Numerical Simulation of Flow Around an In-Line Forced-Oscillating Circular Cylinder by a Vortex Method Combined with Boundary Layer Calculation.

Abstract

In this study, the characteristics of vortex shedding from a circular cylinder forced-oscillating in the direction of a uniform flow were investigated using a vortex method combined with the boundary element method at the Reynolds number Re=5000, in ranges of the amplitude ratio 2a/d=0.1∼0.4 and the oscillation frequency ratio f/fK=0.2∼2.6 (a: half-amplitude of oscillation, d: cylinder diameter, f: oscillation frequency, fK: frequency of vortex shedding from a stationary cylinder). As a result of calculations, it was obtained that the frequency of vortex shedding from the oscillating cylinder tends to be equal to either oscillation frequency or a half of it. This tendency can be considered a sort of lock-in phenomenon. At rather large frequency ratios, a couple of typical patterns of vortex shedding were simulated, one of which is symmetric twin vortex shedding and the other is twin but antisymmetric. On the other hand, at smaller oscillation-frequency ratios, complex flow patterns in incomplete lock-in states were simulated, but there were no distinct differences observed between the natural Karman vortex shedding from a stationary cylinder and the vortex shedding from a cylinder oscillating at a lower frequency. Integrating pressure and viscous stresses along the cylinder surface, fluid forces acting on the oscillating cylinder were calculated.