Experimental investigations of shark skin inspired surfaces in air
Flow separation is detrimental to the performance of a wide array of engineered systems. It is theorized that the shortfin mako shark has evolved a passive flow separation control mechanism – distinct from that of riblet skin-friction reduction – based on the passive flow-actuation of its microscopic scales in regions of incipient separation. Water tunnel studies have supported this theory, demonstrating flow separation control with samples of mako flank skin over a range of experimental conditions. The current study investigates the potential of this mechanism to be applied to systems in air. Characterization of the response of mako skin samples to airflows reveals that natural skin is unsuited to aerodynamic testing. A fabrication methodology for mechanical shark skin facsimiles, or “microflap arrays,” is developed. Prototype microflap arrays are found to be capable of similar passive actuation responses in air to those of mako skin in water. The aerodynamic performance of a NACA 0012 airfoil covered with a microflap array is evaluated at Re = 160000. Microflaps are found to decrease aerodynamic efficiency over a smooth surface, but are successful at passively responding to local flow separation.