Abstract
The influence of the phase difference between a pitching foil and a periodic flow on maneuverability in the lift direction is investigated experimentally at a low Reynolds number of 4.1×103, where the periodic flow is the time-varying freestream in the streamwise direction. A strain gauge force balance is used to measure the thrust and lift forces, and it is found that the phase difference offers control of the lift coefficient without affecting the thrust coefficient. Also, the velocity field in the vicinity of the foil is measured using particle image velocimetry (PIV). From the velocity data, a leading-edge vortex (LEV) is observed only on the upper surface at zero phase difference. A numerical simulation is conducted to reveal how this LEV affects the surface pressure, and it is found that the asymmetry of the LEV formation between the upper and lower surfaces enhances the lift coefficient.
