An Experimental Study of the Effect of a Small-Scale Rectangular Canal’s Wall Roughness on the Flow Patterns in a 90° Sharp Bend with a Radius of Curvature to the Bottom Width Ratio of 2

Subject Areas : Subjects

Y. GH ¹ (فارغ التحصیل کارشناسی ارشد سازه‌های آبی دانشگاه شهید چمران اهواز)
M. SH ² (استاد دانشگاه شهید چمران اهواز)
A. سوزه پور ³ (دانشجوی دکتری سازه‌های آبی دانشگاه شهید چمران اهواز)

Received: 2014-10-01 Accepted : 2014-10-01 Published : 2014-11-22

Keywords: Sharp bend, wall roughness, rotational cell, Shear stress,

Abstract :

The wetted perimeter’s roughness, the radius of curvature and its ratio to the bottom width affect the flow velocity and its patterns. This laboratory study was conducted in a 90° sharp bend flume with a rectangular cross-sectional area, and the radius of curvature to the bottom with ratio of 2. The experiments were conducted under a constant Froude No. of 0.17 with 3 wall roughnesses of 0.5, 2.0 and 5.0 mm. The three components of the flow velocity were measured at 480 points. The flow lines in the high velocity zone of 30° to 60° were mostly deflected towards the inner wall and along the channel depth. However, they gradually turned towards the outer wall where the deflection angle exceeded 60°. Further, the main rotational cell of the secondary flow was formed close to the inner wall at all 3 roughnesses at the 60° alignment of the bend. An increase in the wall roughness delayed the decay of the rotational cell at the bend’s termination. It was also observed that the bed shear stress was increased in the highly stressed area with an increase in the wall roughness. The area delimited by the 70° and 80° was singled out showing the highest shear stress. Moreover, it was established that the secondary flow strength at any cross sectional area decreased with an increased in the wall roughness.