M. Itoh et al., CHARACTERISTICS OF LOW-SPEED STREAKS IN THE FLOW OF DRAG-REDUCING SURFACTANT SOLUTION, JSME international journal. Series B, fluids and thermal engineering, 40(4), 1997, pp. 550-557
The characteristics of low-speed streaks in the turbulent channel flow
of a drag-reducing surfactant solution are studied by employing the h
ydrogen-bubble flow visualization method. The mean velocity profiles a
nd the distributions of streamwise turbulence intensity are also obtai
ned. It is shown that, at a large drag reduction rate DR, the profile
of the streamwise turbulence intensity has a plateau region around its
peak. In the drag-reducing flow, the mean spanwise streak spacing rea
ches minimum at some distance from the wall. In the drag-reducing flow
of high-density (1000 ppm) surfactant solution. the low-speed streaks
appear intermittently at the Reynolds number smaller than those for t
he 'hump' of the f-Re curve (f : friction factor). The mean spanwise s
treak spacing very near the wall increases as DR becomes large. It is
speculated that the nondimensional wall-normal distance y(+) of the ce
nter of streamwise vortices is larger for the flow of large DR compare
d with that for the Newtonian fluid flow.