Experimental study on large-scale streak structure in the core region of turbulent plane Couette flow

A physical experiment confirmed the existence of a large-scale streak structure in the core region of turbulent Couette flow at Re=Uwh∕ν=3750. In the low- or high-speed streak, large-scale wavy-like structures exist, the streamwise and spanwise wavelength of which are (40−65)h and (4−5)h. The low (high) -speed streak pattern is a sequence of wavy and nonwavy (tilted line or irregular) patterns. The large-scale structure is reconstructed using the wavelet components of the streamwise fluctuating velocity that have high energy on a large scale. The reconstructed flow field shows the existence of large-scale structures with a tilted pattern. The tilting angle is ±(3°−5°) against the flow direction. In some places, they constitute a weakly wavy pattern and in other places a simple tilted pattern. The weakly wavy structures appear intermittently in space along the streamwise direction. The rough estimation of the streamwise separation between large-scale structures is 300h.