Unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) was numerically examined using a grid-free vortex method. The flow characteristics and aerodynamical forces were compared among various accelerated or decelerated conditions. The results showed that flow separation occurred under decelerated condition and the lift-drag ratio decreased as the decelerated velocity became high and increased as the accelerated velocity became high.
