Abstract. The background is experimental study of the forming and evolution features of the vortex structures which are generated inside of the cross-streamlined trenches of different depth and length. Purpose. The objective is by means of visualization with photo and video shooting of gas or fluid current pictures in the interior of semi-cylindrical and oval trenches situated on a flat plate to discover the liquid particles trajectories and the objective laws of vortices nucleation and ejections to cocurrent flow. Design/methodology/approach. The investigation was carried out in a wind tunnel and hydrodynamic flume using flow visualization in different current regimes above plate with cavities. In experiments smoke visualization, contrasting dyes and water-soluble coating were used for determination of integral pictures of the vortex systems disposition and interaction, taking into account distinction between its scales. Findings. Regularity of the vortex movement evolution, identification of the local places of vortex structures formation allowed to estimate their sizes, to fix frequencies and location of ejections of small- and large-scale vortex structures out of the trenches depending on flow regimes of the plate with cavity. Received data are useful in the quest for new methods of energy and mass exchange control on streamlined surfaces of thermal, nuclear power plants, flying machines and marine vessels.