Low-Reynolds Number Effects on Plane Turbulent Couette Flow.

Measurements of time-mean velocity, turbulence intensities (u', v') and Reynolds shear stress in plane turbulent Couette flow have been made in the range of 3000≤2hUb/ν≤20000 (Ub, moving belt speed ; 2h, channel height). The main objective of this work is to study the effects of low-Reynolds number on the turbulent Couette flow. Particular importance is that its effect on the law of the wall can be estimated only from the Couette flow experiment. Low-Reynolds number effects are shown as follows ; additive constant of the law of the wall B, a coefficient of defect law and the maximum turbulence intensity u'/u* (u*, friction velocity) decrease as the Reynolds number decreases. From the skewness-and flatness-factors and four quadrant analysis of the fluctuating velocity, the turbulence structure of the Couette flow can be deduced. Except for close to the wall (y+≤12), where the structure is the same as that of the Poiseuille flow, the sweep event becomes more important than in the Poiseuille flow. The central region has a similar structure as a uniformly sheared flow