Fluid flow and heat transfer in a two-dimensional miter-bend have been examined in connection with a corrugated wall channel as a means of augmenting a forced-convection heat transfer with a single-phase flow in a heat exchanger. In the previous paper, experimental results were not in perfect agreement with those of theoretical analysis, because of the effect of unsteady motions due to the instability of the flow in the downstream of the bending corner. In the present paper, the unsteady motions for Reynolds number Re=600, 1000 and 2000 and Prandtl number Pr=0.71 are studied numerically by the finite difference method. Previous experimental results are simulated in outline by numerical calculations, but they do not agree quantitatively with those of numerical calculations for the Strouhal number of fluctuations and the Nusselt number at the concave-side wall.