بررسي آزمايشگاهي الگوي سه بعدي جريان در قوس رودخانه

An Experimental Investigation of Three Dimentional Flow Pattern in River Bend

The process of flow in a river with regard to the riverʹs characteristics such as the kind of bed, roughness coefficient, longitudinal slope as well as the governing conditions in the watershed (basin) is quite varied and complex. These variations along with complexities reach their highest values when flow occurs along a bend or river meander. A study of this phenomenon as it occurs in nature is very complicated, requiring sophisticated equipment and instruments. In order to limit the variables and at the same time introduce a suitable pattern of a river bend (meander) that represents the effective principle dynamic parameters, a physical model, namely a flume of 180° curvature was constructed as a simulation. The bed and sides of the flume were constructed from plexiglass, allowing a uniform flow to occur at a rate of 50 liters per second, at a width and depth of 60 and 20 cm respectively. Three dimentional (x,y,z) velocity measurements were made at different sections using a micropropeller. In total, nineteen cross sections of 10° intervals wer taken for evaluation. A maximum of 49 points of three dimentional velocity measurements were made at each cross section. Results indicate: a maximum of transverse gradient at water surface occurs at 90° curvature while a minimum occurring at 30 and 100 degrees of the bend. A study of in depth three dimentional velocity profiles indicates a maximum flow velocity at a depth of 7.7 cm from bed surface and a minimum at a depth of 5.7 cm below water surface.