The present investigation concentrates on the flow structure around the base of the vertical cylinder mounted on a flat plate for the Reynolds number of Re = 4000. The technique of high-image density particle image velocimetry (PIV) is employed in order to obtain instantaneous representations of the unsteady flow for a specified flow field. The time history of velocity and time-averaging of PIV data, particularly near the juncture, reveal valuable information about the behaviour of the horseshoe vortex system. In the forward face of the cylinder base, three different stagnation points occur, indicating the development of three different horseshoe vortices. These vortices occasionally roll up to combine a single primary vortex. Four different measuring planes were taken across the boundary layer in order to observe the effect of these three-dimensional junction flows arising from the base of the cylinder on the flow structures downstream of the cylinder. (C) 2007 Elsevier Ltd. All rights reserved.