strouhal number and efficiency of the optimal configuration. Tian, Young, and Lai (2014) investigated the effect of active and passive leading and trailing edge deformation of a flapping-plate flow energy harvester, finding that plate flexibility does not significantly affect the power-extraction capability of the plate, but active control on the leading edge of the plate can.…”

An FSI solution technique based on the DSD/SST method and its applications

“…83,101,103,104 Previous effort has been predominantly directed towards understanding the performance of a flapping foil in terms of hydrodynamics forces and efficiency in uniform and shear flows. While hydrodynamic waves are common and can affect the performance of swimming animals and hydropower turbines, we seldom see publications addressing the effects of hydrodynamic waves on swimming and energy harvesting performance.…”