There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry.

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Flow-effected, enhanced heat transfer in a high aspect ratio rectangular mm-scale channel that models a segment of a high-performance, air-cooled heat-sink is characterized. The present investigation reports a novel approach to enhanced cooling without increasing the channel's characteristically low Reynolds number. Heat transport that is governed by the local heat transfer from the fin surface and by subsequent mixing with the core flow is significantly increased by deliberate shedding of unsteady small-scale vortices that are induced by the vibration of a miniature, planar self-oscillating reed. The present investigation focuses on the heat transfer and fluid mechanics that are associated with the small-scale motions induced by the reed. Performance enhancement by reed actuation is quantified in terms of increased power dissipation over a range of flow rates compared to the baseline flow in the absence of the reed. It is demonstrated that the channel's coefficient of performance can be increased by a factor of 4 while accounting for all the losses associated with the reed actuation.

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