The effect of longitudinal vortex on the coherent structure of turbulence in near-wall region was investigated with hydrogen bubble technique in a closed rectangular duct. A highspeed streak region with wider spanwise spacing appears in the downwash part of vortex where secondary flow is directed towards the wall, the flow inside this region is uniform and the streamwise velocity is higher; While a region including low-speed streaks appears in the upwash part of vortex where secondary flow is directed away from the wall, the flow structure in this region is very complicated and streamwise velocity is lower.
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