بررسي آزمايشگاهي الگوي جريان دو بعدي اطراف آب شكن در قوس 90 درجه

Experimental Investigation of 2D Flow Patteren Around Spur Dikes in 90° Channel bend

Spur dike is a structure generally used for bank protection. The flow analysis around the spur dikes used in the outer bank is more complicated. This is mainly due to the interaction between the flow pattern in the bend and the spur dike as well as the effects of the helical currents in the bends. This paper deals with the analysis of this type of flow. Experiments were carried out in a re-circulating rectangular flume having 0.6 m width, 0.7 m height with J.8 m centeral radius of bend. The bends and sides of flume were made of glass supported by metal frame. Experiments were conducted for various discharges {25, 35, 45 1/s), length of spur dikes (5, 10, 15 cm) and the locations of spur dikes in bend (15, 30, 45, 60, 75 degree). Flow pattern were recorded using 2D P-EMS velocimeter. The measurements for each section were done at 65 points and number of section was from 15 to 18. Results show that the distance of location of maximum velocity from channel wall increases from lower layers to upper layers. For third and fourth layers (10 and 11 cm from bed) the zone of maximum velocity is more than other layers. The location of relative maximum shear stress at sections 40° to 50° is close to the inner wall. The ratio of width of separation zone to length of spur dike is from 1.55 to 1.9 and the ratio of length of separation zone to length of spur dike is from 6 to 8.