Performance of Shark Skin Inspired Manufactured Models for Separation Control

Abstract

The skin of fast-swimming sharks has been shown to have mechanisms able to reduce flow separation in both laminar and turbulent flows. This study analyzes arrays of bio-inspired microflaps and scales in a separated region generated by an adverse pressure gradient in a water tunnel environment. In the laminar boundary layer case, the microflap model bristles due to vortex interaction. This bristling controls the separation downstream of the model, reducing overall reversing flow by up to 59%. This investigation finds that the height of the protrusion into the boundary layer is an crucial factor in controlling the reversing flow. For the turbulent boundary layer, arrays of manufactured scales are tested in weak and strong adverse pressure gradients, controlled by a rotating cylinder. It has been found that the scales are ineffective at controlling separation in the weaker adverse pressure gradient case and increase the separation. However, in the stronger adverse pressure gradient conditions, the scales are highly effective at controlling separation, reducing the reversing flow by up to 70%. Additionally, the models are able to reattach the flow in extreme separation conditions.