Synergistic drag reduction of cross-medium propellers using biomimetic leading-edge tubercles and superhydrophobic surfaces

To mitigate efficiency loss and excessive drag of cross-medium propellers operating in air and water, we evaluate a synergistic drag-reduction concept combining biomimetic leading-edge tubercles with a superhydrophobic surface (SHS). Three propellers were fabricated: a smooth baseline (A0), a 2.5%-chord tubercled propeller (A2.5), and a tubercled SHS propeller (AS2.5). Thrust coefficient (KT), torque coefficient (KQ), and efficiency (η) were measured in towing-tank and open-air tests, and surface pressure and skin-friction distributions were analyzed in STAR-CCM+ using multiple reference frame–Reynolds-average Navier–Stokes with the shear stress transport k–ω model. In water at J = 1.0, A2.5 increased KT by 13.5% and η by 1.4% vs A0, while AS2.5 increased KT by 18.6% and η by 3.6%, with a 12.47% higher peak η. In air, AS2.5 improved η by 6.5% at J = 1.0 and raised peak η by 17.1%. Numerical simulations and mechanistic analyses indicate that the biomimetic leading-edge tubercles generate streamwise vortices, redistribute and segment the low-pressure region near the leading edge, and delay local flow separation, whereas the superhydrophobic interface reduces near-wall friction through effective slip. Their integration on the same blade surface couples geometric flow control with interfacial friction reduction, causing the increase in propeller thrust to exceed the accompanying increase in torque and thereby achieving drag reduction and enhanced propulsive efficiency.