Vortex Topology of a Pitching and Rolling Wing in Forward Flight

Abstract

Vortex topology is analyzed from measurements of flow over a flat, rectangular plate with an aspect ratio of 2 which was articulated in pitch and roll, individually and simultaneously. The plate was immersed into a Re = 10,000 flow (based on chord length) to provide forward flight component of the study. Measurements were made using a 3D-3C plenoptic PIV system to allow for the study of complete vortex topology of the entire wing. The prominent focus is the early development of the leading-edge vortex (LEV) and resulting topology. The effect of the wing kinematics on the topology was explored through a parameter space involving multiple values of pitch rate and roll rate at pitch and roll angles up to 50°. Characterization and comparisons across the expansive data set are made possible through the use of a newly defined dimensionless parameter, k_rg. Termed the effective reduced pitch rate, k_rg is a measure of the pitch rate that considers the relative rolling motion of the wing in addition to the pitching motion and freestream velocity. The study has found the addition of a rolling motion to a pitching wing removes the symmetries in the vortical structures, delays vortex evolution, and inhibits the extent of detachment of the LEV. Additionally, it was found that increasing the k_rg parameter accelerates the evolution of the LEV, from formation to detachment, as well as advances the evolution of the LEV in nondimensionalized time.