Performance of Low Reynolds Number Tandem Rotors in Phase-Locked Condition

Rotor-rotor wake interactions in low-Reynolds-number UAVs significantly impact overall vehicle performance. These interactions, coupled with dominant viscous forces, alter the flow dynamics, making it essential to understand them for accurate performance prediction. This study examines the influence of phase-locking on the performance of staggered tandem rotors. A pair of staggered tandem rotors were synchronized in speed to achieve stable phase locking. Thrust and torque were measured across a range of phase angles, horizontal (HS) and vertical separations (VS), at two speed settings. Results reveal that performance varies with both overlap and phase angle, with the most pronounced effects observed at higher overlaps (HS = 1.3R and 1.5R). The downstream rotor exhibited greater sensitivity to phase angle changes than the upstream rotor, particularly in thrust and torque variation. Despite operating at different Reynolds numbers, both RPM cases followed similar performance trends. For maximum overlap, the downstream rotor showed a thrust change of 10.5% and torque change of 7.9% at 5010 RPM as the phase angle shifted from 30 degrees to 150 degrees; at 3000 RPM, the corresponding changes were 9.1% and 10.1%, respectively. Notably, the rotor-rotor phase angle range responsible for peak performance shifts remained consistent across RPMs, underscoring the influence of phase angle in phase-locked configurations.