An experimental study of discrete gust interaction with a propeller in axial flight: Asymmetric loading and gust breakdown mechanisms

Distributed electric propulsion systems in electric vertical takeoff and landing aircraft are expected to encounter unsteady inflow conditions in low-altitude flight, yet the interaction between discrete gusts and small-scale propellers remains insufficiently characterized. This study investigates the response of an isolated propeller subjected to a discrete one-minus-cosine like gust generated by a dual-vane gust generator. The propeller was tested at U∞=10 ms−1 and rotational speeds of 5000, 6000, and 7000 RPM, corresponding to advance ratios of J=0.47,0.39, and 0.34, respectively. Hot-wire anemometry and phase-synchronized stereo particle image velocimetry were used to characterize the incident gust and its evolution through the propeller disk, while synchronized six-axis load measurements quantified the corresponding unsteady propeller response. The results show that the propeller-induced swirl velocity redistributes the imposed gust field, locally attenuating the vertical gust velocity on the upstroke side of the disk and amplifying it on the downstroke side. A direct comparison between the measured combined velocity field and a local kinematic reconstruction confirmed that this gust–swirl interaction captures the main asymmetric inflow mechanism, while discrepancies near the blade-root region coincided with the loss of gust coherence observed in the particle image velocimetry fields, indicating gust breakdown and additional unsteady effects. This redistribution produces asymmetric out-of-plane torque responses and alters the induced velocity field in the wake. Increasing the propeller rotation speed from 5000 to 7000 RPM (J=0.47–0.34) reduced the thrust increment induced by the gust, but strengthened the distortion of the gust field, increasing the affected region by approximately 60%. The measurements identify the gust–swirl interaction and subsequent gust breakdown as the mechanism linking discrete-gust ingestion, asymmetric loading, and wake distortion and provide an experimental dataset for modeling unsteady propeller loading in non-uniform inflows.