چكيده به لاتين
Abstract
Vegetation on the edge of the river bed shape and natural channel walls has a significant effect on the flow characteristics, such that it can change the shape of the velocity distribution, stress, and turbulence intensity. The change in the performance of key parameters in open channels due to the presence of vegetation in the three inlet, bed, and outlet areas of the bed shape has been considered. Failure to pay attention to it has caused huge costs in open channel hydraulic projects. Accordingly, it is necessary to investigate the combined presence of vegetation and bed shape in the walls of sandy open channels, which are mainly observed in mountainous areas, on the velocity distribution and turbulence components more carefully. In this laboratory study, the profiles of velocity distribution, Reynolds stresses, and turbulence intensity along with quadrant analysis for two sets of experiments, one with concave bed shapes that are widely observed in sandy rivers; with the presence of vegetation on the wall and the other without it, are investigated and compared. A total of 38 velocity profiles, 19 of which are in the case of no vegetation on the wall along the central axis of the channel with a fineness ratio (width to depth ratio) of less than 5, are taken and analyzed on a concave bed with an angle of entry into the bed shape of 4 degrees and an angle of exit from the bed shape of 5 degrees. The results show that the velocity profiles in the case of vegetation on the wall at a distance of 5 cm from the vegetation are more affected than the central axis of the channel. The shape of the Reynolds stress distribution on the concave bed shape generally follows a divergent distribution. As we approach the vegetated walls, irregularities in the shear stress distribution and turbulence intensity are observed, but the overall trend of the profiles is divergent. Quadrant analysis shows that in the case of vegetation on the channel wall, sweep and spark events are dominant. The results of this research can be effective in more appropriate estimation of flow resistance and sediment transport parameters and reduce project costs.
