Tip Vortex Meandering Characteristics of a Model Helicopter Rotor with Different Tip Shapes

Abstract

This paper presents the results of an experimental investigation regarding the tip vortex meandering characteristics for a model helicopter rotor with different blade tip shapes. Phase-locked particle image velocimetry measurements are performed at the rotor phase angles between 0 and 72° with 6° increments. The meandering characteristics are presented along the first and the second principal axes of the meandering motion, which are found using the principal component analysis method. For all blades, the results show that the vortex position scattering along the principal axes can be defined with a Gaussian distribution. The scatterings about the second principal axes have a better agreement with the Gaussian distribution, with a fit up to the 95th percentile of the data, than the first axes for all configurations. Streamwise variations of the standard deviation of the meandering motion along the principal axes and the meandering angle, which is the angle between the slipstream and the first principal axis, are analyzed, and a simple empirical meandering model as a function of wake age is proposed. The meandering angle decreases with the vortex age, so the first principal axis becomes more aligned with the slipstream direction () from close to being perpendicular () at the early wake ages.