Abstract: The effect of longitudinal vortices on the turbulent structure of near-wall regionWas investigated with hydrogen bubble technique in a rectangular duct A wider high-speedstreak appears in the downwash region of vortex(where secondary flow is directed towardsthe wall),the flow is stable and the streamwise velocity is higher inside the streak)a regionincluding low-speed streaks is shown in the upwash part of vortex (where the secondaryflow is directed away from the wall),the flow structure is complicated and ...