Wake Dynamics and Thrust Generation of a Foil Flapping Near the Sedimentary Bed

The active flapping of airfoil generates significant wake vortex shedding and thrust force, which provides key insights for understanding the locomotion of marine animals. In this work, experimental efforts with particle image velocimetry and force sensor were conducted to characterize the wake dynamics and thrust generation of a foil flapping near the sedimentary bed, which mimics the swimming of fishes close to the seabed. Overall, the thrust generation is dominated by the Strouhal number defined by the flapping frequency, amplitudes and incoming flow velocity. Results show that with the growing flapping frequency and amplitudes, the difference of thrust generation between solid and sedimentary bed increases. The stronger flapping intensity results in more distinctive sediment suspension, where the distribution of suspended sediments is highly correlated to the wake vortex structures. The characterization of wake statistics shows that at the same flapping frequency and amplitude, cases with solid bed produces stronger ‘jet-style’ wake velocity distributions compared to the sedimentary bed counterparts.