Wandering of a Wing-Tip Vortex: Rapid Scanning and Correction of Fixed-Point Measurements

Oscillations of a wing-tip vortex over planes orthogonal to the freestream direction are typically ascribed to a specific fluid dynamic phenomenon, which is referred to as vortex wandering or meandering. Vortex wandering affects noticeably fixed-point measurements, producing measured vortices with larger size and weaker intensity than the actual ones, and thus methods for correction of wandering smoothing effects are needed. For this survey, the tip vortex generated from a tapered NACA 0012 half-wing is measured through the rapid scanning technique, which consists of quickly traversing a five-hole pressure probe through the vortex core to obtain velocity signals practically not affected by wandering. Rapid scanning allows evaluating probability distributions of the vortex center positions, which are found to be characterized by bivariate normal probability density functions. Estimate of wandering smoothing effects on fixed-point measurements is carried out by comparing rapid scanning data not affected by wandering with fixed-point three-sensor hot-film measurements. The vortex strength seems to be the main vortex parameter controlling wandering; wandering amplitude is reduced by increasing wing angle of attack or freestream velocity or by reducing streamwise distance from the wing. However, a sufficiently strong or concentrated vortex can be weakly affected by wandering.