A technique of particle image velocimetry is employed to characterize the three-dimensional flow structure on a wing subjected to simultaneous pitch-up and rotational motions. Distinctive vortical structures arise, relative to the well-known patterns on a wing undergoing either pure pitch-up or pure rotation. The features associated with these simultaneous motions include: stabilization of the large-scale vortex generated at the leading edge, which, for pure pitch-up motion, rapidly departs from the leading-edge region; preservation of the coherent vortex system involving both the tip vortex and the leading-edge vortex (LEV), which is severely degraded for pure rotational motion; and rapid relaxation of the flow structure upon termination of the pitch-up component, whereby the relaxed flow converges to a similar state irrespective of the pitch rate. Three-dimensional surfaces of iso-
DOI: http://dx.doi.org/10.1017/jfm.2014.458
Fluids Research Laboratory
Lehigh University
Bethlehem, PA 18015
27 Memorial Drive West, Bethlehem, PA 18015