Experimental study of a rapidly pitched flat plate at low reynolds number

We report the results of an experimental and numerical study of a rapidly pitched flat plate airfoil at Re = 5,000. The flat plate airfoil undergoes a 90° pitch-ramp maneuver about the quarter chord point with smooth starting and stopping transients. Reduced frequencies, k = θc/2U_∞, of 0.2 and 1.0 are investigated with dye flow visualization and 2D PIV. The main objective of the research is to determine the leading edge vortex (LEV) and trailing edge vortex (TEV) dynamics, and force generation during the high pitch-rate maneuver. The LEV and TEV formation and evolution are characterized in terms of vortex core location and circulation. The force coefficients are computed using the PIV data and are compared to recent direct force measurements and numerical simulations. Large force coefficients well beyond the steady flow values are measured during the motion. It is shown that as reduced frequency is increased large aerodynamic forces are produced, before formation of the LEV. Vortex topology also changes. For the low reduced frequency the flow topology is characterized by a strong LEV vortex and relatively weak TEV. For the high reduced frequency the TEV forms first and LEV formation is delayed until after completion of the motion.