Propeller Wake Dynamics with Vortex Attenuation Using Circulation Theory

Owing to Helmholtz’s vortex theorems and Kelvin’s circulation theorem, the formation of coherent vortex structures in the wake of a rotating wing is directly attributable to radial gradients in lift production. To mitigate these features, a constrained optimization problem was formulated to attenuate radial gradients in the bound circulation of a rotary wing, local to the propeller tip region. Prototypes of baseline and circulation-optimized propellers were tested in a wind-tunnel environment to verify design thrust characteristics and assess propeller wake flow physics. Phase-averaged stereoscopic particle image velocimetry data were acquired to obtain the wake velocity profiles across a range of wake phase angles. The baseline wake demonstrated typical coherent tip vortex roll-up behavior, resulting in a strong double-helix wake, in direct contrast to the vortex-attenuated propeller, which featured a distributed sheet of wake vorticity arranged in a conical spiral pattern. Additionally, the wake vorticity of the vortex-attenuated propeller dissipated faster than the baseline configuration. The propulsive wake of the baseline configuration behaved as expected with a uniform axial flow distribution, whereas the vortex-attenuated configuration demonstrated significantly higher axial velocities near the axis of rotation due to the axial velocity profile produced by the blade circulation distribution of this propeller configuration.