Experimental study on flow and turbulence characteristics under non-deposition condition in rigid boundary open channels

The impact of sediments on hydraulic properties of current is an important issue in planning rigid boundary channels such as drainage channels, sewer systems, and irrigation channels. The presence of sediment particles in these systems cause problems in terms of both operation and economics. For all these reasons, non-deposition with clean bed (NCB) condition, which is the most reliable and conservative approach for designing sewers and drainage channels, stands out among various design concepts. However, a review of the literature reveals that most of the experimental studies on NCB conditions have focused on the basic properties of flow and sediment for modeling purposes. Previous studies ignored the effect of bed load and particle size on the flow and turbulence characteristics. Therefore, this study investigates the effect of bed load and sediment size on the flow and turbulence characteristics, which has not been studied much in the literature. A set of experiments was carried out in an open channel having 12.5 m long, 0.6 m wide, and 0.7 m deep, with a rectangular cross-section, plexiglass walls, and aluminum bed with automatic control system (ACS). ACS was utilized to change and measure the channel bed slope, sediment discharge, flow discharge, and flow depth. Ultrasonic flow meters and sensors were then used to measure the discharge and flow depth. Three different sediment particle sizes (D50: 1.18 mm, 2.05 mm, and 3.34 mm) and bed slopes (0.1%, 0.3%, and 0.5%) were used in the experiment to investigate the effect of clean water condition and the presence of sediment on flow characteristics. The main motivation for this study was to determine the differences in flow and turbulence characteristics caused by changes in particle size under various hydraulic conditions. Results, showed that the presence of sediment as bed load reduces the velocity in the streamwise direction. The decrease is more significant as the sediment particle size increases. When turbulence intensities were analyzed, the results in the streamwise and vertical directions increased in the case of bed load compared to the clean water case. Reynolds shear stress also increases with the bed load presence. The reason for the increases is a source of roughness and it increases the flow resistance. Although the vertical turbulence intensity increased for larger sediment particles, Reynolds shear stress records showed a significant inconsistency that requires additional investigation. Investigating the sediment particle size as well as particle concentration will help to better understand the particle flow reaction in open channel flow.