Impact of Pool and Vegetated Bottom on Turbulant Flow Structure

摘要

This paper reports a laboratory study of turbulent flow characteristics over a pool bed-form at different cross-sections in a flume. Experiments were conducted for two cases, with and without the presence of vegetative over gravel bed-form, to investigate interactions between pool bed-form, vegetation, and flow non-uniformity. Artificial grass was attached to the bottom of the pool bed as a vegetation, and the median diameter of gravel was 50 mm. To compare the results with those of the previous studies, the flow discharge was chosen as 10 Lit/sec and 40 Lit/sec. The non-uniformity of flow in the pool section and the existence of vegetation affected the flow conditions in the flume, including mean velocity, turbulence components, and Reynolds shear stress distribution. The quadrant analysis method was used to study the Reynolds stress and dominant events of turbulent flow structures. Results showed that the interaction of vegetation and pool changed the distribution of Reynolds shear stress profiles, and intermittent increasing and decreasing representations occurred in the various parts of the bed form, and the occurrence of ejection and sweep events near the vegetation in the experiments with higher Reynolds numbers. The logarithmic law well fitted the double average velocity profiles, which justified the validity of this law. The roughness coefficient in the accelerating section was larger than in the decelerating one and in the middle section of the pool.