INTERACTION OF A STEADY APPROACH FLOW AND A CIRCULAR-CYLINDER UNDERGOING FORCED OSCILLATION

This paper presents a numerical study on the interaction of a steady a pproach flow and the forced transverse oscillation of a circular cylin der. The two-dimensional stream-function/vorticity formulation of the Navier-Stokes equations is solved by a semi-implicit finite-difference scheme. Calculations for flows with different amplitude (a) and frequ ency (f(c)) of the oscillation of the cylinder show a strong effect of the oscillation when f(c) is close to f(so), the vortex shedding freq uency, of the stationary cylinder. Lock-on of vortex shedding, distinc t flow patterns, and increase in both drag and lift coefficients from those of a stationary cylinder are observed for Reynolds number Re = 2 00, a/R (R is the radius of the cylinder) from 1.0 to 2.0, f(c)/f(so) from 0.85 to 1.7. For Re = 855, a/R = 0.26, a large eddy simulation mo del for turbulent flow is used. The results at Re = 855 and a/R = 0.26 show that lock-on has occurred for f(c)/f(so) greater than or equal t o 0.85. The behavior of the drag and lift coefficients is seen to be i nfluenced by the lock-on phenomenon.