Aerodynamics of Small-Scale Propellers Undergoing Dynamic Variations of Rotational Speed

Typical mission profiles of small unmanned air vehicles (SUAVs) often involve maneuvers. SUAVs rapidly vary the rotational speed of their propellers to transition between different flight conditions. If such a transition is sufficiently rapid, the aerodynamic performance can be significantly affected, impacting stability, structural integrity, and noise generation. This study shows that dynamic rotational speed variations primarily influence the flowfield induced by the propellers. A lag effect occurs in the induced velocity owing to the fluid inertia, mainly affecting the angle of attack seen by the blades. This particularly increases during acceleration and decreases during deceleration and may lead to significant variations in thrust and torque. The main vortex structures in the wake are also affected, with rapid maneuvers potentially inducing early vortex breakdown and turbulent transition. The aerodynamic effects of dynamic rotational speed variations are investigated using a midfidelity vortex particle method solver, chosen for its low computational cost and ease of implementing such maneuvers. The code proved to be an efficient tool, supporting investigations of dynamic propeller effects for performance evaluation and the design of future SUAVs.