Effect of RANDALLfoils on the fluid dynamics of rowing

Rowing-blade attachments have the potential to modify blade-fluid interactions during the rowing stroke, however these effects remain difficult to isolate in on-water rowing. This study experimentally investigates the RANDALLfoil, a blade attachment designed to alter the flow around a rowing blade, using 1:4 scaled rowing motions. Force and torque measurements are collected for a standard blade and a RANDALLfoil blade, and two-dimensional particle image velocimetry (PIV) is used to relate the measured loading to leading-edge vortex (LEV) development. For the representative scaled motion, the RANDALLfoil increased propulsive impulse ( Jₓ ) by 9.01% and impulse efficiency ( η J ) by 4.91%, indicating greater momentum transfer in the direction of boat motion and a response consistent with reduced blade slip. Whilst the total integrated pitching torque had negligible difference over the duration of the stroke, the pitching torque of the blade was consistently lower in the first half of the stroke for the RANDALLfoil. PIV results showed that changes in blade-normal force were not explained by LEV circulation magnitude alone. Instead, the force response was better interpreted using circulation magnitude, circulation-growth rate, LEV area, and vortex-core distance from the blade. These results suggest that the RANDALLfoil modifies blade loading by changing both LEV development and blade-vortex coupling during the drive. This study was limited to the submerged drive phase of the rowing stroke at 1:4 scaled geometry and a reduced Reynolds number from full-scale rowing. PIV measurements were performed at the mid-height of the blade so three-dimensional flow structures were not captured.