Measurement and simulation of turbulent flow in a steep open‐channel with smooth boundary

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Abstract
Turbulence measurements were performed in a steep open‐channel with a smooth boundary using a fiber‐optic laser Doppler velocimeter (FLDV). A sophisticated Reynolds‐Stress‐Model (RSM) was chosen to simulate the fully developed turbulent open‐channel flow. The computed mean velocities and turbulence statistical quantities were compared with the high‐accuracy turbulence measurements to explore the capabilities and limitations of the existing turbulence model. The measured mean velocity profiles exhibit a clear retardation effect near the free surface, a feature absent from the numerical simulations. In general, the simulated longitudinal turbulence intensities yielded by the RSM 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. Increase of the turbulence intensities for both the longitudinal and the vertical components near the free surface were found for flows with steep slope gradient and small width‐to‐depth ratio due to the increase of the intensity of secondary current. 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.