  Patterns of vorticity in the wake of a single rectangular winglet (vortex
generator) embedded in a turbulent boundary layer have been studied using
Stereoscopic Particle Image Velocimetry (SPIV). The winglet was mounted
normally to a flat surface with an angle to the oncoming flow. A parametric
study varying the winglet height (constant aspect ratio) and angle has shown,
contrary to the common classical single tip-vortex conception, that the wake
generally consists of a complex system of multiple vortex structures. The
primary vortex has previously been discovered to contain a direct coupling
between the axial and the rotational flow. In the current work, even the
longitudinal secondary structures detected from measured streamwise vorticity
display similar behavior. A regime map depicting the observed stable far wake
states of the multiple vortices as a function of winglet height and angle
reveals complex patterns of the flow topologies not only with the primary tip
vortex, but with the additional secondary structures as well. A bifurcation
diagram shows distinct regimes of the various secondary structures as well as
how the primary vortex is in some cases significantly affected by their
presence. These data should serve as inspiration in the process of generating
longitudinal vortices for enhancement of heat and mass transfer in industrial
devices since the multiple vortex regimes can help improve the conditions for
these exchanges. Further, these results point to a weakness in existing
inviscid models not accounting for the possibility of multiple vortical
structures in the wake.
