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Published on: April 23, 2018
The stability of leading-edge vortices to perturbations on samara-inspired rotors: a novel solution for gust
Adnan M El Makdah1, Laura Sanders, Kai Zhang
1Department of Mechanical and Materials Engineering, Queen's University, Kingston, ON, Canada.
Abstract:
The stability of leading-edge vortices (LEVs) on a samara-inspired rotor during steady and unsteady gusty incoming flow was investigated experimentally using direct rotational speed measurements, as well as time-resolved particle image velocimetry (PIV). The blades of the samara-inspired rotor were designed to match the tip-speed ratio, the aspect ratio, and the distribution of the effective angle of attack of samara seeds to utilize LEVs similar to samara seeds. The flow around the blades of the samara-inspired rotor was compared to a reference rotor, which possesses a constant spanwise effective angle of attack, to investigate the influence of the samara-like spanwise effective angle-of-attack distribution on LEV stability. Furthermore, the unsteady performance of the samara-inspired rotor was compared to a generic low-inertia rotor that possesses blades with a constant effective angle of attack less than the stall angle. During steady rotation, the samara-inspired rotor exhibited a stably-attached LEV, while the reference rotor demonstrated unstable LEV shedding. Compared to a generic low-inertia rotor, the samara-inspired rotor demonstrated a relatively stable tip-speed ratio ([Formula: see text]) during the gust. Furthermore, the LEV remained stably-attached on the rotor's blades with a constant normalized circulation during the gust. Finally, the analysis of the LEV stability during the gust using the vorticity transport equation suggests that LEV stability is coupled with constant tip-speed ratio during gusts.
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