Wind Tunnel Experiments on Rotor Blade Tip Vortices using Hot-Film Anemometry

Abstract

Helicopter rotors produce helical vortex systems originating from the blade tips, which affect the aerodynamic performance, vibrational loads and acoustic emissions of the rotorcraft. Vortex properties include vortex core size, convective trajectory, and swirl velocity distribution. Phenomena linked to blade tip vortices include vortex pairing and blade vortex interaction (BVI). Previous research shows that the vortex properties are strongly influenced by the vortex Reynolds number. Using the same two-bladed rotor as in predecessor measurements, the present study analyzes vortex evolution at lower Reynolds numbers (Re_(c,75%R) = 6 · 104 ). To reduce vortex–vortex interactions, a specially designed single-bladed rotor was also tested. Experiments were conducted in the closed-loop 1-meter wind tunnel (1MG) at the German Aerospace Center (DLR) in Göttingen. Constant-temperature anemometry (CTA) with a hot-film probe was used to resolve the small-scale, high-frequency blade tip vortex structures.