Turbulent characteristics in flow subjected to bed suction and jet injection as a pier-scour countermeasure

The effect of a combined system of the bed suction and jet injection as a pier-scour countermeasure on the turbulent flow field is studied in a laboratory flume using an Acoustic Doppler Velocimeter (ADV). The three components of the velocities in the vertical symmetry plane in the equilibrium scour hole in front and rear of the pier under 3-jet injections and bed suction rate Qs/Q0 = 2% located between 0 < x/D < 2.4, (where x and D are the horizontal distance along the streamwise direction between the suction source and the pier center and the pier diameter respectively); in clear-water scour condition were measured instantaneously. Also, characteristics of turbulence flow (the turbulence intensity, vorticity and turbulent kinetic energy) in the upstream of a circular pier were investigated. The results reveal that turbulence properties, such as turbulence intensities decrease with bed suction and jet injection. Over the entire water depth, they decrease more rapidly near the bed than those near the free surface. As a result, a system of jet injection and bed suction decrease scouring around the pier.