Abstract: Detailed 2D flow fields in low speed wind tunnels are measured with on-line PIV to study the flow structures in the zero-pressure gradient turbulent boundary layer of two non-planar surfaces: the vortex generator surface and the wavy surface. Some typical coherent structures are identified from instantaneous streamwise wall-normal velocity fields, from which vorticity and strain rate fields are also calculated. The influence of flow speed on flow structures in the turbulent boundary layer is investigated. Two distinct and regular shear layers are observed in the boundary layer for the vortex generator surface at 10m/s. The small-scale vortices are generated near the inner shear layer. The wavy surface (at 20m/s) will generate smaller scale vortex than the smooth plate. It is shown that wall surface geometrical structure can greatly influence the generation and development of large-scale transverse vortex. This effect varies significantly with different flow conditions.

Key words: turbulent boundary layer, shear layer, P IV