Propulsive Vortical Patterns and Unsteady Fluid Forces of a Flapping Airfoil

It is known that a flapping airfoil can produce a thrust force through the generation of a reversed Ka´rma´n vortex street and this can be expected to be a new highly effective propulsion system. A flapping airfoil model was made and it was operated within a water channel. The wake formation behind the flapping airfoil was visualized and a dynamic thrust force was measured using a 6-axis force sensor based on force and moment detectors. We have examined various conditions such as reduced frequency and amplitude in a NACA 0010 airfoil. The results of the analysis showed that the unsteady fluid forces of the flapping airfoil increased with Strouhal number.