Secondary Vortex Structures in Vortex Generator Induced Flow

Passive rectangular vane actuators can induce a longitudinal vortex that redistributes the momentum in the boundary layer to control the flow. Recent experiments [1] as well as previous studies [2] have shown that a secondary vortex of opposite sign is generated along with the primary one, supposedly from local separation of the boundary layer due to the primary vortex. 2D flow visualizations of a vortex in the vicinity of a boundary support this hypothesis [3]. These secondary vortices are studied for various configurations -- single generator, counter- and co-rotating cascades. The objective is to study their removal through cancelation in cascades using Stereoscopic Particle Image Velocimetry and flow visualization.\\[4pt] [1] Velte, Hansen and Okulov, {\emph{J. Fluid Mech.}} {\bf{619}}, 2009.\\[0pt] [2] Zhang, {\emph{Int. J. Heat Fluid Flow}} {\bf{21}} 2000.\\[0pt] [3] Harris, Miller and Williamson, {\emph APS abstract} 2009.