Abstract
The flow, thrust generation and sediment dynamics over solid and sedimentary beds in the wake of a pure flapping airfoil were experimentally studied for various flapping amplitude \(A_0\) and frequencies \(f_p\) at Reynolds number Re\(\approx 4.6\times 10^4\). Two dimensional particle image velocimetry and a force sensor were employed to illustrate the flow statistics, sediment distribution and mean thrust. Results dictate that the volume of suspended sediments and the thrust generation is highly modulated by both \(A_0\) or \(f_p\). In particular, presence of boundary-wall reflects the vertical flow under high flapping intensities, resulting in deflected vortex distribution in the wake flow. Amplitude based Strouhal number \(St_A\) was utilized to characterize volume of the suspended sediments and thrust generation. Two regions based on the \(St_A\) were identified with distinctive trends on coefficient of thrust and normalized volume of suspended sediments. For cases with \(St_A\le 0.15\), sediment suspension is negligible and foil experiences drag force. With \(St_A\ge 0.17\) distinctive sediment suspension occurs and foil experiences thrust force. Overall, for sedimentary base, suspended sediments in the wake of the foil diminishes both mean flow flux and wake fluctuation intensities compared to the solid base; this leads to smaller thrust generation.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Acknowledgements
This work was supported by the Department of Mechanical Engineering, the University of Texas at Dallas, as part of the start-up package of Dr. Jin.
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Aju, E.J., Gong, P., Pham, D.T. et al. On the wake dynamics and thrust generation of a foil flapping over solid and sedimentary beds. Exp Fluids 63, 32 (2022). https://doi.org/10.1007/s00348-022-03386-w
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DOI: https://doi.org/10.1007/s00348-022-03386-w