Experimental study of a zero-pressure-gradient turbulent boundary layer over a bioinspired surface with 3D-printed shark scales

This study investigates skin-friction drag modification using three-dimensional-printed biomimetic sharkskin-inspired surfaces within a fully developed zero-pressure-gradient turbulent boundary layer. Experiments were conducted in a recirculating water tunnel using planar particle image velocimetry (PIV) to characterize six scale configurations with systematic variations in scale (2 and 4 mm), spacing, packing compactness, and tip geometry. Two compactness levels were examined: fully compacted (inter-denticle spacing d = 0.75W, where W is the denticle width) and semi-compacted (d = W), and benchmarked against the canonical flat-plate and riblet surfaces. Substantial skin-friction reductions of up to 30% were achieved for the 2 mm fully compacted case with an optimal non-dimensional spacing s+≈15–20, highlighting the critical role of scale and tight denticle packing in achieving favorable roughness functions. Flow field measurements revealed reduced Reynolds shear stress and attenuated near-wall turbulence intensities in drag-reducing cases. The experimental findings align with previous direct numerical simulation and PIV-based studies of structured surfaces and riblets, supporting the view that geometrically optimized biomimetic surfaces can act as effective passive drag-reduction strategies. The results offer practical design guidance for implementing microstructure surfaces in applications demanding drag-reduction control within a range of Reynolds numbers.