Movable shark scales act as a passive dynamic micro-roughness to control flow separation

Area of Science:

• Fluid dynamics
• Biomimetics
• Ichthyology

Background:

• Fast-swimming sharks possess unique scales capable of moving over 50 degrees.
• This scale mobility is hypothesized to influence fluid flow direction and reduce drag.
• Understanding shark skin's properties can inspire novel hydrodynamic designs.

Purpose of the Study:

• To experimentally investigate the flow separation control capabilities of real shark skin.
• To provide evidence for the passive, flow-actuated mechanism of shark scales in managing fluid dynamics.
• To assess the effectiveness of shark skin in preventing flow separation on a hydrofoil.

Main Methods:

• Water tunnel testing was employed to simulate fluid flow conditions.
• Pectoral fin and flank skin samples from the shortfin mako shark (Isurus oxyrinchus) were utilized.
• These skin samples were attached to a NACA 4412 hydrofoil to evaluate separation control.

Main Results:

• Experimental evidence confirmed that real shark skin can control flow separation.
• Separation control was observed under specific conditions on both pectoral fin and flank skin samples.
• The movable shark scales demonstrated a capacity to disrupt flow reversal near the surface.

Conclusions:

• Shark scales act as a passive, flow-actuated mechanism for controlling flow separation.
• The scales function as a dynamic micro-roughness, enhancing hydrodynamic performance.
• This study validates the role of shark scale mobility in efficient aquatic locomotion.