Turbulence modification by compliant skin and strata-corneas desquamation of a swimming dolphin

Direct numerical simulation has been conducted for pulsating or non-pulsating turbulent water flow near the compliant wall with the separation of pieces of the surface with time to examine how much the turbulence is modified and how the drag reduction is performed in swimming dolphins. The surface consists of a model of beads, springs and dashpots to represent the stratum cornea of dolphin skin. The computational results show that the compliant wall contributes to the drag reduction by reducing the number density of hairpin vortices. The small separated pieces increase the wall shear stress, which is consistent with our experimental result for turbulent water flow over a wavy wall covered with small pieces of film. This is because the models in the linear sublayer accelerate the flow between the models and the wall. The Reynolds shear stress decreases due to the attenuation of the hairpin vortices and the Q4 events by many models transported into the buffer region.