Applicability of Spatial Periodic Boundary Conditions to Numerical Computation of Flow in a Channel Obstructed by an Array of Square Rods.

Abstract

Two-dimensional numerical computation has been performed for unsteady laminar flow. Spatial periodic boundary conditions were adopted in the streamwise direction and adequacy of this treatment was particularly studied by changing the computational domain size. The following results were obtained. The Strouhal number and the lift coefficient amplitude may change with the domain size in the same flow conditions. Therefore, the simulation for one unit periodic flow field, a "unit cell", is valid for limited flow condition which depends on the Reynolds number, blockage ratio of the rod and its pitch. Uniqueness of the numerical results, which means calculated results remain unchanged with the domain size, is judged by change of the phase difference between neighboring cells. When the numerical results are unique, the Strouhal number, drag coefficient and the lift coefficient amplitude remarkably increase with the blockage ratio. The lift coefficient amplitude decreases with the increase of the rod pitch.