SPATIAL CORRELATION STRUCTURES OF WATER SURFACE FLUCTUATION WITH TURBULENCE IN OPEN-CHANNEL FLOWS

摘要

Laboratory experiments were conducted to investigate interactions between the water surface fluctuations and turbulence structures in open-channel flows. Instantaneous velocity vectors and the corresponding water surface profiles were measured by a simultaneous image measurement method. The proper orthogonal decomposition (POD) of the water surface fluctuations successfully detected their predominant spatial fluctuation patterns, most of which represented sinusoidal wave shapes. By using the modal amplitudes of the POD eigenvectors, we calculated spatial correlation coefficients between the amplitudes and the velocity fluctuations. The result showed that there existed a thin surface-influence-layer near the water surface in which the turbulent flow seemed to be parallel to the wavy surface and also that there was the specific interaction between the water surface fluctuations and the large-scale turbulence structures that have the same longitudinal scale. Furthermore, it was revealed that the spectral distribution of water surface fluctuations followed the -10/3 power of the wave-number.