Turbulent characteristics of open channel flow around large scale granular mixtures
Published: 2019-04-04 Source: Port & Waterway Engineering 2019-02    Hits: 350    share it:

Abstract:In order to investigate the turbulence characteristics of the flow around large scale granular mixtures, we apply a cube, a sphere and a tetrahedron with the same height of Δ=5 cm to generalize the reef shape in gravel-bed rivers respectively, and study the statistical characteristics of fluctuating velocity, and the turbulence parameters such as turbulence intensity, Reynolds stress and turbulent kinetic energy based on 6 sets of data measured by acoustic doppler velocimeters in an uniform turbulent open-channel flow. The results show that the statistical parameters of fluctuating velocity are closely related to the shape of large scale granular mixtures, the vertical distributions of standard deviation σ+u and kurtosis Ku are more uniform, the longitudinal distribution of σ+u increases first and then decreases, and kurtosises on the vertical line at upstream and downstream sections are larger than 3,most of which present a high narrow peak. The skewness Sk at upstream section is basically negative, while Sk at downstream sections gradually becomes negative with the increase of water depth. The vertical distributions of longitudinal turbulence intensity T+u around the 3 kinds of large scale granular mixtures are more uniform and T+u along the longitudinal sections increases with the increase of Froude number Fr.T+u of the cube is the largest, T+u of the sphere is the second, and T+u of the tetrahedron is the smallest. The vertical distributions of Reynolds stress R+ around the 3 kinds of large scale granular mixtures increase gradually from the free surface to the bed. The vertical distributions of turbulent kinetic energy E+ around the 3 kinds of large scale granular mixtures are small at both ends and large in the middle. R+ and E+ have the maximum value near the 2Δ section of the downstream. The hindrance area of large scale granular mixtures is positively correlated with the intensity and extent of its influence on the downstream flow.

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