Experimental measurement of large-scale three-dimensional structures in a turbulent boundary layer. Part 1. Vortex packets

Experimental measurements of the three-dimensional (3D) velocity field in a moderate Reynolds number zero pressure-gradient boundary layer are presented. The measurements are analysed to produce 3D correlations and conditional averaging techniques are used to further elucidate the underlying structure. The results show clear evidence of vortex-packet-type structures and shed new light on the detailed 3D structure of such packets in a real zero pressure-gradient boundary layer.