Experimental Characterization of an Accelerating and Decelerating Propeller at Low Reynolds Numbers

This study investigates the aerodynamic response of a small-scale UAV propeller under steady and transient conditions at low Reynolds numbers (104–105;). In this regime, phenomena such as laminar separation, transition, and the formation of recirculation bubbles strongly influence airfoil performance. In addition, the flow response to rapid changes in rotational speed is still poorly understood, as most existing models assume quasi-steady behavior. Experiments were conducted in a low-speed wind tunnel using a commercially available 10-inch class propeller (X500 V2 1045). The propeller was subjected to controlled rotor speed ramps, and phase-locked particle image velocimetry (PIV) was combined with synchronized load measurements to track the flow evolution during acceleration and deceleration. A hysteresis was observed in the thrust response when comparing increasing and decreasing rotational speed at identical operating conditions. At the same time, the PIV measurements reveal that the inflow field and the effective angles of attack at the blade scale evolve dynamically throughout the transient. These findings highlight the importance of transient trajectories in low-Reynolds-number propeller operation and show that quasi-steady models are insufficient to describe the observed aerodynamic behavior.