Experimental investigation of transient inflow and wake response of a low-Reynolds two-bladed propeller
Y. Lecomte(1,2), M. Ratz(1,3), C. Schram(1), M.A. Mendez(1,3,4)
1: Environmental and Applied Fluid Dynamics, von Karman Institute for Fluid Dynamics, Belgium
2: Department of Control Engineering and System Analysis, University Libre de Bruxelles, Belgium
3: Aero-Thermo-Mechanics Laboratory, University Libre de Bruxelles, Belgium
4: Experimental Aerodynamics and Propulsion Lab, Universidad Carlos III de Madrid, Spain
DOI:
The growing use of unmanned aerial vehicles (UAVs), together with their deployment in increasingly demanding operating environments, raises the need for a better understanding of transient propeller aerodynamics. Small UAV propellers typically operate at low chord-based Reynolds numbers, of order O(104-105), and are often modeled using quasi-steady assumptions. At these scales, the coexistence of laminar separation, transition sensitivity, high rotational speeds, and compact three-dimensional wake structures makes both numerical prediction and experimental flowfield characterization particularly challenging. This partly explains why transient inflow and wake dynamics remain poorly documented. In this study, phase-locked PIV measurements are performed in the propeller meridian-plane to investigate the transient inflow and wake response of a low-Reynolds-number two-bladed propeller under steady conditions and rotational-speed ramps. During experiments, load measurements reveal a hysteresis in the thrust coefficient between acceleration, deceleration, and steady operation. The inflow field was first examined by extracting the axial velocity along the blade leading-edge line, in order to identify a possible transient signature. However, the resulting profiles did not show a clear systematic difference between the different regimes. In contrast, the wake analysis indicates more noticeable modifications, particularly in the position and shape of downstream vortical structures. These results suggest that the transient load hysteresis is more likely associated with wake adaptation than with a directly measurable inflow variation in the investigated plane.
