The spanwise non-uniformity of nominally two-dimensional turbulent boundary layer. I - Characteristics of spanwise velocity distribution

In order to investigate the factors which affect the spanwise nonuniformity of the boundary layer and its properties, measurements were carried out on the mean velocity, the turbulence intensity, and wall shear stress in the transverse direction in the turbulent boundary layers which developed on two types of smooth flat plates with different shapes of leading edge. The tunnel used had a moderately low turbulence. Various measurements were carried out in the transverse direction at very small intervals. It was found that a steady spatial quasi-periodic variation increased slightly and its pattern remained fixed toward the downstream end. An appreciable negative correlation was calculated between the mean transverse-velocity distribution and the turbulence-intensity distribution in the same cross section. With regard to the open-area ratio of a screen which may affect the spanwise variations, flow patterns through a screen with open-area ratios 0.41, 0.52, 0.57 and 0.68 were observed by flow visualization using the hydrogen-bubble method. From these experimental results, an appropriate value was obtained for the open-area ratio of the screen used in the wind tunnel.