Title: Vortex Flow and Dynamic Thrust of an Unsteady Airfoil
Abstract: In order to clarify the vortex flow behind a pitching/heaving airfoil and the characteristics of dynamic thrust acting on them at low Reynolds number region, we have carried out PIV masurement behind both airfoils and have measured the dynamic thrust acting on them. Increasing the nondimensional velocity in pitching/heaving motion, the thrust producing vortex street is clearly formed behind both airfoils. The averaged dynamic thrust acting on them increased as the nondimensional velocity increased. The hysteresis loops of dynamic thrust acting on a pitching/heaving airfoil had concavity/convexity shape characteristics, respectively. The behaviors of the dynamic thrusts strongly depend on the non-dimensional trailing edge velocity and the non-dimensional heaving velocity. The thrust efficiency of a pitching airfoil increased up to Vp= 0.7 and the maximum thrust efficiency was 0.34. On the other hand, the thrust efficiency of a heaving airfoil increased up to Vh=0.4 and the maximum thrust efficiency was 0.20.