Shark skin inspired low-drag microstructured surfaces in closed channel flow

Living nature is the inspiration for many innovations and continues to serve as an invaluable resource to solve technical challenges. Skin from fast swimming sharks intrigue researchers since its low-drag riblet structure is applicable to many engineering applications. In this study, riblet-lined closed channel (rectangular duct) internal flow was examined since its effect is less understood than with open channel external flow. With one experimental setup and two fluids, this study examines various dimensional aspects of microstructured riblets. Experimental parameters include riblet geometry, fluid velocity (laminar and turbulent flow), fluid viscosity, riblet combinations, channel size, wettability, and scalability. For direct comparison, the sample flow channel was fabricated to accommodate multiple samples with water and air in various flow conditions, where drag is characterized by measuring pressure drop. Results are discussed and conceptual models are shown suggesting the interaction between vortices and the riblet surfaces.

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► With water and air riblets show an improved pressure drop reduction in turbulent flow.
► Several design principles for riblet geometry optimization are derived.
► Placement of riblets is found to affect the pressure drop reduction.