Numerical investigation of flow in a channel obstructed by an array of square rods (2nd report, Investigation of a criterion for judging the uniqueness and validity of numerical results)

Abstract

Two-dimensional numerical computation is performed for unsteady laminar flow. Spatially periodic boundary conditions are adopted in the streamwise direction, and in particular, a criterion for judging the uniqueness of the numerical solution is studied. The following results were obtained. When the numerical result fluctuates with the computational domain size, various low-frequency components are markedly observed in the streamwise velocity of the calculated result. Compared with the channel flow obstructed by a single rod of the same size, the intensities of velocity fluctuation in this study are relatively high, and their distribution throughout the flow field is rather uniform. The spatially averaged kinematic energy of the velocity fluctuation is adopted as a key parameter, and a discrimination map of the uniqueness of the numerical solution is presented using a timescale ratio between mean flow and velocity fluctuation, the rod pitch, and the blockage ratio. The timescale ratio is well correlated with a geometric parameter obtained from the flow configuration, and the discrimination map can be converted such that the geometric parameter and the channel Reynolds number describe it.