Quasi-streamwise counter-rotating vortices generated by convergent riblets in flat plate boundary layer

Flow structures initiated by multiple convergent riblets, arranged in tandem, in the developing laminar boundary layer on a flat plate were qualitatively studied for a flow velocity of 1.5 m/s by means of smoke wire flow visualization. Two different configurations with varying pitch, 3 and 1.5 mm, and a constant height 3 mm, had been considered. Results depict the development of mushroom-like counter-rotating vortices accompanied by symmetrically distributed small-scale co-rotating vortices and subsequent breakdown of the structures. Though the variation of pitch indicates similar flow structures, the point of breakdown of the structures was found to vary significantly. The probable reasons for the breakdown of the structures have also been discussed.