Comparison Of Free-Vortex Wake Models For A Sub-Scale Rotor At Low Speeds

Abstract

During shipboard testing in 1999, the V-22 Osprey tiltrotor experienced two separate uncommanded roll events as a result of an upwind-generated helicopter rotor wake, entrained in the ship's airwake, impinging upon its rotors. A portion of this thesis documents the author's involvement in one of the resulting wind tunnel tests created to investigate these events. The remainder details the attempts to validate the Maryland Free Wake (MFW) and Continuum Dynamics' CHARM free-vortex wake models using that low speed wind tunnel data. Results presented in this thesis show while the models qualitatively predict the downstream wake structure, they exhibit some interesting behavior in the far wake that is not in agreement with the measurements. To improve the correlation, changes to rotor parameters and the wake growth parameter were made, but with limited success. Potential explanations for the behavior are given, and recommendations for future research are also discussed.