Numerical simulations of the turbulent flow around single and side(by(side piles at different spacing ratios (centre to centre distance to the pile diameter) with flow Reynolds number of 10^5 on the fixed flat(bed are presented. The calculations are performed using the computational fluid dynamics model, FLOW(3D, which solves the Navier (Stokes equations in three dimensions with finite volume method. The numerical results of time (averaged flow patterns around single and side(by(side piles are validated using the available experimental measurements. At the downstream of the single pile, dimensionless vortex shedding frequency (Strouhal number) is estimated as 0.22.The maximum values of bed shear stress around side(by(side piles at different spacing ratios are compared with the maximum values obtained for the single pile. Interactions of horseshoe vortices on different cases of side-by-side piles are studied. Numerical results show that the critical arrangement for which the largest bed shear stress was observed is the case with the spacing ratio of 3.

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