Performance evaluation of a humpback whale-inspired hydrofoil design applied to surfboard fins

Abstract

The humpback whale flippers' leading-edge tubercles have received much attention since the 1990's. This paper covers computational fluid dynamics (CFD) analysis and field investigations used to evaluate the performance of a novel method (“Real Whale”, RW) for applying several of the humpback's passive flow control mechanisms, including tubercles, to surfboard fins. CFD analysis was performed at Reynolds numbers (Re) between 105 and 106. Applying the RW design to longboard fins resulted in increased overall lift to drag ratio, and reduction in $\mathrm{C}_{\mathrm{d}}$ compared to a control (C) and tubercled (CT) design above 10° angle of attack ( $\boldsymbol{\alpha}$ ). $\mathrm{C}_{1}$ and delayed stall were improved for RW above $20^{\circ} \boldsymbol{\alpha}$ . High Re improvements were greater than low Re improvements. CFD images of wall shear stress revealed RW applications possibly have less potential to stall and cavitate, thereby improving control. Fieldwork involving surfing of 665 ocean waves (using GPS tracking systems coupled with 9-axis motion sensors), revealed that, compared to a standard longboard fin, the RW fin provided longer rides, and faster max and average speeds, especially in more powerful waves. Both field and CFD results suggest RW designs are more efficient, require less material to manufacture, and provide more control than hydrofoil shapes with straight leading edges or standard tubercled designs.