Wake Structure and Dynamic Thrust of an Unsteady Airfoil

The detailed wake structure behind pitching airfoil and heaving airfoil at a low Reynolds number region was measured by PIV. Moreover, dynamic thrust acting on them in water tunnel was measured by a six-axes sensor. At the high non-dimensional trailing edge velocity and the non-dimensional heaving velocity, the thrust producing vortex street is formed clearly. Moreover, it has been founded that not only the distance between vortices becomes narrow but also vorticity increases as the non-dimensional trailing edge velocity and the non-dimensional heaving velocity increase. The averaged dynamic thrust acting on a pitching airfoil and a heaving airfoil increases as the non-dimensional trailing edge velocity and the non-dimensional heaving velocity increase. The hysteresis loops of dynamic thrust acting on a pitching airfoil and a heaving airfoil show reentrant and convexity shapes characteristics. The dynamic behavior of dynamic thrust acting on a heaving airfoil is different from that on a pitching airfoil. The thrust efficiency of a pitching airfoil increased up to V_p = 0.7 rapidly and maximum thrust efficiency was 0.34. The thrust efficiency of a heaving airfoil increased up to V_p = 0.5 rapidly and the maximum thrust efficiency was 0.20.