Experimental Investigation of the Effects of Height of Bed Roughness on Shear stress and the Strength of Vortex in a 90 Degree Sharp Rectangular Bend

Sozepor, Aziz; Shafai, Mahmmod; Sheikh Rezazadeh Nikou, Neda

Experimental Investigation of the Effects of Height of Bed Roughness on Shear stress and the Strength of Vortex in a 90 Degree Sharp Rectangular Bend

Document Type : Original Article

Authors

aziz sozepor

mahmmod shafai

neda sheikh rezazadeh nikou

Abstract

Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

Keywords

Experimental model

Vortex strength

Shear stress of bed

Height of bed roughness

?? degree bend