يادداشت تحقيقاتي: مطالعه آزمايشگاهي اثر شعاع انحنا بر جريان ثانويه در قوس 90 درجه در شرايط بستر تعادل يافته

Experimental Investigation on the Effect of Curvature of Bend on Secondary Flow in 90 Degree Bend under Equilibrium Bed Condition

Flow pattern in the bend channels is different from that in the straight channels. Flow is affected by both pressure gradient and centrifugal forces in the bend of rivers and their interaction leads to form secondary flow. In the channel bend, radius of curvatures of the bend cause changes in the formation of secondary flow and consequently the flow pattern in the bend. This paper presents variation of flow through measurement of three dimensional velocities of the flow in the layers and different sections of a 90 degree bend under equilibrium bed condition. Experiments were conducted in an experimental channel with three different radius of curvature, i.e. mild, moderate and sharp. Vecterino, a three-dimensional velocity meter, is used to measure the three dimensional velocity of the flow. Formation and changes of secondary flow pattern in the three bends with different radius of curvature is discussed. The results indicate that power of secondary flow and vorticity in the second half of the bend increase with decrease in the radius of curvature of the bend. Also, a flow called seeond secondary flow forms near the outer bank and in the opposite direction of the main secondary flow. This flow is evident in the middle sections of first half of bend up to the end of the bend.