Simulations of Dolphin-inspired High-frequency Oscillation-induced Boundary Layer Flows

  • WANG, DONGYUE (Chiba University)
  • Liu, Hao (Chiba University)

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The compliant skin of dolphin has long been regarded as one of the important reasons for drag reduction due to its flexibility and deformability. Till now most of the subjects associated with the drag reduction by compliant skin have been focused on the static microscopic skin-structure and passive deformation caused by transient flow-indued pressure fluctuations but failed to completely uncover the mystery of dolphin’s fast-swimming behavior. In this study, inspired by that dolphins emit the click signals with high frequency and energy during cruising, we assume that such click signals may act as an internal stimulus to excite a high-frequency dynamic oscillation of dolphin’s skin, altering boundary layer flow adjacent to the skin and substantially reducing flow resistance. A series of numerical simulations have been undertaken for a dolphin-skin-inspired plate model to examine the characteristics of the boundary layer flow induced by the ultrasonic oscillating wall surface. We found a reversed circulation flow located in the lower boundary layer, which enables creation of negative shear stresses against streamwise flow, hence leading to dramatically reducing the friction-based drag. Based on the simulation-based flow structures we further built up a theoretical model for the velocity profiles in association with the transient boundary layer flow. Our results thus unraveled a novel drag reduction mechanism via high-frequency oscillation and provide a possible explanation for the long-standing mystery of the excellent hydrodynamic performance in dolphin swimming.