Hydrodynamic Flow Patterns Around Three Inline Eccentrically Arranged Circular Piers

Abstract

An experiment was conducted under clear-water equilibrium scour state to measure flow formations and characteristics using a velocimeter, in local-scour holes around three identical circular-type piers arranged inline and eccentrically in staggered manner. Two inline piers were positioned towards flow, and eccentric one was placed in middle region of two inline piers. The flume experiment was done for an approach flow depth 0.125 m on uniform bed of sand particles having 0.825 mm median diameter. The hydrodynamic consequences of three-pier arrangement on scour were investigated here. The contour profiles and subsequent distributions of time-independent velocities, turbulence kinetic energy and intensities are well addressed for different vertical azimuthal planes \(0^{\circ }\), \(\pm 45^{\circ }\) and \(\pm 90^{\circ }\) around the piers. Velocity vectors derived from velocity profiles are also utilized to explain further flow attributes. Vorticity and all circulation values for horseshoe vortices, developed at upstream zone of each pier, are determined. The three-pier combination and their interferences caused by them play a key function in the enhancement of greater scour depth near the eccentric-middle pier and more shifting of sand towards the side wall. Flow formations and characteristics of such horseshoe vortices, responsible for above-noted phenomena, are explained here in detail. Vortices strengths for eccentric-middle and inline-rear piers are found greatest and lowest, respectively, compared with strength of inline-front pier.