A hot-wire measurement was conducted in a planar channel flow that originated from a strongly disturbed flow in an entrance channel followed by an expansion channel used to reduce the Reynolds number (Re). From ceasing decrease of the streamwise velocity fluctuation energy and the linear extrapolation of the intermittency factor, the lower marginal Re, which is defined as the minimum Re for partial existence of sustainable turbulence, is estimated around 1400 based on the channel width and the bulk velocity. The upper marginal Re at which the intermittency factor reaches one is about 2600. The flow fields passing a turbulent patch were reconstructed with conditional sampling of the streamwise velocity data based on the time of laminarturbulence interfaces and the reconstructed flow fields indicate a large-scale flow structure across laminar and turbulent parts. This large structure makes it possible for some regions to be at higher Re than the average, so that turbulence can partly survive. The moderate-scale disturbances larger than the turbulent one appear in the non-turbulent parts of the transitional flow, and in these cases the non-turbulent velocity profile is almost identical to the turbulent one. The large-scale fluctuation is observed even over Re = 2600. This leads to the conclusion that a turbulent channel flow close to the upper marginal Re becomes inhomogeneous. C 2012 American Institute of Physics. [http://dx
N . umerical simu [ ations of re [ aminarization fl ' om turbu [ ence in two − dimensional channel fiow are carried out usir 且 g the latt} ce kinetic scheme , whiclL is an imprQved method of the origlnal lattice BoltzmaI 正lk method 、 Ca [ culated turbulent energy in the re [ alninarization shows an exponential decay for 600 ≦ Re ≦ 900 , where Re is the Reynolds number based on the streamwise velocity at the centerliIle aI 玉 d the half width of the channeL A [ so , the ha 星 f−life time of turbulence is investigated in these cases alld the criticai Reynolds number of the relaminarization is estimated as around l l65 . In additiGii , these results indicatethat the present nurnerical method can 辷 )e useful fbr Inicroscopic investigation of such transition problelns .
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