Synergistic Morphology-Material Design in a Hierarchical Composite Surface for High-Efficiency Drag Reduction

Area of Science:

• Fluid Dynamics
• Materials Science
• Biomimetics

Background:

• Shark skin's riblet structures are known to reduce frictional drag.
• The roles of underlying cavities and flexible dermis in drag reduction are not fully understood.
• Existing biomimetic surfaces often imitate single mechanisms, limiting performance.

Purpose of the Study:

• To develop a biomimetic hierarchical composite surface (BHCS) integrating multiple drag reduction mechanisms.
• To investigate the synergistic effects of denticles, flexible substrate, and interfacial chemistry.
• To achieve superior drag reduction beyond single-mechanism biomimetic designs.

Main Methods:

• Multi-material 3D printing and spray-coating were used to create the BHCS.
• The BHCS integrates denticle arrays, a flexible substrate with an elastic gradient, and interfacial chemistry (PDMS molecular brush).
• Systematic experiments and numerical simulations were employed to analyze performance.

Main Results:

• The optimized BHCS achieved a maximum drag reduction (DR) rate of 18.65% in underwater flow.
• Synergistic mechanisms include denticles inducing stable vortices and a flexible substrate enhancing reverse pore flow.
• The surface-grafted PDMS molecular brush reduced interfacial shear by forming a hydrophobic, liquid-like layer.

Conclusions:

• A novel biomimetic design concept integrating multiple mechanisms was demonstrated.
• The synergistic interaction between surface structures, substrate flexibility, and interfacial properties optimizes drag reduction.
• This approach offers a pathway to significantly enhance the performance of biomimetic surfaces for fluid flow applications.