Momentum distribution in the wake of a trapezoidal pitching panel

The oscillation of bioinspired fin-like panels in a uniform freestream flow creates chains of vortex rings, including streamwise segments that induce significant threedimensional effects. With increasing Strouhal number, this wake structure induces flow with increasing nondimensional momentum, defined relative to the freestream velocity, in the downstream direction. This increase in relative momentum with increasing Strouhal number is consistent with greater nondimensional thrust production, which has been shown previously in the literature. These results were obtained via stereoscopic particle image velocimetry water tunnel experiments at Strouhal numbers ranging from 0.17 to 0.56 downstream of a continuously pitching trapezoidal panel. Features of the wake dynamics including spanwise compression, transverse expansion, transverse wake splitting or bifurcation, and wake breakdown are elucidated through analyses of phase-averaged as well as timeaveraged velocity fields, in addition to common vortex identification methods.