| Summary: | 博士 === 國立中興大學 === 土木工程學系 === 91 === Reliable measurements and models for 3-D turbulent open channel flow are limited. In this study, both experimental investigations and numerical simulations were performed to increase our understanding of the flow structure (including secondary current) for the straight, fully developed turbulent open channel flows.
First, data collectioned by Yang (1998) with 2D-FLDV (fiber optic laser Doppler velocimeter) for steep (supercritical) turbulent open channel flows over a smooth boundary were re-analyzed. Several dimensionless semi-empirical formulas were derived for the predictions of mean velocity profiles, turbulence intensities, and Reynolds stresses.
A sophisticated Reynolds-Stress-Model (RSM) was chosen to simulate the fully developed steep turbulent open channel flow over a smooth boundary. The computed mean velocities were consistent with the measured data except for the regions near the side walls and water surface. In general, the simulated longitudinal turbulence intensities were slightly lower than the experimental results, and the simulated vertical turbulence intensities were fairly consistent with the measured data except for the regions near the side walls. The relative magnitude of the longitudinal, vertical and transverse turbulence intensities simulated from RSM was consistent with that for hot film measurements under mild slope conditions.
For the 3-D measurements, all velocity components were measured by making use of an innovative six beams and two probes laser Doppler velocimeter system. All terms in the vorticity equation were investigated with high accuracy. It was found that the secondary current was cause by the anisotropy of the turbulence and the non-homogenious distribution of the Reynolds stress. In addition, the Reynolds-Stress term and the generation term in the vorticity equation have a tendency to balance each other.
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