Abstract:
Rotorcraft flowfields are dominated by the vortices trailing from the blade tips. The formation, evolution and subsequent interaction of these vortices with the following blade(s) is a key to rotor airloads and performance. A fixed-wing wind tunnel test was designed to simulate the aerodynamic environment of a rotor blade tip in hover, using an upstream wing to generate an interacting vortex. Detailed surface pressure and flow field measurements were performed to better understand the relationship between the tip vortex characteristics, such the circulation distribution inside the vortex core, and the loading distribution on the generating wing. The fixed-wing loading distribution differs from a typical loading on a hovering rotor blade in that the maximum bound circulation occurs at the blade root, and not close to the tip; this is similar to a very highly twisted rotor blade, like a tilt-rotor, in hover. The wing-vortex interaction alters the wing loading such that the loading peak moves closer to the tip. The trailed circulation in the wake induced by the vortex interaction may entrain into the interacting vortex. The measurements show that this has a profound impact on the the evolution of both the wing tip vortex and the interacting vortex. These findings can be of significance to engineering models, such as the free vortex wake models typical in rotorcraft comprehensive analyses.