Experimental investigation on flow of trash rack blockage in front of pumping station

Abstract

Trash rack blockage significantly affects the water levels and velocity distributions near trash racks, influencing the performance of subsequent hydraulic systems. An experiment was conducted where alligator weeds, green grasses, woven bags, denim, and cotton fabrics were used as typical trash. Under different amounts of trash, approach velocities and water depths, the movement and aggregation characteristics of the trash were observed and measured. The water level difference and the velocity distributions of cross-sections near trash racks were measured and analysed. A general dimensionless expression was advanced to calculate the head loss coefficient of the trash rack. We introduced the local head loss formula of trash rack blockage based on measured velocity distributions. The results indicate that the water level difference is related to blocked trash characteristics and the approach velocity. The velocity distributions are determined by the blocked location and blocked area on the rack surface. Backflow occurs in severe blockage, which makes the velocity distribution uneven and increases the local head loss.