Nonsinusoidal motion effects on energy extraction performance of a flapping foil

Systematic investigation of the flow evolution and energy extraction performance of a flapping-airfoil power generator

“…5. In the downstroke motion between t/T ¼ 0.25 and 0.5 the flow separation caused by the negative effective AOA leads to a lift force enhancement (Lu et al [15], Kinsey and Dumas [16]), and the downward lift force helps to motivate the downward flapping motion and realize the energy extraction in practical application. Between t/T ¼ 0.55 and 0.75 the plunging motion continues, meanwhile the pitching motion happens.…”

“…By influencing the flow structure development and aerodynamic force, the nonsinusoidal pitching profiles notably increases the output power. Similar investigations by Lu et al [15] explored the effects of four kinds of nonsinusoidal flapping motions to realize the energy harvesting enhancement. It was reported that appropriate nonsinusoidal profiles increase the power coefficients by accelerating the formation and evolution of leading edge vortex.…”

“…At k ¼ 0.5 and q 0 ¼ 40 the effective AOA a e ¼ 0 at t/T ¼ 0.5, and it results in a quite small scale of flow separation area at the lower surface between t/T ¼ 0.5 and 0.55. Previous studies reveal that a larger scale of flow separation is beneficial to lift force generation and output power [15,16], thus it can be concluded that the increasing flapping frequency at a fixed plunging amplitude has a negative effect on the energy extraction performance.…”

“…At the outlet the pressure is set to the freestream value. As the work by Lu et al [15], the computational domain boundary is set to 35c from the no-slip airfoil surface. To model the airfoil an O type mesh is used, and a first cell height of 10 À5 c is used along the airfoil surface.…”

“…As the mesh strategy applied by Lu et al [15,20], two mesh domains with a sliding grid interface are used. In the computations the inner domain employs a moving mesh for the flapping motion, during which the displacement of mesh nodes are realized according to the input kinematic equations defined.…”