Spatial Structure of Large Scale Streaks in Turbulent Couette Flow

Abstract

The spatial structure of large scale streaks in core region of turbulent Couette flow has been studied by using data from hot-wire and smoke-wire visualization. To extract the large scale streaks, two-dimensional discrete wavelet energy spectrum and spanwise correlation of streamwise velocity u'1 were considered. The spanwise size of the extracted large scale streaks is of the order of the channel hight (2h) and the streamwise length of (10-40) × 2h. The streak has partly a zig-zag pattern along streamwise direction and partly straight. The zig-zag pattern has (20-25) × 2h streamwise wavelength. From the visualization of cross section (x2, x3) there exist a large scale motion related to the streamwise vortex in core region. Some near-wall ejection motions are connected to the large scale motions.