关键词: Drag reduction, Warp-knitted swimwear fabrics, Dynamic drag measurement, Pit-structured fabric, Flowseparation control')">Drag reduction, Warp-knitted swimwear fabrics, Dynamic drag measurement, Pit-structured fabric, Flowseparation control

Abstract: Inspired by the aquatic-adapted pit structures of the Cybister beetles that enable high-speed swimming, this study employs warp-knitted technology to fabricate drag-reduction swimwear textiles. Eight distinct fabric morphologies were produced, and a self-developed high-precision dynamic drag measurement device was used to systematically analyze the mechanisms underlying the drag-reduction performance of these biomimetic pit structures. The device incorporates a servomotor, ball screw linkage, and high-precision tension sensor, enabling real-time and accurate detection of fluid drag forces. It effectively overcomes the limitations of traditional indirect measurement methods, including dynamic response lag and insufficient accuracy. Experimental results demonstrate that the hydrophobic small-pit fabric (4^#) achieves an 84% drag reduction at 400 mm/s, outperforming the control sample (warp-knitted fabric 7^#). This significant reduction is attributed to the Cassie state established on the hydrophobic surface, which substantially decreases viscous drag and the microvortices generated by the pit structures, which delay flow separation and effectively minimize pressure drag. Furthermore, small-pit fabrics demonstrate a drag reduction rate 26% to 50% higher than that of large-pit structures, highlighting the critical importance of matching the pit scale to the thickness of the near-wall viscous sublayer for optimal drag reduction. This study establishes a theoretical foundation for the biomimetic design of high-performance drag-reduction swimsuits. The developed drag-measuring device also provides a standardized experimental platform for hydrodynamic studies of flexible materials, supporting a shift from empirical design methodologies to theory-driven approaches in drag-reduction technology and exhibiting significant potential for future advancements.

Key words: Drag reduction, Warp-knitted swimwear fabrics, Dynamic drag measurement, Pit-structured fabric, Flowseparation control')">Drag reduction, Warp-knitted swimwear fabrics, Dynamic drag measurement, Pit-structured fabric, Flowseparation control