The spanwise non-uniformity of nominally two-dimensional turbulent boundary layer : 1st Report Characteristics of spanwise velocity distribution

Abstract

In order to investigate the factors which affect the spanwise non-uniformity of the boundary layer and its property, 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 of which the shapes of leading edge are different. The tunnel used had a moderately low turbulence, that is about 0.05 % of free stream velocity. Measuring stations were 9 cross sections. Various measurements were carried out in the transverse direction at very small intervals in these sections. From the results of experiments, it was found that a steady spatial quasi-periodic variation increased slightly and its pattern remained fixed toward downstream, and 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 ration of a screen which may affect the spanwise variations definitely, flow patterns through a screen with open area ratios 0.41, 0.52, 0.57 and 0.68 were observed by flow visualization by means of hydrogen bubble method. From these experimental results, it was obtained an appropriate value of the open area ratio of the screen used in the wind tunnel.