تنش برشي جداره در كانال هاي با مقطع دايره اي نيمه پر

Boundary Shear Stress in Partially Full Pipe Channels

Boundary shear stress along wetted perimeter has been affected by several parameters which in turn they influence on the structure of flow. In present research the recent studies on the subject for open channels having partially full pipe cross section without sediment as it happens in sewer channels, are considered. A series of measurements has been undertaken for point velocities and boundary shear stress along wetted perimeter. In order to consider the flow structure in open channels and wastewater conduit, the Preston tube technique is used to measure boundary shear stress. The results show that the lateral distributions of boundary shear stress is not only affected by the cross sectional shape but also it is affected by Froude number, Fr. Some perturbations can be seen at higher Froude numbers. The results on the distribution of boundary shear stress also show that for the mild slope channels they are fairly flat, but for the steep ones this is not the case. Distribution of the latter case point to the role of secondary currents and the influence of cross sectional shape. The percentage shear force carried by the walls, %SFW, is analyzed using the boundary shear stress data. The result shows that the %SFW is favorably correlated with the geometry parameter, P\/?w. Thus a new equation is developed for the present channel cross section. The obtained results are quite useful for computer modeling of the channels with the same cross sections.