An experimental study on turbulent-stripe structure in transitional   channel flow
  Turbulent stripe, which would occur in turbulent channel flows at transitional Reynolds numbers, was studied experimentally by flow visualization using reflective flake particles. In a range of bulk mean Reynolds number Re = 1700-2000, the turbulent stripe was observed to be inclined at angles of 20-30 degree against the streamwise direction, and its streamwise wave length was about 60 times of the channel half width ($\delta$). The longitudinal streaks with the spanwise spacing of 1.6$\delta$ were found in the quasi-laminar regions. The critical Reynolds number was Re = 1300. Time traces of the streamwise velocity were measured by laser Doppler velocimetry, revealing similarity to the equilibrium turbulent puff in the transitional pipe flow. 
Takahiro Tsukahara, Yasuo Kawaguchi, Hiroshi Kawamura
physics.flu-dyn