Development of streamwise counter-rotating vortices in flat plate boundary layer pre-set by leading edge patterns

•Streamwise vortices due to some leading edge patterns were experimentally studied.•The edge patterns have the same geometrical wavelength and amplitude.•Similar vortices developed downstream of triangular and sinusoidal patterns.•But the vortices developed due to the notched pattern were more prone to instability. Development of streamwise counter-rotating vortices induced by leading edge patterns with different pattern shape is investigated using hot-wire anemometry in the boundary layer of a flat plate. A triangular, sinusoidal and notched patterns with the same pattern wavelength λ of 15mm and the same pattern amplitude A of 7.5mm were examined for free-stream velocity of 3m/s. The results show a good agreement with earlier studies. The inflection point on the velocity profile downstream of the trough of the patterns at the beginning of the vortex formation indicates that the vortices non-linearly propagate downstream. An additional vortex structure was also observed between the troughs of the notched pattern.