Effect of phase difference on energy absorption performance of undulating airfoils in a triangular array

Abstract

Undulatory flexible body can absorb energy from the flowing fluid under certain motion parameters. The NACA0012 airfoil is used as the two-dimensional model of fishlike body in this paper. Through numerical simulation, the effect of phase difference on the energy absorption performance of each undulating airfoil in the triangular array is studied at Re=1.95×105. For the convenience of analysis, the energy absorption efficiency (EAE) has been calculated separately for each airfoil. The results show that: with the change of phase difference between the upstream airfoil and downstream airfoils, the EAE of each airfoil in the triangular array appears a simple harmonic fluctuation. Under the optimal phase difference, the EAE of the upstream airfoil has decreased by 9.6% while the EAE of downstream airfoils has increased by 13% compared with a single undulating airfoil. When the two downstream airfoils undulate in-phase, their EAE changes synchronously with the phase difference between the upstream airfoil and downstream airfoils. When the two downstream airfoils undulate anti-phase, their EAE shows an antisymmetric form with the period of 360∘. The best arrangement of a triangular array is that the upstream airfoil and downstream airfoils undulate anti-phase, and the two downstream airfoils undulate in-phase.