EXPERIMENTAL STUDY ON TURBULENT STRUCTURES IN UNSTEADY OPEN-CHANNEL FLOWS

Turbulence measurements in unsteady open-channel flows over smooth beds were conducted accurately by the simultaneous use of two-component LDA system and water-wave gauges. In the inner region near the bed, the normalized turbulent structures were almost similar to those in steady and uniform open-channel flows. In contrast, in the outer region near the free surface, especially in depth-varying zone that could first be measured with LDA, the effects of low frequency component like fluctuations of free surface were observed in the distributions of turbulence intensities. As the result, the turbulence intensities did not indicate the universal distribution.