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 $\text {Re} = 10,000$ flow (based on chord length). 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 ${50}^{\circ }$. Characterization and comparisons across the expansive data set are made possible through the use of a newly defined dimensionless parameter, ${\textit{k}_{\text {Rg}}}$. Termed the effective reduced pitch rate, ${\textit{k}_{\text {Rg}}}$, is a measure of the pitch rate that takes into account the relative rolling motion of the wing in addition to the pitching motion and freestream velocity. This study has found that for a purely pitching wing, increasing the reduced pitch rate ${\textit{k}}$ delays the vortex evolution with respect to $\alpha _\mathrm {eff}$. For a purely rolling wing, as the advance coefficient ${\textit{J}}$ is increased, the vortex evolution is advanced with respect to nondimensionalized time and the bifurcation point of the LEV shifts inboard. For a pitching and rolling wing, the addition of roll stabilizes and delays the evolution of the LEV in both nondimensionalized time and effective angle of attack.

Graphic abstract