چكيده به لاتين
Vegetation significantly affects the flow hydrodynamic characteristics as one of the factors affecting the flow resistance, it changes the flow characteristics, including velocity and turbulent intensity. In the presence of irregular distribution of vegetated elements and the 3D bedforms, an extensive comprehension of flow hydraulic seems needful to manage river processes. Although data gathering also carried out in order to properly relate to the field conditions in a cobble-gravel river in the presence of vegetation patches, this research is mainly has been performed to investigate the flow hydraulics on fully submerged rigid elements in the presence of 3D pool in a laboratory flume. Field studies including four separate sections of Padena Marbor River, located in the south of Isfahan province in central Iran, with a total of 10 flexible vegetated patches and various densities, and flume studies, including three different vegetation densities with irregular distribution and also a bed without vegetation, have been performed. Based on field data, three pools were constructed and investigated in a straight flume which is 0.9-m wide, 0.6-m deep, and 14-m long without conducting any dimensional analysis and scaling. In the river section, the grain size distribution of bed material (8 mm580 (Reynolds number of each cylindrical element) and blockage effect for 〖Re〗_d<450 were observed. Meanwhile, the bending deformation results in a significant reduction in the spacing distance between the bodies, causing an intensified sheltering effect and a lower form drag force, which has been observed in most of the vegetated patches. However, the results of flume studies show that the shape of Reynolds stress distribution depends on the entrance and exit slopes of the pool, as well as the irregular distribution pattern of vegetated elements. Inside the pool with the presence of submerged vegetation in the channel bed, the maximum TKE appears above the bed surface with a larger distance depending on the area density of vegetation in the channel bed. However, the momentum exchange and turbulent energy are likely influenced by the secondary circulation of the flows associated with the irregular distribution of vegetated elements in the channel bed. The results show that the irregular distribution of vegetation significantly affects the distribution of Reynolds stress and TKE towards the water surface in the outer region of the boundary layer. These different distributions of Reynolds stress and turbulence energy from the middle of the flow depth towards the water surface are the results of the significant effect of the pressure gradient caused by the interaction of the irregular vegetation and the flow turbulence intensity. Results of the quadrant analysis show that the momentum between the flow, bedform, and submerged rigid vegetated elements are mostly transferred by sweep and ejection events. The outward event tends to grow toward the water surface, and reaches the highest amount near the water surface. At the pool entrance where the flow is decelerating, the ejection event is dominant near the bed while the sweep event is strong near the water surface. In the present of an irregular distribution of submerged vegetated elements in the pool bed, ejections become dominant and then the outward become stronger as the area density of vegetation decreases. However, in the presence of 3D bed forms and irregular distribution of vegetated elements in submerged conditions, with increasing flow depth, the anisotropic behavior of turbulence is noticeably revealed in the component distribution of turbulence
