STABILITY IN A CIRCULAR CYLINDER WAKE AT THE LOW REYNOLDS NUMBER

Abstract

This study elucidates stability in a cylinder wake at the low Reynolds number by numerical calculation solving the two-dimensional Navier-Stokes equations and the continuity equation. The wake has a bubble and begins to oscillate at Re=6.0-6.5, where Re is the Reynolds number. The bubble is not stable but unstable; the bubble is composed of two asymmetric standing eddies. Since the flow state outside the bubble is steady and symmetric, instability occurring near the rear stagnant point at 6.5≤Re≤6.0 is not transported in the downstream. Since centipedes in the unite streaklines occur in the downstream at 16.0≤Re, instability is transported in the downstream. A change of the centipedes with an increase of the Reynolds number can give a clear insight on a process of the shift of the wake patterns, viz. the centipede flow, the wavy wake, and the Karman vortex street.