Abstract
It has been thought that one of several factors vibrated a fuel rod in a reactor was an unsteady flow around spacer-ribs setteled on a fuel rod surface. A numerical analysis was then performed in order to investigate a production process of the unsteady flow pattern around the obstacle using STREAM code. Strouhal numbers of vortexes behind several rectangular obstacles were calculated and compared with the results of a vertical cylinder. On the other hand vortex street was not generated behind a trapezoid obstacle simulated a spacer-rib.
