An Experimental Study on the Effects of Obstacle Diameters on Suspended Sediment Concentration in the Case of Transverse Waves

Abstract

There are many cases in open channel flows where the steady flow of water passes through a cluster of vertical cylinders. As a fluid flow is encountered with several obstacles, an overlapping of opposite forces is resulted by vortex shedding, and shear layers in the wake area takes place and transverse waves are formed along the width of the channel. The present study focused on this phenomenon and the effects of obstacle diameters on suspended sediment concentration based on laboratory tests in a rectangular flume. Wooden obstacles were used in an in-line arrangement only in the half part of a channel width divided by putting a plexi glass sheet. Firstly, in the similar condition of discharge, transverse and perpendicular obstacles distances, hydraulic conditions in maximum wave amplitude for different obstacle diameters were determined. Then, the transportation of suspended sediment from upstream to downstream of obstacles and no-obstacle zone for wave modes 1 and 2 was compared to normal flow condition. Along with this, the suspended sediment concentration variations at downstream of obstacles zone were compared to no-obstacle zone. The results showed that transverse waves had a significant impact on reducing the suspended sediment concentration at downstream of obstacles zone rather than no obstacle zone and the maximum of reduced concentration percentages at downstream of obstacles zone versus the condition with no-obstacle zone, for wave modes 1 and 2 was about 11.2% and 8.3%, respectively. Therefore, wave mode 1 had more effect on the reduction of suspended sediment transportation than wave mode 2. In addition, an increase in obstacle diameters cause to increase the maximum values of the dimensionless displacement (A/H) by about 26% and 37% for wave modes 1 and 2, respectively. However, reduced concentration percentages at downstream of obstacles for wave mode 1 and 2 was decreased about 8%.