Surf Fin Hydrodynamics

PhyMo played a major role in providing guidance and consulting for Computational Fluid Dynamics (CFD) testing of several hydrofoil prototypes in a patent-pending project. The CFD results were crucial in confirming whether the humpback whale-inspired design methods were worth pursuing, allowing performance evaluation using only CAD models of the designed parts, without the need for physical prototypes.

Humpback whales are renowned for their impressive maneuverability, which scientists attribute to the leading-edge bumps, called tubercles, on their pectoral fins. These tubercles are believed to delay stall and enhance maneuverability. The CFD research, directed with support from Artificial Twin, aimed to explore additional passive flow control features found on the humpback’s pectoral fin.

Three hydrofoil designs were tested at both low and high Reynolds numbers: a control with a straight leading edge, a standard tubercled leading edge commonly used in research, and a “real whale” (RW) patent-pending hydrofoil. Later, a fourth, unswept version of the RW hydrofoil was added for comparison.

Validation and further analysis

Since the patent application, additional CFD studies have been conducted on high-performance surfboard fins, known as thrusters. A standard fin with a straight leading edge (PS) was compared to the RW design and to a fin with a grooved trailing edge (PG). Consistent with previous findings, the RW design again demonstrated the highest lift coefficients. The PS and PG fins were developed by Marc in het Panhuis and his research group at the University of Wollongong.

Advanced post-processing of wall shear stresses enabled identification of areas with potential for cavitation on the fin surface. A custom “cavitation/separation potential” metric was developed, showing that the RW fin had the lowest risk of cavitation or flow separation.

The CFD results for thruster fins are being validated with prototypes and data collected using a Trace sports tracking device. Preliminary findings indicate a 35% increase in turning power for a surfer using the RW fin compared to a professional surfer, and nearly a 50% increase compared to the same surfer using standard commercial fins. Power calculations followed the methods described in Gately et al., 2017.

Validating our CFD results with field tests provides robust verification of the designs, offering greater confidence than CFD or field testing alone. Additionally, CFD analysis helps us identify and address potential issues in complex RW designs, enabling improvements for future applications, such as drone propellers, before physical prototypes are built.