Vortex shedding and wake structure of a plunging wing

The structure and dynamics of leading-edge and trailing-edge vortices (LEV and TEV) are investigated for a plunging flat plate airfoil at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and interactions of the LEV and TEV. A classification scheme is established to describe the qualitative structure of the wake, which is shown to be dependent primarily on Strouhal number. However, convection of the LEV in the chordwise direction, and its resulting interaction with the TEV is also strongly influenced by plunge amplitude. The development of the leading-edge and trailing-edge vortices is tracked using phase-locked measurements throughout the cycle and the circulations of the LEV and TEV structures are measured. A scaling parameter proposed by Buchholz, Green, and Smits²⁰ for the circulation shed by a pitching panel reduces the variability of the circulation measurements but is found to be lacking physics relevant to the present problem. A modified parameter, taking into account the effect of free-stream velocity, is proposed, which provides an improved scaling of the circulation data.