An experimental study of interaction of Von Kármán vortices and coherent structures in a turbulent boundary layer

This experimental study looks into the interaction of vortex shedding and a turbulent boundary layer (TBL) over a flat plate. The aim of the study is to further the understanding of the organization and interaction between large and small coherent structures, with special attention to the outer region. In previous studies, a correlation between them through amplitude modulation and conditional averaging has been described (Mathis et al, 2009; Chung & McKeon, 2010) and structures such as hairpin vortices have been observed to organize in a certain manner in the outer region (Adrian et al, 2000 & 2007). In this study, the interaction between externally-generated small vortices and coherent structures in a TBL over a flate plate is analyzed in the 381mm × 381mm subsonic wind tunnel facility at University of Illinois, Urbana-Champaign, and compared to a canonical TBL over a flat plate in the same facility. The small vortices are generated through the formation of a Von Kármán vortex street in the wake of a cylindrical rod (d=1.905mm) at a fixed wall-normal position with the longitudinal axis pointing span-wise. Using 2D-2C Particle Image Velocimetry (PIV), measurements are taken immediately downstream of the cylinder.