The influence of trailing edge shape on the wake circulation and time-averaged wake of bio-inspired pitching panels

Abstract The influence of trailing edge shape and Strouhal number on the performance and wakes of bio-inspired pitching panels is investigated. Measurements of thrust and efficiency show that positive mean thrust and efficiency only develop for panels of reduced aspect ratio that have straight or pointed trailing edges, and high aspect ratio panels with forked trailing edges fail to produce positive mean thrust. Wake behaviors reveal that forked panels can produce strong trailing edge vortices while minimizing the three-dimensional effects of tip vortices, yet still do not generate positive mean thrust. Regardless of planform, the time-averaged wake contains one or more jets of surplus streamwise momentum when Strouhal number is large enough. As Strouhal number and trailing edge convexity increase, streamwise momentum in the time-averaged wake grows, and different jet structures may arise. Multiple jets of large inclination angles can be present during high performance, and single or dual jets of negligible or small inclination angles may be present during degraded performance. Just as recent work has demonstrated that direct connections between time-varying vortex patterns and mean performance are difficult to establish, caution must be used when connecting time-averaged jet structures to performance characteristics.